Sewage sludge is the residual, semi-solid material that is produced as a by-product during sewage treatment of industrial or municipal wastewater. The term " septage " also refers to sludge from simple wastewater treatment but is connected to simple on-site sanitation systems, such as septic tanks .
91-479: 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 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
182-414: A public relations term. Sewage sludge treatment is the process of removing contaminants from wastewater . Sewage sludge is produced from the treatment of wastewater in sewage treatment plants and consists of two basic forms — raw primary sludge and secondary sludge, also known as activated sludge in the case of the activated sludge process. Sewage sludge is usually treated by one or several of
273-527: A waste-to-energy facility for direct production of electricity and steam for district heating or industrial uses. Thermal processes can greatly reduce the volume of the sludge, as well as achieve remediation of all or some of the biological concerns. Direct waste-to-energy incineration and complete combustion systems (such as the Gate 5 Energy System) will require multi-step cleaning of the exhaust gas, to ensure no hazardous substances are released. In addition,
364-557: A concentration), 40–60 g/person/d for BOD (250–400 mg/L), 80–120 g/person/d for COD (450–800 mg/L), 6–10 g/person/d for total nitrogen (35–60 mg/L), 3.5–6 g/person/d for ammonia-N (20–35 mg/L) and 0.7–2.5 g/person/d for total phosphorus (4–15 mg/L). Sewerage (or sewage system) is the infrastructure that conveys sewage or surface runoff ( stormwater , meltwater , rainwater ) using sewers. It encompasses components such as receiving drains , manholes , pumping stations , storm overflows, and screening chambers of
455-612: A first-of-its-kind criminal investigation into waste management giant Synagro over PFAS-contaminated sewage sludge it is selling to Texas farmers as a cheap alternative to fertilizer. As of 2023, 11% of sludge produced in the EU was disposed of in landfills. The EU is attempting to phase out the disposal of sludge in landfills. It used to be common practice to dump sewage sludge into the ocean, however, this practice has stopped in many nations due to environmental concerns as well to domestic and international laws and treaties. Ronald Reagan signed
546-545: 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 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
637-521: A low cost treatment option with practically no energy requirements but they require a lot of land. Due to their technical simplicity, most of the savings (compared with high tech systems) are in terms of operation and maintenance costs. Examples for systems that can provide full or partial treatment for toilet wastewater only: Examples for more high-tech, intensive or mechanized, often relatively expensive sewage treatment systems are listed below. Some of them are energy intensive as well. Many of them provide
728-413: 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 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
819-406: A month of the application, and about a fourth were affected by Staphylococcus aureus , including two deaths. The number of reported S. aureus infections was 25 times as high as in hospitalized patients, a high-risk group. The authors point out that regulations call for protective gear when handling Class B biosolids and that similar protections could be considered for residents in nearby areas given
910-814: A network of pipes and pump stations to a municipal treatment plant. This is called a centralized system (see also sewerage and pipes and infrastructure ). A large number of sewage treatment technologies have been developed, mostly using biological treatment processes (see list of wastewater treatment technologies ). Very broadly, they can be grouped into high tech (high cost) versus low tech (low cost) options, although some technologies might fall into either category. Other grouping classifications are intensive or mechanized systems (more compact, and frequently employing high tech options) versus extensive or natural or nature-based systems (usually using natural treatment processes and occupying larger areas) systems. This classification may be sometimes oversimplified, because
1001-472: A practice that subjects neighbors and workers to substantial risk of disease." They further suggest that even Class A treated sludge may have chemical contaminants (including heavy metals , such as lead ) or endotoxins present, and a precautionary approach may be justified on this basis, though the vast majority of incidents reported by Lewis, et al. have been correlated with exposure to Class B untreated sludge and not Class A treated sludge. A 2005 report by
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#17327826702441092-833: A review article published in 2012, it was reported that a total amount of 10.1 million tn DS/year were produced in EU-27 countries. As of 2023, the EU produced 2 to 3 million tons of sludge each year. Worldwide it is estimated that as much as 75 Million Mg of dry sewage sludge per year. Production of sewage sludge can be reduced by conversion from flush toilets to dry toilets such as urine-diverting dry toilets and composting toilets . Sewage sludge deposition in landfills can circulate human-virulent species of Cryptosporidium and Giardia pathogens. Sonication and quicklime stabilization are most effective in inactivation of these pathogens; microwave energy disintegration and top-soil stabilization were less effective. A Texas county has launched
1183-403: A significant health issue if sewage sludge is properly treated and site-specific management practices are followed. One of the main concerns in the treated sludge is the concentrated metals content ( lead , arsenic , cadmium , thallium , etc.); certain metals are regulated while others are not. Leaching methods can be used to reduce the metal content and meet the regulatory limit. In 2009,
1274-753: A sludge which can be settled and separated. After separation, a liquid remains that is almost free of solids, and with a greatly reduced concentration of pollutants. Secondary treatment can reduce organic matter (measured as biological oxygen demand) from sewage, using aerobic or anaerobic processes. The organisms involved in these processes are sensitive to the presence of toxic materials, although these are not expected to be present at high concentrations in typical municipal sewage. Advanced sewage treatment generally involves three main stages, called primary, secondary and tertiary treatment but may also include intermediate stages and final polishing processes. The purpose of tertiary treatment (also called advanced treatment )
1365-644: A study at the United States National Research Council (NRC) to determine the health risks of sludge. In this document the NRC pointed out that many of the dangers of sludge are unknown and unassessed. The NRC published "Biosolids Applied to Land: Advancing Standards and Practices" in July 2002. The NRC concluded that while there is no documented scientific evidence that sewage sludge regulations have failed to protect public health, there
1456-422: A suitable sewage treatment process, decision makers need to take into account technical and economical criteria. Therefore, each analysis is site-specific. A life cycle assessment (LCA) can be used, and criteria or weightings are attributed to the various aspects. This makes the final decision subjective to some extent. A range of publications exist to help with technology selection. In industrialized countries ,
1547-513: A suitable technology. Often, 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
1638-758: 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 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
1729-426: A treatment plant may involve a combination of processes, and the interpretation of the concepts of high tech and low tech, intensive and extensive, mechanized and natural processes may vary from place to place. Examples for more low-tech, often less expensive sewage treatment systems are shown below. They often use little or no energy. Some of these systems do not provide a high level of treatment, or only treat part of
1820-540: A very high level of treatment. For example, broadly speaking, the activated sludge process achieves a high effluent quality but is relatively expensive and energy intensive. There are other process options which may be classified as disposal options, although they can also be understood as basic treatment options. These include: Application of sludge , irrigation , soak pit , leach field , fish pond , floating plant pond, water disposal/ groundwater recharge , surface disposal and storage. The application of sewage to land
1911-408: A wastewater treatment process is the sum of sludge from primary settling tanks (if they are part of the process configuration) plus excess sludge from the biological treatment step. For example, primary sedimentation produces about 110–170 kg/ML of so-called primary sludge, with a value of 150 kg/ML regarded as being typical for municipal wastewater in the U.S. or Europe. The sludge production
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#17327826702442002-466: Is a parameter used in the design of sewage treatment plants. This concept is known as population equivalent (PE). The base value used for PE can vary from one country to another. Commonly used definitions used worldwide are: 1 PE equates to 60 gram of BOD per person per day, and it also equals 200 liters of sewage per day. This concept is also used as a comparison parameter to express the strength of industrial wastewater compared to sewage. When choosing
2093-507: Is achieved by removing contaminants from the sewage. It is a form of waste management . With regards to biological treatment of sewage, the treatment objectives can include various degrees of the following: to transform or remove organic matter, nutrients (nitrogen and phosphorus), pathogenic organisms, and specific trace organic constituents (micropollutants). Some types of sewage treatment produce sewage sludge which can be treated before safe disposal or reuse. Under certain circumstances,
2184-402: Is an agglomeration of concentrated wastes, and therefore it contains many potentially extractable and useable components. These can include using sludge to produce energy, create carbon-based components, extract phosphorus and nitrogen , or make bricks or other construction materials. Recycling of phosphate is regarded as especially important because the phosphate industry predicts that at
2275-403: Is both: a type of treatment and a type of final disposal. It leads to groundwater recharge and/or to evapotranspiration. Land application include slow-rate systems, rapid infiltration, subsurface infiltration, overland flow. It is done by flooding, furrows, sprinkler and dripping. It is a treatment/disposal system that requires a large amount of land per person. The per person organic matter load
2366-406: Is brought to the sewage treatment plant in vacuum trucks ). Flow equalization basins require variable discharge control, typically include provisions for bypass and cleaning, and may also include aerators and odor control. In some larger plants, fat and grease are removed by passing the sewage through a small tank where skimmers collect the fat floating on the surface. Air blowers in the base of
2457-403: Is called "digested" sludge and may be disposed of by drying and then landfilling . Following treatment, sewage sludge is either landfilled, dumped in the ocean, incinerated, applied on agricultural land or, in some cases, retailed or given away for free to the general public. According to a review article published in 2012, sludge reuse (including direct agricultural application and composting)
2548-462: Is defined as part of the EPA 503 rule. The components of sludge have pollutant limits defined by the EPA. "A Pollutant is an organic substance, an inorganic substance, a combination of organic and inorganic substances, or a pathogenic organism that, after discharge and upon exposure, ingestion, inhalation, or assimilation into an organism either directly from the environment or indirectly by ingestion through
2639-469: Is expressed as kg of dry solids produced per ML of wastewater treated; one mega litre (ML) is 10 m . Of the biological treatment processes, the activated sludge process produces about 70–100 kg/ML of waste activated sludge, and a trickling filter process produces slightly less sludge from the biological part of the process: 60–100 kg/ML. This means that the total sludge production of an activated sludge process that uses primary sedimentation tanks
2730-409: Is in the range of 180–270 kg/ML, being the sum of primary sludge and waste activated sludge. United States municipal wastewater treatment plants in 1997 produced about 7.7 million dry tons of sewage sludge, and about 6.8 million dry tons in 1998 according to EPA estimates. As of 2004, about 60% of all sewage sludge was applied to land as a soil amendment and fertilizer for growing crops. In
2821-489: Is often encouraged. Disinfection of treated sewage aims to kill pathogens (disease-causing microorganisms) prior to disposal. It is increasingly effective after more elements of the foregoing treatment sequence have been completed. The purpose of disinfection in the treatment of sewage is to substantially reduce the number of pathogens in the water to be discharged back into the environment or to be reused. The target level of reduction of biological contaminants like pathogens
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2912-695: Is often regulated by the presiding governmental authority. The effectiveness of disinfection depends on the quality of the water being treated (e.g. turbidity , pH, etc.), the type of disinfection being used, the disinfectant dosage (concentration and time), and other environmental variables. Water with high turbidity 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 . Monochloramine , which
3003-438: Is part of the field of sanitation . Sanitation also includes the management of human waste and solid waste as well as stormwater (drainage) management. The term sewage treatment plant is often used interchangeably with the term wastewater treatment plant . The term sewage treatment plant (STP) (or sewage treatment works ) is nowadays often replaced with the term wastewater treatment plant (WWTP). Strictly speaking,
3094-662: Is persistent uncertainty on possible adverse health effects. The NRC noted that further research is needed and made about 60 recommendations for addressing public health concerns, scientific uncertainties, and data gaps in the science underlying the sewage sludge standards. The EPA responded with a commitment to conduct research addressing the NRC recommendations. Residents living near Class B sludge processing sites may experience asthma or pulmonary distress due to bioaerosols released from sludge fields. A 2004 survey of 48 individuals near affected sites found that most reported irritation symptoms, about half reported an infection within
3185-413: Is sometimes defined as anything more than primary and secondary treatment in order to allow discharge into a highly sensitive or fragile ecosystem such as estuaries , low-flow rivers or 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
3276-411: Is that only some of the sludge is used and the rest still needs disposal. It can also be very expensive to develop and use appropriate technologies for extracting resources. The specific content of sewage sludge is affected by what enters the sewage stream, and how the sewage is treated and processed. As wastewater treatment policies are passed or amended to allow or regulate potential contaminants into
3367-534: Is then consumed by humans. A PhD thesis studying the addition of sludge to neutralize soil acidity concluded that the practice was not recommended if large amounts are used because the sludge produces acids when it oxidizes. Studies have indicated that pharmaceuticals and personal care products, which often adsorb to sludge during wastewater treatment, can persist in agricultural soils following biosolid application. Some of these chemicals, including potential endocrine disruptor triclosan, can also travel through
3458-570: Is to provide a final treatment stage to further improve the effluent quality before it is discharged to the receiving water body or reused. 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 . Tertiary treatment may include biological nutrient removal (alternatively, this can be classified as secondary treatment), disinfection and removal of micropollutants, such as environmental persistent pharmaceutical pollutants . Tertiary treatment
3549-561: Is unknown, but the link to human and land animal health is likely tied to the capacity for plants to absorb and accumulate these chemicals in their consumed tissues. Studies of this kind are in early stages, but evidence of root uptake and translocation to leaves did occur for both triclosan and triclocarban in soybeans . This effect was not present in corn when tested in a different study. A cautionary approach to land application of biosolids has been advocated by some for regions where soils have lower capacities for toxics absorption or due to
3640-572: Is used for drinking water, is not used in the treatment of sewage because of its persistence. Municipal wastewater treatment Too Many Requests If you report this error to the Wikimedia System Administrators, please include the details below. Request from 172.68.168.236 via cp1112 cp1112, Varnish XID 945510669 Upstream caches: cp1112 int Error: 429, Too Many Requests at Thu, 28 Nov 2024 08:31:10 GMT Sewage sludge After treatment, and dependent upon
3731-511: The combined sewer or sanitary sewer . Sewerage ends at the entry to a sewage treatment plant or at the point of discharge into the environment . It is the system of pipes, chambers, manholes or inspection chamber, etc. that conveys the sewage or storm water. Sewage can be treated close to where the sewage is created, which may be called a decentralized system or even an on-site system ( on-site sewage facility , septic tanks , etc.). Alternatively, sewage can be collected and transported by
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3822-659: The irrigation of a golf course, greenway or park. If it is sufficiently clean, it can also be used for groundwater recharge or agricultural purposes. Sand filtration removes much of the residual suspended matter. Filtration over activated carbon , also called carbon adsorption, removes residual toxins . Micro filtration or synthetic membranes are used in membrane bioreactors and can also remove pathogens. Settlement and further biological improvement of treated sewage may be achieved through storage in large human-made ponds or lagoons. These lagoons are highly aerobic, and colonization by native macrophytes , especially reeds,
3913-479: The sedimentation tank before this happens. This is accomplished in one of two ways. Most commonly, the fresh sludge is continuously extracted from the bottom of a hopper-shaped tank by mechanical scrapers and passed to separate sludge-digestion tanks. In some treatment plants an Imhoff tank is used: sludge settles through a slot into the lower story or digestion chamber, where it is decomposed by anaerobic bacteria , resulting in liquefaction and reduced volume of
4004-922: The EPA released the Targeted National Sewage Sludge Study , which reports on the level of metals , chemicals , hormones , and other materials present in a statistical sample of sewage sludges. Some highlights include: Micro-pollutants are compounds which are normally found at concentrations up to microgram per liter and milligram per kilogram in the aquatic and terrestrial environment, respectively, and they are considered to be potential threats to environmental ecosystems. They can become concentrated in sewage sludge. Each of these disposal options comes with myriad potential—and in some cases proven—human health and environment impacts. Several organic micro-pollutants such as endocrine disrupting compounds, pharmaceuticals and per-fluorinated compounds have been detected in sewage sludge samples around
4095-425: The EU is via application to agricultural lands. As of 2023, 40% of sludge produced in the EU was used on agricultural land. Since the 1960s there has been cooperative activity with industry to reduce the inputs of persistent substances from factories. This has been very successful and, for example, the content of cadmium in sewage sludge in major European cities is now only 1% of what it was in 1970. Sewage sludge
4186-737: The EU was incinerated. Biosolids is a term widely used to denote the byproduct of domestic and commercial sewage and wastewater treatment that is to be used in agriculture. National regulations that dictate the practice of land application of treated sewage sludge differ widely and e.g. in the US there are widespread disputes about this practice. Depending on their level of treatment and resultant pollutant content, biosolids can be used in regulated applications for non-food agriculture, food agriculture, or distribution for unlimited use. Treated biosolids can be produced in cake, granular, pellet, or liquid form and are spread over land before being incorporated into
4277-498: The UK, Europe and China agriculturally for more than 80 years, though there is increasing pressure in some countries to stop the practice of land application due to farm land contamination and negative public opinion. In the 1990s, there was pressure in some European countries to ban the use of sewage sludge as a fertilizer. Switzerland, Sweden, Austria, and others introduced a ban. Still, the dominant method for disposal of sewage sludge in
4368-490: The activated sludge process has a high energy consumption because it includes an aeration step. Some sewage treatment plants produce biogas from their sewage sludge treatment process by using a process called anaerobic digestion . This process can produce enough energy to meet most of the energy needs of the sewage treatment plant itself. For activated sludge treatment plants in the United States, around 30 percent of
4459-418: The annual operating costs is usually required for energy. Most of this electricity is used for aeration, pumping systems and equipment for the dewatering and drying of sewage sludge . Advanced sewage treatment plants, e.g. for nutrient removal, require more energy than plants that only achieve primary or secondary treatment. Small rural plants using trickling filters may operate with no net energy requirements,
4550-548: The ash material readily usable as a LEEDs preferred additive to concrete or asphalt. Examples of other ways to use dried sewage sludge as an energy resource include the Gate 5 Energy System, an innovative process to power a steam turbine using heat from burning milled and dried sewage sludge, or combining dried sewage sludge with coal in coal-fired power stations . In both cases this allows for production of electricity with less carbon-dioxide emissions than conventional coal-fired power stations. As of 2023, 27% of sludge produced in
4641-414: The ash produced by incineration or incomplete combustion processes (such as fluidized-bed dryers) may be difficult to use without subsequent treatment due to high heavy metal content; solutions to this include leaching of the ashes to remove heavy metals or in the case of ash produced in a complete-combustion process, or with biochar produced from a pyrolytic process, the heavy metals may be fixed in place and
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#17327826702444732-457: The average flows. Such basins can improve the performance of the biological treatment processes and the secondary clarifiers. Disadvantages include the basins' capital cost and space requirements. Basins can also provide a place to temporarily hold, dilute and distribute batch discharges of toxic or high-strength wastewater which might otherwise inhibit biological secondary treatment (such was wastewater from portable toilets or fecal sludge that
4823-414: The collected sludge towards a hopper in the base of the tank where it is pumped to sludge treatment facilities. Sewage treatment plants that are connected to a combined sewer system sometimes have a bypass arrangement after the primary treatment unit. This means that during very heavy rainfall events, the secondary and tertiary treatment systems can be bypassed to protect them from hydraulic overloading, and
4914-426: The current rate of extraction the economic reserves will be exhausted in 100 or at most 250 years. Phosphate can be recovered with minimal capital expenditure as technology currently exists, but municipalities have little political will to attempt nutrient extraction, instead opting for a "take all the other stuff" mentality. One potential drawback of extracting products from sludge — as opposed to land application —
5005-446: The exposed residents, including excessive secretion of tears, abdominal bloating, jaundice, skin ulcer, dehydration, weight loss, and general weakness. The frequency of reported occurrence of bronchitis, upper respiratory infection, and giardiasis were also statistically significantly elevated. The findings suggest an increased risk for certain respiratory, gastrointestinal, and other diseases among residents living near farm fields on which
5096-597: The factories themselves to reduce the pollutant load , before discharge to the sewer. The pretreatment has the following two main aims: Firstly, to prevent toxic or inhibitory compounds entering the biological stage of the sewage treatment plant and reduce its efficiency. And secondly to avoid toxic compounds from accumulating in the produced sewage sludge which would reduce its beneficial reuse options. Some industrial wastewater may contain pollutants which cannot be removed by sewage treatment plants. Also, variable flow of industrial waste associated with production cycles may upset
5187-422: The finer grit passes through the grit removal flows under normal conditions. During periods of high flow deposited grit is resuspended and the quantity of grit reaching the treatment plant increases substantially. Equalization basins can be used to achieve flow equalization. This is especially useful for combined sewer systems which produce peak dry-weather flows or peak wet-weather flows that are much higher than
5278-602: The following aspects are included in the selection process: Odors, vector attraction, sludge transportation, sanitary risks, air contamination , soil and subsoil contamination, surface water pollution or groundwater contamination , devaluation of nearby areas, inconvenience to the nearby population. Odors emitted by sewage treatment are typically an indication of an anaerobic or septic condition. 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
5369-527: The following treatment steps: lime stabilization, thickening, dewatering, drying, anaerobic digestion or composting . Some treatment processes, such as composting and alkaline stabilization, that involve significant amendments may affect contaminant strength and concentration: depending on the process and the contaminant in question, treatment may decrease or in some cases increase the bioavailability and/or solubility of contaminants. Regarding sludge stabilization processes, anaerobic and aerobic digestion seem to be
5460-534: The food chain, could, on the basis of information available to the Administrator of EPA, cause death , disease , behavioral abnormalities , cancer , genetic mutations , physiological malfunctions (including malfunction in reproduction ), or physical deformations in either organisms or offspring of the organisms ." The maximum component pollutant limits by the US EPA are: In 2011, the EPA commissioned
5551-748: The frequency of tank cleaning caused by excessive accumulation of grit; and (3) protect moving mechanical equipment from abrasion and accompanying abnormal wear. The removal of grit is essential for equipment with closely machined metal surfaces such as comminutors, fine screens, centrifuges, heat exchangers, and high pressure diaphragm pumps. Grit chambers come in three types: horizontal grit chambers, aerated grit chambers, and vortex grit chambers. Vortex grit chambers include mechanically induced vortex, hydraulically induced vortex, and multi-tray vortex separators. Given that traditionally, grit removal systems have been designed to remove clean inorganic particles that are greater than 0.210 millimetres (0.0083 in), most of
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#17327826702445642-418: The homes in the U.S. Sewage treatment often involves two main stages, called primary and secondary treatment, while advanced treatment also incorporates a tertiary treatment stage with polishing processes. Different types of sewage treatment may utilize some or all of the process steps listed below. Preliminary treatment (sometimes called pretreatment) removes coarse materials that can be easily collected from
5733-414: The latter is a broader term that can also refer to industrial wastewater treatment. The terms water recycling center or water reclamation plants are also in use as synonyms. The overall aim of treating sewage is to produce an effluent that can be discharged to the environment while causing as little water pollution as possible, or to produce an effluent that can be reused in a useful manner. This
5824-423: The law that prohibited ocean dumping as a means of disposal of sewage sludge in the US in 1988. Sludge can also be incinerated in sludge incineration plants which comes with its own set of environmental concerns (air pollution, disposal of the ash). Pyrolysis of the sludge to create syngas and potentially biochar is possible, as is combustion of biofuel produced from drying sewage sludge or incineration in
5915-666: The main important factors to be considered when evaluating and selecting sewage treatment processes are numerous. They include: process applicability, applicable flow, acceptable flow variation, influent characteristics, inhibiting or refractory compounds, climatic aspects, process kinetics and reactor hydraulics , performance, treatment residuals, sludge processing, environmental constraints, requirements for chemical products, energy and other resources; requirements for personnel, operating and maintenance; ancillary processes, reliability, complexity, compatibility, area availability. With regards to environmental impacts of sewage treatment plants
6006-417: The mixture of sewage and storm-water receives primary treatment only. Primary sedimentation tanks remove about 50–70% of the suspended solids, and 25–40% of the biological oxygen demand (BOD). The main processes involved in secondary sewage treatment are designed to remove as much of the solid material as possible. They use biological processes to digest and remove the remaining soluble material, especially
6097-443: The most common used methods in EU-27. When fresh sewage or wastewater enters a primary settling tank , approximately 50% of the suspended solid matter will settle out in an hour and a half. This collection of solids is known as raw sludge or primary solids and is said to be "fresh" before anaerobic processes become active. The sludge will become putrescent in a short time once anaerobic bacteria take over, and must be removed from
6188-409: The most important parameters in process selection are typically efficiency, reliability, and space requirements. In developing countries , they might be different and the focus might be more on construction and operating costs as well as process simplicity. Choosing the most suitable treatment process is complicated and requires expert inputs, often in the form of feasibility studies . This is because
6279-517: The odors with carbon reactors, a contact media with bio-slimes, small doses of chlorine , or circulating fluids to biologically capture and metabolize the noxious gases. Other methods of odor control exist, including addition of iron salts, hydrogen peroxide , calcium nitrate , etc. to manage hydrogen sulfide levels. The energy requirements vary with type of treatment process as well as sewage strength. For example, constructed wetlands and stabilization ponds have low energy requirements. In comparison,
6370-400: The organic fraction. This can be done with either suspended-growth or biofilm processes. The microorganisms that feed on the organic matter present in the sewage grow and multiply, constituting the biological solids, or biomass. These grow and group together in the form of flocs or biofilms and, in some specific processes, as granules. The biological floc or biofilm and remaining fine solids form
6461-509: 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. At the global level, an estimated 52% of sewage is treated. However, sewage treatment rates are highly unequal for different countries around the world. For example, while high-income countries treat approximately 74% of their sewage, developing countries treat an average of just 4.2%. The treatment of sewage
6552-434: The population dynamics of biological treatment units. Urban residents in many parts of the world rely on on-site sanitation systems without sewers, such as septic tanks and pit latrines , and fecal sludge management in these cities is an enormous challenge. For sewage treatment the use of septic tanks and other on-site sewage facilities (OSSF) is widespread in some rural areas, for example serving up to 20 percent of
6643-617: The presence of unknowns in sewage biosolids. In 2007 the Northeast Regional Multi-State Research Committee (NEC 1001) issued conservative guidelines tailored to the soils and conditions typical of the northeastern US. Use of sewage sludge is prohibited for produce to be labeled USDA-certified organic . In 2014 the United States grocery chain Whole Foods banned produce grown in sewage sludge. Treated sewage sludge has been used in
6734-675: The quality of sludge produced (for example with regards to heavy metal content), sewage sludge is most commonly either disposed of in landfills , dumped in the ocean or applied to land for its fertilizing properties, as pioneered by the product Milorganite . The term " Biosolids " is often used as an alternative to the term sewage sludge in the United States, particularly in conjunction with reuse of sewage sludge as fertilizer after sewage sludge treatment . Biosolids can be defined as organic wastewater solids that can be reused after stabilization processes such as anaerobic digestion and composting . Opponents of sewage sludge reuse reject this term as
6825-428: The raw sewage before they damage or clog the pumps and sewage lines of primary treatment clarifiers . The influent in sewage water passes through a bar screen to remove all large objects like cans, rags, sticks, plastic packets, etc. carried in the sewage stream. This is most commonly done with an automated mechanically raked bar screen in modern plants serving large populations, while in smaller or less modern plants,
6916-475: The sewage (for example only the toilet wastewater ), or they only provide pre-treatment, like septic tanks. On the other hand, some systems are capable of providing a good performance, satisfactory for several applications. Many of these systems are based on natural treatment processes, requiring large areas, while others are more compact. In most cases, they are used in rural areas or in small to medium-sized communities. For example, waste stabilization ponds are
7007-403: The sewage stream, the content of the sewage sludge reflects those changes. For example, the EU's Urban Waste Water Treatment Directive shapes the types of contaminants that enter the EU's sewage treatment stream. Bacteria in treated sludge products can actually regrow under certain environmental conditions. Pathogens could easily remain undetected in untreated sewage sludge. Pathogens are not
7098-402: The sludge. The secondary treatment process also generates a sludge largely composed of bacteria and protozoa with entrained fine solids, and this is removed by settlement in secondary settlement tanks. Both sludge streams are typically combined and are processed by anaerobic or aerobic treatment process at either elevated or ambient temperatures. After digesting for an extended period, the result
7189-441: The soil column and leach into agricultural tile drainage at detectable levels. Other studies, however, have shown that these chemicals remain adsorbed to surface soil particles, making them more susceptible to surface erosion than infiltration. These studies are also mixed in their findings regarding the persistence of chemicals such as triclosan , triclocarban , and other pharmaceuticals. The impact of this persistence in soils
7280-587: The soil or injected directly into the soil by specialist contractors. Such use was pioneered by the production of Milorganite in 1926. Use of sewage sludge has shown an increase in level of soil available phosphorus and soil salinity . The findings of a 20-year field study of air, land, and water in Arizona, concluded that use of biosolids is sustainable and improves the soil and crops. Other studies report that plants uptake large quantities of heavy metals and toxic pollutants that are retained by produce, which
7371-523: The source of PCB contamination. In February 2014, the city of Charlotte admitted PCBs have entered their sewage treatment centers as well. Contaminants of concern in sewage sludge are plasticizers, PDBEs, PFASs ("forever chemicals"), and others generated by human activities, including personal care products and medicines. Synthetic fibers from fabrics persist in treated sewage sludge as well as in biosolids-treated soils and may thus serve as an indicator of past biosolids application. The term "pollutant"
7462-413: The surface and are skimmed off. These basins are called primary sedimentation tanks or primary clarifiers and typically have a hydraulic retention time (HRT) of 1.5 to 2.5 hours. The settled and floating materials are removed and the remaining liquid may be discharged or subjected to secondary treatment. Primary settling tanks are usually equipped with mechanically driven scrapers that continually drive
7553-432: 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 is the "removal of a portion of the suspended solids and organic matter from the sewage".It consists of allowing sewage to pass slowly through a basin where heavy solids can settle to the bottom while oil, grease and lighter solids float to
7644-648: The treated sewage sludge might be termed biosolids and can be used as a fertilizer . Typical values for physical–chemical characteristics of raw sewage in developing countries have been published as follows: 180 g/person/d for total solids (or 1100 mg/L when expressed as a concentration), 50 g/person/d for BOD (300 mg/L), 100 g/person/d for COD (600 mg/L), 8 g/person/d for total nitrogen (45 mg/L), 4.5 g/person/d for ammonia-N (25 mg/L) and 1.0 g/person/d for total phosphorus (7 mg/L). The typical ranges for these values are: 120–220 g/person/d for total solids (or 700–1350 mg/L when expressed as
7735-484: The treatment plant, and can cause substantial damage and inefficiency in the process. Grit consists of sand , gravel , rocks, and other heavy materials. Preliminary treatment may include a sand or grit removal channel or chamber, where the velocity of the incoming sewage is reduced to allow the settlement of grit. Grit removal is necessary to (1) reduce formation of deposits in primary sedimentation tanks, aeration tanks, anaerobic digesters, pipes, channels, etc. (2) reduce
7826-449: The use of biosolids was permitted." Although correlation does not imply causation , such extensive correlations may lead reasonable people to conclude that precaution is necessary in dealing with sludge and sludged farmlands. Harrison and Oakes suggest that, in particular, "until investigations are carried out that answer these questions (...about the safety of Class B sludge...), land application of Class B sludges should be viewed as
7917-448: The whole process being driven by gravitational flow, including tipping bucket flow distribution and the desludging of settlement tanks to drying beds. This is usually only practical in hilly terrain and in areas where the treatment plant is relatively remote from housing because of the difficulty in managing odors. In highly regulated developed countries, industrial wastewater usually receives at least pretreatment if not full treatment at
8008-485: The wind conditions. In 2007, a health survey of persons living in close proximity to Class B sludged land was conducted. A sample of 437 people exposed to Class B sludge (living within 1-mile (1.6 km) of sludged land) - and using a control group of 176 people not exposed to sludge (not living within 1-mile (1.6 km) of sludged land) reported the following: "Results revealed that some reported health-related symptoms were statistically significantly elevated among
8099-828: The world at concentrations ranging up to some hundreds mg/kg of dried sludge. Sterols and other hormones have also been detected. Sewage treatment plants receive various forms of hazardous waste from hospitals, nursing homes, industry and households. Low levels of constituents such as PCBs , dioxin , and brominated flame retardants , may remain in treated sludge. There are potentially thousands of other components of sludge that remain untested/undetected disposed of from modern society that also end up in sludge (pharmaceuticals, nano particles, etc.) which have been proven to be hazardous to both human and ecological health. In 2013, in South Carolina PCBs were discovered in very high levels in wastewater sludge. The problem
8190-584: Was not discovered until thousands of acres of farm land in South Carolina were discovered to be contaminated by this hazardous material. SCDHEC issued emergency regulatory order banning all PCB laden sewage sludge from being land applied on farm fields or deposited into landfills in South Carolina. Also in 2013, after DHEC request, the city of Charlotte decided to stop land applying sewage sludge in South Carolina while authorities investigated
8281-616: Was the predominant choice for sludge management in EU-15 (53% of produced sludge), following by incineration (21% of produced sludge). On the other hand, the most common disposal method in EU-12 countries was landfilling. The amount of sewage sludge produced is proportional to the amount and concentration of wastewater treated, and it also depends on the type of wastewater treatment process used. It can be expressed as kg dry solids per cubic metre of wastewater treated. The total sludge production from
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