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Encyclopedia > Sewage treatment

Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater, both runoff and domestic. It includes physical, chemical and biological processes to remove physical, chemical and biological contaminants. Its objective is to produce a waste stream (or treated effluent) and a solid waste or sludge also suitable for discharge or reuse back into the environment. This material is often inadvertently contaminated with toxic organic and inorganic compounds. Pollution is the release of harmful environmental contaminants, or the substances so released. ... In the context of creating Plutonium at the Hanford Site, effluent refers to the cooling water that is discharged from a nuclear reactor that may or may not be radioactive. ... SLUDGE (Scripting Language for Unhindered Development of a Gaming Environment) is a shareware adventure game engine developed by Hungry Software. ...


Sewage is created by residences, institutions, and commercial and industrial establishments. It can be treated close to where it is created (in septic tanks, biofilters or aerobic treatment systems), or collected and transported via a network of pipes and pump stations to a municipal treatment plant (see sewerage and pipes and infrastructure). Sewage collection and treatment is typically subject to local, state and federal regulations and standards (regulation and controls). Industrial sources of wastewater often require specialized treatment processes (see Industrial wastewater treatment). A septic tank, the key component of a septic system, is a small scale sewage treatment system common in areas with no connection to main sewerage pipes provided by private corporations or local governments. ... Biofiltration is a pollution control technique using living material to filter or chemically process pollutants. ... An aerobic treatment system or ATS, often called (incorrectly) an aerobic septic system is a small scale sewage treatment system similar to a septic tank system, but which uses an aerobic process for digestion rather than the anaerobic process used in septic systems. ... The word sewerage means the provision of pipes etc to collect and dispose of sewage. ... Urban areas require some methods for collection and disposal of sewage. ... Sewage disposal regulation and administration Regulation USA Sewer systems in the United States are regulated by multiple agencies on the local, state, and federal levels. ... Industrial wastewater treatment covers the mechanisms and processes used to treat waters that have been contaminated in some way by mans industrial or commercial activities prior to its release into the environment or its re-use. ...


Typically, sewage treatment involves three stages, called primary, secondary and tertiary treatment. First, the solids are separated from the wastewater stream. Then dissolved biological matter is progressively converted into a solid mass by using indigenous, water-borne bacteria. Finally, the biological solids are neutralized then disposed of or re-used, and the treated water may be disinfected chemically or physically (for example by lagoons and micro-filtration). The final effluent can be discharged into a stream, river, bay, lagoon or wetland, or it can be used for the irrigation of a golf course, green way or park. If it is sufficiently clean, it can also be used for groundwater recharge. Irrigation is the artificial application of water to the soil usually for assisting in growing crops. ... Missing main definition------ someone add if you know it please. ...

Contents

Description

Raw influent (sewage) is the liquid waste from toilets, baths, showers, kitchens, sinks etc. Household waste that is disposed of via sewers. In many areas sewage also includes some liquid waste from industry and commerce. In the United Kingdom, the waste from toilets is termed foul waste, the waste from items such as basins, baths, kitchens is termed sullage water, and the industrial and commercial waste is termed trade waste. For other uses, see Toilet (disambiguation). ... Children bathing in a small metal bathtub Bathing is the immersion of the body in fluid, usually water, or an aqueous solution. ... It has been suggested that Steam shower be merged into this article or section. ... A kitchen is a room used for food preparation and sometimes entertainment. ... For other uses, see Sink (disambiguation). ... Mixed municipal waste, Hiriya, Tel Aviv Municipal solid waste (MSW) is a waste type that includes predominantly household waste (domestic waste) with sometimes the addition of commercial wastes collected by a municipality within a given area. ... A sewer is an artificial conduit or system of conduits used to remove sewage (human liquid waste) and to provide drainage. ...


The division of household water drains into greywater and blackwater is becoming more common in the developed world, with greywater being permitted to be used for watering plants or recycled for flushing toilets. A lot of sewage also includes some surface water from roofs or hard-standing areas. Municipal wastewater therefore includes residential, commercial, and industrial liquid waste discharges, and may include stormwater runoff. Sewage systems capable of handling stormwater are known as combined systems. Such systems are usually avoided since they complicate and thereby reduce the efficiency of sewage treatment plants owing to their seasonality. The variability in flow also leads to often larger than necessary, and subsequently more expensive, treatment facilities. In addition, heavy storms that contribute more flows than the treatment plant can handle may overwhelm the sewage treatment system, causing a spill or overflow (called a combined sewer overflow, or CSO, in the United States). It is preferable to have a separate storm drain system for stormwater in areas that are developed with sewer systems. Greywater, sometimes spelled graywater, grey water or gray water and also known as sullage, is non-industrial wastewater generated from domestic processes such as washing dishes, laundry and bathing. ... Blackwater (waste) is a relatively recent term used to describe water containing Feacal matter and Urine: its is also known as foul water, or as sewage. ... Stormwater is a term used to describe water that originates during precipitation events. ... Storm drain in use A storm drain, storm sewer, stormwater drain (Australia and New Zealand) or surface water system (UK) is designed to drain excess rain and ground water from paved streets, parking lots, sidewalks, and roofs. ...


The construction of combined sewers is a less common practice in the U.S. and Canada than in the past and is no longer accepted within building regulations in the UK and other European countries. Instead, liquid waste and stormwater are collected and conveyed in separate sewer systems, referred to as sanitary sewers and storm sewers in the U.S. and as foul sewers and surface water sewers in the UK. The UK building regulations are statutory instruments that seek to ensure that the policies set out in the Building Act 1984 are carried out in the construction of buildings. ... For other uses, see Europe (disambiguation). ...


As rainfall runs over the surface of roofs and the ground, it may pick up various contaminants including soil particles and other sediment, heavy metals, organic compounds, animal waste, and oil and grease. Some jurisdictions require stormwater to receive some level of treatment before being discharged directly into waterways. Examples of treatment processes used for stormwater include sedimentation basins, wetlands, buried concrete vaults with various kinds of filters, and vortex separators (to remove coarse solids). Loess field in Germany Surface-water-gley developed in glacial till, Northern Ireland Soil is a complex mixture of materials, principally ground up rock and water. ... This article or section cites very few or no references or sources. ... A heavy metal is any of a number of higher atomic weight elements, which has the properties of a metallic substance at room temperature. ... Benzene is the simplest of the arenes, a family of organic compounds An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. ... Synthetic motor oil For other uses, see Oil (disambiguation). ... Pumpjack pumping an oil well near Lubbock, Texas Ignacy Łukasiewicz - inventor of the refining of kerosene from crude oil. ... This article does not cite any references or sources. ... // A constructed wetland is an artificial marsh or swamp, created for anthropogenic discharge such as wastewater, stormwater runoff or sewage treatment, and as habitat for wildlife, or for land reclamation after mining or other disturbance. ...


The site where the raw wastewater is processed before it is discharged back to the environment is called a wastewater treatment plant (WWTP). The order and types of mechanical, chemical and biological systems that comprise the wastewater treatment plant are typically the same for most developed countries:

  • Mechanical treatment;
Influx (Influent)
Removal of large objects
Removal of sand and grit
Pre-precipitation
  • Biological treatment;
Oxidation bed (oxidizing bed) or aeration system
Post precipitation
Effluent
  • Chemical treatment (this step is usually combined with settling and other processes to remove solids, such as filtration. The combination is referred to in the U.S. as physical-chemical treatment.).

Aeration is the process by which air is circulated through, mixed with or dissolved in a liquid (usually water) or substance (such as soil). ...

Treatment stages

Primary treatment

Primary treatment removes the materials that can be easily collected from the raw wastewater and disposed of. The typical materials that are removed during primary treatment include fats, oils, and greases (also referred to as FOG), sand, gravels and rocks (also referred to as grit), larger settleable solids including human waste and floating materials. This step is done entirely with machinery, hence the name mechanical treatment. For other uses, see Sand (disambiguation). ...


Influx (influent) and removal of large objects

In the mechanical treatment, the influx (influent) of sewage water is strained to remove all large objects that are deposited in the sewer system, such as rags, sticks, condoms, sanitary towels (sanitary napkins) or tampons, cans, fruit, etc. This is most commonly done with a manual or automated mechanically raked screen. This type of waste is removed because it can damage or clog the equipment in the sewage treatment plant. It has been suggested that Textile be merged into this article or section. ... This article is about the male contraceptive device. ... A sanitary towel (U.K.) or sanitary napkin (U.S.) is an absorbent piece of material worn by a woman while she is menstruating, to absorb the flow of blood from the vagina. ... For the commune of Réunion, see Le Tampon. ... For the American naval slang term, see destroyer. ... For other uses, see Fruit (disambiguation). ...


Sand and grit removal

Primary treatment typically includes a sand or grit channel or chamber where the velocity of the incoming wastewater is carefully controlled to allow sand grit and stones to settle, while keeping the majority of the suspended organic material in the water column. This equipment is called a detritor or sand catcher. Sand grit and stones need to be removed early in the process to avoid damage to pumps and other equipment in the remaining treatment stages. Sometimes there is a sand washer (grit classifier) followed by a conveyor that transports the sand to a container for disposal. The contents from the sand catcher may be fed into the incinerator in a sludge processing plant, but in many cases, the sand and grit is sent to a landfill. This article is about a mechanical device. ... Look up landfill in Wiktionary, the free dictionary. ...

Primary sedimentation tank at a rural treatment plant
Primary sedimentation tank at a rural treatment plant

Download high resolution version (1296x972, 566 KB)sewage treatment primary sedimentation tank File links The following pages link to this file: Sewage treatment Categories: GFDL images ... Download high resolution version (1296x972, 566 KB)sewage treatment primary sedimentation tank File links The following pages link to this file: Sewage treatment Categories: GFDL images ...

Sedimentation

Many plants have a sedimentation stage where the sewage is allowed to pass slowly through large tanks, commonly called "primary clarifiers" or "primary sedimentation tanks". The tanks are large enough that fecal solids can settle and floating material such as grease and oils can rise to the surface and be skimmed off. The main purpose of the primary stage is to produce a generally homogeneous liquid capable of being treated biologically and a sludge that can be separately treated or processed. Primary settlement tanks are usually equipped with mechanically driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank from where it can be pumped to further sludge treatment stages. Horse feces Feces, faeces, or fæces (see spelling differences) is a waste product from an animals digestive tract expelled through the anus (or cloaca) during defecation. ...


Secondary treatment is designed to substantially degrade the biological content of the sewage such as are derived from human waste, food waste, soaps and detergent. The majority of municipal and industrial plants treat the settled sewage liquor using aerobic biological processes. For this to be effective, the biota require both oxygen and a substrate on which to live. There are number of ways in which this is done. In all these methods, the bacteria and protozoa consume biodegradable soluble organic contaminants (e.g. sugars, fats, organic short-chain carbon molecules, etc.) and bind much of the less soluble fractions into floc. Secondary treatment systems are classified as fixed film or suspended growth. Fixed-film treatment process including trickling filter and rotating biological contactors where the biomass grows on media and the sewage passes over its surface. In suspended growth systems—such as activated sludge—the biomass is well mixed with the sewage and can be operated in a smaller space than fixed-film systems that treat the same amount of water. However, fixed-film systems are more able to cope with drastic changes in the amount of biological material and can provide higher removal rates for organic material and suspended solids than suspended growth systems. General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... Leishmania donovani, (a species of protozoan) in a bone marrow cell Protozoa (in Greek proto = first and zoa = animals) are one-celled eukaryotes (that is, unicellular microbes whose cells have membrane-bound nuclei) that commonly show characteristics usually associated with animals, mobility and heterotrophy. ... This article is about sugar as food and as an important and widely traded commodity. ... The trickling filter is known by several other names, among them percolating filter and biological filter Biological filter is also used, especially in the USA, to mean a biological odour The trickling filter is one of the oldest forms of sewage treatment, and is effectively a process-intensified form of... A Rotating biological contactor or RBC is a biological treatment process used in the treatment of wastewater following primary treatment. ...


Roughing filters are intended to treat particularly strong or variable organic loads, typically industrial, to allow them to then be treated by conventional secondary treatment processes. Characteristics include typically tall, circular filters filled with open synthetic filter media to which wastewater is applied at a relatively high rate. They are designed to allow high hydraulic loading and a high flow-through of air. On larger installations, air is forced through the media using blowers. The resultant wastewater is usually within the normal range for conventional treatment processes.

A generalized, schematic diagram of an activated sludge process.
A generalized, schematic diagram of an activated sludge process.

Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...

Activated sludge

Main article: Activated sludge

Activated sludge is a process dealing with the treatment of sewage and industrial wastewaters.[1][2] In general, activated sludge plants encompass a variety of mechanisms and processes that use dissolved oxygen to promote the growth of biological floc that substantially removes organic material. Activated sludge is a process in sewage treatment in which air or oxygen is forced into sewage liquor to develop a biological floc which reduces the organic content of the sewage. ... Activated sludge is a process in sewage treatment in which air or oxygen is forced into sewage liquor to develop a biological floc which reduces the organic content of the sewage. ... Sewage is the mainly liquid waste containing some solids produced by humans which typically consists of washing water, faeces, urine, laundry waste and other material which goes down drains and toilets from households and industry. ... Sewage treatment is the process that removes the majority of the contaminants from waste-water or sewage and produces both a liquid effluent suitable for disposal to the natural environment and a sludge. ...


The process traps particulate material and can, under ideal conditions, convert ammonia to nitrite and nitrate and ultimately to nitrogen gas, (see also denitrification). For other uses, see Ammonia (disambiguation). ... // Definition The nitrite ion is NO2−. A nitrite compound is one that contains this group, either an ionic compound, or an analogous covalent one. ... Trinitrate redirects here. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... This does not cite its references or sources. ...


Surface-aerated basins

A Typical Surface-Aerated Basin (using motor-driven floating aerators)
A Typical Surface-Aerated Basin (using motor-driven floating aerators)
Main article: Aerated lagoon

Most biological oxidation processes for treating industrial wastewaters have in common the use of oxygen (or air) and microbial action. Surface-aerated basins achieve 80 to 90% removal of BOD with retention times of 1 to 10 days.[3] The basins may range in depth from 1.5 to 5.0 metres and utilize motor-driven aerators floating on the surface of the wastewater.[3] Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... An aerated lagoon is a holding and/or treatment pond that speeds up the natural process of biological decomposition of organic waste by stimulating the growth and activity of bacteria that degrade organic waste. ... BOD may refer to: Biochemical oxygen demand 4-methyl-2,5,beta-trimethoxy-phenethylamine, a psychedelic drug IATA code for Bordeaux - Mérignac Airport Brian ODriscoll, Irish international Rugby Union player. ...


In an aerated basin system, the aerators provide two functions: they transfer air into the basins required by the biological oxidation reactions, and they provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater and microbes). Typically, the floating surface aerators are rated to deliver the amount of air equivalent to 1.8 to 2.7 kg O2/kWh. However, they do not provide as good mixing as is normally achieved in activated sludge systems and therefore aerated basins do not achieve the same performance level as activated sludge units.[3] General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... Kwai Lo is Chinese slang for foreigner or ghost person. ...


Biological oxidation processes are sensitive to temperature and, between 0 °C and 40 °C, the rate of biological reactions increase with temperature. Most surface aerated vessels operate at between 4 °C and 32 °C.[3]


Fluidized bed reactors

The carbon adsorption following biological treatment was particularly effective in reducing both the BOD and COD to low levels. A fluidized bed reactor is a combination of the most common stirred tank packed bed, continuous flow reactors. It is very important to chemical engineering because of its excellent heat and mass transfer characteristics. In a fluidized bed reactor, the substrate is passed upward through the immobilized enzyme bed at a high velocity to lift the particles. However the velocity must not be so high that the enzymes are swept away from the reactor entirely. This causes low mixing; these type of reactors are highly suitable for the exothermic reactions. It is most often applied in immobilized enzyme catalysis.

Trickling filter bed using plastic media
Trickling filter bed using plastic media
Schematic diagram of a complete trickle filter process in waste treatment plants

Download high resolution version (1296x972, 664 KB)Sewage Treatment trickling filter bed - small rural treatment plant Author: User:Velela. ... Download high resolution version (1296x972, 664 KB)Sewage Treatment trickling filter bed - small rural treatment plant Author: User:Velela. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...

Filter beds (oxidising beds)

Main article: Trickling filter

In older plants and plants receiving more variable loads, trickling filter beds are used where the settled sewage liquor is spread onto the surface of a deep bed made up of coke (carbonised coal), limestone chips or specially fabricated plastic media. Such media must have high surface areas to support the biofilms that form. The liquor is distributed through perforated rotating arms radiating from a central pivot. The distributed liquor trickles through this bed and is collected in drains at the base. These drains also provide a source of air which percolates up through the bed, keeping it aerobic. Biological films of bacteria, protozoa and fungi form on the media’s surfaces and eat or otherwise reduce the organic content. This biofilm is grazed by insect larvae and worms which help maintain an optimal thickness. Overloading of beds increases the thickness of the film leading to clogging of the filter media and ponding on the surface. The trickling filter is known by several other names, among them percolating filter and biological filter Biological filter is also used, especially in the USA, to mean a biological odour The trickling filter is one of the oldest forms of sewage treatment, and is effectively a process-intensified form of... The trickling filter is known by several other names, among them percolating filter and biological filter Biological filter is also used, especially in the USA, to mean a biological odour The trickling filter is one of the oldest forms of sewage treatment, and is effectively a process-intensified form of... Coke Coke is a solid carbonaceous material derived from destructive distillation of low-ash, low-sulfur bituminous coal. ... For other uses, see Limestone (disambiguation). ... Staphylococcus aureus biofilm on an indwelling catheter. ...


Biological aerated filters

Biological Aerated (or Anoxic) Filter (BAF) or Biofilters combine filtration with biological carbon reduction, nitrification or denitrification. BAF usually includes a reactor filled with a filter media. The media is either in suspension or supported by a gravel layer at the foot of the filter. The dual purpose of this media is to support highly active biomass that is attached to it and to filter suspended solids. Carbon reduction and ammonia conversion occurs in aerobic mode and sometime achieved in a single reactor while nitrate conversion occurs in anoxic mode. BAF is operated either in upflow or downflow configuration depending on design specified by manufacturer. Nitrogen cycle Nitrification is the biological oxidation of ammonia with oxygen into nitrite followed by the oxidation of these nitrites into nitrates. ... An industrial water filter with geared motor A water filter is a device which removes impurities from water by means of a fine physical barrier, chemical processes and/or biological process. ... It has been suggested that Anoxic sea water, Oxygen minimum zone, and Hypoxic zone be merged into this article or section. ...

Secondary Sedimentation tank at a rural treatment plant
Secondary Sedimentation tank at a rural treatment plant

Download high resolution version (1296x972, 636 KB)sewage treatment secondary settlement tank File links The following pages link to this file: Sewage treatment Categories: GFDL images ... Download high resolution version (1296x972, 636 KB)sewage treatment secondary settlement tank File links The following pages link to this file: Sewage treatment Categories: GFDL images ...

Membrane biological reactors

Membrane biological reactors (MBR) combines activated sludge treatment with a membrane liquid-solid separation process. The membrane component utilizes low pressure microfiltration or ultra filtration membranes and eliminates the need for clarification and tertiary filtration. The membranes are typically immersed in the aeration tank (however, some applications utilize a separate membrane tank). One of the key benefits of a membrane bioreactor system is that it effectively overcomes the limitations associated with poor settling of sludge in conventional activated sludge (CAS) processes. The technology permits bioreactor operation with considerably higher mixed liquor suspended solids (MLSS) concentration than CAS systems, which are limited by sludge settling. The process is typically operated at MLSS in the range of 8,000–12,000 mg/L, while CAS are operated in the range of 2,000–3,000 mg/L. The elevated biomass concentration in the membrane bioreactor process allows for very effective removal of both soluble and particulate biodegradable materials at higher loading rates. Thus increased Sludge Retention Times (SRTs)—usually exceeding 15 days—ensure complete nitrification even under extreme cold weather operating conditions.


The cost of building and operating a MBR is usually higher than conventional wastewater treatment, however, as the technology has become increasingly popular and has gained wider acceptance throughout the industry, the life-cycle costs have been steadily decreasing. As well, in developed urban areas where the footprint of the treatment plant is considered a limiting factor MBR facilities can be considered a desirable option.


Secondary sedimentation

The final step in the secondary treatment stage is to settle out the biological floc or filter material and produce sewage water containing very low levels of organic material and suspended matter.


Rotating biological contactors

Main article: Rotating biological contactor

Rotating biological contactors (RBCs) are mechanical secondary treatment systems, which are robust and capable of withstanding surges in organic load. RBCs were first installed in Germany in 1960 and have since been developed and refined into a reliable operating unit. The rotating disks support the growth of bacteria and micro-organisms present in the sewage, which breakdown and stabilise organic pollutants. To be successful, micro-organisms need both oxygen to live and food to grow. Oxygen is obtained from the atmosphere as the disks rotate. As the micro-organisms grow, they build up on the media until they are sloughed off due to shear forces provided by the rotating discs in the sewage. Effluent from the RBC is then passed through final clarifiers where the micro-organisms in suspension settle as a sludge. The sludge is withdrawn from the clarifier for further treatment. Schematic diagram of a typical rotating biological contactor (RBC). ...


Tertiary treatment

Tertiary treatment provides a final stage to raise the effluent quality before it is discharged to the receiving environment (sea, river, lake, ground, etc.). More than one tertiary treatment process may be used at any treatment plant. If disinfection is practiced, it is always the final process. It is also called "effluent polishing".


Filtration

Sand filtration removes much of the residual suspended matter. Filtration over activated carbon removes residual toxins. A sand filter is a basic tool water purification. ... Activated carbon Activated carbon, also called activated charcoal or activated coal, is a general term which covers carbon material mostly derived from charcoal. ... For other uses, see Toxin (disambiguation). ...


Lagooning

Lagooning provides settlement and further biological improvement through storage in large man-made ponds or lagoons. These lagoons are highly aerobic and colonization by native macrophytes, especially reeds, is often encouraged. Small filter feeding invertebrates such as Daphnia and species of Rotifera greatly assist in treatment by removing fine particulates. Invertebrate is an English word that describes any animal without a spinal column. ... Species Subgenus Daphnia Subgenus Hyalodaphnia D. galeata Subgenus Ctenodaphnia Daphnia are small, mostly planktonic, crustaceans, between 0. ... Classes Seisonoidea Bdelloidea Monogononta The rotifers make up a phylum of microscopic, pseudocoelomate animals. ...


Constructed wetlands

Constructed wetlands include engineered reedbeds and a range of similar methodologies, all of which provide a high degree of aerobic biological improvement and can often be used instead of secondary treatment for small communities, also see phytoremediation. One example is a small reedbed used to clean the drainage from the elephants' enclosure at Chester Zoo in England. // A constructed wetland is an artificial marsh or swamp, created for anthropogenic discharge such as wastewater, stormwater runoff or sewage treatment, and as habitat for wildlife, or for land reclamation after mining or other disturbance. ... A reedbed in summer Reedbeds are basically ’temporary’ habitats. ... Phytoremediation describes the treatment of environmental problems (bioremediation) through the use of plants. ... Genera and Species Loxodonta Loxodonta cyclotis Loxodonta africana Elephas Elephas maximus Elephas antiquus † Elephas beyeri † Elephas celebensis † Elephas cypriotes † Elephas ekorensis † Elephas falconeri † Elephas iolensis † Elephas planifrons † Elephas platycephalus † Elephas recki † Stegodon † Mammuthus † Elephantidae (the elephants) is a family of pachyderm, and the only remaining family in the order Proboscidea... Chester Zoo is a Zoological Garden located in the North of England. ... For other uses, see England (disambiguation). ...


Waste removal

Wastewater may contain high levels of the nutrients nitrogen and phosphorus. Excessive release to the environment can lead to a build up of nutrients, called eutrophication, which can in turn encourage the overgrowth of weeds, algae, and cyanobacteria (blue-green algae). This may cause an algal bloom, a rapid growth in the population of algae. The algae numbers are unsustainable and eventually most of them die. The decomposition of the algae by bacteria uses up so much of oxygen in the water that most or all of the animals die, which creates more organic matter for the bacteria to decompose. In addition to causing deoxygenation, some algal species produce toxins that contaminate drinking water supplies. Different treatment processes are required to remove nitrogen and phosphorus. General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... General Name, symbol, number phosphorus, P, 15 Chemical series nonmetals Group, period, block 15, 3, p Appearance waxy white/ red/ black/ colorless Standard atomic weight 30. ... Eutrophication, strictly speaking, means an increase in chemical nutrients -- typically compounds containing nitrogen or phosphorus -- in an ecosystem. ... Algae have conventionally been regarded as simple plants within the study of botany. ... Orders The taxonomy is currently under revision. ... Algal blooms can present problems for ecosystems and human society An algal bloom is a relatively rapid increase in the population of (usually) phytoplankton algae in an aquatic system. ... Drinking water Mineral Water Drinking water is water that is intended to be ingested by humans. ...


Nitrogen removal

The removal of nitrogen is effected through the biological oxidation of nitrogen from ammonia (nitrification) to nitrate, followed by denitrification, the reduction of nitrate to nitrogen gas. Nitrogen gas is released to the atmosphere and thus removed from the water. Illustration of a redox reaction Redox (shorthand for oxidation/reduction reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... For other uses, see Ammonia (disambiguation). ... Nitrogen cycle Nitrification is the biological oxidation of ammonia with oxygen into nitrite followed by the oxidation of these nitrites into nitrates. ... Trinitrate redirects here. ... This does not cite its references or sources. ...


Nitrification itself is a two-step aerobic process, each step facilitated by a different type of bacteria. The oxidation of ammonia (NH3) to nitrite (NO2) is most often facilitated by Nitrosomonas spp. (nitroso=ammonium). Nitrite oxidation to nitrate (NO3), though traditionally believed to be facilitated by Nitrobacter spp. (nitro=nitrite), is now known to be facilitated in the environment almost exclusively by Nitrospira spp.


Denitrification requires anoxic conditions to encourage the appropriate biological communities to form. It is facilitated by a wide diversity of bacteria. Sand filters, lagooning and reed beds can all be used to reduce nitrogen, but the activated sludge process (if designed well) can do the job the most easily. Since denitrification is the reduction of nitrate to dinitrogen gas, an electron donor is needed. This can be, depending on the wastewater, organic matter (from faeces), sulfide, or an added donor like methanol. An electron donor is a compound that gives up or donates an electron during cellular respiration, resulting in the release of energy. ... Formally, sulfide is the dianion, S2−, which exists in strongly alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2S. Sulfide is exceptionally basic and, with a pKa > 14, it does not exist in appreciable concentrations even in highly alkaline water. ... Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naptha or wood spirits, is a chemical compound with chemical formula CH3OH. It is the simplest alcohol, and is a light, volatile, colourless, flammable, poisonous liquid with a distinctive odor that is somewhat milder and sweeter than ethanol (ethyl alcohol). ...


Sometimes the conversion of toxic ammonia to nitrate alone is referred to as tertiary treatment.


Phosphorus removal

Phosphorus can be removed biologically in a process called enhanced biological phosphorus removal. In this process, specific bacteria, called polyphosphate accumulating organisms, are selectively enriched and accumulate large quantities of phosphorus within their cells (up to 20% of their mass). When the biomass enriched in these bacteria is separated from the treated water, these biosolids have a high fertilizer value. Enhanced biological phosphorus removal (EBPR) is a wastewater treatment configuration applied to activated sludge systems. ... Spreading manure, an organic fertilizer Fertilizers (also spelled fertilisers) are compounds given to plants to promote growth; they are usually applied either via the soil, for uptake by plant roots, or by foliar feeding, for uptake through leaves. ...


Phosphorus removal can also be achieved by chemical precipitation, usually with salts of iron (e.g. ferric chloride) or aluminum (e.g. alum). The resulting chemical sludge is difficult to handle and the added chemicals can be expensive. Despite this, chemical phosphorus removal requires significantly smaller equipment footprint than biological removal, is easier to operate and can be more reliable in areas that have wastewater compositions that make biological phosphorus removal difficult. For other uses, see Salt (disambiguation). ... For other uses, see Iron (disambiguation). ... Ferric chloride (FeCl3) is an iron-based salt. ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... A crystal of alum Alum, (IPA: ) (aluminium potassium sulfate,) in chemistry, is a term given to the crystallized double sulfates of the typical formula M+2SO4·M3+2(SO4)3·12H2O, where M+ is the sign of an alkali metal (or generally monovalent cation) (lithium, sodium, potassium, rubidium, or caesium...


Disinfection

The purpose of disinfection in the treatment of wastewater is to substantially reduce the number of microorganisms in the water to be discharged back into the environment. The effectiveness of disinfection depends on the quality of the water being treated (e.g., cloudiness, pH, etc.), the type of disinfection being used, the disinfectant dosage (concentration and time), and other environmental variables. Cloudy water will be treated less successfully since solid matter can shield organisms, especially from ultraviolet light or if contact times are low. Generally, short contact times, low doses and high flows all militate against effective disinfection. Common methods of disinfection include ozone, chlorine, or ultraviolet light. Chloramine, which is used for drinking water, is not used in wastewater treatment because of its persistence. Disinfection is the destruction of pathogenic and other kinds of microorganisms by physical or chemical means. ... A cluster of Escherichia coli bacteria magnified 10,000 times. ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... For other uses, see Ozone (disambiguation). ... General Name, symbol, number chlorine, Cl, 17 Chemical series halogens Group, period, block 17, 3, p Appearance yellowish green Standard atomic weight 35. ... Chloramine (monochloramine) is chemical compound with the formula NH2Cl. ...

Chlorination remains the most common form of wastewater disinfection in North America due to its low cost and long-term history of effectiveness. One disadvantage is that chlorination of residual organic material can generate chlorinated-organic compounds that may be carcinogenic or harmful to the environment. Residual chlorine or chloramines may also be capable of chlorinating organic material in the natural aquatic environment. Further, because residual chlorine is toxic to aquatic species, the treated effluent must also be chemically dechlorinated, adding to the complexity and cost of treatment.
Ultraviolet (UV) light can be used instead of chlorine, iodine, or other chemicals. Because no chemicals are used, the treated water's taste is more natural and pure as compared to other methods. UV radiation causes damage to the genetic structure of bacteria, viruses, and other pathogens, making them incapable of reproduction. The key disadvantages of UV disinfection are the need for frequent lamp maintenance and replacement and the need for a highly treated effluent to ensure that the target microorganisms are not shielded from the UV radiation (i.e., any solids present in the treated effluent may protect microorganisms from the UV light). In the United Kingdom, light is becoming the most common means of disinfection because of the concerns about the impacts of chlorine in chlorinating residual organics in the wastewater and in chlorinating organics in the receiving water. Edmonton, Alberta, Canada also uses UV light for its water treatment.
Ozone O3 is generated by passing oxygen O2 through a high voltage potential resulting in a third oxygen atom becoming attached and forming O3. Ozone is very unstable and reactive and oxidizes most organic material it comes in contact with, thereby destroying many pathogenic microorganisms. Ozone is considered to be safer than chlorine because, unlike chlorine which has to be stored on site (highly poisonous in the event of an accidental release), ozone is generated onsite as needed. Ozonation also produces fewer disinfection by-products than chlorination. A disadvantage of ozone disinfection is the high cost of the ozone generation equipment and the requirements for highly skilled operators.

Chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water. ... North America North America is a continent[1] in the Earths northern hemisphere and (chiefly) western hemisphere. ... In pathology, a carcinogen is any substance or agent that promotes cancer. ... For other uses, see Ultraviolet (disambiguation). ... For other uses, see Gene (disambiguation). ... This article is about biological infectious particles. ... A pathogen or infectious agent is a biological agent that causes disease or illness to its host. ... For other places with the same name, see Edmonton (disambiguation). ... For other uses, see Alberta (disambiguation). ... For other uses, see Ozone (disambiguation). ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... International safety symbol Caution, risk of electric shock (ISO 3864), colloquially known as high voltage symbol. ... Properties For other meanings of Atom, see Atom (disambiguation). ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ...

Package plants and batch reactors

In order to use less space, treat difficult waste, deal with intermittent flow or achieve higher environmental standards, a number of designs of hybrid treatment plants have been produced. Such plants often combine all or at least two stages of the three main treatment stages into one combined stage. In the UK, where a large number of sewage treatment plants serve small populations, package plants are a viable alternative to building discrete structures for each process stage.


One type of system that combines secondary treatment and settlement is the sequencing batch reactor (SBR). Typically, activated sludge is mixed with raw incoming sewage and mixed and aerated. The resultant mixture is then allowed to settle producing a high quality effluent. The settled sludge is run off and re-aerated before a proportion is returned to the head of the works. SBR plants are now being deployed in many parts of the world including North Liberty, Iowa, and Llanasa, North Wales. Sequencing batch reactors (SBR) or sequential batch reactors are industrial processing tanks for the treatment of waste water. ... North Liberty is a city located in Johnson County, Iowa. ... Approximate extent of North Wales North Wales (known in some archaic texts as Northgalis) is the northernmost unofficial region of Wales, bordered to the south by Mid Wales. ...


The disadvantage of such processes is that precise control of timing, mixing and aeration is required. This precision is usually achieved by computer controls linked to many sensors in the plant. Such a complex, fragile system is unsuited to places where such controls may be unreliable, or poorly maintained, or where the power supply may be intermittent.


Package plants may be referred to as high charged or low charged. This refers to the way the biological load is processed. In high charged systems, the biological stage is presented with a high organic load and the combined floc and organic material is then oxygenated for a few hours before being charged again with a new load. In the low charged system the biological stage contains a low organic load and is combined with floculate for a relatively long time.


Sludge treatment and disposal

The sludges accumulated in a wastewater treatment process must be treated and disposed of in a safe and effective manner. The purpose of digestion is to reduce the amount of organic matter and the number of disease-causing microorganisms present in the solids. The most common treatment options include anaerobic digestion, aerobic digestion, and composting. Bold textSewage sludge treatment described the processes used to manage and dispose of the sludges produced during sewage treatment. ... This article does not cite any references or sources. ... A cluster of Escherichia coli bacteria magnified 10,000 times. ... Two-stage, low-solids, UASB anaerobic digesters as part of a mechanical biological treatment system, with sequencing batch reactor Anaerobic digestion (AD) is where the naturally occurring processes of anaerobic degradation is harnessed and contained. ... An active compost heap, steaming on a cold winter morning. ...


The choice of a wastewater solid treatment method depends on the amount of solids generated and other site-specific conditions. However, in general, composting is most often applied to smaller-scale applications followed by aerobic digestion and then lastly anaerobic digestion for the larger-scale municipal applications.


Anaerobic digestion

Main article: Anaerobic digestion

Anaerobic digestion is a bacterial process that is carried out in the absence of oxygen. The process can either be thermophilic digestion, in which sludge is fermented in tanks at a temperature of 55°C, or mesophilic, at a temperature of around 36°C. Though allowing shorter retention time (and thus smaller tanks), thermophilic digestion is more expensive in terms of energy consumption for heating the sludge. Two-stage, low-solids, UASB anaerobic digesters as part of a mechanical biological treatment system, with sequencing batch reactor Anaerobic digestion (AD) is where the naturally occurring processes of anaerobic degradation is harnessed and contained. ... This article is about a type of organism. ... For other uses, see Fermentation. ... A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, typically between 25 and 40 °C (68 and 113 °F). ...


One major feature of anaerobic digestion is the production of biogas, which can be used in generators for electricity production and/or in boilers for heating purposes. Biogas-bus in Bern, Switzerland Biogas typically refers to a (biofuel) gas produced by the anaerobic digestion or fermentation of organic matter including manure, sewage sludge, municipal solid waste, biodegradable waste or any other biodegradable feedstock, under anaerobic conditions. ...


Aerobic digestion

Aerobic digestion is a bacterial process occurring in the presence of oxygen. Under aerobic conditions, bacteria rapidly consume organic matter and convert it into carbon dioxide. The operating costs are characteristically much greater than for anaerobic digestion because of the energy costs needed to add oxygen to the process. Aerobic and anaerobic bacteria can be identified by growning them in liquid culture: 1: Obligate aerobic bacteria gather at the top of the test tube in order to absorb maximal amount of oxygen. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ...


Composting

Composting is also an aerobic process that involves mixing the wastewater solids with sources of carbon such as sawdust, straw or wood chips. In the presence of oxygen, bacteria digest both the wastewater solids and the added carbon source and, in doing so, produce a large amount of heat. An active compost heap, steaming on a cold winter morning. ... For other uses, see Carbon (disambiguation). ...


Thermal depolymerization

Thermal depolymerization uses hydrous pyrolysis to convert reduced complex organics to oil. Thermal depolymerization (TDP) is a process for the reduction of complex organic materials (usually waste products of various sorts, often known as biomass) into light crude oil. ... Hydrous pyrolysis refers to the chemical processes which take place when material is heated to high temperatures in the presence of water. ...


Sludge disposal

When a liquid sludge is produced, further treatment may be required to make it suitable for final disposal. Typically, sludges are thickened (dewatered) to reduce the volumes transported off-site for disposal. There is no process which completely eliminates the need to dispose of biosolids. There is, however, an additional step some cities are taking to superheat the wastewater sludge and convert it into small pelletized granules that are high in nitrogen and other organic materials. This product is then sold to local farmers and turf farms as a soil amendment or fertilizer, reducing the amount of space required to dispose of sludge in landfills[1].


Treatment in the receiving environment

The outlet of a wastewater treating plant flows into a small river
The outlet of a wastewater treating plant flows into a small river

Many processes in a wastewater treatment plant are designed to mimic the natural treatment processes that occur in the environment, whether that environment is a natural water body or the ground. If not overloaded, bacteria in the environment will consume organic contaminants, although this will reduce the levels of oxygen in the water and may significantly change the overall ecology of the receiving water. Native bacterial populations feed on the organic contaminants, and the numbers of disease-causing microorganisms are reduced by natural environmental conditions such as predation exposure to ultraviolet radiation, for example. Consequently, in cases where the receiving environment provides a high level of dilution, a high degree of wastewater treatment may not be required. However, recent evidence has demonstrated that very low levels of certain contaminants in wastewater, including hormones (from animal husbandry and residue from human hormonal contraception methods) and synthetic materials such as phthalates that mimic hormones in their action, can have an unpredictable adverse impact on the natural biota and potentially on humans if the water is re-used for drinking water[2]. In the US and EU, uncontrolled discharges of wastewater to the environment are not permitted under law, and strict water quality requirements are to be met. A significant threat in the coming decades will be the increasing uncontrolled discharges of wastewater within rapidly developing countries. Image File history File links Download high resolution version (1296x972, 128 KB) Please see the file description page for further information. ... Image File history File links Download high resolution version (1296x972, 128 KB) Please see the file description page for further information. ... For the journal, see Ecology (journal). ... For other uses, see Ultraviolet (disambiguation). ... For other uses, see Hormone (disambiguation). ... In general stewardship is responsibility for taking good care of resources entrusted to one. ... Hormonal contraception refers to birth control methods that act on the hormonal system. ... R,R=CnH2n+1; n=4-15 Phthalates are a group of chemical compounds that are mainly used as plasticizers -- substances added to plastics to increase their flexibility. ...


Sewage treatment in developing countries

There are few reliable figures on the share of the wastewater collected in sewers that is being treated in the world. In many developing countries the bulk of domestic and industrial wastewater is discharged without any treatment or after primary treatment only. In Latin America about 15% of collected wastewater passes through treatment plants (with varying levels of actual treatment). In Venezuela, a below average country in South America with respect to wastewater treatment, 97 percent of the country’s sewage is discharged raw into the environment[4]. Even a highly industrialized country such as the People's Republic of China discharges about 55 percent of all sewage without treatment of any type[5]. In a relatively developed Middle Eastern country such as Iran, Tehran's majority of population has totally untreated sewage injected to the city’s groundwater[6]. Most of sub-Saharan Africa is without wastewater treatment. South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ... Sewage is the mainly liquid waste containing some solids produced by humans which typically consists of washing water, faeces, urine, laundry waste and other material which goes down drains and toilets from households and industry. ... A map showing countries commonly considered to be part of the Middle East The Middle East is a region comprising the lands around the southern and eastern parts of the Mediterranean Sea, a territory that extends from the eastern Mediterranean Sea to the Persian Gulf. ... For other uses, see Tehran (disambiguation). ... A political map showing national divisions in relation to the ecological break (Sub-Saharan Africa in green) A geographical map of Africa, showing the ecological break that defines the sub-Saharan area Sub-Saharan Africa is the term used to describe the area of the African continent which lies south...


Water utilities in developing countries are chronically underfunded because of low water tariffs, the inexistence of sanitation tariffs in many cases, low billing efficiency (i.e. many users that are billed do not pay) and poor operational efficiency (i.e. there are overly high levels of staff, there are high physical losses, and many users have illegal connections and are thus not being billed). In addition, wastewater treatment typically is the process within the utility that receives the least attention, partly because enforcement of environmental standards is poor. As a result of all these factors, operation and maintenance of many wastewater treatment plants is poor. This is evidenced by the frequent breakdown of equipment, shutdown of electrically operated equipment due to power outages or to reduce costs, and sedimentation due to lack of sludge removal. Developing countries as diverse as Egypt, Algeria, China or Colombia have invested substantial sums in wastewater treatment without achieving a significant impact in terms of environmental improvement. Even if wastewater treatment plants are properly operating, it can be argued that the environmental impact is limited in cases where the assimilative capacity of the receiving waters (ocean with strong currents or large rivers) is high, as it is often the case.


Benefits of wastewater treatment compared to benefits of sewage collection in developing countries

Waterborne diseases that are prevalent in developing countries, such as diarrhea, typhus and cholera, are caused primarily by poor hygiene practices and the absence of improved household sanitation facilities. The public health impact of the discharge of untreated wastewater is comparatively much lower. Hygiene promotion, on-site sanitation and low-cost sanitation thus are likely to have a much greater impact on public health than wastewater treatment. E. Coli bacteria under magnification Sanitation is the hygienic disposal or recycling of waste, as well as the policy and practice of protecting health through hygienic measures. ...


See also

Agricultural wastewater treatment relates to the treatment of wastewaters produced in the course of agricultural activities. ... The trickling filter is known by several other names, among them percolating filter and biological filter Biological filter is also used, especially in the USA, to mean a biological odour The trickling filter is one of the oldest forms of sewage treatment, and is effectively a process-intensified form of... Schematic diagram of a typical rotating biological contactor (RBC). ... Two-stage, low-solids, UASB anaerobic digesters as part of a mechanical biological treatment system, with sequencing batch reactor Anaerobic digestion (AD) is where the naturally occurring processes of anaerobic degradation is harnessed and contained. ... Ecological sanitation, also known as EcoSan, is a modern alternative to conventional sanitation techniques. ... Humanure is a neologism designating human waste (feces and urine) that is recycled via composting for agricultural or other purposes. ... River in Madagascar relatively free of sediment load An hydrological transport model is a mathematical model used to simulate river or stream flow and calculate water quality parameters. ... Industrial wastewater treatment covers the mechanisms and processes used to treat waters that have been contaminated in some way by mans industrial or commercial activities prior to its release into the environment or its re-use. ... Dr. John Todd (1939- ) is an important biologist working in the field of ecological design. ... The following page consist of a list of waste water treatment technologies: Activated sludge Anaerobic digestion Anaerobic lagoon Cesspit Combined sewer overflow Composting toilet Constructed wetland Imhoff tank Floculation Reed bed Septic tank Sequencing batch reactor UASB Aerobic Granular Reactor This list is incomplete; you can help by expanding it. ... Decentralized wet weather overflow event Sanitary sewer overflow (SSO} is a condition whereby untreated sewage is discharged into the environment, escaping wastewater treatment. ... This article or section does not cite its references or sources. ... The Select Society of Sanitary Sludge Shovelers (5S) is used by water environment associations (i. ... Control room and schematics of the water purification plant to Bret lake. ... William Lindley (September 7, 1808 - May 22, 1900), was a famous British engineer who together with his sons designed water and sewerage systems for over 30 cities across Europe. ...

References

  1. ^ Tchobanoglous, G., Burton, F.L., and Stensel, H.D. (2003). Wastewater Engineering (Treatment Disposal Reuse) / Metcalf & Eddy, Inc., 4th Edition, McGraw-Hill Book Company. ISBN 0-07-041878-0. 
  2. ^ Beychok, Milton R. (1967). Aqueous Wastes from Petroleum and Petrochemical Plants, 1st Edition, John Wiley & Sons Ltd. LCCN 67019834. 
  3. ^ a b c d Beychok, M.R. (1971). "Performance of surface-aerated basins". Chemical Engineering Progress Symposium Series 67 (107): 322-339.  Available at CSA Illumina website
  4. ^ Appropriate Technology for Sewage Pollution Control in the Wider Caribbean Region, Caribbean Environment Programme Technical Report #40 1998
  5. ^ World Bank Supports China's Wastewater Treatment, The People’s Daily, Friday, November 30, 2001, Beijing
  6. ^ Massoud Tajrishy and Ahmad Abrishamchi, Integrated Approach to Water and Wastewater Management for Tehran, Iran, Water Conservation, Reuse, and Recycling: Proceedings of the Iranian-American Workshop, National Academies Press (2005)

Aqueous Wastes from Petroleum and Petrochemical Plants is a book about the composition and treatment of the various wastewater streams produced in the hydrocarbon processing industries (i. ... The Library of Congress Control Number or LCCN is a serially based system of numbering books in the Library of Congress in the United States. ... West Indies redirects here. ... The World Bank logo The World Bank (the Bank) is a part of the World Bank Group (WBG), is a bank that makes loans to developing countries for development programs with the stated goal of reducing poverty. ...

External links

  • Anaerobic Industrial Wastewater Treatment: Perspectives for Closing Water and Resource Cycles.
  • UK Water Industry Research Reports
  • California State Water Resources Control Board - Review of Technologies for the Onsite Treatment of Wastewater in California
  • Aerated Lagoons for Wastewater Treatment
  • The Straight Dope - What happens to all the stuff that goes down the toilet?
  • Photos of various waste water treatment plants.
  • Sewer History
  • Illustrated explanation of how decentralized wastewater is collected and treated
  • Boston Sewage tour by MIT
  • Tour of a Washington state sewage plant written by an employee
  • Activated Carbon Waste Water Treatment
  • UniFED wastewater treatment process
  • The ammount of plant biomass on water surface

  Results from FactBites:
 
Sewage Treatment (370 words)
The rest receives some form of treatment to improve the quality of the water (which makes up 99.9% of sewage) before it is released for reuse.
The simplest, and least effective, method of treatment is to allow the undissolved solids in raw sewage to settle out of suspension forming sludge.
After chlorination to remove its content of bacteria, the effluent from secondary treatment is returned to the local surface water.
Sewage treatment Summary (9058 words)
The objective of the treatment is to produce both a clean wastestream (or treated effluent) suitable for discharge or reuse back into the environment, and a solid waste or sludge also suitable for proper disposal or reuse.
Typically, sewage treatment is achieved by the initial physical separation of solids from the raw wastewater stream followed by the progressive conversion of dissolved biological matter into a solid biological mass using indigenous, water-borne bacteria.
In the mechanical treatment, the influx (influent) of sewage water is strained to remove all large objects that are deposited in the sewer system, such as rags, sticks, condoms, sanitary towels (sanitary napkins) or tampons, cans, fruit, etc. This is most commonly done using a manual or automated mechanically raked screen.
  More results at FactBites »

 
 

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