Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater, both runoff (effluents) and domestic. Pollution is the introduction of contaminants into an environment that causes instability disorder harm or discomfort to the physical systems or living organisms they are in RUNOFF was the first Computer Text formatting program to see significant use Effluent is an outflowing of water from a natural body of water or from a man-made structure 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 suitable for discharge or reuse back into the environment. Effluent is an outflowing of water from a natural body of water or from a man-made structure SLUDGE (Scripting Language for Unhindered Development of a Gaming Environment is a open source adventure game engine developed by Hungry Software This material is often inadvertently contaminated with many toxic organic and inorganic compounds. Toxicity is the degree to which a substance is able to damage an exposed organism

Sewage is created by residences, institutions, hospitals 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). Description A septic tank generally consists of tanks between the size of 1000 and 2000 gallons (4000 - 7500 litres which is connected to an inlet wastewater pipe at one end and Biofiltration is a Pollution control technique using living material to capture and biologically degrade 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 Urban areas require some methods for collection and disposal of Sewage. Sewage collection and treatment is typically subject to local, state and federal regulations and standards. Industrial sources of wastewater often require specialized treatment processes (see Industrial wastewater treatment). Industrial wastewater treatment covers the mechanisms and processes used to treat waters that have been contaminated in some way by Anthropogenic industrial or commercial activities

The 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 microorganisms. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually 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. A stream is a body of Water with a current, confined within a bed and stream-banks "Riverine" redirects here For the use of that term in Maritime geography, see there Headlands and bays are two related features of the coastal environment A lagoon is a body of comparatively shallow salt or Brackish water separated from the deeper Sea by a shallow or exposed sandbank, coral A wetland is an area of Land consisting of Soil that is Saturated with Moisture, such as a Swamp, Marsh, or Bog Irrigation is an artificial application of water to the soil usually for assisting in growing crops If it is sufficiently clean, it can also be used for groundwater recharge. Groundwater is Water located beneath the Ground surface in Soil pore spaces and in the Fractures of lithologic formations

Description

Raw influent (sewage) includes household waste liquid from toilets, baths, showers, kitchens, sinks, and so forth that is disposed of via sewers. A toilet is a Plumbing fixture and disposal system primarily intended for the disposal of the bodily wastes: Urine and fecal matter. Bathing is the immersion of the body in a Fluid, usually Water or an aqueous solution A shower (also called shower bath is a booth for washing usually in a Bathroom, having an overhead nozzle that sprays water down on the body For the Banana Yashimoto novel see Kitchen (novel A kitchen, is a room or part of a room (sometimes called "kitchen In Plumbing, a sink or basin is a bowl-shaped fixture that is used for washing hands or small objects such as Food, dishes In many areas, sewage also includes liquid waste from industry and commerce. The draining of household waste into greywater and blackwater is becoming more common in the developed world, with greywater being permitted to be used for watering plants or recycled for flushing toilets. Greywater, also known as sullage, is non-industrial wastewater generated from domestic processes such as dish washing Blackwater is a relatively recent term used to describe water containing fecal matter and Urine. 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. Stormwater is a term used to describe water that originates during precipitation events Sewage systems capable of handling stormwater are known as combined systems or combined sewers. A combined sewer is a type of Sewer system which provides partially separated channels for sanitary Sewage and Stormwater runoff. 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). The United States of America —commonly referred to as the It is preferable to have a separate storm drain system for stormwater in areas that are developed with sewer systems. A storm drain, storm sewer ( US) stormwater drain ( Australia and New Zealand) or surface water system ( UK)

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. Soil, often typeset as SOiL, is a four piece rock band from Chicago Illinois United States founded by Shaun Glass Tom Schofield Tim King and Adam Zadel Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of An organic compound is any member of a large class of Chemical compounds whose Molecules contain Carbon. An oil is a substance that is in a viscous Liquid state ( "oily") at ambient temperatures or slightly warmer and is Petroleum ( L petroleum, from Greek πετρέλαιον, lit Some jurisdictions require stormwater to receive some level of treatment before being discharged directly into waterways. In Law, jurisdiction (from the Latin ius iuris meaning "law" and dicere meaning "to speak" is the practical Authority 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). A constructed wetland or wetpark is an artificial Marsh or Swamp, created for anthropogenic discharge such as Wastewater, Stormwater

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
• Chemical treatment (this step is usually combined with settling and other processes to remove solids, such as filtration. Aeration is the Process by which Air is circulated through mixed with or dissolved in a Liquid or substance The combination is referred to in the U. S. as physical-chemical treatment.

Treatment stages

Typical Process Flow Diagram

Primary treatment

Primary treatment removes the materials that can be easily collected from the raw wastewater and disposed of. A process flow diagram (PFD is a diagram commonly used in chemical and Process engineering to indicate the general flow of plant processes and equipment 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 and floating materials (such as rags and flushed feminine hygiene products). Sand is a naturally occurring Granular material composed of finely divided rock and Mineral particles This step is done entirely with machinery.

Removal of large objects from influent sewage

In primary treatment, the influent sewage water is strained to remove all large objects that are deposited in the sewer system, such as rags, sticks, tampons, cans, fruit, etc. A textile is a flexible material comprised of a network of natural or artificial Fibres often referred to as thread or Yarn. A tampon is a plug of Cotton or other absorbent material inserted into a Body cavity or Wound to absorb bodily fluid A tin can, also called a tin (especially in British English) or a can, is an air-tight container for the distribution or storage of The term fruit has different meanings dependent on context and the term is not synonymous in Food preparation and Biology. This is most commonly done with a manual or automated mechanically raked screen. The raking action of a mechanical bar screen is typically paced according to the accumulation on the bar screens and/or flow rate. The bar screen is used because large solids can damage or clog the equipment used later in the sewage treatment plant. The solids are collected in a dumpster and later disposed in a landfill.

Sand and grit removal

Primary treatment also 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. For information on Wikipedia project-related discussions see WikipediaVillage pump. 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. For other uses see Water treatment and Land reclamation. A landfill, also known as a dump (and historically as

Primary sedimentation tank at a rural treatment plant

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 sludge 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 clarification stage is to produce both a generally homogeneous liquid capable of being treated biologically and a sludge that can be separately treated or processed. Primary settling tanks are usually equipped with mechanically driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank from where it can be pumped to further sludge treatment stages.

Secondary treatment

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. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the There are number of ways in which this is done. In all these methods, the bacteria and protozoa consume biodegradable soluble organic contaminants (e. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Protozoa (in Greek πρῶτον proton "first" and ζῷα zoia "animals" are unicellular Eukaryotes (singular g. sugars, fats, organic short-chain carbon molecules, etc. Sugar is a class of edible Crystalline substances mainly Sucrose, Lactose, and Fructose. ) and bind much of the less soluble fractions into floc. Flocculation is a process where a Solute comes out of Solution in the form of floc or flakes 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. A trickling filter consists of a fixed bed of rocks Gravel, Slag, Polyurethane Foam, sphagnum Peat moss, or plastic media A rotating biological contactor or RBC is a Biological treatment process used in the treatment of Wastewater following primary treatment 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.

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. Roughing filters provide pretreatment for Turbid water or simple low maintenance treatment when high water quality is not needed 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.

Activated sludge

Main article: Activated sludge

In general, activated sludge plants encompass a variety of mechanisms and processes that use dissolved oxygen to promote the growth of biological floc that substantially removes organic material. Activated sludge is a process dealing with the treatment of Sewage and industrial wastewaters.

The process traps particulate material and can, under ideal conditions, convert ammonia to nitrite and nitrate and ultimately to nitrogen gas, (see also denitrification). Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor The nitrite Ion is NO2− The anion is bent being Isoelectronic with O3. In Inorganic chemistry, a nitrate is a salt of Nitric acid with an Ion composed of one Nitrogen and three Oxygen atoms Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Denitrification is a microbially facilitated process of dissimilatory nitrate reduction that may ultimately produce molecular Nitrogen (N2 through a series of intermediate

Surface-aerated basins

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. An aerated lagoon or aerated basin is a holding and/or treatment Pond provided with artificial Aeration to promote the biological oxidation of Wastewaters Surface-aerated basins achieve 80 to 90% removal of BOD with retention times of 1 to 10 days. ^[1] The basins may range in depth from 1. 5 to 5. 0 metres and use motor-driven aerators floating on the surface of the wastewater. ^[1]

In an aerated basin system, the aerators provide two functions: they transfer air into the basins required by the biological oxidation reactions, and they provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater and microbes). Typically, the floating surface aerators are rated to deliver the amount of air equivalent to 1. 8 to 2. 7 kg O₂/kW·h. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the 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. ^[1]

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. ^[1]

Fluidized bed reactors

The carbon absorption following biological treatment is 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

Schematic diagram of a complete trickle filter process in waste treatment plants

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. A trickling filter consists of a fixed bed of rocks Gravel, Slag, Polyurethane Foam, sphagnum Peat moss, or plastic media A trickling filter consists of a fixed bed of rocks Gravel, Slag, Polyurethane Foam, sphagnum Peat moss, or plastic media Coke is a solid Carbonaceous material derived from Destructive distillation of low-ash low-sulfur Bituminous coal. Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 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. A biofilm is a structured community of Microorganisms encapsulated within a self-developed polymeric matrix and adherent to a living or inert surface Overloading of beds increases the thickness of the film leading to clogging of the filter media and ponding on the surface.

Biological aerated filters

Biological Aerated (or Anoxic) Filter (BAF) or Biofilters combine filtration with biological carbon reduction, nitrification or denitrification. Nitrification is the biological oxidation of Ammonia with oxygen into Nitrite followed by the oxidation of these nitrites into Nitrates Degradation 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. For other uses of the term "hypoxia" see Hypoxia. Hypoxia or oxygen depletion is a phenomenon that occurs in aquatic environments BAF is operated either in upflow or downflow configuration depending on design specified by manufacturer.

Secondary Sedimentation tank at a rural treatment plant

Membrane bioreactors

Membrane bioreactors (MBR) combines activated sludge treatment with a membrane liquid-solid separation process. Membrane bioreactor (MBR is the combination of a Membrane process like Microfiltration or Ultrafiltration with a suspended growth Bioreactor The membrane component uses 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. Membrane bioreactor (MBR is the combination of a Membrane process like Microfiltration or Ultrafiltration with a suspended growth Bioreactor Activated sludge is a process dealing with the treatment of Sewage and industrial wastewaters. 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. Membrane bioreactor (MBR is the combination of a Membrane process like Microfiltration or Ultrafiltration with a suspended growth Bioreactor Thus increased Sludge Retention Times (SRTs)—usually exceeding 15 days—ensure complete nitrification even in extremely cold weather.

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

Schematic diagram of a typical rotating biological contactor (RBC). A rotating biological contactor or RBC is a Biological treatment process used in the treatment of Wastewater following primary treatment The treated effluent clarifier/settler is not included in the diagram.

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. Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. 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.

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. Sand filters are used for Water purification. There are three main types rapid (gravity sand filters upflow sand filters Slow sand Filtration over activated carbon removes residual toxins. Activated carbon, also called activated charcoal or activated coal, is a form of Carbon that has been processed to make it extremely porous and thus to A toxin ( Greek:, toxikon, lit (poison for use on arrows is a Poisonous substance produced by living cells or organisms that is active at very low

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. An invertebrate is an Animal lacking a Vertebral column. The group includes 98% of all animal Species — all animals except those in the Chordate Daphnia are small Planktonic Crustaceans between.2 and 5  mm in length The rotifers make up a Phylum of microscopic and near-microscopic pseudocoelomate Animals They were first described by Rev

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. A constructed wetland or wetpark is an artificial Marsh or Swamp, created for anthropogenic discharge such as Wastewater, Stormwater Reed beds are a natural habitat found in Floodplains waterlogged depressions and estuaries. Phytoremediation describes the treatment of environmental problems ( Bioremediation) through the use of Plants The word's etymology comes from One example is a small reedbed used to clean the drainage from the elephants' enclosure at Chester Zoo in England. Elephants ( family: Elephantidae) are large land Mammals of the order Proboscidea. Chester Zoo is a Zoological garden located in Cheshire in north west England. England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland

Nutrient removal

Wastewater may contain high levels of the nutrients nitrogen and phosphorus. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Phosphorus, (ˈfɒsfərəs is the Chemical element that has the symbol P and Atomic number 15 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). Eutrophication is an increase in chemical Nutrients -- typically compounds containing Nitrogen or Phosphorus -- in an Ecosystem, and may occur Algae ( sing. alga are a large and diverse group of simple typically Autotrophic organisms ranging from Unicellular to Multicellular forms Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of Bacteria that obtain their energy This may cause an algal bloom, a rapid growth in the population of algae. An algal bloom is a rapid increase in the population of Algae in an aquatic system 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. Water of sufficient quality to serve as drinking water is termed potable water whether it is used for drinking or not Different treatment processes are required to remove nitrogen and phosphorus.

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. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Nitrification is the biological oxidation of Ammonia with oxygen into Nitrite followed by the oxidation of these nitrites into Nitrates Degradation In Inorganic chemistry, a nitrate is a salt of Nitric acid with an Ion composed of one Nitrogen and three Oxygen atoms Denitrification is a microbially facilitated process of dissimilatory nitrate reduction that may ultimately produce molecular Nitrogen (N2 through a series of intermediate Nitrogen gas is released to the atmosphere and thus removed from the water.

Nitrification itself is a two-step aerobic process, each step facilitated by a different type of bacteria. The oxidation of ammonia (NH₃) to nitrite (NO₂⁻) is most often facilitated by Nitrosomonas spp. (nitroso referring to the formation of a nitroso functional group). Nitroso refers to a Functional group in Organic chemistry which has the general formula RNO Nitrite oxidation to nitrate (NO₃⁻), though traditionally believed to be facilitated by Nitrobacter spp. (nitro referring the formation of a nitro functional group), is now known to be facilitated in the environment almost exclusively by Nitrospira spp. Nitro compounds are Organic compounds that contain one or more nitro Functional groups (-2

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. An electron donor is a chemical entity that donates Electrons to another compound This can be, depending on the wastewater, organic matter (from faeces), sulfide, or an added donor like methanol. The term sulfide ( sulphide in British English) refers to several types of Chemical compounds containing Sulfur in its lowest Oxidation Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naphtha or wood spirits, is a Chemical compound

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. Enhanced biological phosphorus removal (EBPR is a Wastewater treatment configuration applied to Activated sludge systems for the removal of Phosphate. 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. Fertilizers ( also spelt fertiliser are chemical compounds given to Plants to promote growth they are usually applied either through the soil for uptake by plant

Phosphorus removal can also be achieved by chemical precipitation, usually with salts of iron (e. Precipitation is the formation of a Solid in a Solution during a Chemical reaction. Salt is a Dietary mineral composed primarily of Sodium chloride that is essential for Animal life but toxic to most land plants Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 g. ferric chloride) or aluminum (e. Iron chloride redirects here For Iron(II chloride see Iron(II chloride. WikipediaNaming g. alum). For the purely-slang term alum meaning "graduate" see Alumnus. 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.

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. Disinfectants are Antimicrobial agents that are applied to non-living objects to destroy Microorganisms, the process of which is known as disinfection. A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually 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. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Generally, short contact times, low doses and high flows all militate against effective disinfection. Common methods of disinfection include ozone, chlorine, or ultraviolet light. OZONE is an object oriented Operating system written in the C programming language. Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and Chloramine, which is used for drinking water, is not used in wastewater treatment because of its persistence. Chloramine (monochloramine is a 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. 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 One disadvantage is that chlorination of residual organic material can generate chlorinated-organic compounds that may be carcinogenic or harmful to the environment. The term carcinogen refers to any substance Radionuclide or radiation that is an agent directly involved in the promotion of Cancer or in the fatation of its propagation 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. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Because no chemicals are used, the treated water has no adverse effect on organisms that later consume it, as may be the case with other methods. UV radiation causes damage to the genetic structure of bacteria, viruses, and other pathogens, making them incapable of reproduction. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious 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. Edmonton (ˈɛdmɨntɨn is the capital of the Canadian province of Alberta. Alberta (ælˈbɝtə is one of Canada's prairie provinces. It became a province on September 1 1905

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 an object oriented Operating system written in the C programming language. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Ozone is very unstable and reactive and oxidizes most organic material it comes in contact with, thereby destroying many pathogenic microorganisms. Ozone is considered to be safer than chlorine because, unlike chlorine which has to be stored on site (highly poisonous in the event of an accidental release), ozone is generated onsite as needed. Ozonation also produces fewer disinfection by-products than chlorination. A disadvantage of ozone disinfection is the high cost of the ozone generation equipment and the requirements for special operators.

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). Sequencing batch reactors ( SBR) or sequential batch reactors are industrial processing tanks for the treatment of Wastewater. 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. North Liberty is a city in Johnson County, Iowa, United States. North Wales (Gogledd Cymru is the northernmost unofficial region of Wales, bordered to the south by Mid Wales and to the east by England.

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

Main article: Sewage sludge treatment

The sludges accumulated in a wastewater treatment process must be treated and disposed of in a safe and effective manner. Sewage sludge treatment described the processes used to manage and dispose of the sludges produced during Sewage treatment. The purpose of digestion is to reduce the amount of organic matter and the number of disease-causing microorganisms present in the solids. Organic matter (or organic material) is Matter that has come from a once-living Organism; is capable of A microorganism (also spelled micro organism or micro-organism and also called a microbe) is an Organism that is Microscopic (usually The most common treatment options include anaerobic digestion, aerobic digestion, and composting. Anaerobic digestion is a series of processes in which Microorganisms break down Biodegradable material in the absence of Oxygen. Composting is the Aerobic decomposition of Biodegradable Organic matter, producing Compost. Composting is the Aerobic decomposition of Biodegradable Organic matter, producing Compost.

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. Anaerobic digestion is a series of processes in which Microorganisms break down Biodegradable material 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. A thermophile is an organism &mdash a type of Extremophile &mdash which thrives at relatively high temperatures between 45 and 80 °C (113 and 176 °F Fermentation is the process of deriving energy from the oxidation of organic compounds such as carbohydrates using an endogenous electron acceptor which is A mesophile is an Organism that grows best in moderate Temperature, neither too hot nor too cold typically between 15 and 40 °C (77 and 104 °F Though allowing shorter retention time (and thus smaller tanks), thermophilic digestion is more expensive in terms of energy consumption for heating the sludge.

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. See also Natural gas, Biofuel Biogas typically refers to a Gas produced by the biological breakdown of Organic matter in the

Aerobic digestion

Aerobic digestion is a bacterial process occurring in the presence of oxygen. An aerobic organism or aerobe is an Organism that has an Oxygen based Metabolism. Under aerobic conditions, bacteria rapidly consume organic matter and convert it into carbon dioxide. An aerobic organism or aerobe is an Organism that has an Oxygen based Metabolism. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single The operating costs are characteristically much greater for aerobic digestion because of the energy costs needed to add oxygen to the process.

Composting

Composting is also an aerobic process that involves mixing the sludge with sources of carbon such as sawdust, straw or wood chips. Composting is the Aerobic decomposition of Biodegradable Organic matter, producing Compost. Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 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.

Thermal depolymerization

Thermal depolymerization uses hydrous pyrolysis to convert reduced complex organics to oil. Thermal depolymerization ( TDP) is a process using Hydrous pyrolysis for the reduction of complex Organic materials (usually Waste products of Hydrous Pyrolysis refers to the thermal decomposition which takes place when organic compounds are 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

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. Ecology (from Greek grc οἶκος oikos, "house(hold" and grc -λογία -logia) is the scientific study of 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. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays 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]. Hormones (from Greek ὁρμή - "impetus" are chemicals released by cells that affect cells in other parts of the body Animal husbandry, also called Animal science, stockbreeding or simple husbandry, is the agricultural practice of breeding Hormonal contraception refers to Birth control methods that act on the hormonal system Phthalates, or phthalate esters, are esters of Phthalic acid and are mainly used as Plasticizers (substances added to Plastics to increase their 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.

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^[2]. Venezuela (ˌvɛnəˈzweɪlə) officially the Bolivarian Republic of Venezuela (Spanish República Bolivariana de Venezuela) is a country on the South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a Sewage is the mainly liquid Waste containing some solids produced by humans which typically consists of washing water Feces, Urine, laundry waste and other 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^[3]. The Middle East is a Subcontinent with no clear boundaries often used as a synonym to Near East, in opposition to Far East. For a topic outline on this subject see List of basic Iran topics. Tehran (or Teheran) ( Persian: تهران Tehrān) is the capital and largest City of Iran, and the administrative center of Most of sub-Saharan Africa is without wastewater treatment. Sub-Saharan Africa is a geographical term used to describe the area of the African continent which lies south of the Sahara, or those African countries

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 typhus and cholera, are caused primarily by poor hygiene practices and the absence of improved household sanitation facilities. Sanitation is the hygienic means of preventing human contact from the hazards of wastes to promote health 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.

See also

• Agricultural wastewater treatment
• Anaerobic digestion
• Combined sewer
• Ecological sanitation
• Effluent guidelines
• Humanure
• Hydrological transport model
• Industrial wastewater treatment
• John Todd
• List of waste water treatment technologies
• Rotating biological contactor
• Sanitary sewer overflow
• Sedimentation (water treatment)
• Select Society of Sanitary Sludge Shovelers
• Trickling filter
• Wastewater garden
• Water framework directive
• Water purification
• William Lindley - pioneering 19th century engineer

References

External links

• Activated Carbon Waste Water Treatment - Chemiviron Carbon / Calgon
• Aerated Lagoons for Wastewater Treatment - Maine Lagoons Task Froce
• "Anaerobic Industrial Wastewater Treatment: Perspectives for Closing Water and Resource Cycles." Jules B. The Caribbean (ˌkærəˡbiən kæ'rəbiən Cariben|Caraïben or Caraïben; Caraïbe or more commonly Antilles; Caribe is a Region consisting van Lier, Wageningen University, The Netherlands
• Boston Sewage Tour - MIT Sea Grant
• Interactive Diagram of Wastewater Treatment - "Go with the Flow" - Water Environment Federation
• Phosphorus Recovery - Technische Universität Darmstadt & CEEP
• Photos of various waste water treatment plants
• Review of Technologies for the Onsite Treatment of Wastewater in California - California State Water Resources Control Board
• Sewer History
• The Straight Dope - What happens to all the stuff that goes down the toilet? - Syndicated column by Cecil Adams
• Tour of a Washington state sewage plant written by an employee
• UniFED wastewater treatment process