Wastewater treatment is a process which removes and eliminates contaminants from wastewater . It thus converts it into an effluent that can be returned to the water cycle . Once back in the water cycle, the effluent creates an acceptable impact on the environment. It is also possible to reuse it. This process is called water reclamation . The treatment process takes place in a wastewater treatment plant. There are several kinds of wastewater which are treated at the appropriate type of wastewater treatment plant. For domestic wastewater the treatment plant is called a Sewage Treatment . Municipal wastewater or sewage are other names for domestic wastewater . For industrial wastewater, treatment takes place in a separate Industrial wastewater treatment , or in a sewage treatment plant. In the latter case it usually follows pre-treatment. Further types of wastewater treatment plants include Agricultural wastewater treatment and leachate treatment plants.
51-466: WWT may refer to: Wastewater treatment Wildfowl & Wetlands Trust WorldWide Telescope Newtok Airport , with IATA code WWT World Wide Technology WWT (AM) - 1922 Buffalo, New York radio station Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title WWT . If an internal link led you here, you may wish to change
102-400: A membrane liquid-solid phase separation process. The membrane component uses low pressure microfiltration or ultrafiltration membranes and eliminates the need for a secondary clarifier or 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
153-738: A sanitary sewer or to a surface water in the environment. Some industrial facilities generate wastewater that can be treated in sewage treatment plants . Most industrial processes, such as petroleum refineries , chemical and petrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters into sewers or into rivers, lakes or oceans . This applies to industries that generate wastewater with high concentrations of organic matter (e.g. oil and grease), toxic pollutants (e.g. heavy metals, volatile organic compounds ) or nutrients such as ammonia . Some industries install
204-662: 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. Aerobic granular sludge can be formed by applying specific process conditions that favour slow growing organisms such as PAOs (polyphosphate accumulating organisms) and GAOs (glycogen accumulating organisms). Another key part of granulation
255-831: A combined sewer. Smaller sewage treatment plants may experience dilution from cooling water discharges, major plumbing leaks, firefighting, or draining large swimming pools. A similar problem occurs as BOD concentrations drop when low flow increases waste residence time within the secondary treatment bioreactor. Secondary treatment ecosystems of college communities acclimated to waste loading fluctuations from student work/sleep cycles may have difficulty surviving school vacations. Secondary treatment systems accustomed to routine production cycles of industrial facilities may have difficulty surviving industrial plant shutdown. Populations of species feeding on incoming waste initially decline as concentration of those food sources decrease. Population decline continues as ecosystem predator populations compete for
306-648: A declining population of lower trophic level organisms. High BOD concentrations initially exceed the ability of the secondary treatment ecosystem to utilize available food. Ecosystem populations of aerobic organisms increase until oxygen transfer limitations of the secondary treatment bioreactor are reached. Secondary treatment ecosystem populations may shift toward species with lower oxygen requirements, but failure of those species to use some food sources may produce higher effluent BOD concentrations. More extreme increases in BOD concentrations may drop oxygen concentrations before
357-694: A network of pipes and pump stations (called sewerage ) which convey the sewage to a treatment plant. For cities that have a combined sewer , the sewers will also carry urban runoff (stormwater) to the sewage treatment plant. Sewage treatment often involves two main stages, called primary and secondary treatment , while advanced treatment also incorporates a tertiary treatment stage with polishing processes and nutrient removal. Secondary treatment can reduce organic matter (measured as biological oxygen demand ) from sewage, using aerobic or anaerobic biological processes. A so-called quarternary treatment step (sometimes referred to as advanced treatment) can also be added for
408-471: A pre-treatment system to remove some pollutants (e.g., toxic compounds), and then discharge the partially treated wastewater to the municipal sewer system. Agricultural wastewater treatment is a farm management agenda for controlling pollution from confined animal operations and from surface runoff that may be contaminated by chemicals in fertilizer , pesticides , animal slurry , crop residues or irrigation water. Agricultural wastewater treatment
459-487: A smaller space than fixed-film trickling filter systems that treat the same amount of water; but fixed-film systems are better 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. Wastewater flow variations may be reduced by limiting stormwater collection by the sewer system, and by requiring industrial facilities to discharge batch process wastes to
510-426: A solution of soluble sugars. Others may find compatible agricultural wastes, or offer disposal incentives to septic tank pumpers during low use periods. Waste containing biocide concentrations exceeding the secondary treatment ecosystem tolerance level may kill a major fraction of one or more important ecosystem species. BOD reduction normally accomplished by that species temporarily ceases until other species reach
561-421: A source of air which percolates up through the bed, keeping it aerobic. Biofilms of bacteria, protozoa and fungi form on the media’s surfaces and eat or otherwise reduce the organic content. The filter removes a small percentage of the suspended organic matter, while the majority of the organic matter supports microorganism reproduction and cell growth from the biological oxidation and nitrification taking place in
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#1732776608556612-528: A suitable population to utilize that food source, or the original population recovers as biocide concentrations decline. Waste containing unusually low BOD concentrations may fail to sustain the secondary treatment population required for normal waste concentrations. The reduced population surviving the starvation event may be unable to completely utilize available BOD when waste loads return to normal. Dilution may be caused by addition of large volumes of relatively uncontaminated water such as stormwater runoff into
663-504: A treatment sequence to remove solids generated during oxidation or polishing. Grease and oil may be recovered for fuel or saponification . Solids often require dewatering of sludge in a wastewater treatment plant . Disposal options for dried solids vary with the type and concentration of impurities removed from water. Solids such as stones , grit, and sand may be removed from wastewater by gravity when density differences are sufficient to overcome dispersion by turbulence . This
714-587: A variety of mechanisms and processes using dissolved oxygen to promote growth of biological floc that substantially removes organic material. Biological floc is an ecosystem of living biota subsisting on nutrients from the inflowing primary clarifier effluent. These mostly carbonaceous dissolved solids undergo aeration to be broken down and either biologically oxidized to carbon dioxide or converted to additional biological floc of reproducing micro-organisms. Nitrogenous dissolved solids (amino acids, ammonia , etc.) are similarly converted to biological floc or oxidized by
765-471: Is phase separation , such as sedimentation. Biological and chemical processes such as oxidation are another example. Polishing is also an example. The main by-product from wastewater treatment plants is a type of sludge that is usually treated in the same or another wastewater treatment plant. Biogas can be another by-product if the process uses anaerobic treatment. Treated wastewater can be reused as reclaimed water . The main purpose of wastewater treatment
816-629: Is also typically included in the definition of conventional secondary treatment." Biological nutrient removal is regarded by some sanitary engineers as secondary treatment and by others as tertiary treatment. After this kind of treatment, the wastewater may be called secondary-treated wastewater. Secondary treatment systems are classified as fixed-film or suspended-growth systems A great number of secondary treatment processes exist, see List of wastewater treatment technologies . The main ones are explained below. In older plants and those receiving variable loadings, trickling filter beds are used where
867-690: Is being treated. Secondary treatment bioreactors may be followed by a physical phase separation to remove biological solids from the treated water. Upset duration of fixed film secondary treatment systems may be longer because of the time required to recolonize the treatment surfaces. Suspended growth ecosystems may be restored from a population reservoir. Activated sludge recycle systems provide an integrated reservoir if upset conditions are detected in time for corrective action. Sludge recycle may be temporarily turned off to prevent sludge washout during peak storm flows when dilution keeps BOD concentrations low. Suspended growth activated sludge systems can be operated in
918-404: Is expected to remove at least 85 percent of the BOD and suspended solids from domestic sewage. The EPA regulations describe stabilization ponds as providing treatment equivalent to secondary treatment removing 65 percent of the BOD and suspended solids from incoming sewage and discharging approximately 50 percent higher effluent concentrations than modern bioreactors. The regulations also recognize
969-467: Is for the treated wastewater to be able to be disposed or reused safely. However, before it is treated, the options for disposal or reuse must be considered so the correct treatment process is used on the wastewater. The term "wastewater treatment" is often used to mean " sewage treatment ". Wastewater treatment plants may be distinguished by the type of wastewater to be treated. There are numerous processes that can be used to treat wastewater depending on
1020-1206: Is required for continuous confined animal operations like milk and egg production. It may be performed in plants using mechanized treatment units similar to those used for industrial wastewater . Where land is available for ponds, settling basins and facultative lagoons may have lower operational costs for seasonal use conditions from breeding or harvest cycles. Animal slurries are usually treated by containment in anaerobic lagoons before disposal by spray or trickle application to grassland. Constructed wetlands are sometimes used to facilitate treatment of animal wastes. Leachate treatment plants are used to treat leachate from landfills . Treatment options include: biological treatment, mechanical treatment by ultrafiltration , treatment with active carbon filters, electrochemical treatment including electrocoagulation by various proprietary technologies and reverse osmosis membrane filtration using disc tube module technology. The unit processes involved in wastewater treatment include physical processes such as settlement or flotation and biological processes such oxidation or anaerobic treatment. Some wastewaters require specialized treatment methods. At
1071-695: Is run off and re-aerated before a proportion is returned to the headworks. The disadvantage of the CASSBR 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. Membrane bioreactors (MBR) are activated sludge systems using
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#17327766085561122-400: Is selective wasting whereby slow settling floc-like sludge is discharged as waste sludge and faster settling biomass is retained. This process has been commercialized as Nereda process . Aerated lagoons are a low technology suspended-growth method of secondary treatment using motor-driven aerators floating on the water surface to increase atmospheric oxygen transfer to the lagoon and to mix
1173-532: Is the most common method used in municipal wastewater treatment. Secondary treatment Secondary treatment (mostly biological wastewater treatment ) is the removal of biodegradable organic matter (in solution or suspension) from sewage or similar kinds of wastewater . The aim is to achieve a certain degree of effluent quality in a sewage treatment plant suitable for the intended disposal or reuse option. A " primary treatment " step often precedes secondary treatment, whereby physical phase separation
1224-475: Is typically achieved using a grit channel designed to produce an optimum flow rate that allows grit to settle and other less-dense solids to be carried forward to the next treatment stage. Gravity separation of solids is the primary treatment of sewage , where the unit process is called "primary settling tanks" or "primary sedimentation tanks". It is also widely used for the treatment of other types of wastewater. Solids that are denser than water will accumulate at
1275-602: Is used to remove settleable solids . During secondary treatment, biological processes are used to remove dissolved and suspended organic matter measured as biochemical oxygen demand (BOD). These processes are performed by microorganisms in a managed aerobic or anaerobic process depending on the treatment technology . Bacteria and protozoa consume biodegradable soluble organic contaminants (e.g. sugars , fats, and organic short-chain carbon molecules from human waste, food waste , soaps and detergent) while reproducing to form cells of biological solids. Secondary treatment
1326-411: Is widely used for disinfection. Advanced oxidation processes are used to remove some persistent organic pollutants and concentrations remaining after biochemical oxidation. Disinfection by chemical oxidation kills bacteria and microbial pathogens by adding hydroxyl radicals such as ozone , chlorine or hypochlorite to wastewater. These hydroxyl radical then break down complex compounds in
1377-408: Is widely used in sewage treatment and is also applicable to many agricultural and industrial wastewaters . Secondary treatment systems are classified as fixed-film or suspended-growth systems, and as aerobic versus anaerobic. Fixed-film or attached growth systems include trickling filters , constructed wetlands , bio-towers, and rotating biological contactors , where the biomass grows on media and
1428-496: 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
1479-613: The United States (1 million gal./day or less) use aerated lagoons. The United States Environmental Protection Agency (EPA) defined secondary treatment based on the performance observed at late 20th-century bioreactors treating typical United States municipal sewage. Secondary treated sewage is expected to produce effluent with a monthly average of less than 30 mg/L BOD and less than 30 mg/L suspended solids . Weekly averages may be up to 50 percent higher. A sewage treatment plant providing both primary and secondary treatment
1530-423: The aerobic secondary treatment systems include a secondary clarifier to settle out and separate biological floc or filter material grown in the secondary treatment bioreactor. Primary treatment settling removes about half of the solids and a third of the BOD from raw sewage. Secondary treatment is defined as the "removal of biodegradable organic matter (in solution or suspension) and suspended solids. Disinfection
1581-401: The bioreactor ecosystem. Measures creating uniform wastewater loadings tend to reduce the probability of upsets. Fixed-film or attached growth secondary treatment bioreactors are similar to a plug flow reactor model circulating water over surfaces colonized by biofilm , while suspended-growth bioreactors resemble a continuous stirred-tank reactor keeping microorganisms suspended while water
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1632-629: The bottom of quiescent settling basins . More complex clarifiers also have skimmers to simultaneously remove floating grease such as soap scum and solids such as feathers, wood chips, or condoms . Containers like the API oil-water separator are specifically designed to separate non-polar liquids. Oxidation reduces the biochemical oxygen demand of wastewater, and may reduce the toxicity of some impurities. Secondary treatment converts organic compounds into carbon dioxide , water , and biosolids through oxidation and reduction reactions. Chemical oxidation
1683-435: The difficulty of meeting the specified removal percentages from combined sewers , dilute industrial wastewater, or Infiltration/Inflow . Process upsets are temporary decreases in treatment plant performance caused by significant population change within the secondary treatment ecosystem. Conditions likely to create upsets include toxic chemicals and unusually high or low concentrations of organic waste BOD providing food for
1734-461: The filter. With this aerobic oxidation and nitrification, the organic solids are converted into biofilm grazed by insect larvae, snails, and worms which help maintain an optimal thickness. Overloading of beds may increase biofilm thickness leading to anaerobic conditions and possible bioclogging of the filter media and ponding on the surface. Activated sludge is a common suspended-growth method of secondary treatment. Activated sludge plants encompass
1785-467: The floc and cause process upsets. Elevated concentrations of toxic wastes including pesticides, industrial metal plating waste, or extreme pH, can kill the biota of an activated sludge reactor ecosystem. One type of system that combines secondary treatment and settlement is the cyclic activated sludge (CASSBR), or sequencing batch reactor (SBR). Typically, activated sludge is mixed with raw incoming sewage, and then mixed and aerated. The settled sludge
1836-416: The floc to nitrites , nitrates , and, in some processes, to nitrogen gas through denitrification . While denitrification is encouraged in some treatment processes, denitrification often impairs the settling of the floc causing poor quality effluent in many suspended aeration plants. Overflow from the activated sludge mixing chamber is sent to a clarifier where the suspended biological floc settles out while
1887-480: The lagoon contents. The floating surface aerators are typically rated to deliver the amount of air equivalent to 1.8 to 2.7 kg O 2 / kW·h . Aerated lagoons provide less effective mixing than conventional activated sludge systems and do not achieve the same performance level. The basins may range in depth from 1.5 to 5.0 metres. Surface-aerated basins achieve 80 to 90 percent removal of BOD with retention times of 1 to 10 days. Many small municipal sewage systems in
1938-465: 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
1989-408: The link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=WWT&oldid=1228725043 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Wastewater treatment One common process in wastewater treatment
2040-483: The main criteria for selection are: desired effluent quality, expected construction and operating costs, availability of land, energy requirements and sustainability aspects. In developing countries and in rural areas with low population densities, sewage is often treated by various on-site sanitation systems and not conveyed in sewers. These systems include septic tanks connected to drain fields , on-site sewage systems (OSS), vermifilter systems and many more. On
2091-415: The organic matter carried in the wastewater. Constructed wetlands are also being used. An example for an anaerobic secondary treatment system is the upflow anaerobic sludge blanket reactor . 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. Most of
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2142-764: The organic pollutants into simple compounds such as water, carbon dioxide, and salts . Anaerobic wastewater treatment processes (for example UASB , EGSB ) are also widely applied in the treatment of industrial wastewaters and biological sludge. Polishing refers to treatments made in further advanced treatment steps after the above methods (also called "fourth stage" treatment). These treatments may also be used independently for some industrial wastewater. Chemical reduction or pH adjustment minimizes chemical reactivity of wastewater following chemical oxidation. Carbon filtering removes remaining contaminants and impurities by chemical absorption onto activated carbon . Filtration through sand (calcium carbonate) or fabric filters
2193-437: The other hand, advanced and relatively expensive sewage treatment plants may include tertiary treatment with disinfection and possibly even a fourth treatment stage to remove micropollutants. Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater (or effluent) may be reused or released to
2244-460: The removal of organic micropollutants, such as pharmaceuticals. This has been implemented in full-scale for example in Sweden. A large number of sewage treatment technologies have been developed, mostly using biological treatment processes. Design engineers and decision makers need to take into account technical and economical criteria of each alternative when choosing a suitable technology. Often,
2295-412: 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
2346-428: The sewage passes over its surface. The fixed-film principle has further developed into moving bed biofilm reactors (MBBR) and Integrated Fixed-Film Activated Sludge (IFAS) processes. Suspended-growth systems include activated sludge , which is an aerobic treatment system, based on the maintenance and recirculation of a complex biomass composed of micro-organisms ( bacteria and protozoa ) able to absorb and adsorb
2397-429: The sewer over a time interval rather than immediately after creation. Discharge of appropriate organic industrial wastes may be timed to sustain the secondary treatment ecosystem through periods of low residential waste flow. Sewage treatment systems experiencing holiday waste load fluctuations may provide alternative food to sustain secondary treatment ecosystems through periods of reduced use. Small facilities may prepare
2448-456: The simplest level, treatment of most wastewaters is carried out through separation of solids from liquids , usually by sedimentation . By progressively converting dissolved material into solids, usually a biological floc or biofilm , which is then settled out or separated, an effluent stream of increasing purity is produced. Phase separation transfers impurities into a non-aqueous phase . Phase separation may occur at intermediate points in
2499-429: The surrounding environment or an intended reuse application, thereby preventing water pollution from raw sewage discharges. Sewage contains wastewater from households and businesses and possibly pre-treated industrial wastewater . There are a high number of sewage treatment processes to choose from. These can range from decentralized systems (including on-site treatment systems) to large centralized systems involving
2550-408: The treated water moves into tertiary treatment or disinfection. Settled floc is returned to the mixing basin to continue growing in primary effluent. Like most ecosystems, population changes among activated sludge biota can reduce treatment efficiency. Nocardia , a floating brown foam sometimes misidentified as sewage fungus , is the best known of many different fungi and protists that can overpopulate
2601-403: The type and extent of contamination. The treatment steps include physical, chemical and biological treatment processes. Types of wastewater treatment plants include: Sewage treatment (or domestic wastewater treatment , municipal wastewater treatment ) is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to
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