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70-502: A state revolving fund ( SRF ) is a fund administered by a U.S. state for the purpose of providing low-interest loans for investments in water and sanitation infrastructure (e.g., sewage treatment , stormwater management facilities, drinking water treatment), as well as for the implementation of nonpoint source pollution control and estuary protection projects. An SRF receives its initial capital from federal grants and state contributions. It then emits bonds that are guaranteed by

140-559: 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

210-399: A floating layer in their primary settling tank, consisting of low-density liquids such as oils, buoyant solids, and soap foam. This is referred to as scum and is slowly decomposed by microorganisms, eventually falling to the bottom of the settling tank as part of the sludge. When private septic tanks are emptied of solids, the tank is typically vacuumed empty and the incompletely digested scum

280-525: 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

350-413: 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

420-438: A more cooperative approach. Effective management of onsite systems requires rigorous planning, design, installation, operation, maintenance, monitoring, and controls. State and tribal agencies report that onsite septic systems currently constitute the third most common source of groundwater pollution and that these systems have failed because of inappropriate siting or design or inadequate long-term maintenance (USEPA, 1996a). In

490-694: 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

560-814: 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

630-655: A permit is required to do so and how to obtain it, the type, size and location of the system (usually according to on-site soil characteristics and other factors), etc. : The potential market volume of on-site treatment is suggested to be about 35 million population equivalents for Europe. In the United States, on site sewage facilities collect, treat, and release about 4 billion US gallons (15,000,000 m ) of treated effluent per day from an estimated 26 million homes, businesses, and recreational facilities nationwide (U.S. Census Bureau, 1997). Recognition of

700-754: 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 )

770-431: 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 ,

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840-426: 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

910-544: 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

980-467: 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

1050-428: Is a shared power between federal and provincial governments. However, waste water management mostly falls within provincial, territorial and municipal jurisdiction, while the federal government has jurisdiction over wastewater on federal land and on First Nations reserves . Each province and territory has its own norms and regulations concerning the design and installation of onsite sewage facilities, such as whether

1120-573: 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 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

1190-509: 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,

1260-400: Is added to the incompletely digested sludge, further adding to its aroma and bioactivity. If left completely undisturbed and exposed to the open air through a vent, the sludge and scum in a settling tank will eventually be turned completely into low-odor compost. By building two tanks side by side, and diverting sewage between them, one tank can be allowed to rest while the other is in use, and

1330-679: Is because 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

1400-405: 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

1470-491: 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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1540-697: 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

1610-444: 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,

1680-414: 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

1750-609: Is still the primary mechanism of sewage disposal. Giving the organisms the time they need to decompose wastes is accomplished by establishing minimum sewage retention and settling times, and minimum liquid flow distances between sewage disposal sites and surface water or water wells . It is normal for animals such as mice, rats, flies, and parasites to participate in the fully natural biological waste recycling process. Engineered facilities typically attempt to exclude them to prevent out of control population explosions and infestation , and prevent spread of vermin and disease . Although

1820-570: 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

1890-769: Is used for drinking water, is not used in the treatment of sewage because of its persistence. Onsite sewage facility A septic tank and drainfield combination is a fairly common type of on-site sewage facility in the Western world. OSSFs account for approximately 25% of all domestic wastewater treatment in the US. Onsite sewage facilities may also be based on small-scale aerobic and biofilter units, membrane bioreactors or sequencing batch reactors . These can be thought of as scaled down versions of municipal sewage treatment plants, and are also known as " package plants ." The primary mechanism of biological waste recycling in

1960-511: 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

2030-665: 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,

2100-531: The 1996 Clean Water Needs Survey (USEPA, 1996b), states and tribes also identified more than 500 communities as having failed septic systems that have caused public health problems. The discharge of partially treated sewage from malfunctioning onsite systems was identified as a principal or contributing source of degradation in 32 percent of all harvest-limited shellfish growing areas. Onsite wastewater treatment systems have also contributed to an overabundance of nutrients in ponds, lakes, and coastal estuaries, leading to

2170-429: 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

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2240-422: 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,

2310-585: The assimilative capacity of regional ground water or surface waters, water quality objectives, and public health goals. Wastewater flow and pollutant content help define system design and size and can be estimated by comparing the size and type of facility with measured effluent outputs from similar, existing facilities. Site evaluations integrate detailed analyses of regional hydrology, geology, and water resources with site specific characterization of soils, slopes, structures, property lines, and other site features to further define system design requirements and determine

2380-399: 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

2450-472: The bottom while oil, grease and lighter solids float to 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

2520-416: 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

2590-693: The creation of the Drinking Water State Revolving Fund program, EPA evaluated the adequacy of state public water systems during its early implementation of the 1974 Safe Drinking Water Act. The agency’s goal was to devolve "primacy" (i.e. oversight of local public water systems) to states that were prepared to accept the responsibility and to use the new funds provided by Congress in EPA’s budget to give states financial support. Sewage treatment Sewage treatment (or domestic wastewater treatment , municipal wastewater treatment )

2660-702: The drain. Most onsite wastewater treatment systems are of the conventional type, consisting of a septic tank and a subsurface wastewater infiltration system (SWIS). Site limitations and more stringent performance requirements have led to significant improvements in the design of wastewater treatment systems and how they are managed. Over the past 20 years the onsite wastewater treatment system (OWTS) industry has developed many new treatment technologies that can achieve high performance levels on sites with size, soil, ground water, and landscape limitations that might preclude installing conventional systems. New technologies and improvements to existing technologies are based on defining

2730-645: The environment. Onsite systems are recognized as viable, low-cost, long-term, decentralized approaches to wastewater treatment if they are planned, designed, installed, operated, and maintained properly (USEPA, 1997). NOTE: In addition to existing state and local oversight, decentralized wastewater treatment systems that serve more than 20 people might become subject to regulation under the USEPA's Underground Injection Control Program, although EPA has proposed not to include them (64FR22971:5/7/01). Although some onsite wastewater management programs have functioned successfully in

2800-597: 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

2870-437: 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 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

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2940-423: 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

3010-605: 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

3080-748: 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

3150-420: 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

3220-488: The impacts of onsite systems on ground water and surface water quality (e.g., nitrate and bacteria contamination, nutrient inputs to surface waters) has increased interest in optimizing the systems' performance. Public health and environmental protection officials now acknowledge that onsite systems are not just temporary installations that will be replaced eventually by centralized sewage treatment services, but permanent approaches to treating wastewater for release and reuse in

3290-400: The incomplete state of decomposition, when removed from an onsite sewage facility, these solids are typically referred to as sludge rather than compost , and have powerful offensive odors arising from the microorganisms still consuming nutrients in the sludge. Engineered facilities that use water suspension to transport solids (private septic systems and municipal facilities) typically form

3360-848: The initial capital. It then "revolves" through the repayment of principal and the payment of interest on outstanding loans. There are currently two SRFs, the Clean Water State Revolving Fund created in 1987 under the Clean Water Act , and the Drinking Water State Revolving Fund created in 1997 under the Safe Drinking Water Act . Both programs are managed at the federal level by the Environmental Protection Agency (EPA). Prior to

3430-415: 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

3500-483: 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

3570-421: 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

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3640-400: 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

3710-535: The natural environment is performed by other organisms such as animals, insects, soil microorganisms, plants, and fungi, which consume all available nutrients in the waste, leaving behind fully decomposed solids that become part of topsoil , and pure drinking water that has been stripped of everything that can possibly be consumed and utilized. This natural biological purification requires time and space to process wastes. In virtually all engineered onsite sewage facilities, recycling and decomposition by natural organisms

3780-520: 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,

3850-400: 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

3920-512: 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

3990-494: The past, problems persist. Most current onsite regulatory programs focus on permitting and installation. Few programs address onsite system operation and maintenance, resulting in failures that lead to unnecessary costs and risks to public health and water resources. Moreover, the lack of coordination among agencies that oversee land use planning, zoning, development, water resource protection, public health initiatives, and onsite systems causes problems that could be prevented through

4060-421: The performance requirements of the system, characterizing wastewater flow and pollutant loads, evaluating site conditions, defining performance and design boundaries, and selecting a system design that addresses these factors. Performance requirements can be expressed as numeric criteria (e.g., pollutant concentration or mass loading limits) or narrative criteria (e.g., no odors or visible sheen) and are based on

4130-734: The physical placement of system components. Most of the alternative treatment technologies applied today treat wastes after they exit the septic tank; the tank retains settleable solids, grease, and oils and provides an environment for partial digestion of settled organic wastes. Post-tank treatment can include aerobic (with oxygen) or anaerobic (with no or low oxygen) biological treatment in suspended or fixed-film reactors, physical/chemical treatment, soil infiltration, fixed-media filtration , and/or disinfection. The application and sizing of treatment units based on these technologies are defined by performance requirements, wastewater characteristics, and site conditions. Under Canadian federalism , environment

4200-436: 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

4270-429: 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,

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4340-460: 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,

4410-438: The resting tank can be safely and easily cleaned out by hand before it is used again. This has been proposed as a solution for onsite sewage facilities in subsistence agriculture economies where hand labor is the most abundant. Although human body waste is no different from the waste of any other animal, municipal facilities may be required to bury the collected solids in landfills, due to the risk of toxic contaminants placed into

4480-475: 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

4550-432: The shared communal sewage system, by humans unaware of the harm they are causing. Municipal facilities may also collect runoff from roadways, which contains traces of all the various chemicals used in vehicles such as brake fluid and engine oil, and those used in melting ice and snow. Private septic systems typically do not experience these issues, as the homeowner is directly aware that they must not pour toxic chemicals down

4620-402: The solids collected by onsite sewage facilities can potentially be used as compost to build topsoil, these solids are often incompletely decomposed due to either a lack of onsite storage space to wait for decomposition (municipal facilities), or because the solids are being stacked in a layered structure of new waste solids on top of previously decomposed solids (septic tanks and outhouses). Due to

4690-650: 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

4760-486: 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

4830-450: 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

4900-409: Was wastewater from portable toilets or fecal sludge that 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

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