Water supply and sanitation-related diseases (such as diarrheal diseases, hepatitis,cholera, typhoid)
posted by NEO SEP 060157
In 2002, water-borne diseases had been reported: 3, 601 cases of hepatitis, 365 cases of choleraand 853 cases of typhoid fever. These are associated with poor drinking water quality andinadequate sanitation.
Friday, September 14, 2007
posted by NEO SEP 060157
Water pollution (frequency of exceeding national water quality standards, drinking waterquality standards)
The estimated number of water pollution sources for 2002 of Malaysia was 13,540 comprising mainly ofsewage treatment plants, agro-based industries, manufacturing industries and animal farms. About53 percent of the total number of sources was domestic sewage facilities (7,126 sources), followedby manufacturing industries (5, 137 or 38 percent), pig farms (807 sources or 6 percent) and agrobasedindustries (470 sources or 3 percent). Of the total number of effluent sources identified,Johor had the highest number (1 675, 29.9 percent), followed by Selangor (1 485, 26.5 percent),Perak (573, 10.2 percent) and Perlis had the least number (14, 0.25 percent).1.3.3 Solid waste (generation of municipal solid waste, proportion of recyclables
Water pollution (frequency of exceeding national water quality standards, drinking waterquality standards)
The estimated number of water pollution sources for 2002 of Malaysia was 13,540 comprising mainly ofsewage treatment plants, agro-based industries, manufacturing industries and animal farms. About53 percent of the total number of sources was domestic sewage facilities (7,126 sources), followedby manufacturing industries (5, 137 or 38 percent), pig farms (807 sources or 6 percent) and agrobasedindustries (470 sources or 3 percent). Of the total number of effluent sources identified,Johor had the highest number (1 675, 29.9 percent), followed by Selangor (1 485, 26.5 percent),Perak (573, 10.2 percent) and Perlis had the least number (14, 0.25 percent).1.3.3 Solid waste (generation of municipal solid waste, proportion of recyclables
posted by NEO SEP060157
In support of Vision 2020 (towards achieving developed nation status), Malaysia will conserve and manage its water resources to ensure adequate and safe water for all (including the environment). Such is the Malaysian vision for water in the 21st century.
The key objectives of the vision are as follows:
Water for people: all have access to safe, adequate and affordable water supply, hygiene and sanitation.
Water for food and rural development: provision of sufficient water that will ensure national food security and promote rural development.
Water for economic development: provision of sufficient water to spur and sustain economic growth within the context of a knowledge-based economy and e-commerce.
Water for the environment: protection of the water environment to preserve water resources (both surface water and groundwater) and natural flow regimes, bio-diversity and the cultural heritage, along with mitigation of water-related hazards.
The set of initiatives that need to take place in order to achieve the key objectives of the vision is evaluated based on the four challenges towards a better water future, which are (a) managing our water resources efficiently and effectively (addressing both quantity and quality aspects), (b) moving towards integrated river basin management, (c) translating awareness into political will and capacity and (d) moving towards adequate, safe and affordable water services, as will befit developed-nation status by 2020.
The actions for a better water future are also determined based on milestones and targets and they have to do with (a) institutional and legal aspects, (b) participatory approach in the decision-making process, (c) development of innovative technologies, (d) efficient use of water resources, (e) extensive research and development, (f) shift from water-supply to water-demand management, (g) establishment of river basin organizations, (h) integrated water resources management, (i) promotion of water awareness and water education, (j) promotion of networking in the water sector, (k) good databases and dissemination, (l) resource assessment, monitoring and protection, (m) water ecosystems protection, (n) flood and drought contingency plans, (o) water-quality management, (p) frequent dialogues with the stakeholders, (q) a Water Sector Master Plan and (r) formation of a National Water Institute.
The way forward to realize the national water vision is to establish associated programmes in the Eighth Malaysian Plan (2001-2005) and the Third Outline Perspective Plan (2001-2010)
In support of Vision 2020 (towards achieving developed nation status), Malaysia will conserve and manage its water resources to ensure adequate and safe water for all (including the environment). Such is the Malaysian vision for water in the 21st century.
The key objectives of the vision are as follows:
Water for people: all have access to safe, adequate and affordable water supply, hygiene and sanitation.
Water for food and rural development: provision of sufficient water that will ensure national food security and promote rural development.
Water for economic development: provision of sufficient water to spur and sustain economic growth within the context of a knowledge-based economy and e-commerce.
Water for the environment: protection of the water environment to preserve water resources (both surface water and groundwater) and natural flow regimes, bio-diversity and the cultural heritage, along with mitigation of water-related hazards.
The set of initiatives that need to take place in order to achieve the key objectives of the vision is evaluated based on the four challenges towards a better water future, which are (a) managing our water resources efficiently and effectively (addressing both quantity and quality aspects), (b) moving towards integrated river basin management, (c) translating awareness into political will and capacity and (d) moving towards adequate, safe and affordable water services, as will befit developed-nation status by 2020.
The actions for a better water future are also determined based on milestones and targets and they have to do with (a) institutional and legal aspects, (b) participatory approach in the decision-making process, (c) development of innovative technologies, (d) efficient use of water resources, (e) extensive research and development, (f) shift from water-supply to water-demand management, (g) establishment of river basin organizations, (h) integrated water resources management, (i) promotion of water awareness and water education, (j) promotion of networking in the water sector, (k) good databases and dissemination, (l) resource assessment, monitoring and protection, (m) water ecosystems protection, (n) flood and drought contingency plans, (o) water-quality management, (p) frequent dialogues with the stakeholders, (q) a Water Sector Master Plan and (r) formation of a National Water Institute.
The way forward to realize the national water vision is to establish associated programmes in the Eighth Malaysian Plan (2001-2005) and the Third Outline Perspective Plan (2001-2010)
Thursday, September 13, 2007
Aerobic Wastewater Treatment
Post by Voon Chen Li
From Pipeline by National Small Flows Clearinghouse,
This publication has been adapted for use in Indiana by Purdue University*
Why Choose Aerobic Treatment?, Are Aerobic Systems Right for My Community?, Aerobic Treatment: Pro's and Con's,
How Aerobic Treatment Works, Other Design Considerations, Aerobic System Do's and Don't, Aerobic System Maintenance,
How Much Does Aerobic Treatment Cost?, For More Information
From Pipeline by National Small Flows Clearinghouse,
This publication has been adapted for use in Indiana by Purdue University*
Why Choose Aerobic Treatment?, Are Aerobic Systems Right for My Community?, Aerobic Treatment: Pro's and Con's,
How Aerobic Treatment Works, Other Design Considerations, Aerobic System Do's and Don't, Aerobic System Maintenance,
How Much Does Aerobic Treatment Cost?, For More Information
Many homes in the U.S. are located in small or rural communities where houses are spaced widely apart. In these communities, central sewerage systems are often not cost-effective, so many homeowners rely on septic systems or other systems that treat and dispose of household wastewater onsite. Some homes for which septic systems are not a good option rely on individual home aerobic systems for wastewater treatment.
Aerobic systems are similar to septic systems in that they both use natural processes to treat wastewater. But unlike septic (anaerobic) treatment, the aerobic treatment process requires oxygen. Aerobic treatment units, therefore, use a mechanism to inject and circulate air inside the treatment tank. This mechanism requires electricity to operate.
For this reason, aerobic systems cost more to operate and need more routine maintenance than most septic systems. However, when properly operated and maintained, aerobic systems can provide a high quality wastewater treatment alternative to septic systems.
Aerobic systems are similar to septic systems in that they both use natural processes to treat wastewater. But unlike septic (anaerobic) treatment, the aerobic treatment process requires oxygen. Aerobic treatment units, therefore, use a mechanism to inject and circulate air inside the treatment tank. This mechanism requires electricity to operate.
For this reason, aerobic systems cost more to operate and need more routine maintenance than most septic systems. However, when properly operated and maintained, aerobic systems can provide a high quality wastewater treatment alternative to septic systems.
Why Choose Aerobic Treatment?
Although there have been home aerobic systems in the U.S. for more than 50 years, their use has been fairly limited. This is due, in part, to the widespread use of septic systems.
Septic tank-soil absorption systems are relatively inexpensive and are easy to maintain. They are the most common onsite wastewater treatment systems used in rural areas. However, there are many households for which a septic system may not be the best wastewater treatment option.
For example, septic systems are not suitable for every lot. In fact, approximately two-thirds of all the land area in the U.S. is estimated to be unsuitable for the installation of septic systems. Some homes may not have enough land area or appropriate soil conditions to accommodate a full sized soil absorption drainfield. In some communities, the water table is too high to allow the drainfield to give adequate treatment to the wastewater before it is returned to the groundwater.
Other site-related concerns include homes located on wooded lots or on lots close to a body of water. Homeowners in wooded areas may not want to clear enough land to install a septic tank and drainfield and the wastewater treated by a septic system is often not of high enough quality to be discharged very close to a body of water.
But one of the most common reasons that aerobic wastewater treatment units are chosen by communities is to replace failing septic systems. Failing septic systems are a major source of groundwater pollution in some areas. If a failed septic system needs to be replaced or if a site is inappropriate for conventional systems, aerobic wastewater treatment becomes a viable option.
Although there have been home aerobic systems in the U.S. for more than 50 years, their use has been fairly limited. This is due, in part, to the widespread use of septic systems.
Septic tank-soil absorption systems are relatively inexpensive and are easy to maintain. They are the most common onsite wastewater treatment systems used in rural areas. However, there are many households for which a septic system may not be the best wastewater treatment option.
For example, septic systems are not suitable for every lot. In fact, approximately two-thirds of all the land area in the U.S. is estimated to be unsuitable for the installation of septic systems. Some homes may not have enough land area or appropriate soil conditions to accommodate a full sized soil absorption drainfield. In some communities, the water table is too high to allow the drainfield to give adequate treatment to the wastewater before it is returned to the groundwater.
Other site-related concerns include homes located on wooded lots or on lots close to a body of water. Homeowners in wooded areas may not want to clear enough land to install a septic tank and drainfield and the wastewater treated by a septic system is often not of high enough quality to be discharged very close to a body of water.
But one of the most common reasons that aerobic wastewater treatment units are chosen by communities is to replace failing septic systems. Failing septic systems are a major source of groundwater pollution in some areas. If a failed septic system needs to be replaced or if a site is inappropriate for conventional systems, aerobic wastewater treatment becomes a viable option.
Aerobic Wastewater Treatment may be a Good Option when ...
The soil quality is not appropriate for a septic system
There is high groundwater or shallow bedrock
A higher level of wastewater treatment is required
A septic system has failed
There is not enough land available for a septic system
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The soil quality is not appropriate for a septic system
There is high groundwater or shallow bedrock
A higher level of wastewater treatment is required
A septic system has failed
There is not enough land available for a septic system
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Are Aerobic Systems Right for My Community?
Aerobic treatment systems are not accepted in all areas. Regulations for onsite systems can vary from one local government to the next. A major reason that aerobic systems are not more widely used is concern about improper operation and maintenance by homeowners. Aerobic systems require regular maintenance, and abuse or neglect can easily lead to system failure.
In answer to these concerns, NSF International (formerly the National Sanitation Foundation) has tested aerobic units according to the requirements of ANSI/NSF Standard 40. NSF International is a nonprofit organization devoted to the protection of public health and the environment through the development of product standards, product evaluations, research, education, and training. The American National Standards Institute (ANSI) is the recognized accreditor in the U.S. for organizations that develop consumer standards and for those that provide independent product evaluations. NSF is accredited by ANSI for both of these areas of service. Aerobic units that satisfy the requirements of ANSI/NSF Standard 40 may carry the NSF mark.
In addition to testing their units, NSF requires manufacturers to include the cost of the first two years of service in the price of purchase. During this initial service contract, each piece of equipment must be serviced a minimum of two times per year, and emergency service must be available to the homeowner. Manufacturers must also offer the homeowner the option of renewing the service contract after the two years.
In most cases, the service contract is carried out by the dealer selling the aerobic unit, who represents the manufacturer. Standard 40 details what type of service is to be performed and what records need to be kept. Both the manufacturers and their distributors are inspected annually by NSF to ensure continued compliance with the requirements.
Some state and local governments that allow aerobic treatment require that units carry the NSF approval. Your local health department will be familiar with the regulations and permit requirements for your area, as well as which onsite options are best for your particular property.
Aerobic treatment systems are not accepted in all areas. Regulations for onsite systems can vary from one local government to the next. A major reason that aerobic systems are not more widely used is concern about improper operation and maintenance by homeowners. Aerobic systems require regular maintenance, and abuse or neglect can easily lead to system failure.
In answer to these concerns, NSF International (formerly the National Sanitation Foundation) has tested aerobic units according to the requirements of ANSI/NSF Standard 40. NSF International is a nonprofit organization devoted to the protection of public health and the environment through the development of product standards, product evaluations, research, education, and training. The American National Standards Institute (ANSI) is the recognized accreditor in the U.S. for organizations that develop consumer standards and for those that provide independent product evaluations. NSF is accredited by ANSI for both of these areas of service. Aerobic units that satisfy the requirements of ANSI/NSF Standard 40 may carry the NSF mark.
In addition to testing their units, NSF requires manufacturers to include the cost of the first two years of service in the price of purchase. During this initial service contract, each piece of equipment must be serviced a minimum of two times per year, and emergency service must be available to the homeowner. Manufacturers must also offer the homeowner the option of renewing the service contract after the two years.
In most cases, the service contract is carried out by the dealer selling the aerobic unit, who represents the manufacturer. Standard 40 details what type of service is to be performed and what records need to be kept. Both the manufacturers and their distributors are inspected annually by NSF to ensure continued compliance with the requirements.
Some state and local governments that allow aerobic treatment require that units carry the NSF approval. Your local health department will be familiar with the regulations and permit requirements for your area, as well as which onsite options are best for your particular property.
Aerobic Treatment: Pros and Cons
Advantages
Can provide a higher level of treatment than a septic tank
Helps to protect valuable water resources where septic systems are failing
Provides an alternative for sites not suited for septic systems
May extend the life of a drainfield
May allow for a reduction in drainfield size
Disadvantages
More expensive to operate than a septic system
Requires electricity
Includes mechanical parts that can break down
Requires more frequent routine maintenance than a septic tank
Subject to upsets under sudden heavy loads or when neglected
May release more nitrates to groundwater than a septic system
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Advantages
Can provide a higher level of treatment than a septic tank
Helps to protect valuable water resources where septic systems are failing
Provides an alternative for sites not suited for septic systems
May extend the life of a drainfield
May allow for a reduction in drainfield size
Disadvantages
More expensive to operate than a septic system
Requires electricity
Includes mechanical parts that can break down
Requires more frequent routine maintenance than a septic tank
Subject to upsets under sudden heavy loads or when neglected
May release more nitrates to groundwater than a septic system
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How Aerobic Treatment Works
Aerobic systems treat wastewater using natural processes that require oxygen. Bacteria that thrive in oxygen-rich environments work to break down and digest the wastewater inside the aerobic treatment unit. Like most onsite systems, aerobic systems treat the wastewater in stages. Sometimes the wastewater receives pretreatment before it enters the aerobic unit. Treated wastewater leaving the unit requires additional treatment (passage through a soil absorption field) before being returned to the environment. Wastewater discharge from individual residential on-site disposal systems to Indiana waters is not permitted.
Such a variety of designs exist for home aerobic units and systems that it is impossible to describe a typical system. Instead, it is more practical to discuss how some common design features of aerobic systems work and the different stages of aerobic treatment.
Aerobic systems treat wastewater using natural processes that require oxygen. Bacteria that thrive in oxygen-rich environments work to break down and digest the wastewater inside the aerobic treatment unit. Like most onsite systems, aerobic systems treat the wastewater in stages. Sometimes the wastewater receives pretreatment before it enters the aerobic unit. Treated wastewater leaving the unit requires additional treatment (passage through a soil absorption field) before being returned to the environment. Wastewater discharge from individual residential on-site disposal systems to Indiana waters is not permitted.
Such a variety of designs exist for home aerobic units and systems that it is impossible to describe a typical system. Instead, it is more practical to discuss how some common design features of aerobic systems work and the different stages of aerobic treatment.
Pretreatment
Some aerobic systems include a pretreatment step to reduce the amount of solids in the wastewater going into the aerobic unit. Solids include greases, oils, toilet paper, and other materials that are put down the drain or flushed into the system. Too much solid material can clog the unit and prevent effective treatment. Some pretreatment methods include a septic tank, a primary settling compartment in the treatment unit, or a trash trap.
Some aerobic systems include a pretreatment step to reduce the amount of solids in the wastewater going into the aerobic unit. Solids include greases, oils, toilet paper, and other materials that are put down the drain or flushed into the system. Too much solid material can clog the unit and prevent effective treatment. Some pretreatment methods include a septic tank, a primary settling compartment in the treatment unit, or a trash trap.
Aerobic Treatment Units
The main function of the aerobic unit is to collect and treat household wastewater, which includes all water from toilets, bathtubs, showers, sinks, and laundry. Aerobic units themselves come in many sizes and shapes-rectangular, conical, and some shapes that defy classification.
The main function of the aerobic unit is to collect and treat household wastewater, which includes all water from toilets, bathtubs, showers, sinks, and laundry. Aerobic units themselves come in many sizes and shapes-rectangular, conical, and some shapes that defy classification.
Suspended Growth Units
The process most aerobic units use to treat wastewater is referred to as suspended growth. These units include a main compartment called an aeration chamber in which air is mixed with the wastewater. Since most home aerobic units are buried underground like septic tanks, the air must be forced into the aeration chamber by an air blower or a compressor.
The forced air mixes with wastewater in the aeration chamber, and the oxygen supports the growth of aerobic bacteria that digest the solids in the wastewater. This mixture of wastewater and oxygen is called the mixed liquor. The treatment occurring in the mixed liquor is referred to as suspended growth because the bacteria grow as they are suspended in the liquid unattached to any surface.
Unfortunately, the bacteria cannot digest all of the solids in the mixed liquor, and these solids eventually settle out as sludge. Many aerobic units include a secondary chamber called a settling chamber or clarifier where excess solids can settle. Other designs allow the sludge to accumulate at the bottom of the tank.
In aerobic units designed with a separate settling compartment, the sludge returns to the aeration chamber (either by gravity or by a pumping device). The sludge contains bacteria that also aid in the treatment process. Although, in theory, the aerobic treatment process should eventually be able to consume the sludge completely, in practice, the sludge does build up in most units and will need to be pumped out at least once a year so that solids don't clog the unit.
The process most aerobic units use to treat wastewater is referred to as suspended growth. These units include a main compartment called an aeration chamber in which air is mixed with the wastewater. Since most home aerobic units are buried underground like septic tanks, the air must be forced into the aeration chamber by an air blower or a compressor.
The forced air mixes with wastewater in the aeration chamber, and the oxygen supports the growth of aerobic bacteria that digest the solids in the wastewater. This mixture of wastewater and oxygen is called the mixed liquor. The treatment occurring in the mixed liquor is referred to as suspended growth because the bacteria grow as they are suspended in the liquid unattached to any surface.
Unfortunately, the bacteria cannot digest all of the solids in the mixed liquor, and these solids eventually settle out as sludge. Many aerobic units include a secondary chamber called a settling chamber or clarifier where excess solids can settle. Other designs allow the sludge to accumulate at the bottom of the tank.
In aerobic units designed with a separate settling compartment, the sludge returns to the aeration chamber (either by gravity or by a pumping device). The sludge contains bacteria that also aid in the treatment process. Although, in theory, the aerobic treatment process should eventually be able to consume the sludge completely, in practice, the sludge does build up in most units and will need to be pumped out at least once a year so that solids don't clog the unit.
Attached Growth Units
An alternative design for aerobic treatment is the attached growth system. These units treat wastewater by taking a surface made of material that the bacteria can attach to, and then exposing that surface alternately to wastewater and air. This is done either by rotating the surface in and out of the wastewater or by dosing the wastewater onto the surface. Pretreatment is required. The air needed for the process is either naturally present or is supplied mechanically.
Attached growth systems, such as trickling filters and rotating disks, are less common than suspended growth systems, but have certain advantages. For example, there is no need for mixing, and solids are less likely to be washed out of the system during periods of heavy household water use
An alternative design for aerobic treatment is the attached growth system. These units treat wastewater by taking a surface made of material that the bacteria can attach to, and then exposing that surface alternately to wastewater and air. This is done either by rotating the surface in and out of the wastewater or by dosing the wastewater onto the surface. Pretreatment is required. The air needed for the process is either naturally present or is supplied mechanically.
Attached growth systems, such as trickling filters and rotating disks, are less common than suspended growth systems, but have certain advantages. For example, there is no need for mixing, and solids are less likely to be washed out of the system during periods of heavy household water use
Flow Design
The way and the rate in which wastewater is received by and flows through the aerobic unit differs from design to design. Continuous flow designs simply allow the wastewater to flow through the unit at the same rate that it leaves the home. Other designs employ devices (such as pretreatment tanks, surge chambers, and baffles) to control the amount of the incoming flow. Batch process designs use pumps or siphons to control the amount of wastewater in the aeration tank and/or to discharge the treated wastewater in controlled amounts after a certain period of time.
Controlling the flow of wastewater helps to protect the treatment process. When too much wastewater is flushed into the system all at once, it can become overburdened and the quality of treatment can suffer. The disadvantages to mechanical flow control devices are that, like all mechanical components, they need maintenance and run the risk of malfunctioning.
Homeowners can help their system's performance by conserving water. Leaking faucets and running toilets should be repaired, and washing machines and dishwashers should be used only when full. Installing water saving devices in toilets, faucets, and showers can reduce water use by up to 50 percent. Also, homeowners should try to space out activities requiring heavy water use (like laundry) to avoid overloading their systems.
The way and the rate in which wastewater is received by and flows through the aerobic unit differs from design to design. Continuous flow designs simply allow the wastewater to flow through the unit at the same rate that it leaves the home. Other designs employ devices (such as pretreatment tanks, surge chambers, and baffles) to control the amount of the incoming flow. Batch process designs use pumps or siphons to control the amount of wastewater in the aeration tank and/or to discharge the treated wastewater in controlled amounts after a certain period of time.
Controlling the flow of wastewater helps to protect the treatment process. When too much wastewater is flushed into the system all at once, it can become overburdened and the quality of treatment can suffer. The disadvantages to mechanical flow control devices are that, like all mechanical components, they need maintenance and run the risk of malfunctioning.
Homeowners can help their system's performance by conserving water. Leaking faucets and running toilets should be repaired, and washing machines and dishwashers should be used only when full. Installing water saving devices in toilets, faucets, and showers can reduce water use by up to 50 percent. Also, homeowners should try to space out activities requiring heavy water use (like laundry) to avoid overloading their systems.
Final Treatment And Disposal
Although properly operated and maintained aerobic units are very effective, the wastewater leaving the units is not ready to be returned to the environment and must receive final treatment. Methods for final treatment include discharge to a soil absorption field and/or a sand filter. Soil absorption fields (or drainfields) are the most common method of final treatment. An aerobic unit can sometimes help to prolong the life of a drainfield. Your health department is familiar with local regulations and the treatment options that are best in your area and for your property.
The amount of dissolved oxygen contained in wastewater from an aerobic unit can help the growth of microorganisms that treat the wastewater in the soil, and can help prevent the pores in the soil from clogging. However, when aerobic units malfunction, they can release solids that can clog the drainfield, which may cancel out any potential benefits.
Sand filters are sometimes used to treat the wastewater from aerobic units. The wastewater is pumped evenly over several layers of sand and gravel, which are located either above or below ground. As with soil treatment systems, the purification process is aided by bacteria that occur naturally in the sand.
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Although properly operated and maintained aerobic units are very effective, the wastewater leaving the units is not ready to be returned to the environment and must receive final treatment. Methods for final treatment include discharge to a soil absorption field and/or a sand filter. Soil absorption fields (or drainfields) are the most common method of final treatment. An aerobic unit can sometimes help to prolong the life of a drainfield. Your health department is familiar with local regulations and the treatment options that are best in your area and for your property.
The amount of dissolved oxygen contained in wastewater from an aerobic unit can help the growth of microorganisms that treat the wastewater in the soil, and can help prevent the pores in the soil from clogging. However, when aerobic units malfunction, they can release solids that can clog the drainfield, which may cancel out any potential benefits.
Sand filters are sometimes used to treat the wastewater from aerobic units. The wastewater is pumped evenly over several layers of sand and gravel, which are located either above or below ground. As with soil treatment systems, the purification process is aided by bacteria that occur naturally in the sand.
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Controls and Alarms
Most aerobic units have controls that can be switched on and off by the homeowner in case of emergency. Aerobic units also are required to have alarms to alert the homeowner of malfunctions. Depending on the design of the system, controls and alarms can be located either inside or outside the home, and alarms can be visible, audible, or both.
Homeowners should make sure that controls and alarms are always protected from corrosion, and that the aerobic unit is turned back on if there is a power outage or if it is turned off temporarily.
Most aerobic units have controls that can be switched on and off by the homeowner in case of emergency. Aerobic units also are required to have alarms to alert the homeowner of malfunctions. Depending on the design of the system, controls and alarms can be located either inside or outside the home, and alarms can be visible, audible, or both.
Homeowners should make sure that controls and alarms are always protected from corrosion, and that the aerobic unit is turned back on if there is a power outage or if it is turned off temporarily.
Size
Aerobic units should be large enough to allow enough time for the solids to settle and for the wastewater to be treated. The size of most units range from 300 to 1,500 gallons per day, but local regulations often require that the unit be at least large enough to handle 500 gallons of wastewater per day.
The needed size of an aerobic unit is often estimated the same way the size of a septic tank is estimated, by the number of bedrooms (not bathrooms) in the house. It is assumed that each person will use approximately 75 to 100 gallons of water per day, and that each bedroom can accommodate two people. When calculated this way, a three-bedroom house will require a unit with a capacity of 450 to 600 gallons per day.
Some health departments require that aerobic units be sized at least as large as a septic tank in case the aerobic unit malfunctions and oxygen doesn't mix with the wastewater. In such cases, the aerobic unit will work as a septic tank-which will, at least, provide partial treatment for the wastewater.
Aerobic units should be large enough to allow enough time for the solids to settle and for the wastewater to be treated. The size of most units range from 300 to 1,500 gallons per day, but local regulations often require that the unit be at least large enough to handle 500 gallons of wastewater per day.
The needed size of an aerobic unit is often estimated the same way the size of a septic tank is estimated, by the number of bedrooms (not bathrooms) in the house. It is assumed that each person will use approximately 75 to 100 gallons of water per day, and that each bedroom can accommodate two people. When calculated this way, a three-bedroom house will require a unit with a capacity of 450 to 600 gallons per day.
Some health departments require that aerobic units be sized at least as large as a septic tank in case the aerobic unit malfunctions and oxygen doesn't mix with the wastewater. In such cases, the aerobic unit will work as a septic tank-which will, at least, provide partial treatment for the wastewater.
Temperature
Lower temperatures tend to slow down most biological processes, and higher temperatures tend to speed them up. The aerobic process itself creates heat, which, along with the heat from the electrical components, may help to keep the treatment process active. However, cold weather can have adverse effects on the performance of aerobic units.
In one study of aerobic units, there were problems when the temperature of the wastewater inside some of the units fell below 15 degrees Celsius (59 degrees Fahrenheit). Problems can sometimes be avoided by insulating around the units. Your health department should know whether aerobic systems are suitable for your area.
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Lower temperatures tend to slow down most biological processes, and higher temperatures tend to speed them up. The aerobic process itself creates heat, which, along with the heat from the electrical components, may help to keep the treatment process active. However, cold weather can have adverse effects on the performance of aerobic units.
In one study of aerobic units, there were problems when the temperature of the wastewater inside some of the units fell below 15 degrees Celsius (59 degrees Fahrenheit). Problems can sometimes be avoided by insulating around the units. Your health department should know whether aerobic systems are suitable for your area.
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Do’s
Do maintain the contract service arrangement offered by the manufacturer after the initial two-year period has expired (unless your community offers its own management program). It is extremely important that aerobic systems receive regular maintenance.
Do keep your system accessible for inspections and pumping, yet protected from unauthorized entrance. If access to your system is locked, make sure that your service contractor has a key.
Do call a service professional whenever you experience problems with your system, whenever the alarm is activated, or whenever there are any signs of system failure.
Do keep detailed records about your aerobic system, including a map of where it is, and general information, such as model name, capacity, state license, date installed, contract service agreement, records of service visits, and maintenance performed.
Do conserve water to avoid overloading the system. Be sure to repair any leaky faucets or toilets.
Do divert other sources of water, like roof drains, house footing drains, and sump pumps away from the aerobic system.
Do become familiar with how your own particular system operates, and the way it looks, sounds, and smells when it is working correctly. This way, you may be able to identify problems before they become serious and alert your service provider to anything unusual.
Do be sure to ask your service provider questions about how to know if your unit is malfunctioning.
Do maintain the contract service arrangement offered by the manufacturer after the initial two-year period has expired (unless your community offers its own management program). It is extremely important that aerobic systems receive regular maintenance.
Do keep your system accessible for inspections and pumping, yet protected from unauthorized entrance. If access to your system is locked, make sure that your service contractor has a key.
Do call a service professional whenever you experience problems with your system, whenever the alarm is activated, or whenever there are any signs of system failure.
Do keep detailed records about your aerobic system, including a map of where it is, and general information, such as model name, capacity, state license, date installed, contract service agreement, records of service visits, and maintenance performed.
Do conserve water to avoid overloading the system. Be sure to repair any leaky faucets or toilets.
Do divert other sources of water, like roof drains, house footing drains, and sump pumps away from the aerobic system.
Do become familiar with how your own particular system operates, and the way it looks, sounds, and smells when it is working correctly. This way, you may be able to identify problems before they become serious and alert your service provider to anything unusual.
Do be sure to ask your service provider questions about how to know if your unit is malfunctioning.
Don’ts
Don't allow anyone to drive over or park on any part of the system.
Don't make or allow unauthorized repairs or changes to your aerobic system without obtaining the required health department permits.
Don't use your toilet as a trash can or poison your treatment system and the groundwater by pouring harmful chemicals down the drain. Harsh chemicals can kill the beneficial bacteria that treat your wastewater.
Don't use a garbage disposal without checking with your local regulatory agency to make sure that your aerobic system can accommodate this additional waste.
Don't attempt to clean or perform maintenance on any sealed aerobic unit components.
Do Not Flush...
coffee grounds
dental floss
disposable diapers
paints
pesticides
kitty litter
sanitary napkins
tampons
varnishes
photographic solutions
cigarette butts
condoms
gauze
thinners
bandages
fat, grease, or oil
paper towels
waste oils
These items can overtax or destroy the biological digestion taking place within your system.
Don't allow anyone to drive over or park on any part of the system.
Don't make or allow unauthorized repairs or changes to your aerobic system without obtaining the required health department permits.
Don't use your toilet as a trash can or poison your treatment system and the groundwater by pouring harmful chemicals down the drain. Harsh chemicals can kill the beneficial bacteria that treat your wastewater.
Don't use a garbage disposal without checking with your local regulatory agency to make sure that your aerobic system can accommodate this additional waste.
Don't attempt to clean or perform maintenance on any sealed aerobic unit components.
Do Not Flush...
coffee grounds
dental floss
disposable diapers
paints
pesticides
kitty litter
sanitary napkins
tampons
varnishes
photographic solutions
cigarette butts
condoms
gauze
thinners
bandages
fat, grease, or oil
paper towels
waste oils
These items can overtax or destroy the biological digestion taking place within your system.
Aerobic System Maintenance
It is important that mechanical components in aerobic systems receive regular inspection and maintenance. For example, air compressors sometimes need to be oiled, and vanes, filters, and seals may need to be replaced. Malfunctions are common during the first few months after installation. In most cases, homeowners do not have the expertise to inspect, repair, and maintain their own systems.
If your unit carries the NSF approval, it will include the first two years of service visits with the purchase price and an option to renew the service contract after two years. It is a good idea for homeowners to renew their service agreements after two years, or to find another service organization to take over the job. This may be a requirement of the permit.
In addition to routine maintenance, NSF requires service contractors to stock replacement parts for mechanical components and to be available for emergency servicing. Under the original two-year agreement, failed equipment is replaced at no additional cost to the homeowner.
The service contract may or may not cover such problems as damage from power failures, breaking or crushing of pipes leading to and from the system, flooding, fires, homeowner misuse, and other catastrophes beyond the control of the manufacturer.
Service visits will most likely be carried out by the dealer or another independent service organization that has an agreement with the manufacturer. In other cases, health departments will have maintenance management programs, such as sanitary districts, for aerobic systems and other onsite systems in their area. In general, we recommend a professional inspection and maintenance every three months.
It is important that mechanical components in aerobic systems receive regular inspection and maintenance. For example, air compressors sometimes need to be oiled, and vanes, filters, and seals may need to be replaced. Malfunctions are common during the first few months after installation. In most cases, homeowners do not have the expertise to inspect, repair, and maintain their own systems.
If your unit carries the NSF approval, it will include the first two years of service visits with the purchase price and an option to renew the service contract after two years. It is a good idea for homeowners to renew their service agreements after two years, or to find another service organization to take over the job. This may be a requirement of the permit.
In addition to routine maintenance, NSF requires service contractors to stock replacement parts for mechanical components and to be available for emergency servicing. Under the original two-year agreement, failed equipment is replaced at no additional cost to the homeowner.
The service contract may or may not cover such problems as damage from power failures, breaking or crushing of pipes leading to and from the system, flooding, fires, homeowner misuse, and other catastrophes beyond the control of the manufacturer.
Service visits will most likely be carried out by the dealer or another independent service organization that has an agreement with the manufacturer. In other cases, health departments will have maintenance management programs, such as sanitary districts, for aerobic systems and other onsite systems in their area. In general, we recommend a professional inspection and maintenance every three months.
Warning Signs of Aerobic System Problems
Alarms or lights going off
Any changes in the system's normal operating sound
Any changes in the normal color of the wastewater in the aeration on chamber (for example if the color is greyish brown rather than chocolate brown this can sometimes indicate problems)
Excessive solids, foam, or scum in the unit
Plumbing backups
Sewage odors in the house or yard
Alarms or lights going off
Any changes in the system's normal operating sound
Any changes in the normal color of the wastewater in the aeration on chamber (for example if the color is greyish brown rather than chocolate brown this can sometimes indicate problems)
Excessive solids, foam, or scum in the unit
Plumbing backups
Sewage odors in the house or yard
What to Expect at a Typical Service Visit
The first service visit should be scheduled immediately after the system is installed to make sure that everything is working correctly. The service contractor may also arrange a meeting with the homeowner to go over issues, such as proper operation, what to do in case of emergency, etc… For seasonal properties, homeowners will need to know how to shut the system down in the off season and start it again when needed. After the first visit, the maintenance service contract is issued to the homeowner.
The maintenance contract may include at least two service visits per year for the next two years. The number of visits and service performed will differ from unit to unit and location to location depending on manufacturers' recommendations and local regulations.
During a typical visit, the service provider will remove the unit's cover and check its general appearance. He or she will check pipes and the inside of the aeration chamber, and will note the appearance of the wastewater inside the unit and its color and odor. Samples may be taken of the mixed liquor from the aeration chamber, as well as the final treated wastewater. The operator will also check to see that all mechanical parts, alarms, and controls are in working order, and that solids are pumped from the system if needed. The soil absorption field, sand filter, or other method of final treatment may also be inspected by the service provider.
The first service visit should be scheduled immediately after the system is installed to make sure that everything is working correctly. The service contractor may also arrange a meeting with the homeowner to go over issues, such as proper operation, what to do in case of emergency, etc… For seasonal properties, homeowners will need to know how to shut the system down in the off season and start it again when needed. After the first visit, the maintenance service contract is issued to the homeowner.
The maintenance contract may include at least two service visits per year for the next two years. The number of visits and service performed will differ from unit to unit and location to location depending on manufacturers' recommendations and local regulations.
During a typical visit, the service provider will remove the unit's cover and check its general appearance. He or she will check pipes and the inside of the aeration chamber, and will note the appearance of the wastewater inside the unit and its color and odor. Samples may be taken of the mixed liquor from the aeration chamber, as well as the final treated wastewater. The operator will also check to see that all mechanical parts, alarms, and controls are in working order, and that solids are pumped from the system if needed. The soil absorption field, sand filter, or other method of final treatment may also be inspected by the service provider.
Record Keeping
It is a good idea for the homeowner or the service provider to keep detailed records about the system and service visits. NSF approved units are required to include a user's manual that describes such things as the manufacturer's recommendations for the unit, the system design, how to operate and maintain it, as well as how to tell if it is working properly. The state license, the date the system was installed, the type of disinfection, and any modifications to the system should also be recorded.
Other important information to keep on hand includes where to contact the owner if nobody is home, where to find a key to the system, and the schedule for service visits. Homeowners should keep their own copies of all records and permits.
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It is a good idea for the homeowner or the service provider to keep detailed records about the system and service visits. NSF approved units are required to include a user's manual that describes such things as the manufacturer's recommendations for the unit, the system design, how to operate and maintain it, as well as how to tell if it is working properly. The state license, the date the system was installed, the type of disinfection, and any modifications to the system should also be recorded.
Other important information to keep on hand includes where to contact the owner if nobody is home, where to find a key to the system, and the schedule for service visits. Homeowners should keep their own copies of all records and permits.
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How much does aerobic treatment cost?
The cost of aerobic treatment varies depending on factors, such as design, size, location, and operation and maintenance requirements. Some of the factors affecting the cost of aerobic treatment are as follows:
unit price
cost of unit installation and electricians' fees
cost of construction of the drainfield or cost of other method of additional treatment if required
cost of electricity (per year)
maintenance service contract fee (per year)
cost of disinfection (if applicable)
The price of some of these factors, such as unit price, may be adversely affected by the lack of demand for aerobic systems in certain areas. Installation costs may be higher for aerobic units than for septic tanks because of the electrical work required. All of these factors need to be carefully considered when determining the cost-effectiveness of aerobic treatment versus other treatment methods. Your local health official can help you evaluate your options.
The cost of aerobic treatment varies depending on factors, such as design, size, location, and operation and maintenance requirements. Some of the factors affecting the cost of aerobic treatment are as follows:
unit price
cost of unit installation and electricians' fees
cost of construction of the drainfield or cost of other method of additional treatment if required
cost of electricity (per year)
maintenance service contract fee (per year)
cost of disinfection (if applicable)
The price of some of these factors, such as unit price, may be adversely affected by the lack of demand for aerobic systems in certain areas. Installation costs may be higher for aerobic units than for septic tanks because of the electrical work required. All of these factors need to be carefully considered when determining the cost-effectiveness of aerobic treatment versus other treatment methods. Your local health official can help you evaluate your options.
For more Information:
Health Departments: If you would like more information about aerobic units or are interested in utilizing one, contact your local health department or the Indiana State Department of Health at (317) 233-7177 for assistance. (Local health department phone numbers are usually listed in the government section of local phone directories.)
National Small Flows Clearinghouse (NSFC): The National Small Flows Clearinghouse (NSFC), which specializes in on-site technology, operation, maintenance, regulations, management, finance, and education, has a variety of free and low-cost products available. NSFC can be reached at (800) 624-8301.
Extension Service: Extension service offices can provide assistance and information about many of the wastewater treatment issues discussed. To locate the extension office in your area, call Purdue University at (888) 398-4636, the U.S. Department of Agriculture at (202) 720-3377 or NSFC.
NSF International (formerly the National Sanitation Foundation): NSF International is a private, nonprofit organization devoted to research, education, service, and training that tests and publishes standards for products relating to public health and the environment. To order the ANSI/NSF Standard 40, see the listing at the bottom of this page. For more information, you may contact NSF at (800) NSF-MARK.
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To Purdue Wastewater Articles On-Line
Pipeline, Winter, 1996. Vol. 7, No. 1.
*Catherine Taylor and Joseph Yahner, Agronomy (765) 494-4773, Don Jones, Agricultural Engineering (765) 494-1167, Purdue University and Alan Dunn, Indiana State Department of Health (317) 233-7177. The On-Site Project is in cooperation with the Indiana State Department of Health.
Health Departments: If you would like more information about aerobic units or are interested in utilizing one, contact your local health department or the Indiana State Department of Health at (317) 233-7177 for assistance. (Local health department phone numbers are usually listed in the government section of local phone directories.)
National Small Flows Clearinghouse (NSFC): The National Small Flows Clearinghouse (NSFC), which specializes in on-site technology, operation, maintenance, regulations, management, finance, and education, has a variety of free and low-cost products available. NSFC can be reached at (800) 624-8301.
Extension Service: Extension service offices can provide assistance and information about many of the wastewater treatment issues discussed. To locate the extension office in your area, call Purdue University at (888) 398-4636, the U.S. Department of Agriculture at (202) 720-3377 or NSFC.
NSF International (formerly the National Sanitation Foundation): NSF International is a private, nonprofit organization devoted to research, education, service, and training that tests and publishes standards for products relating to public health and the environment. To order the ANSI/NSF Standard 40, see the listing at the bottom of this page. For more information, you may contact NSF at (800) NSF-MARK.
to top
To Purdue Wastewater Articles On-Line
Pipeline, Winter, 1996. Vol. 7, No. 1.
*Catherine Taylor and Joseph Yahner, Agronomy (765) 494-4773, Don Jones, Agricultural Engineering (765) 494-1167, Purdue University and Alan Dunn, Indiana State Department of Health (317) 233-7177. The On-Site Project is in cooperation with the Indiana State Department of Health.
Sewage Treatment
Post by Voon Chen Li
From Wikipedia, the free encyclopedia
• Learn more about using Wikipedia for research •
Jump to: navigation, search
Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater, both runoff and domestic. It includes physical, chemical and biological processes to remove physical, chemical and biological contaminants. Its objective is to produce a waste stream (or treated effluent) and a solid waste or sludge also suitable for discharge or reuse back into the environment. This material is often inadvertently contaminated with toxic organic and inorganic compounds.
Sewage is created by residences, institutions, and commercial and industrial establishments. It can be treated close to where it is created (in septic tanks, Biofilters or aerobic treatment systems), or collected and transported via a network of pipes and pump stations to a municipal treatment plant (see sewerage and pipes and infrastructure). Sewage collection and treatment is typically subject to local, state and federal regulations and standards (regulation and controls). Industrial sources of wastewater often require specialized treatment processes (see Industrial wastewater treatment).
Typically, sewage treatment involves three stages, called primary, secondary and tertiary treatment. First, the solids are separated from the wastewater stream. Then dissolved biological matter is progressively converted into a solid mass by using indigenous, water-borne bacteria. Finally, the biological solids are neutralized then disposed of or re-used, and the treated water may be disinfected chemically or physically (for example by lagoons and micro-filtration). The final effluent can be discharged into a stream, river, bay, lagoon or wetland, or it can be used for the irrigation of a golf course, green way or park. If it is sufficiently clean, it can also be used for groundwater recharge.
Description
Raw influent (sewage) is the liquid waste from toilets, baths, showers, kitchens, sinks etc. Household waste that is disposed of via sewers. In many areas sewage also includes some liquid waste from industry and commerce. In the United Kingdom, the waste from toilets is termed foul waste, the waste from items such as basins, baths, kitchens is termed sullage water, and the industrial and commercial waste is termed trade waste.
The division of household water drains into greywater and blackwater is becoming more common in the developed world, with greywater being permitted to be used for watering plants or recycled for flushing toilets. A lot of sewage also includes some surface water from roofs or hard-standing areas. Municipal wastewater therefore includes residential, commercial, and industrial liquid waste discharges, and may include stormwater runoff. Sewage systems capable of handling stormwater are known as combined systems. Such systems are usually avoided since they complicate and thereby reduce the efficiency of sewage treatment plants owing to their seasonality. The variability in flow also leads to often larger than necessary, and subsequently more expensive, treatment facilities. In addition, heavy storms that contribute more flows than the treatment plant can handle may overwhelm the sewage treatment system, causing a spill or overflow (called a combined sewer overflow, or CSO, in the United States). It is preferable to have a separate storm drain system for stormwater in areas that are developed with sewer systems.
The construction of combined sewers is a less common practice in the U.S. and Canada than in the past and is no longer accepted within building regulations in the UK and other European countries. Instead, liquid waste and stormwater are collected and conveyed in separate sewer systems, referred to as sanitary sewers and storm sewers in the U.S. and as foul sewers and surface water sewers in the UK.
As rainfall runs over the surface of roofs and the ground, it may pick up various contaminants including soil particles and other sediment, heavy metals, organic compounds, animal waste, and oil and grease. Some jurisdictions require stormwater to receive some level of treatment before being discharged directly into waterways. Examples of treatment processes used for stormwater include sedimentation basins, wetlands, buried concrete vaults with various kinds of filters, and vortex separators (to remove coarse solids).
The site where the raw wastewater is processed before it is discharged back to the environment is called a wastewater treatment plant (WWTP). The order and types of mechanical, chemical and biological systems that comprise the wastewater treatment plant are typically the same for most developed countries:
Mechanical treatment;
Influx (Influent)
Removal of large objects
Removal of sand and grit
Pre-precipitation
Biological treatment;
Oxidation bed (oxidizing bed) or aeration system
Post precipitation
Effluent
Chemical treatment (this step is usually combined with settling and other processes to remove solids, such as filtration. The combination is referred to in the U.S. as physical-chemical treatment.).
Treatment stages
Primary treatment
Primary treatment removes the materials that can be easily collected from the raw wastewater and disposed of. The typical materials that are removed during primary treatment include to fats, oils, and greases (also referred to as FOG), sand, gravels and rocks (also referred to as grit), larger settleable solids including human waste, and floating materials. This step is done entirely with machinery, hence the name mechanical treatment.
Influx (influent) and removal of large objects
In the mechanical treatment, the influx (influent) of sewage water is strained to remove all large objects that are deposited in the sewer system, such as rags, sticks, condoms, sanitary towels (sanitary napkins) or tampons, cans, fruit, etc. This is most commonly done with a manual or automated mechanically raked screen. This type of waste is removed because it can damage or clog the equipment in the sewage treatment plant.
Sand and grit removal
Primary treatment typically includes a sand or grit channel or chamber where the velocity of the incoming wastewater is carefully controlled to allow sand grit and stones to settle, while keeping the majority of the suspended organic material in the water column. This equipment is called a detritor or sand catcher. Sand grit and stones need to be removed early in the process to avoid damage to pumps and other equipment in the remaining treatment stages. Sometimes there is a sand washer (grit classifier) followed by a conveyor that transports the sand to a container for disposal. The contents from the sand catcher may be fed into the incinerator in a sludge processing plant, but in many cases, the sand and grit is sent to a landfill.
Primary sedimentation tank at a rural treatment plant
Sedimentation
Many plants have a sedimentation stage where the sewage is allowed to pass slowly through large tanks, commonly called "primary clarifiers" or "primary sedimentation tanks". The tanks are large enough that fecal solids can settle and floating material such as grease and oils can rise to the surface and be skimmed off. The main purpose of the primary stage is to produce a generally homogeneous liquid capable of being treated biologically and a sludge that can be separately treated or processed. Primary settlement tanks are usually equipped with mechanically driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank from where it can be pumped to further sludge treatment stages.
Secondary treatment
Secondary treatment is designed to substantially degrade the biological content of the sewage such as are derived from human waste, food waste, soaps and detergent. The majority of municipal and industrial plants treat the settled sewage liquor using aerobic biological processes. For this to be effective, the biota require both oxygen and a substrate on which to live. There are number of ways in which this is done. In all these methods, the bacteria and protozoa consume biodegradable soluble organic contaminants (e.g. sugars, fats, organic short-chain carbon molecules, etc.) and bind much of the less soluble fractions into floc. Secondary treatment systems are classified as fixed film or suspended growth. Fixed-film treatment process including trickling filters and rotating biological contactors where the biomass grows on media and the sewage passes over its surface. In suspended growth systems—such as activated sludge—the biomass is well mixed with the sewage and can be operated in a smaller space than fixed-film systems that treat the same amount of water. However, fixed-film systems are more able to cope with drastic changes in the amount of biological material and can provide higher removal rates for organic material and suspended solids than suspended growth systems.
Roughing filters are intended to treat particularly strong or variable organic loads, typically industrial, to allow them to then be treated by conventional secondary treatment processes. Characteristics include typically tall, circular filters filled with open synthetic filter media to which wastewater is applied at a relatively high rate. They are designed to allow high hydraulic loading and a high flow-through of air. On larger installations, air is forced through the media using blowers. The resultant wastewater is usually within the normal range for conventional treatment processes.
Activated Sludge
Activated sludge plants use a variety of mechanisms and processes to use dissolved oxygen to promote the growth of biological floc that substantially removes organic material. It also traps particulate material and can, under ideal conditions, convert ammonia to nitrite and nitrate ultimately to nitrogen gas, (see also denitrification).
Fluidized bed reactors
The carbon adsorption following biological treatment was particularly effective in reducing both the BOD and COD to low levels. A fluidized bed reactor is a combination of the most common stirred tank packed bed, continuous flow reactors. It is very important to chemical engineering because of its excellent heat and mass transfer characteristics. In a fluidized bed reactor, the substrate is passed upward through the immobilized enzyme bed at a high velocity to lift the particles. However the velocity must not be so high that the enzymes are swept away from the reactor entirely. This causes high mixing; these type of reactors are highly suitable for the exothermic reactions. It is most often applied in immobilized enzyme catalysis.
Filter beds (oxidising beds)
Trickling filter bed using plastic media
In older plants and plants receiving more variable loads, trickling filter beds are used where the settled sewage liquor is spread onto the surface of a deep bed made up of coke (carbonised coal), limestone chips or specially fabricated plastic media. Such media must have high surface areas to support the biofilms that form. The liquor is distributed through perforated rotating arms radiating from a central pivot. The distributed liquor trickles through this bed and is collected in drains at the base. These drains also provide a source of air which percolates up through the bed, keeping it aerobic. Biological films of bacteria, protozoa and fungi form on the media’s surfaces and eat or otherwise reduce the organic content. This biofilm is grazed by insect larvae and worms which help maintain an optimal thickness. Overloading of beds increases the thickness of the film leading to clogging of the filter media and ponding on the surface.
Biological aerated filters
Biological Aerated (or Anoxic) Filter (BAF) or Biofilters combine filtration with biological carbon reduction, nitrification or denitrification. BAF usually includes a reactor filled with a filter media. The media is either in suspension or supported by a gravel layer at the foot of the filter. The dual purpose of this media is to support highly active biomass that is attached to it and to filter suspended solids. Carbon reduction and ammonia conversion occurs in aerobic mode and sometime achieved in a single reactor while nitrate conversion occurs in anoxic mode. BAF is operated either in upflow or downflow configuration depending on design specified by manufacturer.
Secondary Sedimentation tank at a rural treatment plant
Membrane biological reactors
Membrane biological reactors (MBR) combines activated sludge treatment with a membrane liquid-solid separation process. The membrane component utilizes low pressure microfiltration or ultra filtration membranes and eliminates the need for clarification and tertiary filtration. The membranes are typically immersed in the aeration tank (however, some applications utilize a separate membrane tank). One of the key benefits of a membrane bioreactor system is that it effectively overcomes the limitations associated with poor settling of sludge in conventional activated sludge (CAS) processes. The technology permits bioreactor operation with considerably higher mixed liquor suspended solids (MLSS) concentration than CAS systems, which are limited by sludge settling. The process is typically operated at MLSS in the range of 8,000–12,000 mg/L, while CAS are operated in the range of 2,000–3,000 mg/L. The elevated biomass concentration in the membrane bioreactor process allows for very effective removal of both soluble and particulate biodegradable materials at higher loading rates. Thus increased Sludge Retention Times (SRTs)—usually exceeding 15 days—ensure complete nitrification even under extreme cold weather operating conditions.
The cost of building and operating a MBR is usually higher than conventional wastewater treatment, however, as the technology has become increasingly popular and has gained wider acceptance throughout the industry, the life-cycle costs have been steadily decreasing. As well, in developed urban areas where the footprint of the treatment plant is considered a limiting factor MBR facilities can be considered a desirable option.
Secondary sedimentation
The final step in the secondary treatment stage is to settle out the biological floc or filter material and produce sewage water containing very low levels of organic material and suspended matter.
Rotating biological contactors
Rotating biological contactors (RBCs) are mechanical secondary treatment systems, which are robust and capable of withstanding surges in organic load. RBCs were first installed in Germany in 1960 and have since been developed and refined into a reliable operating unit. The rotating disks support the growth of bacteria and micro-organisms present in the sewage, which breakdown and stabilise organic pollutants. To be successful, micro-organisms need both oxygen to live and food to grow. Oxygen is obtained from the atmosphere as the disks rotate. As the micro-organisms grow, they build up on the media until they are sloughed off due to shear forces provided by the rotating discs in the sewage. Effluent from the RBC is then passed through final clarifiers where the micro-organisms in suspension settle as a sludge. The sludge is withdrawn from the clarifier for further treatment.
Tertiary treatment
Tertiary treatment provides a final stage to raise the effluent quality before it is discharged to the receiving environment (sea, river, lake, ground, etc.). More than one tertiary treatment process may be used at any treatment plant. If disinfection is practiced, it is always the final process. It is also called "effluent polishing".
Filtration
Sand filtration removes much of the residual suspended matter. Filtration over activated carbon removes residual toxins.
Lagooning
Lagooning provides settlement and further biological improvement through storage in large man-made ponds or lagoons. These lagoons are highly aerobic and colonization by native macrophytes, especially reeds, is often encouraged. Small filter feeding invertebrates such as Daphnia and species of Rotifera greatly assist in treatment by removing fine particulates.
Constructed wetlands
Constructed wetlands include engineered reedbeds and a range of similar methodologies, all of which provide a high degree of aerobic biological improvement and can often be used instead of secondary treatment for small communities, also see phytoremediation. One example is a small reedbed used to clean the drainage from the elephants' enclosure at Chester Zoo in England.
Waste removal
Wastewater may contain high levels of the nutrients nitrogen and phosphorus. Excessive release to the environment can lead to a build up of nutrients, called eutrophication, which can in turn encourage the overgrowth of weeds, algae, and cyanobacteria (blue-green algae). This may cause an algal bloom, a rapid growth in the population of algae. The algae numbers are unsustainable and eventually most of them die. The decomposition of the algae by bacteria uses up so much of oxygen in the water that most or all of the animals die, which creates more organic matter for the bacteria to decompose. In addition to causing deoxygenation, some algal species produce toxins that contaminate drinking water supplies. Different treatment processes are required to remove nitrogen and phosphorus.
Nitrogen removal
The removal of nitrogen is effected through the biological oxidation of nitrogen from ammonia (nitrification) to nitrate, followed by denitrification, the reduction of nitrate to nitrogen gas. Nitrogen gas is released to the atmosphere and thus removed from the water.
Nitrification itself is a two-step aerobic process, each step facilitated by a different type of bacteria. The oxidation of ammonia (NH3) to nitrite (NO2−) is most often facilitated by Nitrosomonas spp. (nitroso=ammonium). Nitrite oxidation to nitrate (NO3−), though traditionally believed to be facilitated by Nitrobacter spp. (nitro=nitrite), is now known to be facilitated in the environment almost exclusively by Nitrospira spp.
Denitrification requires anoxic conditions to encourage the appropriate biological communities to form. It is facilitated by a wide diversity of bacteria. Sand filters, lagooning and reed beds can all be used to reduce nitrogen, but the activated sludge process (if designed well) can do the job the most easily. Since denitrification is the reduction of nitrate to dinitrogen gas, an electron donor is needed. This can be, depending on the wastewater, organic matter (from faeces), sulfide, or an added donor like methanol.
Sometimes the conversion of toxic ammonia to nitrate alone is referred to as tertiary treatment.
Phosphorus removal
Phosphorus can be removed biologically in a process called enhanced biological phosphorus removal. In this process, specific bacteria, called polyphosphate accumulating organisms, are selectively enriched and accumulate large quantities of phosphorus within their cells (up to 20% of their mass). When the biomass enriched in these bacteria is separated from the treated water, these biosolids have a high fertilizer value.
Phosphorus removal can also be achieved by chemical precipitation, usually with salts of iron (e.g. ferric chloride) or aluminum (e.g. alum). The resulting chemical sludge is difficult to handle and the added chemicals can be expensive. Despite this, chemical phosphorus removal requires significantly smaller equipment footprint than biological removal, is easier to operate and can be more reliable in areas that have wastewater compositions that make biological phosphorus removal difficult.
Disinfection
The purpose of disinfection in the treatment of wastewater is to substantially reduce the number of microorganisms in the water to be discharged back into the environment. The effectiveness of disinfection depends on the quality of the water being treated (e.g., cloudiness, pH, etc.), the type of disinfection being used, the disinfectant dosage (concentration and time), and other environmental variables. Cloudy water will be treated less successfully since solid matter can shield organisms, especially from ultraviolet light or if contact times are low. Generally, short contact times, low doses and high flows all militate against effective disinfection. Common methods of disinfection include ozone, chlorine, or ultraviolet light. Chloramine, which is used for drinking water, is not used in wastewater treatment because of its persistence.
Chlorination remains the most common form of wastewater disinfection in North America due to its low cost and long-term history of effectiveness. One disadvantage is that chlorination of residual organic material can generate chlorinated-organic compounds that may be carcinogenic or harmful to the environment. Residual chlorine or chloramines may also be capable of chlorinating organic material in the natural aquatic environment. Further, because residual chlorine is toxic to aquatic species, the treated effluent must also be chemically dechlorinated, adding to the complexity and cost of treatment.
Ultraviolet (UV) light can be used instead of chlorine, iodine, or other chemicals. Because no chemicals are used, the treated water's taste is more natural and pure as compared to other methods. UV radiation causes damage to the genetic structure of bacteria, viruses, and other pathogens, making them incapable of reproduction. The key disadvantages of UV disinfection are the need for frequent lamp maintenance and replacement and the need for a highly treated effluent to ensure that the target microorganisms are not shielded from the UV radiation (i.e., any solids present in the treated effluent may protect microorganisms from the UV light). In the United Kingdom, light is becoming the most common means of disinfection because of the concerns about the impacts of chlorine in chlorinating residual organics in the wastewater and in chlorinating organics in the receiving water. Edmonton, Alberta, Canada also uses UV light for its water treatment.
Ozone O3 is generated by passing oxygen O2 through a high voltage potential resulting in a third oxygen atom becoming attached and forming O3. Ozone is very unstable and reactive and oxidizes most organic material it comes in contact with, thereby destroying many pathogenic microorganisms. Ozone is considered to be safer than chlorine because, unlike chlorine which has to be stored on site (highly poisonous in the event of an accidental release), ozone is generated onsite as needed. Ozonation also produces fewer disinfection by-products than chlorination. A disadvantage of ozone disinfection is the high cost of the ozone generation equipment and the requirements for highly skilled operators.
From Wikipedia, the free encyclopedia
• Learn more about using Wikipedia for research •
Jump to: navigation, search
Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater, both runoff and domestic. It includes physical, chemical and biological processes to remove physical, chemical and biological contaminants. Its objective is to produce a waste stream (or treated effluent) and a solid waste or sludge also suitable for discharge or reuse back into the environment. This material is often inadvertently contaminated with toxic organic and inorganic compounds.
Sewage is created by residences, institutions, and commercial and industrial establishments. It can be treated close to where it is created (in septic tanks, Biofilters or aerobic treatment systems), or collected and transported via a network of pipes and pump stations to a municipal treatment plant (see sewerage and pipes and infrastructure). Sewage collection and treatment is typically subject to local, state and federal regulations and standards (regulation and controls). Industrial sources of wastewater often require specialized treatment processes (see Industrial wastewater treatment).
Typically, sewage treatment involves three stages, called primary, secondary and tertiary treatment. First, the solids are separated from the wastewater stream. Then dissolved biological matter is progressively converted into a solid mass by using indigenous, water-borne bacteria. Finally, the biological solids are neutralized then disposed of or re-used, and the treated water may be disinfected chemically or physically (for example by lagoons and micro-filtration). The final effluent can be discharged into a stream, river, bay, lagoon or wetland, or it can be used for the irrigation of a golf course, green way or park. If it is sufficiently clean, it can also be used for groundwater recharge.
Description
Raw influent (sewage) is the liquid waste from toilets, baths, showers, kitchens, sinks etc. Household waste that is disposed of via sewers. In many areas sewage also includes some liquid waste from industry and commerce. In the United Kingdom, the waste from toilets is termed foul waste, the waste from items such as basins, baths, kitchens is termed sullage water, and the industrial and commercial waste is termed trade waste.
The division of household water drains into greywater and blackwater is becoming more common in the developed world, with greywater being permitted to be used for watering plants or recycled for flushing toilets. A lot of sewage also includes some surface water from roofs or hard-standing areas. Municipal wastewater therefore includes residential, commercial, and industrial liquid waste discharges, and may include stormwater runoff. Sewage systems capable of handling stormwater are known as combined systems. Such systems are usually avoided since they complicate and thereby reduce the efficiency of sewage treatment plants owing to their seasonality. The variability in flow also leads to often larger than necessary, and subsequently more expensive, treatment facilities. In addition, heavy storms that contribute more flows than the treatment plant can handle may overwhelm the sewage treatment system, causing a spill or overflow (called a combined sewer overflow, or CSO, in the United States). It is preferable to have a separate storm drain system for stormwater in areas that are developed with sewer systems.
The construction of combined sewers is a less common practice in the U.S. and Canada than in the past and is no longer accepted within building regulations in the UK and other European countries. Instead, liquid waste and stormwater are collected and conveyed in separate sewer systems, referred to as sanitary sewers and storm sewers in the U.S. and as foul sewers and surface water sewers in the UK.
As rainfall runs over the surface of roofs and the ground, it may pick up various contaminants including soil particles and other sediment, heavy metals, organic compounds, animal waste, and oil and grease. Some jurisdictions require stormwater to receive some level of treatment before being discharged directly into waterways. Examples of treatment processes used for stormwater include sedimentation basins, wetlands, buried concrete vaults with various kinds of filters, and vortex separators (to remove coarse solids).
The site where the raw wastewater is processed before it is discharged back to the environment is called a wastewater treatment plant (WWTP). The order and types of mechanical, chemical and biological systems that comprise the wastewater treatment plant are typically the same for most developed countries:
Mechanical treatment;
Influx (Influent)
Removal of large objects
Removal of sand and grit
Pre-precipitation
Biological treatment;
Oxidation bed (oxidizing bed) or aeration system
Post precipitation
Effluent
Chemical treatment (this step is usually combined with settling and other processes to remove solids, such as filtration. The combination is referred to in the U.S. as physical-chemical treatment.).
Treatment stages
Primary treatment
Primary treatment removes the materials that can be easily collected from the raw wastewater and disposed of. The typical materials that are removed during primary treatment include to fats, oils, and greases (also referred to as FOG), sand, gravels and rocks (also referred to as grit), larger settleable solids including human waste, and floating materials. This step is done entirely with machinery, hence the name mechanical treatment.
Influx (influent) and removal of large objects
In the mechanical treatment, the influx (influent) of sewage water is strained to remove all large objects that are deposited in the sewer system, such as rags, sticks, condoms, sanitary towels (sanitary napkins) or tampons, cans, fruit, etc. This is most commonly done with a manual or automated mechanically raked screen. This type of waste is removed because it can damage or clog the equipment in the sewage treatment plant.
Sand and grit removal
Primary treatment typically includes a sand or grit channel or chamber where the velocity of the incoming wastewater is carefully controlled to allow sand grit and stones to settle, while keeping the majority of the suspended organic material in the water column. This equipment is called a detritor or sand catcher. Sand grit and stones need to be removed early in the process to avoid damage to pumps and other equipment in the remaining treatment stages. Sometimes there is a sand washer (grit classifier) followed by a conveyor that transports the sand to a container for disposal. The contents from the sand catcher may be fed into the incinerator in a sludge processing plant, but in many cases, the sand and grit is sent to a landfill.
Primary sedimentation tank at a rural treatment plant
Sedimentation
Many plants have a sedimentation stage where the sewage is allowed to pass slowly through large tanks, commonly called "primary clarifiers" or "primary sedimentation tanks". The tanks are large enough that fecal solids can settle and floating material such as grease and oils can rise to the surface and be skimmed off. The main purpose of the primary stage is to produce a generally homogeneous liquid capable of being treated biologically and a sludge that can be separately treated or processed. Primary settlement tanks are usually equipped with mechanically driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank from where it can be pumped to further sludge treatment stages.
Secondary treatment
Secondary treatment is designed to substantially degrade the biological content of the sewage such as are derived from human waste, food waste, soaps and detergent. The majority of municipal and industrial plants treat the settled sewage liquor using aerobic biological processes. For this to be effective, the biota require both oxygen and a substrate on which to live. There are number of ways in which this is done. In all these methods, the bacteria and protozoa consume biodegradable soluble organic contaminants (e.g. sugars, fats, organic short-chain carbon molecules, etc.) and bind much of the less soluble fractions into floc. Secondary treatment systems are classified as fixed film or suspended growth. Fixed-film treatment process including trickling filters and rotating biological contactors where the biomass grows on media and the sewage passes over its surface. In suspended growth systems—such as activated sludge—the biomass is well mixed with the sewage and can be operated in a smaller space than fixed-film systems that treat the same amount of water. However, fixed-film systems are more able to cope with drastic changes in the amount of biological material and can provide higher removal rates for organic material and suspended solids than suspended growth systems.
Roughing filters are intended to treat particularly strong or variable organic loads, typically industrial, to allow them to then be treated by conventional secondary treatment processes. Characteristics include typically tall, circular filters filled with open synthetic filter media to which wastewater is applied at a relatively high rate. They are designed to allow high hydraulic loading and a high flow-through of air. On larger installations, air is forced through the media using blowers. The resultant wastewater is usually within the normal range for conventional treatment processes.
Activated Sludge
Activated sludge plants use a variety of mechanisms and processes to use dissolved oxygen to promote the growth of biological floc that substantially removes organic material. It also traps particulate material and can, under ideal conditions, convert ammonia to nitrite and nitrate ultimately to nitrogen gas, (see also denitrification).
Fluidized bed reactors
The carbon adsorption following biological treatment was particularly effective in reducing both the BOD and COD to low levels. A fluidized bed reactor is a combination of the most common stirred tank packed bed, continuous flow reactors. It is very important to chemical engineering because of its excellent heat and mass transfer characteristics. In a fluidized bed reactor, the substrate is passed upward through the immobilized enzyme bed at a high velocity to lift the particles. However the velocity must not be so high that the enzymes are swept away from the reactor entirely. This causes high mixing; these type of reactors are highly suitable for the exothermic reactions. It is most often applied in immobilized enzyme catalysis.
Filter beds (oxidising beds)
Trickling filter bed using plastic media
In older plants and plants receiving more variable loads, trickling filter beds are used where the settled sewage liquor is spread onto the surface of a deep bed made up of coke (carbonised coal), limestone chips or specially fabricated plastic media. Such media must have high surface areas to support the biofilms that form. The liquor is distributed through perforated rotating arms radiating from a central pivot. The distributed liquor trickles through this bed and is collected in drains at the base. These drains also provide a source of air which percolates up through the bed, keeping it aerobic. Biological films of bacteria, protozoa and fungi form on the media’s surfaces and eat or otherwise reduce the organic content. This biofilm is grazed by insect larvae and worms which help maintain an optimal thickness. Overloading of beds increases the thickness of the film leading to clogging of the filter media and ponding on the surface.
Biological aerated filters
Biological Aerated (or Anoxic) Filter (BAF) or Biofilters combine filtration with biological carbon reduction, nitrification or denitrification. BAF usually includes a reactor filled with a filter media. The media is either in suspension or supported by a gravel layer at the foot of the filter. The dual purpose of this media is to support highly active biomass that is attached to it and to filter suspended solids. Carbon reduction and ammonia conversion occurs in aerobic mode and sometime achieved in a single reactor while nitrate conversion occurs in anoxic mode. BAF is operated either in upflow or downflow configuration depending on design specified by manufacturer.
Secondary Sedimentation tank at a rural treatment plant
Membrane biological reactors
Membrane biological reactors (MBR) combines activated sludge treatment with a membrane liquid-solid separation process. The membrane component utilizes low pressure microfiltration or ultra filtration membranes and eliminates the need for clarification and tertiary filtration. The membranes are typically immersed in the aeration tank (however, some applications utilize a separate membrane tank). One of the key benefits of a membrane bioreactor system is that it effectively overcomes the limitations associated with poor settling of sludge in conventional activated sludge (CAS) processes. The technology permits bioreactor operation with considerably higher mixed liquor suspended solids (MLSS) concentration than CAS systems, which are limited by sludge settling. The process is typically operated at MLSS in the range of 8,000–12,000 mg/L, while CAS are operated in the range of 2,000–3,000 mg/L. The elevated biomass concentration in the membrane bioreactor process allows for very effective removal of both soluble and particulate biodegradable materials at higher loading rates. Thus increased Sludge Retention Times (SRTs)—usually exceeding 15 days—ensure complete nitrification even under extreme cold weather operating conditions.
The cost of building and operating a MBR is usually higher than conventional wastewater treatment, however, as the technology has become increasingly popular and has gained wider acceptance throughout the industry, the life-cycle costs have been steadily decreasing. As well, in developed urban areas where the footprint of the treatment plant is considered a limiting factor MBR facilities can be considered a desirable option.
Secondary sedimentation
The final step in the secondary treatment stage is to settle out the biological floc or filter material and produce sewage water containing very low levels of organic material and suspended matter.
Rotating biological contactors
Rotating biological contactors (RBCs) are mechanical secondary treatment systems, which are robust and capable of withstanding surges in organic load. RBCs were first installed in Germany in 1960 and have since been developed and refined into a reliable operating unit. The rotating disks support the growth of bacteria and micro-organisms present in the sewage, which breakdown and stabilise organic pollutants. To be successful, micro-organisms need both oxygen to live and food to grow. Oxygen is obtained from the atmosphere as the disks rotate. As the micro-organisms grow, they build up on the media until they are sloughed off due to shear forces provided by the rotating discs in the sewage. Effluent from the RBC is then passed through final clarifiers where the micro-organisms in suspension settle as a sludge. The sludge is withdrawn from the clarifier for further treatment.
Tertiary treatment
Tertiary treatment provides a final stage to raise the effluent quality before it is discharged to the receiving environment (sea, river, lake, ground, etc.). More than one tertiary treatment process may be used at any treatment plant. If disinfection is practiced, it is always the final process. It is also called "effluent polishing".
Filtration
Sand filtration removes much of the residual suspended matter. Filtration over activated carbon removes residual toxins.
Lagooning
Lagooning provides settlement and further biological improvement through storage in large man-made ponds or lagoons. These lagoons are highly aerobic and colonization by native macrophytes, especially reeds, is often encouraged. Small filter feeding invertebrates such as Daphnia and species of Rotifera greatly assist in treatment by removing fine particulates.
Constructed wetlands
Constructed wetlands include engineered reedbeds and a range of similar methodologies, all of which provide a high degree of aerobic biological improvement and can often be used instead of secondary treatment for small communities, also see phytoremediation. One example is a small reedbed used to clean the drainage from the elephants' enclosure at Chester Zoo in England.
Waste removal
Wastewater may contain high levels of the nutrients nitrogen and phosphorus. Excessive release to the environment can lead to a build up of nutrients, called eutrophication, which can in turn encourage the overgrowth of weeds, algae, and cyanobacteria (blue-green algae). This may cause an algal bloom, a rapid growth in the population of algae. The algae numbers are unsustainable and eventually most of them die. The decomposition of the algae by bacteria uses up so much of oxygen in the water that most or all of the animals die, which creates more organic matter for the bacteria to decompose. In addition to causing deoxygenation, some algal species produce toxins that contaminate drinking water supplies. Different treatment processes are required to remove nitrogen and phosphorus.
Nitrogen removal
The removal of nitrogen is effected through the biological oxidation of nitrogen from ammonia (nitrification) to nitrate, followed by denitrification, the reduction of nitrate to nitrogen gas. Nitrogen gas is released to the atmosphere and thus removed from the water.
Nitrification itself is a two-step aerobic process, each step facilitated by a different type of bacteria. The oxidation of ammonia (NH3) to nitrite (NO2−) is most often facilitated by Nitrosomonas spp. (nitroso=ammonium). Nitrite oxidation to nitrate (NO3−), though traditionally believed to be facilitated by Nitrobacter spp. (nitro=nitrite), is now known to be facilitated in the environment almost exclusively by Nitrospira spp.
Denitrification requires anoxic conditions to encourage the appropriate biological communities to form. It is facilitated by a wide diversity of bacteria. Sand filters, lagooning and reed beds can all be used to reduce nitrogen, but the activated sludge process (if designed well) can do the job the most easily. Since denitrification is the reduction of nitrate to dinitrogen gas, an electron donor is needed. This can be, depending on the wastewater, organic matter (from faeces), sulfide, or an added donor like methanol.
Sometimes the conversion of toxic ammonia to nitrate alone is referred to as tertiary treatment.
Phosphorus removal
Phosphorus can be removed biologically in a process called enhanced biological phosphorus removal. In this process, specific bacteria, called polyphosphate accumulating organisms, are selectively enriched and accumulate large quantities of phosphorus within their cells (up to 20% of their mass). When the biomass enriched in these bacteria is separated from the treated water, these biosolids have a high fertilizer value.
Phosphorus removal can also be achieved by chemical precipitation, usually with salts of iron (e.g. ferric chloride) or aluminum (e.g. alum). The resulting chemical sludge is difficult to handle and the added chemicals can be expensive. Despite this, chemical phosphorus removal requires significantly smaller equipment footprint than biological removal, is easier to operate and can be more reliable in areas that have wastewater compositions that make biological phosphorus removal difficult.
Disinfection
The purpose of disinfection in the treatment of wastewater is to substantially reduce the number of microorganisms in the water to be discharged back into the environment. The effectiveness of disinfection depends on the quality of the water being treated (e.g., cloudiness, pH, etc.), the type of disinfection being used, the disinfectant dosage (concentration and time), and other environmental variables. Cloudy water will be treated less successfully since solid matter can shield organisms, especially from ultraviolet light or if contact times are low. Generally, short contact times, low doses and high flows all militate against effective disinfection. Common methods of disinfection include ozone, chlorine, or ultraviolet light. Chloramine, which is used for drinking water, is not used in wastewater treatment because of its persistence.
Chlorination remains the most common form of wastewater disinfection in North America due to its low cost and long-term history of effectiveness. One disadvantage is that chlorination of residual organic material can generate chlorinated-organic compounds that may be carcinogenic or harmful to the environment. Residual chlorine or chloramines may also be capable of chlorinating organic material in the natural aquatic environment. Further, because residual chlorine is toxic to aquatic species, the treated effluent must also be chemically dechlorinated, adding to the complexity and cost of treatment.
Ultraviolet (UV) light can be used instead of chlorine, iodine, or other chemicals. Because no chemicals are used, the treated water's taste is more natural and pure as compared to other methods. UV radiation causes damage to the genetic structure of bacteria, viruses, and other pathogens, making them incapable of reproduction. The key disadvantages of UV disinfection are the need for frequent lamp maintenance and replacement and the need for a highly treated effluent to ensure that the target microorganisms are not shielded from the UV radiation (i.e., any solids present in the treated effluent may protect microorganisms from the UV light). In the United Kingdom, light is becoming the most common means of disinfection because of the concerns about the impacts of chlorine in chlorinating residual organics in the wastewater and in chlorinating organics in the receiving water. Edmonton, Alberta, Canada also uses UV light for its water treatment.
Ozone O3 is generated by passing oxygen O2 through a high voltage potential resulting in a third oxygen atom becoming attached and forming O3. Ozone is very unstable and reactive and oxidizes most organic material it comes in contact with, thereby destroying many pathogenic microorganisms. Ozone is considered to be safer than chlorine because, unlike chlorine which has to be stored on site (highly poisonous in the event of an accidental release), ozone is generated onsite as needed. Ozonation also produces fewer disinfection by-products than chlorination. A disadvantage of ozone disinfection is the high cost of the ozone generation equipment and the requirements for highly skilled operators.
Drinking Water
Post by Voon Chen Li
Safe drinking water is everybody's business. Managing drinking water supplies properly, from the source water to the consumer's tap, takes a great deal of knowledge and coordination among multiple stakeholders--from governments and businesses, to individuals like you and me.
A shared responsibility
In Canada, the responsibility for making sure drinking water supplies are safe is shared between the provincial, territorial, federal and municipal governments. The day-to-day responsibility of providing safe drinking water to the public generally rests with the provinces and territories, while municipalities usually oversee the day to day operations of the treatment facilities.
Health Canada's Water Quality and Health Bureau plays a leadership role in science and research. Its mandate and expertise lies in protecting the health of all Canadians by developing the Guidelines for Canadian Drinking Water Quality in partnership with the provinces and territories. These guidelines are used by every jurisdiction in Canada and are the basis for establishing drinking water quality requirements for all Canadians.
Health Canada is recognized as a World Health Organisation/Pan American Health Organisation (WHO/PAHO) Collaborating Centre for Water Quality, and participates in the development of WHO guidelines for drinking water. The Bureau also works closely and shares information with other government agencies such as the United States Environmental Protection Agency.
The multi-barrier approach
The best way to make sure drinking water supplies are kept clean, safe and reliable is to take a preventive risk management approach. This means understanding each water supply from its beginning in nature to where it reaches you, the consumer. This understanding--about the water's characteristics, the ways it could become contaminated, and the type of treatment it needs--comes from collecting and studying data.
The drinking water supply can be broken down into three parts: the source water, the drinking water treatment system, and the distribution system which carries the treated water to homes, businesses, schools, and other buildings. The plumbing inside your home is an extension of the distribution system.
As drinking water travels on its journey to you, it can become contaminated in many ways. The multi-barrier approach to managing drinking water supplies is a preventive risk management approach that identifies all known and potential hazards and makes sure barriers are in place to reduce or eliminate the risk of contamination.
Drinking water guidelines
In order to know whether their drinking water management program is working, drinking water authorities need to have benchmarks for water quality. These benchmarks come in the form of drinking water guidelines. Guidelines make it possible for drinking water to be tested at various points along its journey and analysed to determine whether it is safe to drink. The Guidelines for Canadian Drinking Water Quality are established by the Federal-Provincial-Territorial Committee on Drinking Water and published by Health Canada.
The guidelines for some contaminants, like E.coli which indicates the presence of microbiological pathogens, are very clear and should never be exceeded because people will become sick soon after drinking contaminated water. Others, like many of the chemical guidelines, are based on the best available science and give a good indication of health effects that might be seen in some people if we consume high amounts of the chemical in drinking water over a period of decades.
Products and materials that come into contact with drinking water
Another way that drinking water can become contaminated is by the products and materials with which it comes into contact. Water is a solvent and can leach metals and other chemicals from pipes, fittings, fixtures, and other products. Health Canada works with national and international standards-setting organizations to develop health-based performance standards for these products and materials to make sure they are not contributing harmful contaminants to your drinking water.
What information you can find here
This site includes many publications that explain what it takes to keep our drinking water supplies clean, safe and reliable.
If you are looking for general information about substances that could be found in tap water and how these may affect your health, check out our It's Your Health series of publications. For slightly more technical information, you may be interested in our Water Talk series.
If you have a scientific or technical background and would like to understand in detail how a particular guideline was developed and why, see the supporting documents for the Guidelines for Canadian Drinking Water Quality. You are also invited to participate in current consultations on draft guidelines.
If you work in the drinking water industry, you can find technical information about the multi-barrier approach to ensuring safe drinking water, documents about specific drinking water guidelines, and information about standards for products and materials that come into contact with drinking water. You'll also find information about the Federal-Provincial-Territorial Committee on Drinking Water, including membership, meeting minutes, and processes for developing guidelines.
Safe drinking water is everybody's business. Managing drinking water supplies properly, from the source water to the consumer's tap, takes a great deal of knowledge and coordination among multiple stakeholders--from governments and businesses, to individuals like you and me.
A shared responsibility
In Canada, the responsibility for making sure drinking water supplies are safe is shared between the provincial, territorial, federal and municipal governments. The day-to-day responsibility of providing safe drinking water to the public generally rests with the provinces and territories, while municipalities usually oversee the day to day operations of the treatment facilities.
Health Canada's Water Quality and Health Bureau plays a leadership role in science and research. Its mandate and expertise lies in protecting the health of all Canadians by developing the Guidelines for Canadian Drinking Water Quality in partnership with the provinces and territories. These guidelines are used by every jurisdiction in Canada and are the basis for establishing drinking water quality requirements for all Canadians.
Health Canada is recognized as a World Health Organisation/Pan American Health Organisation (WHO/PAHO) Collaborating Centre for Water Quality, and participates in the development of WHO guidelines for drinking water. The Bureau also works closely and shares information with other government agencies such as the United States Environmental Protection Agency.
The multi-barrier approach
The best way to make sure drinking water supplies are kept clean, safe and reliable is to take a preventive risk management approach. This means understanding each water supply from its beginning in nature to where it reaches you, the consumer. This understanding--about the water's characteristics, the ways it could become contaminated, and the type of treatment it needs--comes from collecting and studying data.
The drinking water supply can be broken down into three parts: the source water, the drinking water treatment system, and the distribution system which carries the treated water to homes, businesses, schools, and other buildings. The plumbing inside your home is an extension of the distribution system.
As drinking water travels on its journey to you, it can become contaminated in many ways. The multi-barrier approach to managing drinking water supplies is a preventive risk management approach that identifies all known and potential hazards and makes sure barriers are in place to reduce or eliminate the risk of contamination.
Drinking water guidelines
In order to know whether their drinking water management program is working, drinking water authorities need to have benchmarks for water quality. These benchmarks come in the form of drinking water guidelines. Guidelines make it possible for drinking water to be tested at various points along its journey and analysed to determine whether it is safe to drink. The Guidelines for Canadian Drinking Water Quality are established by the Federal-Provincial-Territorial Committee on Drinking Water and published by Health Canada.
The guidelines for some contaminants, like E.coli which indicates the presence of microbiological pathogens, are very clear and should never be exceeded because people will become sick soon after drinking contaminated water. Others, like many of the chemical guidelines, are based on the best available science and give a good indication of health effects that might be seen in some people if we consume high amounts of the chemical in drinking water over a period of decades.
Products and materials that come into contact with drinking water
Another way that drinking water can become contaminated is by the products and materials with which it comes into contact. Water is a solvent and can leach metals and other chemicals from pipes, fittings, fixtures, and other products. Health Canada works with national and international standards-setting organizations to develop health-based performance standards for these products and materials to make sure they are not contributing harmful contaminants to your drinking water.
What information you can find here
This site includes many publications that explain what it takes to keep our drinking water supplies clean, safe and reliable.
If you are looking for general information about substances that could be found in tap water and how these may affect your health, check out our It's Your Health series of publications. For slightly more technical information, you may be interested in our Water Talk series.
If you have a scientific or technical background and would like to understand in detail how a particular guideline was developed and why, see the supporting documents for the Guidelines for Canadian Drinking Water Quality. You are also invited to participate in current consultations on draft guidelines.
If you work in the drinking water industry, you can find technical information about the multi-barrier approach to ensuring safe drinking water, documents about specific drinking water guidelines, and information about standards for products and materials that come into contact with drinking water. You'll also find information about the Federal-Provincial-Territorial Committee on Drinking Water, including membership, meeting minutes, and processes for developing guidelines.
WHO Guidelines for drinking-water quality
Post by Voon Chen Li No. Matrix: SEP060160
Drinking-water quality is an issue of concern for human health in developing and developed countries world-wide. The risks arise from infectious agents, toxic chemicals and radiological hazards. Experience highlights the value of preventive management approaches spanning from water resource to consumer.
WHO produces international norms on water quality and human health in the form of guidelines that are used as the basis for regulation and standard setting, in developing and developed countries world-wide.
WHO produces international norms on water quality and human health in the form of guidelines that are used as the basis for regulation and standard setting, in developing and developed countries world-wide.
Guidelines for drinking-water quality, third edition, incorporating first addendum
Volume 1 - Recommendations
The first and second editions of the Guidelines for Drinking-water Quality were used by developing and developed countries worldwide as the basis for regulation and standard setting to ensure the safety of drinking-water. They recognized the priority that should be given to ensuring microbial safety and provided guideline values for a large number of chemical hazards.
The third edition of the Guidelines has been comprehensively updated to take account of developments in risk assessment and risk management since the second edition. It describes a “Framework for Drinking-water Safety” and discusses the roles and responsibilities of different stakeholders, including the complementary roles of national regulators, suppliers, communities and independent “surveillance” agencies.
Developments in the third edition of the Guidelines include significantly expanded guidance on ensuring the microbial safety of drinking-water – in particular through comprehensive system-specific “water safety plans”. Information on many chemicals has been revised to account for new scientific information and information on chemicals not previously considered has been included. For the first time, reviews of many waterborne pathogens are provided.
Recognizing the need for different tools and approaches in supporting large and community supplies, in the third edition continues to describe the principal characteristics of the approaches to each. New sections deal with the application of the Guidelines to specific circumstances, such as emergencies and disasters, large buildings, packaged/bottled water, travellers, desalination systems, food production and processing and water safety on ships and in aviation.
The first addendum, which updates the third edition, has been incorporated inthis volume. It includes more guidance on management of emergencies and unforeseen events, additions concerning chlorination by-products and developing standards for volatile substances, and several new fact sheets for chemical substances.
The first and second editions of the Guidelines for Drinking-water Quality were used by developing and developed countries worldwide as the basis for regulation and standard setting to ensure the safety of drinking-water. They recognized the priority that should be given to ensuring microbial safety and provided guideline values for a large number of chemical hazards.
The third edition of the Guidelines has been comprehensively updated to take account of developments in risk assessment and risk management since the second edition. It describes a “Framework for Drinking-water Safety” and discusses the roles and responsibilities of different stakeholders, including the complementary roles of national regulators, suppliers, communities and independent “surveillance” agencies.
Developments in the third edition of the Guidelines include significantly expanded guidance on ensuring the microbial safety of drinking-water – in particular through comprehensive system-specific “water safety plans”. Information on many chemicals has been revised to account for new scientific information and information on chemicals not previously considered has been included. For the first time, reviews of many waterborne pathogens are provided.
Recognizing the need for different tools and approaches in supporting large and community supplies, in the third edition continues to describe the principal characteristics of the approaches to each. New sections deal with the application of the Guidelines to specific circumstances, such as emergencies and disasters, large buildings, packaged/bottled water, travellers, desalination systems, food production and processing and water safety on ships and in aviation.
The first addendum, which updates the third edition, has been incorporated inthis volume. It includes more guidance on management of emergencies and unforeseen events, additions concerning chlorination by-products and developing standards for volatile substances, and several new fact sheets for chemical substances.
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