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Thread: Water Treatment Notes

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    Doc 32 Water Treatment Notes

    Sewage treatment 1Sewage treatment
    The objective of sewage treatment is to produce a disposable effluent
    without causing harm to the surrounding environment, and also
    prevent pollution.[1]
    Sewage treatment is the process of removing
    contaminants from wastewater and household sewage,
    both runoff (effluents) and domestic. It includes
    physical, chemical, and biological processes to remove
    physical, chemical and biological contaminants. Its
    objective is to produce an environmentally-safe fluid
    waste stream (or treated effluent) and a solid waste (or
    treated sludge) suitable for disposal or reuse (usually as
    farm fertilizer). Using advanced technology it is now
    possible to re-use sewage effluent for drinking water,
    although Singapore is the only country to implement
    such technology on a production scale in its production
    of NEWater.[2]
    Origins of sewage
    Sewage is generated by residential, institutional, and commercial and industrial establishments. It includes household
    waste liquid from toilets, baths, showers, kitchens, sinks and so forth that is disposed of via sewers. In many areas,
    sewage also includes liquid waste from industry and commerce. The separation and draining of household waste 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.
    Sewage may include stormwater runoff, sewerage systems capable of handling stormwater are known as combined
    systems. Combined sewer systems are usually avoided now because precipitation causes widely varying flows
    reducing sewage treatment plant efficiency. Combined sewers require much larger and more expensive treatment
    facilities than sanitary sewers. Heavy storm runoff may overwhelm the sewage treatment system, causing a spill or
    overflow. Sanitary sewers are typically much smaller than combined sewers, and they are not designed to transport
    stormwater. Backups of raw sewage can occur if excessive infiltration/inflow is allowed into a sanitary sewer
    Modern sewered developments tend to be provided with separate storm drain systems for rainwater.[3] As rainfall
    travels over 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. (See urban runoff.)[4] Some jurisdictions require
    stormwater to receive some level of treatment before being discharged directly into waterways. Examples of
    treatment processes used for stormwater include retention basins, wetlands, buried vaults with various kinds of
    media filters, and vortex separators (to remove coarse solids).
    Process overview
    Sewage can be treated close to where it is created, a decentralised system (in septic tanks, biofilters or aerobic
    treatment systems), or be collected and transported via a network of pipes and pump stations to a municipal
    treatment plant, a centralised system (see sewerage and pipes and infrastructure). Sewage collection and treatment is
    typically subject to local, state and federal regulations and standards. Industrial sources of sewage often require
    specialized treatment processes (see Industrial wastewater treatment).
    Sewage treatment generally involves three stages, called primary, secondary and tertiary treatment.
    Sewage treatment 2
    • Primary treatment consists of temporarily holding the sewage in a quiescent basin where heavy solids can settle
    to the bottom while oil, grease and lighter solids float to the surface. The settled and floating materials are
    removed and the remaining liquid may be discharged or subjected to secondary treatment.
    • Secondary treatment removes dissolved and suspended biological matter. Secondary treatment is typically
    performed by indigenous, water-borne micro-organisms in a managed habitat. Secondary treatment may require a
    separation process to remove the micro-organisms from the treated water prior to discharge or tertiary treatment.
    • Tertiary treatment is sometimes defined as anything more than primary and secondary treatment in order to allow
    rejection into a highly sensitive or fragile ecosystem (estuaries, low-flow rivers, coral reefs,...). Treated water is
    sometimes disinfected chemically or physically (for example, by lagoons and microfiltration) prior to discharge
    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 or agricultural purposes.
    Process Flow Diagram for a typical large-scale treatment plant
    Process Flow Diagram for a typical treatment plant via Subsurface Flow Constructed
    Wetlands (SFCW)
    Pre-treatment removes materials that can be easily collected from the raw sewage before they damage or clog the
    pumps and sewage lines of primary treatment clarifiers (trash, tree limbs, leaves, branches etc.).
    The influent sewage water passes through a bar screen to remove all large objects like cans, rags, sticks, plastic
    packets etc. carried in the sewage stream.[5] This is most commonly done with an automated mechanically raked bar
    screen in modern plants serving large populations, whilst in smaller or less modern plants, a manually cleaned screen
    may be used. The raking action of a mechanical bar screen is typically paced according to the accumulation on the
    bar screens and/or flow rate. The solids are collected and later disposed in a landfill, or incinerated. Bar screens or
    Sewage treatment 3
    mesh screens of varying sizes may be used to optimize solids removal. If gross solids are not removed, they become
    entrained in pipes and moving parts of the treatment plant, and can cause substantial damage and inefficiency in the
    Grit removal
    Pre-treatment may include a sand or grit channel or chamber, where the velocity of the incoming sewage is adjusted
    to allow the settlement of sand, grit, stones, and broken glass. These particles are removed because they may damage
    pumps and other equipment. For small sanitary sewer systems, the grit chambers may not be necessary, but grit
    removal is desirable at larger plants.[6] Grit chambers come in 3 types: horizontal grit chambers, aerated grit
    chambers and vortex grit chambers.
    Flow equalization
    Clarifiers and mechanized secondary treatment are more efficient under uniform flow conditions. Equalization
    basins may be used for temporary storage of diurnal or wet-weather flow peaks. Basins provide a place to
    temporarily hold incoming sewage during plant maintenance and a means of diluting and distributing batch
    discharges of toxic or high-strength waste which might otherwise inhibit biological secondary treatment (including
    portable toilet waste, vehicle holding tanks, and septic tank pumpers). Flow equalization basins require variable
    discharge control, typically include provisions for bypass and cleaning, and may also include aerators. Cleaning may
    be easier if the basin is downstream of screening and grit removal.[7]
    Fat and grease removal
    In some larger plants, fat and grease is removed by passing the sewage through a small tank where skimmers collect
    the fat floating on the surface. Air blowers in the base of the tank may also be used to help recover the fat as a froth.
    Many plants, however, use primary clarifiers with mechanical surface skimmers for fat and grease removal.
    Primary treatment
    In the primary sedimentation stage, sewage flows through large tanks, commonly called "pre-settling basins",
    "primary sedimentation tanks" or "primary clarifiers"[8]. The tanks are used to settle sludge while grease and oils rise
    to the surface and are skimmed off. Primary settling tanks are usually equipped with mechanically driven scrapers
    that continually drive the collected sludge towards a hopper in the base of the tank where it is pumped to sludge
    treatment facilities.[6]:9-11 Grease and oil from the floating material can sometimes be recovered for saponification.
    The dimensions of the tank should be designed to effect removal of a high percentage of the floatables and sludge. A
    typical sedimentation tank may remove from 50 to 70 percent of suspended solids, and from 30 to 35 percent of
    biochemical oxygen demand (BOD) from the sewage.
    Secondary treatment
    Secondary treatment is designed to substantially degrade the biological content of the sewage which are derived
    from human waste, food waste, soaps and detergent. The majority of municipal plants treat the settled sewage liquor
    using aerobic biological processes. To be effective, the biota require both oxygen and food to live. 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 systems.
    • Fixed-film or attached growth systems include trickling filters, biotowers, and rotating biological contactors,
    where the biomass grows on media and the sewage passes over its surface.[6]:11-13 The fixed-film principal has
    further developed into Moving Bed Biofilm Reactors (MBBR [9]), and Integrated Fixed-Film Activated Sludge
    (IFAS [10]) processes. An MBBR system typically requires smaller footprint than suspended-growth systems.
    Sewage treatment 4
    (Black & Veatch [11])
    • Suspended-growth systems include activated sludge, where the biomass is mixed with the sewage and can be
    operated in a smaller space than trickling filters 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.[6]:11-13
    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 filters filled with media to
    which wastewater is applied. They are designed to allow high hydraulic loading and a high level of aeration. On
    larger installations, air is forced through the media using blowers. The resultant wastewater is usually within the
    normal range for conventional treatment processes.
    A generalized, schematic diagram of an activated sludge process.
    A filter removes a small percentage of the
    suspended organic matter, while the
    majority of the organic matter undergoes a
    change of character, only due to the
    biological oxidation and nitrification taking
    place in the filter. With this aerobic
    oxidation and nitrification, the organic
    solids are converted into coagulated
    suspended mass, which is heavier and
    bulkier, and can settle to the bottom of a
    tank. The effluent of the filter is therefore
    passed through a sedimentation tank, called
    a secondary clarifier, secondary settling tank
    or humus tank.
    Activated sludge
    In general, activated sludge plants encompass a variety of mechanisms and processes that use dissolved oxygen to
    promote the growth of biological floc that substantially removes organic material.[6]:12-13
    The process traps particulate material and can, under ideal conditions, convert ammonia to nitrite and nitrate
    ultimately to nitrogen gas. (See also denitrification).
    Sewage treatment 5
    A Typical Surface-Aerated Basin (using motor-driven floating aerators)
    Surface-aerated basins (Lagoons)
    Many small municipal sewage systems
    in the United States (1 million gal./day
    or less) use aerated lagoons.[12]
    Most biological oxidation processes for
    treating industrial wastewaters have in
    common the use of oxygen (or air) and
    microbial action. Surface-aerated basins
    achieve 80 to 90 percent removal of
    BOD with retention times of 1 to 10
    days.[13] The basins may range in depth
    from 1.5 to 5.0 metres and use
    motor-driven aerators floating on the
    surface of the wastewater.[13]
    In an aerated basin system, the aerators
    provide two functions: they transfer air into the basins required by the biological oxidation reactions, and they
    provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater and
    microbes). Typically, the floating surface aerators are rated to deliver the amount of air equivalent to 1.8 to 2.7 kg
    O2/kW·h. However, they do not provide as good mixing as is normally achieved in activated sludge systems and
    therefore aerated basins do not achieve the same performance level as activated sludge units.[13]
    Biological oxidation processes are sensitive to temperature and, between 0 °C and 40 °C, the rate of biological
    reactions increase with temperature. Most surface aerated vessels operate at between 4 °C and 32 °C.[13]
    Filter beds (oxidizing beds)
    In older plants and those receiving variable loadings, trickling filter beds are used where the settled sewage liquor is
    spread onto the surface of a bed made up of coke (carbonized coal), limestone chips or specially fabricated plastic
    media. Such media must have large surface areas to support the biofilms that form. The liquor is typically distributed
    through perforated spray arms. The distributed liquor trickles through the 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.[6]:12 This
    biofilm is often grazed by insect larvae, snails, 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. Recent
    advances in media and process micro-biology design overcome many issues with trickling filter designs.
    Constructed wetlands
    Constructed wetlands (can either be surface flow or subsurface flow, horizontal or vertical flow), include engineered
    reedbeds and belong to the family of phytorestoration and ecotechnologies; they provide a high degree of biological
    improvement and depending on design, act as a primary, secondary and sometimes tertiary treatment, also see
    phytoremediation. One example is a small reedbed used to clean the drainage from the elephants' enclosure at
    Chester Zoo in England; numerous CWs are used to recycle the water of the city of Honfleur in France and
    numerous other towns in Europe, the US, Asia and Australia. They are known to be highly productive systems as
    they copy natural wetlands, called the "kidneys of the earth" for their fundamental recycling capacity of the
    hydrological cycle in the biosphere. Robust and reliable, their treatment capacities improve as time go by, at the
    opposite of conventional treatment plants whose machinery age with time. They are being increasingly used,
    although adequate and experienced design are more fundamental than for other systems and space limitation may
    Sewage treatment 6
    impede their use.
    Soil bio-technology
    A new process called soil bio-technology (SBT) developed at IIT Bombay has shown tremendous improvements in
    process efficiency enabling total water reuse, due to extremely low operating power requirements of less than 50
    joules per kg of treated water.[14] Typically SBT systems can achieve chemical oxygen demand (COD) levels less
    than 10 mg/L from sewage input of COD 400 mg/L.[15] SBT plants exhibit high reductions in COD values and
    bacterial counts as a result of the very high microbial densities available in the media. Unlike conventional treatment
    plants, SBT plants produce insignificant amounts of sludge, precluding the need for sludge disposal areas that are
    required by other technologies.[16]
    In the Indian context, conventional sewage treatment plants fall into systemic disrepair due to 1) high operating
    costs, 2) equipment corrosion due to methanogenesis and hydrogen sulphide, 3) non-reusability of treated water due
    to high COD (>30 mg/L) and high fecal coliform (>3000 NFU) counts, 4) lack of skilled operating personnel and 5)
    equipment replacement issues. Examples of such systemic failures has been documented by Sankat Mochan
    Foundation at the Ganges basin after a massive cleanup effort by the Indian government in 1986 by setting up
    sewage treatment plants under the Ganga Action Plan failed to improve river water quality.
    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.
    Schematic diagram of a typical rotating biological contactor (RBC). The treated effluent
    clarifier/settler is not included in the diagram.
    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 break down and
    stabilize 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.
    A functionally similar biological filtering system has become popular as part of home aquarium filtration and
    purification. The aquarium water is drawn up out of the tank and then cascaded over a freely spinning corrugated
    fiber-mesh wheel before passing through a media filter and back into the aquarium. The spinning mesh wheel
    Sewage treatment 7
    develops a biofilm coating of microorganisms that feed on the suspended wastes in the aquarium water and are also
    exposed to the atmosphere as the wheel rotates. This is especially good at removing waste urea and ammonia
    urinated into the aquarium water by the fish and other animals.
    Membrane bioreactors
    Membrane bioreactors (MBR) combine activated sludge treatment with a membrane liquid-solid separation process.
    The membrane component uses low pressure microfiltration or ultrafiltration 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 an MBR 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 MBR process allows for very effective removal of both soluble and particulate biodegradable
    materials at higher loading rates. Thus increased sludge retention times, usually exceeding 15 days, ensure complete
    nitrification even in extremely cold weather.
    The cost of building and operating an MBR is often higher than conventional methods of sewage treatment.
    Membrane filters can be blinded with grease or abraded by suspended grit and lack a clarifier's flexibility to pass
    peak flows. The technology has become increasingly popular for reliably pretreated waste streams and has gained
    wider acceptance where infiltration and inflow have been controlled, however, and the life-cycle costs have been
    steadily decreasing. The small footprint of MBR systems, and the high quality effluent produced, make them
    particularly useful for water reuse applications.[17]
    Secondary sedimentation
    Secondary Sedimentation tank at a rural
    treatment plant.
    The final step in the secondary treatment stage is to settle out the biological
    floc or filter material through a secondary clarifier and to produce sewage
    water containing low levels of organic material and suspended matter.
    Tertiary treatment
    The purpose of tertiary treatment is to provide a final treatment 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."
    Sewage treatment 8
    Sand filtration removes much of the residual suspended matter.[6]:22-23 Filtration over activated carbon, also called
    carbon adsorption, removes residual toxins.[6]:19
    A sewage treatment plant and lagoon in Everett,
    Washington, United States.
    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.
    Nutrient 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 the 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
    Nitrogen removal
    The removal of nitrogen is effected through the biological oxidation of nitrogen from ammonia to nitrate
    (nitrification), 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 referring to the formation of
    a nitroso functional group). Nitrite oxidation to nitrate (NO3
    −), though traditionally believed to be facilitated by
    Nitrobacter spp. (nitro referring the formation of a nitro functional group), 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.[6]:17-18 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. The sludge in the anoxic tanks (denitrification tanks)
    must be mixed well (mixture of recirculated mixed liquor, return activated sludge [RAS], and raw influent) e.g. by
    using submersible mixers in order to achieve the desired denitrification.
    Sometimes the conversion of toxic ammonia to nitrate alone is referred to as tertiary treatment.
    Many sewage treatment plants use centrifugal pumps to transfer the nitrified mixed liquor from the aeration zone to
    the anoxic zone for denitrification. These pumps are often referred to as Internal Mixed Liquor Recycle(IMLR)
    Sewage treatment 9
    Phosphorus removal
    Each person excretes between 200 and 1000 grams of phosphorus annually. Studies of United States sewage in the
    late 1960s estimated mean per capita contributions of 500 grams in urine and feces, 1000 grams in synthetic
    detergents, and lesser variable amounts used as corrosion and scale control chemicals in water supplies.[18] Source
    control via alternative detergent formulations has subsequently reduced the largest contribution, but the content of
    urine and feces will remain unchanged. Phosphorus removal is important as it is a limiting nutrient for algae growth
    in many fresh water systems. (For a description of the negative effects of algae, see Nutrient removal). It is also
    particularly important for water reuse systems where high phosphorus concentrations may lead to fouling of
    downstream equipment such as reverse osmosis.
    Phosphorus can be removed biologically in a process called enhanced biological phosphorus removal. In this
    process, specific bacteria, called polyphosphate accumulating organisms (PAOs), are selectively enriched and
    accumulate large quantities of phosphorus within their cells (up to 20 percent 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),
    aluminum (e.g. alum), or lime.[6]:18 This may lead to excessive sludge production as hydroxides precipitates and the
    added chemicals can be expensive. Chemical phosphorus removal requires significantly smaller equipment footprint
    than biological removal, is easier to operate and is often more reliable than biological phosphorus removal. Another
    method for phosphorus removal is to use granular laterite.
    Once removed, phosphorus, in the form of a phosphate-rich sludge, may be stored in a land fill or resold for use in
    The purpose of disinfection in the treatment of waste water is to substantially reduce the number of microorganisms
    in the water to be discharged back into the environment for the later use of drinking, bathing, irrigation, etc. 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, ultraviolet light, or sodium hypochlorite.[6]:16
    Chloramine, which is used for drinking water, is not used in the treatment of waste water because of its persistence.
    After multiple steps of disinfection, the treated water is ready to be released back into the water cycle by means of
    the nearest body of water or agriculture. Afterwards, the water can be transferred to reserves for everyday human
    Chlorination remains the most common form of waste water 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 has no adverse effect on organisms that later consume it, as may be the case with 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, UV light is becoming the most common means of disinfection because of the concerns about the
    Sewage treatment 10
    impacts of chlorine in chlorinating residual organics in the wastewater and in chlorinating organics in the receiving
    water. Some sewage treatment systems in Canada and the US also use UV light for their effluent water
    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
    special operators.
    Odor control
    Odors emitted by sewage treatment are typically an indication of an anaerobic or "septic" condition.[21] Early stages
    of processing will tend to produce foul smelling gases, with hydrogen sulfide being most common in generating
    complaints. Large process plants in urban areas will often treat the odors with carbon reactors, a contact media with
    bio-slimes, small doses of chlorine, or circulating fluids to biologically capture and metabolize the obnoxious
    gases.[22] Other methods of odor control exist, including addition of iron salts, hydrogen peroxide, calcium nitrate,
    etc. to manage hydrogen sulfide levels. High-density solids pumps are suitable to reduce odors by conveying sludge
    through hermetic closed pipework.
    Package plants and batch reactors
    To use less space, treat difficult waste and intermittent flows, a number of designs of hybrid treatment plants have
    been produced. Such plants often combine at least two stages of the three main treatment stages into one combined
    stage. In the UK, where a large number of wastewater treatment plants serve small populations, package plants are a
    viable alternative to building a large structure for each process stage. In the US, package plants are typically used in
    rural areas, highway rest stops and trailer parks.[23]
    One type of system that combines secondary treatment and settlement is the sequencing batch reactor (SBR).
    Typically, activated sludge is mixed with raw incoming sewage, and then mixed and aerated. The settled sludge is
    run off and re-aerated before a proportion is returned to the headworks.[24] SBR plants are now being deployed in
    many parts of the world.
    The disadvantage of the SBR process is that it requires a precise control of timing, mixing and aeration. This
    precision is typically achieved with computer controls linked to sensors. Such a complex, fragile system is unsuited
    to places where controls may be unreliable, poorly maintained, or where the power supply may be intermittent.
    Extended aeration package plants use separate basins for aeration and settling, and are somewhat larger than SBR
    plants with reduced timing sensitivity.[25]
    Package plants may be referred to as high charged or low charged. This refers to the way the biological load is
    processed. In high charged systems, the biological stage is presented with a high organic load and the combined floc
    and organic material is then oxygenated for a few hours before being charged again with a new load. In the low
    charged system the biological stage contains a low organic load and is combined with flocculate for longer times.
    Sewage treatment 11
    Sludge treatment and disposal
    The sludges accumulated in a wastewater treatment process must be treated and disposed of in a safe and effective
    manner. The purpose of digestion is to reduce the amount of organic matter and the number of disease-causing
    microorganisms present in the solids. The most common treatment options include anaerobic digestion, aerobic
    digestion, and composting. Incineration is also used albeit to a much lesser degree.[6]:19-21
    The equipment used in treatment plants are the following: first, the sludge is passed trough a so-called pre-thickener
    or main sludge thickener[26] This dewaters the sludge. Types of pre-thickeners include[27]: centrifugal sludge
    thickeners[28], rotary drum sludge thickeners, and belt filter presses.[29] After this, the actual digestion is done in a
    tank, and after this, the remaining solid is moved off.
    Sludge treatment depends on the amount of solids generated and other site-specific conditions. Composting is most
    often applied to small-scale plants with aerobic digestion for mid sized operations, and anaerobic digestion for the
    larger-scale operations.
    Anaerobic digestion
    Anaerobic digestion is a bacterial process that is carried out in the absence of oxygen. The process can either be
    thermophilic digestion, in which sludge is fermented in tanks at a temperature of 55°C, or mesophilic, at a
    temperature of around 36°C. Though allowing shorter retention time (and thus smaller tanks), thermophilic digestion
    is more expensive in terms of energy consumption for heating the sludge.
    Anaerobic digestion is the most common (mesophilic) treatment of domestic sewage in septic tanks, which normally
    retain the sewage from one day to two days, reducing the BOD by about 35 to 40 percent. This reduction can be
    increased with a combination of anaerobic and aerobic treatment by installing Aerobic Treatment Units (ATUs) in
    the septic tank.
    Mesophilic Anaerobic Digestion (MAD) is also the most common method for treating sludge produced at Sewage
    Treatment Plants. The sludge is fed into large tanks and held for a minimum of 12 days to allow the digestion
    process to perform the 4 stages necessary to digest the sludge. These are Hydrolysis, acidogenesis, Acetogenesis and
    Methanogenesis. In this process the complex proteins and sugars are broken down to form more simple compounds
    such as water, carbon dioxide and methane.</ref>f>http:/ / www. esru. strath. ac. uk/ EandE/ Web_sites/ 03-04/
    biomass/ background%20info8. html</ref>
    One major feature of anaerobic digestion is the production of biogas (with the most useful component being
    methane), which can be used in generators for electricity production and/or in boilers for heating purposes. Many
    larger sites utilize the biogas for combined heat and power, using the cooling water from the generators to maintain
    the temperature of the digestion plant at the required 35 degrees +/- 3
    Aerobic digestion
    Aerobic digestion is a bacterial process occurring in the presence of oxygen. Under aerobic conditions, bacteria
    rapidly consume organic matter and convert it into carbon dioxide. The operating costs used to be characteristically
    much greater for aerobic digestion because of the energy used by the blowers, pumps and motors needed to add
    oxygen to the process.
    Aerobic digestion can also be achieved by using diffuser systems or jet aerators to oxidize the sludge. Fine bubble
    diffusers are typically the more cost-efficient diffusion method, however, plugging is typically a problem due to
    sediment settling into the smaller air holes. Coarse bubble diffusers are more commonly used in activated sludge
    tanks (generally a side process in waste water management) or in the flocculation stages. A key component for
    selecting diffuser type is to ensure it will produce the required oxygen transfer rate.
    Sewage treatment 12
    Composting is also an aerobic process that involves mixing the sludge with sources of carbon such as sawdust, straw
    or wood chips. In the presence of oxygen, bacteria digest both the wastewater solids and the added carbon source
    and, in doing so, produce a large amount of heat.[6]:20
    Incineration of sludge is less common because of air emissions concerns and the supplemental fuel (typically natural
    gases or fuel oil) required to burn the low calorific value sludge and vaporize residual water. Stepped multiple hearth
    incinerators with high residence time and fluidized bed incinerators are the most common systems used to combust
    wastewater sludge. Co-firing in municipal waste-to-energy plants is occasionally done, this option being less
    expensive assuming the facilities already exist for solid waste and there is no need for auxiliary fuel.[6]:20-21
    Sludge disposal
    When a liquid sludge is produced, further treatment may be required to make it suitable for final disposal. Typically,
    sludges are thickened (dewatered) to reduce the volumes transported off-site for disposal. There is no process which
    completely eliminates the need to dispose of biosolids. There is, however, an additional step some cities are taking to
    superheat sludge and convert it into small pelletized granules that are high in nitrogen and other organic materials. In
    New York City, for example, several sewage treatment plants have dewatering facilities that use large centrifuges
    along with the addition of chemicals such as polymer to further remove liquid from the sludge. The removed fluid,
    called centrate, is typically reintroduced into the wastewater process. The product which is left is called "cake" and
    that is picked up by companies which turn it into fertilizer pellets. This product is then sold to local farmers and turf
    farms as a soil amendment or fertilizer, reducing the amount of space required to dispose of sludge in landfills. Much
    sludge originating from commercial or industrial areas is contaminated with toxic materials that are released into the
    sewers from the industrial processes.[30] Elevated concentrations of such materials may make the sludge unsuitable
    for agricultural use and it may then have to be incinerated or disposed of to landfill.
    Treatment in the receiving environment
    The outlet of the Karlsruhe sewage treatment
    plant flows into the Alb.
    Many processes in a wastewater treatment plant are designed to mimic
    the natural treatment processes that occur in the environment, whether
    that environment is a natural water body or the ground. If not
    overloaded, bacteria in the environment will consume organic
    contaminants, although this will reduce the levels of oxygen in the
    water and may significantly change the overall ecology of the
    receiving water. Native bacterial populations feed on the organic
    contaminants, and the numbers of disease-causing microorganisms are
    reduced by natural environmental conditions such as predation or
    exposure to ultraviolet radiation. Consequently, in cases where the
    receiving environment provides a high level of dilution, a high degree
    of wastewater treatment may not be required. However, recent
    evidence has demonstrated that very low levels of specific contaminants in wastewater, including hormones (from
    animal husbandry and residue from human hormonal contraception methods) and synthetic materials such as
    phthalates that mimic hormones in their action, can have an unpredictable adverse impact on the natural biota and
    potentially on humans if the water is re-used for drinking water.[31] In the US and EU, uncontrolled discharges of
    wastewater to the environment are not permitted under law, and strict water quality requirements are to be met, as
    Sewage treatment 13
    clean drinking water is essential. (For requirements in the US, see Clean Water Act.) A significant threat in the
    coming decades will be the increasing uncontrolled discharges of wastewater within rapidly developing countries.
    Effects on Biology
    Sewage treatment plants can have multiple effects on nutrient levels in the water that the treated sewage flows into.
    These effects on nutrients can have large effects on the biological life in the water in contact with the effluent.
    Stabilization ponds (or treatment ponds) can include any of the following:
    • Oxidation ponds, which are aerobic bodies of water usually 1–2 meters in depth that receive effluent from
    sedimentation tanks or other forms of primary treatment.
    • Dominated by algae
    • Polishing ponds are similar to oxidation ponds but receive effluent from an oxidation pond or from a plant with an
    extended mechanical treatment.
    • Dominated by zooplankton
    • Facultative lagoons, raw sewage lagoons, or sewage lagoons are ponds where sewage is added with no primary
    treatment other than coarse screening. These ponds provide effective treatment when the surface remains aerobic;
    although anaerobic conditions may develop near the layer of settled sludge on the bottom of the pond.[32]
    • Anaerobic lagoons are heavily loaded ponds.
    • Dominated by bacteria
    • Sludge lagoons are aerobic ponds, usually 2–5 meters in depth, that receive anaerobically digested primary
    sludge, or activated secondary sludge under water.
    • Upper layers are dominated by algae [33]
    Phosphorus limitation is a possible result from sewage treatment and results in flagellate-dominated plankton,
    particularly in summer and fall.[34]
    At the same time a different study found high nutrient concentrations linked to sewage effluents. High nutrient
    concentration leads to high chlorophyll a concentrations, which is a proxy for primary production in marine
    environments. High primary production means high phytoplankton populations and most likely high zooplankton
    populations because zooplankton feed on phytoplankton. However, effluent released into marine systems also leads
    to greater population instability.[35]
    A study done in Britain found that the quality of effluent affected the planktonic life in the water in direct contact
    with the wastewater effluent. Turbid, low-quality effluents either did not contain ciliated protozoa or contained only
    a few species in small numbers. On the other hand, high-quality effluents contained a wide variety of ciliated
    protozoa in large numbers. Due to these findings, it seems unlikely that any particular component of the industrial
    effluent has, by itself, any harmful effects on the protozoan populations of activated sludge plants.[36]
    The planktonic trends of high populations close to input of treated sewage is contrasted by the bacterial trend. In a
    study of Aeromonas spp. in increasing distance from a wastewater source, greater change in seasonal cycles was
    found the furthest from the effluent. This trend is so strong that the furthest location studied actually had an inversion
    of the Aeromonas spp. cycle in comparison to that of fecal coliforms. Since there is a main pattern in the cycles that
    occurred simultaneously at all stations it indicates seasonal factors (temperature, solar radiation, phytoplankton)
    control of the bacterial population. The effluent dominant species changes from Aeromonas caviae in winter to
    Aeromonas sobria in the spring and fall while the inflow dominant species is Aeromonas caviae, which is constant
    throughout the seasons.[37]
    Sewage treatment 14
    Sewage treatment in developing countries
    Few reliable figures exist on the share of the wastewater collected in sewers that is being treated in the world. In
    many developing countries the bulk of domestic and industrial wastewater is discharged without any treatment or
    after primary treatment only. In Latin America about 15% of collected wastewater passes through treatment plants
    (with varying levels of actual treatment). In Venezuela, a below average country in South America with respect to
    wastewater treatment, 97 percent of the country’s sewage is discharged raw into the environment.[38] In a relatively
    developed Middle Eastern country such as Iran, the majority of Tehran's population has totally untreated sewage
    injected to the city’s groundwater.[39] However now the construction of major parts of the sewage system, collection
    and treatment, in Tehran is almost complete, and under development, due to be fully completed by the end of 2012.
    In Isfahan, Iran's third largest city, sewage treatment was started more than 100 years ago.
    In Israel, about 50 percent of agricultural water usage (total use was 1 billion cubic metres in 2008) is provided
    through reclaimed sewer water. Future plans call for increased use of treated sewer water as well as more
    desalination plants.[40]
    Most of sub-Saharan Africa is without wastewater treatment.
    [1] Khopkar, S. M. (2004). Environmental Pollution Monitoring And Control (http:/ / books. google. com/ ?id=TAk21grzDZgC). New Delhi:
    New Age International. p. 299. ISBN 81-224-1507-5. . Retrieved 2009-06-28.
    [2] History of the NEWater (http:/ / www. pub. gov. sg/ about/ historyfuture/ Pages/ NEWater. aspx)
    [3] Burrian, Steven J., et al. (1999). "The Historical Development of Wet-Weather Flow Management." (http:/ / www. epa. gov/ nrmrl/ pubs/
    600ja99275/ 600ja99275. pdf) US Environmental Protection Agency (EPA). National Risk Management Research Laboratory, Cincinnati,
    OH. Document No. EPA/600/JA-99/275.
    [4] Stormwater Effects Handbook: A Toolbox for Watershed Managers, Scientists, and Engineers (http:/ / unix. eng. ua. edu/ ~rpitt/ Publications/
    BooksandReports/ Stormwater Effects Handbook by Burton and Pitt book/ MainEDFS_Book. html). New York: CRC/Lewis Publishers. 2001.
    ISBN 0-87371-924-7. . Chapter 2.
    [5] Water and Environmental Health at London and Loughborough (1999). "Waste water Treatment Options." (http:/ / www. lut. ac. uk/ well/
    resources/ technical-briefs/ 64-wastewater-treatment-options. pdf)Technical brief no. 64. London School of Hygiene & Tropical Medicine and
    Loughborough University.
    [6] EPA. Washington, DC (2004). "Primer for Municipal Waste water Treatment Systems." (http:/ / www. epa. gov/ npdes/ pubs/ primer. pdf)
    Document no. EPA 832-R-04-001.
    [7] Weston, Roy F. Process Design Manual for Upgrading Existing Wastewater Treatment Plants (1971) United States Environmental Protection
    Agency chapter 3
    [8] Primary and secundary clarifier term (http:/ / www. huber. de/ products/ sedimentation-tanks. html)
    [9] http:/ / www. waterworld. com/ index/ webcasts/ webcast-display/ 5792747027/ webcasts/ waterworld/ live-events/ evaluation_-application.
    [10] http:/ / www. aqwise. com/ page. asp?cat=151& type=2& lang=1
    [11] http:/ / www. bv. com/ Downloads/ Resources/ Brochures/ rsrc_WTR_IFASMBBR. pdf
    [12] Maine Department of Environmental Protection. Augusta, ME. "Aerated Lagoons - Wastewater Treatment." (http:/ / www. lagoonsonline.
    com) Maine Lagoon Systems Task Force. Accessed 2010-07-11.
    [13] Beychok, M.R. (1971). "Performance of surface-aerated basins". Chemical Engineering Progress Symposium Series 67 (107): 322–339.
    Available at CSA Illumina website (http:/ / md1. csa. com/ partners/ viewrecord. php?requester=gs& collection=ENV& recid=7112203& q=&
    uid=788301038& setcookie=yes)
    [14] Kadam, A.; Ozaa, G.; Nemadea, P.; Duttaa, S.; Shankar, H. (2008). "Municipal wastewater treatment using novel constructed soil filter
    system". Chemosphere (Elsevier) 71 (5): 975–981. doi:10.1016/j.chemosphere.2007.11.048. PMID 18207216.
    [15] Nemade, P.D.; Kadam, A.M.; Shankar, H.S. (2009). "Wastewater renovation using constructed soil filter (CSF): A novel approach" (http:/ /
    www. che. iitb. ac. in/ online/ bibliography/ wastewater-renovation-using-constructed-soil-filter-csf-a-novel-approach). Journal of Hazardous
    Materials (Elsevier) 170 (2-3): 657–665. doi:10.1016/j.jhazmat.2009.05.015. PMID 19501460. .
    [16] A documentary video detailing a 3 MLD SBT plant deployed at the Brihanmumbai Municipal Corporation for Mumbai city can be seen at
    "SBT at BMC Mumbai." (http:/ / www. youtube. com/ watch?v=dKWVtZ81mY0)
    [17] EPA. Washington, DC (2007). "Membrane Bioreactors." (http:/ / www. epa. gov/ owm/ mtb/ etfs_membrane-bioreactors. pdf) Wastewater
    Management Fact Sheet.
    [18] Black & Veatch Process Design Manual for Phosphorus Removal (1971) United States Environmental Protection Agency p.2-1
    Sewage treatment 15
    [19] Das, Tapas K. (08 2001). "Ultraviolet disinfection application to a wastewater treatment plant". Clean Technologies and Environmental
    Policy (Springer Berlin/Heidelberg) 3 (2): 69–80. doi:10.1007/S100980100108.
    [20] Florida Department of Environmental Protection. Talahassee, FL. "Ultraviolet Disinfection for Domestic Waste water." (http:/ / www. dep.
    state. fl. us/ water/ wastewater/ dom/ domuv. htm) 2010-03-17.
    [21] Harshman, Vaughan; Barnette, Tony (05 2000). "Wastewater Odor Control: An Evaluation of Technologies" (http:/ / www. wwdmag. com/
    Wastewater-Odor-Control-An-Evaluation-of-Technologies-article1698). Water Engineering & Management. ISSN 0273-2238. .
    [22] Walker, James D. and Welles Products Corporation (1976). "Tower for removing odors from gases." (http:/ / www. freepatentsonline. com/
    4421534. html) U.S. Patent No. 4421534.
    [23] EPA. Washington, DC (2000). "Package Plants." (http:/ / www. epa. gov/ owm/ mtb/ package_plant. pdf) Wastewater Technology Fact
    Sheet. Document no. EPA 832-F-00-016.
    [24] EPA. Washington, DC (1999). "Sequencing Batch Reactors." (http:/ / www. epa. gov/ owm/ mtb/ sbr_new. pdf) Wastewater Technology
    Fact Sheet. Document no. EPA 832-F-99-073.
    [25] Hammer, Mark J. (1975). Water and Waste-Water Technology. John Wiley & Sons. pp. 390–391. ISBN 0-471-34726-4.
    [26] Pre-thickener: the first step in sludge disposal (http:/ / www. krohne. com/ Pre-thickener_main_sludge_thickener. 17188. 0. html)
    [27] Pre-thickeners (http:/ / www. globalspec. com/ learnmore/ manufacturing_process_equipment/ filtration_separation_products/
    [28] Centrifugal sludge thickener (http:/ / www. ipec. ca/ products3. html?id=15#)
    [29] Belt filter press (http:/ / www. mine-engineer. com/ mining/ belt_fp. html)
    Institute for Environment and Sustainability Soil and Waste Unit H. Langenkamp & P. Part (http:/ / ec. europa. eu/ environment/ waste/
    sludge/ pdf/ organics_in_sludge. pdf)
    [31] (http:/ / www. environment-agency. gov. uk/ business/ 444304/ 1290036/ 1290100/ 1290353/ 1294402/
    1314667/ )
    [32] Metcalf & Eddy, Inc. (1972). Wastewater Engineering. McGraw-Hill Book Company. pp. 552–554. ISBN 0-07-041675-3.
    [33] Haughey, A. (1968) The Planktonic Algae of Auckland Sewage Treatment Ponds, New Zealand Journal of Marine and Freshwater Research
    [34] Nutrients and Phytoplankton in Lake Washington Edmondson, WT; Nutrients and Eutrophication: The Limiting Nutrient Controversy,
    American Society of Limnology and Oceanography Special Symposia Vol.1
    [35] Caperon, Cattell, and Krasnick (1971) Phytoplankton Kinetics in a Subtropical Estuary: Eutrophication, Limnology and Oceanography
    [36] Curds and Cockburn (1969) Protozoa in Biological Sewage-Treatment Processes -- I. A Survey of the Protozoan Fauna of British
    Percolating filters and Activated-Sludge Plants, Water Research
    [37] Monfort and Baleux (1990) Dynamics of Aeromonas hydrophila, Aeromonas sobria, and Aeromonas caviae in a Sewage Treatment Pond,
    Applied and Environmental Microbiology
    [38] Caribbean Environment Programme (1998). Appropriate Technology for Sewage Pollution Control in the Wider Caribbean Region (http:/ /
    www. cep. unep. org/ publications-and-resources/ technical-reports/ tr40en. pdf). Kingston, Jamaica: United Nations Environment
    Programme. . Retrieved 2009-10-12. Technical Report No. 40.
    [39] Massoud Tajrishy and Ahmad Abrishamchi, Integrated Approach to Water and Wastewater Management for Tehran, Iran, Water
    Conservation, Reuse, and Recycling: Proceedings of the Iranian-American Workshop, National Academies Press (2005)
    [40] Martin, Andrew (2008-08-10). "Farming in Israel, without a drop to spare" (http:/ / www. iht. com/ articles/ 2008/ 08/ 10/ business/ 10feed.
    php). New York Times. .
    External links
    • "Anaerobic Industrial Wastewater Treatment: Perspectives for Closing Water and Resource Cycles." (http:/ /
    edepot. wur. nl/ 39480) Jules B. van Lier, Wageningen University, The Netherlands
    • Arcata, California Constructed Wetland: A Cost-Effective Alternative for Wastewater Treatment (http:/ /
    ecotippingpoints. org/ our-stories/ indepth/ usa-california-arcata-constructed-wetland-wastewater. html)
    • Boston Sewage Tour (http:/ / seagrant. mit. edu/ education/ resources/ bostonsewage/ introduction. html) - MIT
    Sea Grant
    • Interactive Diagram of Wastewater Treatment - "Go with the Flow" (http:/ / wef. org/ apps/ gowithflow/ theflow.
    htm) - Water Environment Federation
    • Phosphorus Recovery (http:/ / www. phosphorus-recovery. tu-darmstadt. de) - Technische Universität Darmstadt
    & CEEP
    • Heavy metals recovery (http:/ / enviropark. ru/ course/ category. php?id=10) - Mendeleev University Science Park
    • Sewer History (http:/ / www. sewerhistory. org)
    • The Straight Dope - What happens to all the stuff that goes down the toilet? (http:/ / www. straightdope. com/
    mailbag/ msolidwaste. html) - Syndicated column by Cecil Adams
    Sewage treatment 16
    • Tour of a Washington state sewage plant written by an employee (http:/ / www. poopreport. com/ Consumer/
    poop_plant. html)
    • National Water Engineering of Pakistan - Wastewater Treatment Plants in Pakistan (http:/ / www. nwepk. com/ )
    Article Sources and Contributors 17
    Article Sources and Contributors
    Sewage treatment Source: Contributors: 14zip34b, 28421u2232nfenfcenc, 2over0, 4twenty42o, A Stop at Willoughby, ABCD,
    Aaavinash, Abdallahdjabi, Abhishank.jajur, AdultSwim, Afluent Rider, Aitias, Alansohn, Aldie, Ale jrb, Alf ea, [email protected], Allstarecho, AlphaEta, Amalthea, Andrewpmk, Andy Dingley,
    Anlace, AnnaLore, Antandrus, Anthere, Anthony Appleyard, AntiVan, Anwar saadat, Arjun01, Arnavwik, AubreyEllenShomo, Auntof6, Aurista25, Awanta, Awickert, AxelBoldt, Aymatth2,
    Azaroonus, BWKA, Badgernet, Bantman, Bartledan, Basar, BaseballDetective, Basseysam, Beetstra, Belg4mit, Ben James Ben, Bendzh, Benzy16, Berwinc, Bettymnz4, Bhadani, Bkonrad,
    Bletch, Bloodshedder, Bobjgalindo, Bobo192, Bogelund, Boilerup12, Bollyjeff, Bongwarrior, Bookofjude, Boxidon, BozMo, Brian0918, Brownstone Mr, BruceDLimber, Brutaldeluxe, Bryan
    Derksen, Bucketsofg, Bugtrio, Bumm13, Burn, Burpelson AFB, Burschik, Bushytails, C.lettingaAV, CDM2, CDN99, CactusWriter, Camembert, Can't sleep, clown will eat me, CanisRufus,
    Capricorn42, Captain-n00dle, Carlog3, Cathydunham, Cessator, Cfailde, Cgeers, Chongkian, Chris 73, Chris the speller, Chriswaterguy, Clairekcarpenter, Clarknova714, Cocacola789123,
    Cohesion, Cointyro, ComputerGuy, Control.optimization, Cromwellt, Cureden, Curps, DMahalko, DanMS, Daniel Collins, DanielCD, Davidlburton, Davnor, Deen rose, Deirdre, Dejitarob,
    DennyColt, DerHexer, Dfrg.msc, Digitalminddubai, Dirkbb, Discospinster, Dlohcierekim's sock, Dmanning, DocWatson42, Dougher, DouglasHeld, Dralwik, Dsmithsmithy, Dtaylor1984, Dureo,
    EERichards, Echuck215, Eclecticos, EdBever, Edgar181, Eequor, EgbertW, Elite782, Elvirs, Eng.Kalaji, EnvironmentalDynamics, Espoo, EthanL, EuTuga, Evertype, Everyking, Ewen, Excirial,
    F. Cosoleto, Falcon8765, Faradayplank, Farras Octara, Favonian, Felyza, Fieldday-sunday, Finngall, Fir0002, Fish Bass, Fkt1, Flockmeal, Fnfd, Fooscope, Fvw, Fæ, Gail, Garyvines, Gene
    Nygaard, GeorgeLouis, GerardM, Gilliam, Giraffedata, Gregalton, Grunt, Gscshoyru, Guanaco, Guthrie, Gyrobo, Hadal, Hai398, HalfShadow, Hard Raspy Sci, Henrygb, HiDrNick, Hmains,
    Horses136, Hu12, Hubba, Hut 8.5, Iainscott, Ianmcaldwell, Ijwatson,, In06uddin, Ineck, Instinct, Inuyasha85, Irchang, Isidore, Iste Praetor, Ithunn, Ixfd64, Izehar, J. Finkelstein, J.delanoy,
    J04n, JFreeman, JNortheast09, JRR Trollkien, JTN, Ja 62, Jacksterh, Jaganath, Janedodgersfan, Jarble, Jeff G., JeffreyN, Jerry schneider, Jj137, Jobber, Johnjohnston, Jonathan.s.kt,
    Jonomacdrones, Jonur, Joopwiki, Joyous!, Jrtayloriv, Jthiller, Juandev, K8TEK, KGasso, Kaarel, Kalathalan, Karcoo, Katalaveno, Kekel, KellyCoinGuy, Ken Gallager, KerathFreeman,
    Kilo-Lima, Kjkolb, KlaasNekeman, Klilidiplomus, Klonimus, Konstable, Korealover-jisung, Kotjze, Kozuch, Kracksman, Krazykillaz, Kubigula, KudzuVine, Kukini, Kutu su, Kuyabribri,
    Kwamikagami, Kychot, Leonard G., Lion789, LizardJr8, Locust43, Lotje, Lucinos, Luna Santin, Lyrl, M brannock, MADe, MER-C, Mac, Mahkciwnad, MaiusGermanicus, Malene, Mandarax,
    Marek69, Marshman, Martin fed, Mathonius, Mato, Mbell, Mbeychok, Michael Frind, Midgrid, Mikoak, Moloch09, Moreau1, Morphriz, Mostiquera, MrOllie, Mschiffler, Mufka, Mukadderat,
    N5iln, NHRHS2010, Nabla, Nakon, Newstrens, Night of the Big Wind Turbo, Nikai, Nn123645, Noisy, Noodlez84, Nopetro, Northernhenge, Norvy, Nyckrazi, Oatmeal batman, Odie1344,
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    Image Sources, Licenses and Contributors
    File:Sewer Plant.jpg Source: License: Creative Commons Attribution 3.0 Contributors: Rjgalindo
    File:ESQUEMPEQUE-EN.jpg Source: License: Creative Commons Attribution-Sharealike 2.5 Contributors: Leonard
    File:SchemConstructedWetlandSewage.jpg Source: License: Public Domain Contributors: Yayasan
    IDEP Foundation and Wastewater Gardens
    File:Activated Sludge 1.png Source: License: Public Domain Contributors: Original uploader was Mbeychok at
    File:Surface-Aerated Basin.png Source: License: Public Domain Contributors: Mbeychok
    File:Rotating Biological Contactor.png Source: License: Public Domain Contributors: Mbeychok
    File:Secondary sedimentation tank 1 w.JPG Source: License: GNU Free Documentation License
    Contributors: Mailer diablo, Million Moments, Velella, Vortexrealm
    File:Everett sewage.jpg Source: License: Public Domain Contributors: Beyond My Ken, ComputerGuy
    File:MiRO3.jpg Source: License: Creative Commons Attribution 2.0 Contributors:
    Creative Commons Attribution-Share Alike 3.0 Unported

    Last edited by faadoo.nitika; 15th June 2012 at 12:00 PM.

  2. #2

    Re: Water Treatment Notes Free

    I want environmental engineering by Howards s peavy, Please post , if anybody have...

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