control in the United States is wastewater treatment. The country has a vast system of collection sewers, pumping stations, and treatment plants. Sewers collect. PDF | Users must concentrate their Sewage/Wastewater treatment process to nature under controlled conditions in treatment facilities of. Sewage treatment is the process of removing contaminants from municipal wastewater, "IFAS/MBBR Sustainable Wastewater Treatment Solutions" (PDF ).
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Generally, a plant treating water after an industrial process, is termed an Industrial Effluent Plant. A Sewage Treatment. Plant (or Municipal Waste Water. Small Scale Wastewater Treatment Plants. Phase 1. Small Scale Wastewater Treatment Plant Project. REPORT ON PROJECT CRITERIA, GUIDELINES AND. percentage of water treated in wastewater treatment plants in relation to that medical-site.info
Aerobic Sewage Treatment In this process, aerobic bacteria digest the pollutants. Aerobic conditions lead to an aerobic bacterial colony being established. The effluent produced by this process is non-polluting and can be discharged to a watercourse Conventional sewage water treatment involves either two or three stages, called primary, secondary and tertiary treatment.
Before these treatments, preliminary removal of rags, cloths, sanitary items, etc. Primary Treatment This is usually Anerobic. They settle out at the base of a primary settlement tank. The sludge is continuously being reduced in volume by the anerobic process, resulting in a vastly reduced total mass when compared to the original volume entering the system. Secondary Treatment This is Aerobic.
The liquid from the Primary treatment contains dissolved and particulate biological matter. This is progressively converted into clean water by using indigenous, water-borne aerobic micro-organisms and bacteria which digest the pollutants. In most cases, this effluent is clean enough for discharge directly to rivers. Tertiary Treatment In some cases, the effluent resulting from secondary treatment is not clean enough for discharge.
It is usually either Phosphorous or Ammoniacal Nitrogen or both that the E. Tertiary treatment involves this process. If Phosphorous is the culprit, then a continuous dosing system to remove it is the tertiary treatment.
Clarifiers and mechanized secondary treatment are more efficient under uniform flow conditions. Equalization basins may be used for temporary storage of diurnal or wet-weather flow peaks.
Basins provide a place to temporarily hold incoming sewage during plant maintenance and a means of diluting and distributing batch discharges of toxic or high-strength waste which might otherwise inhibit biological secondary treatment including portable toilet waste, vehicle holding tanks, and septic tank pumpers.
Flow equalization basins require variable discharge control, typically include provisions for bypass and cleaning, and may also include aerators. Cleaning may be easier if the basin is downstream of screening and grit removal. In some larger plants, fat and grease are removed by passing the sewage through a small tank where skimmers collect the fat floating on the surface.
Air blowers in the base of the tank may also be used to help recover the fat as a froth. Many plants, however, use primary clarifiers with mechanical surface skimmers for fat and grease removal. In the primary sedimentation stage, sewage flows through large tanks, commonly called "pre-settling basins", "primary sedimentation tanks" or "primary clarifiers ". 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 where it is pumped to sludge treatment facilities.
Secondary treatment is designed to substantially degrade the biological content of the sewage which are derived from human waste, food waste, soaps and detergent. The majority of municipal plants treat the settled sewage liquor using aerobic biological processes.
To be effective, the biota require both oxygen and food to live. The bacteria and protozoa consume biodegradable soluble organic contaminants e. Some secondary treatment methods include a secondary clarifier to settle out and separate biological floc or filter material grown in the secondary treatment bioreactor.
The purpose of tertiary treatment is to provide a final treatment stage to further improve the effluent quality before it is discharged to the receiving environment sea, river, lake, wet lands, ground, etc. More than one tertiary treatment process may be used at any treatment plant. If disinfection is practised, it is always the final process. It is also called "effluent polishing. Sand filtration removes much of the residual suspended matter.
Lagoons or ponds provide 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.
Biological nutrient removal BNR is regarded by some as a type of secondary treatment process,  and by others as a tertiary or "advanced" treatment process. Wastewater may contain high levels of the nutrients nitrogen and phosphorus. Excessive release to the environment can lead to a buildup 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 the 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. Nitrogen is removed through the biological oxidation of nitrogen from ammonia to nitrate nitrification , followed by denitrification , the reduction of nitrate to nitrogen gas. 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. 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.
This can be, depending on the waste water, organic matter from feces , sulfide , or an added donor like methanol. The sludge in the anoxic tanks denitrification tanks must be mixed well mixture of recirculated mixed liquor, return activated sludge [RAS], and raw influent e.
Over time, different treatment configurations have evolved as denitrification has become more sophisticated. An initial scheme, the Ludzack—Ettinger Process, placed an anoxic treatment zone before the aeration tank and clarifier, using the return activated sludge RAS from the clarifier as a nitrate source.
Influent wastewater either raw or as effluent from primary clarification serves as the electron source for the facultative bacteria to metabolize carbon, using the inorganic nitrate as a source of oxygen instead of dissolved molecular oxygen. This denitrification scheme was naturally limited to the amount of soluble nitrate present in the RAS.
Nitrate reduction was limited because RAS rate is limited by the performance of the clarifier. The "Modified Ludzak—Ettinger Process" MLE is an improvement on the original concept, for it recycles mixed liquor from the discharge end of the aeration tank to the head of the anoxic tank to provide a consistent source of soluble nitrate for the facultative bacteria.
In this instance, raw wastewater continues to provide the electron source, and sub-surface mixing maintains the bacteria in contact with both electron source and soluble nitrate in the absence of dissolved oxygen. Many sewage treatment plants use centrifugal pumps to transfer the nitrified mixed liquor from the aeration zone to the anoxic zone for denitrification.
At times, the raw or primary effluent wastewater must be carbon-supplemented by the addition of methanol, acetate, or simple food waste molasses, whey, plant starch to improve the treatment efficiency. These carbon additions should be accounted for in the design of a treatment facility's organic loading.
Bardenpho and Biodenipho processes include additional anoxic and oxidative processes to further polish the conversion of nitrate ion to molecular nitrogen gas.
Use of an anaerobic tank following the initial anoxic process allows for luxury uptake of phosphorus by bacteria, thereby biologically reducing orthophosphate ion in the treated wastewater. Even newer improvements, such as Anammox Process, interrupt the formation of nitrate at the nitrite stage of nitrification, shunting nitrite-rich mixed liquor activated sludge to treatment where nitrite is then converted to molecular nitrogen gas, saving energy, alkalinity, and secondary carbon sourcing.
Every adult human excretes between and 1, grams 7. Phosphorus removal is important as it is a limiting nutrient for algae growth in many fresh water systems. For a description of the negative effects of algae, see Nutrient removal.
It is also particularly important for water reuse systems where high phosphorus concentrations may lead to fouling of downstream equipment such as reverse osmosis. Phosphorus can be removed biologically in a process called enhanced biological phosphorus removal.
In this process, specific bacteria, called polyphosphate-accumulating organisms PAOs , are selectively enriched and accumulate large quantities of phosphorus within their cells up to 20 percent of their mass.
When the biomass enriched in these bacteria is separated from the treated water, these biosolids have a high fertilizer value. Phosphorus removal can also be achieved by chemical precipitation , usually with salts of iron e. Chemical phosphorus removal requires significantly smaller equipment footprint than biological removal, is easier to operate and is often more reliable than biological phosphorus removal. Some systems use both biological phosphorus removal and chemical phosphorus removal.
The chemical phosphorus removal in those systems may be used as a backup system, for use when the biological phosphorus removal is nor removing enough phosphorus, or may be used continuously. In either case, using both biological and chemical phosphorus removal has the advantage of not increasing sludge production as much as chemical phosphorus removal on its own, with the disadvantage of the increased initial cost associated with installing two different systems.
Once removed, phosphorus, in the form of a phosphate-rich sewage sludge , may be dumped in a landfill or used as fertilizer. In the latter case, the treated sewage sludge is also sometimes referred to as biosolids. The purpose of disinfection in the treatment of waste water is to substantially reduce the number of microorganisms in the water to be discharged back into the environment for the later use of drinking, bathing, irrigation, etc.
The effectiveness of disinfection depends on the quality of the water being treated e. 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 , ultraviolet light , or sodium hypochlorite.
After multiple steps of disinfection, the treated water is ready to be released back into the water cycle by means of the nearest body of water or agriculture. Afterwards, the water can be transferred to reserves for everyday human uses. Chlorination remains the most common form of waste water 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 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. 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.
In the United Kingdom, UV 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. Some sewage treatment systems in Canada and the US also use UV light for their effluent water disinfection. Ozone O 3 is generated by passing oxygen O 2 through a high voltage potential resulting in a third oxygen atom becoming attached and forming O 3.
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 on-site as needed from the oxygen in the ambient air.
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. Micropollutants such as pharmaceuticals, ingredients of household chemicals, chemicals used in small businesses or industries, environmental persistent pharmaceutical pollutant EPPP or pesticides may not be eliminated in the conventional treatment process primary, secondary and tertiary treatment and therefore lead to water pollution.
For pharmaceuticals , the following substances have been identified as "toxicologically relevant": Techniques for elimination of micropollutants via a fourth treatment stage during sewage treatment are implemented in Germany, Switzerland, Sweden [ citation needed ] and the Netherlands and tests are ongoing in several other countries. Such process steps mainly consist of activated carbon filters that adsorb the micropollutants. The combination of advanced oxidation with ozone followed by GAC, Granulated Activated Carbon, has been suggested as a cost-effective treatment combination for pharmaceutical residues.
For a full reduction of microplasts the combination of ultra filtration followed by GAC has beed suggested. Also the use of enzymes such as the enzyme laccase is under investigation. To reduce pharmaceuticals in water bodies, also "source control" measures are under investigation, such as innovations in drug development or more responsible handling of drugs. Odors emitted by sewage treatment are typically an indication of an anaerobic or "septic" condition.
Large process plants in urban areas will often treat the odors with carbon reactors, a contact media with bio-slimes, small doses of chlorine , or circulating fluids to biologically capture and metabolize the noxious gases. High-density solids pumps are suitable for reducing odors by conveying sludge through hermetic closed pipework.
For conventional sewage treatment plants, around 30 percent of the annual operating costs is usually required for energy. For example, constructed wetlands have a lower energy requirement than activated sludge plants, as less energy is required for the aeration step. In conventional secondary treatment processes, most of the electricity is used for aeration, pumping systems and equipment for the dewatering and drying of sewage sludge.
Advanced wastewater treatment plants, e. 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. Incineration is also used, albeit to a much lesser degree. Sludge treatment depends on the amount of solids generated and other site-specific conditions.
Composting is most often applied to small-scale plants with aerobic digestion for mid-sized operations, and anaerobic digestion for the larger-scale operations. The sludge is sometimes passed through a so-called pre-thickener which de-waters the sludge. Types of pre-thickeners include centrifugal sludge thickeners  rotary drum sludge thickeners and belt filter presses. 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 or exposure to ultraviolet radiation.
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 specific 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.
A significant threat in the coming decades will be the increasing uncontrolled discharges of wastewater within rapidly developing countries. Sewage treatment plants can have multiple effects on nutrient levels in the water that the treated sewage flows into. These nutrients can have large effects on the biological life in the water in contact with the effluent.
Stabilization ponds or sewage treatment ponds can include any of the following:. Phosphorus limitation is a possible result from sewage treatment and results in flagellate-dominated plankton , particularly in summer and fall. A phytoplankton study found high nutrient concentrations linked to sewage effluents. High nutrient concentration leads to high chlorophyll a concentrations, which is a proxy for primary production in marine environments.
High primary production means high phytoplankton populations and most likely high zooplankton populations, because zooplankton feed on phytoplankton.
However, effluent released into marine systems also leads to greater population instability. The planktonic trends of high populations close to input of treated sewage is contrasted by the bacterial trend. In a study of Aeromonas spp. This trend is so strong that the furthest location studied actually had an inversion of the Aeromonas spp. Since there is a main pattern in the cycles that occurred simultaneously at all stations it indicates seasonal factors temperature, solar radiation, phytoplankton control of the bacterial population.
The effluent dominant species changes from Aeromonas caviae in winter to Aeromonas sobria in the spring and fall while the inflow dominant species is Aeromonas caviae , which is constant throughout the seasons. With suitable technology, it is possible to reuse sewage effluent for drinking water, although this is usually only done in places with limited water supplies, such as Windhoek and Singapore. In arid countries, treated wastewater is often used in agriculture.
For example, in Israel, about 50 percent of agricultural water use total use was one billion cubic metres 3. Future plans call for increased use of treated sewer water as well as more desalination plants as part of water supply and sanitation in Israel.
Constructed wetlands fed by wastewater provide both treatment and habitats for flora and fauna. Another example for reuse combined with treatment of sewage are the East Kolkata Wetlands in India.
These wetlands are used to treat Kolkata 's sewage, and the nutrients contained in the wastewater sustain fish farms and agriculture. Few reliable figures exist on the share of the wastewater collected in sewers that is being treated in the world. In Latin America about 15 percent of collected wastewater passes through treatment plants with varying levels of actual treatment.
In Isfahan, Iran's third largest city, sewage treatment was started more than years ago. Only few cities in sub-Saharan Africa have sewer-based sanitation systems, let alone wastewater treatment plants, an exception being South Africa and — until the late s — Zimbabwe.
Basic sewer systems were used for waste removal in ancient Mesopotamia , where vertical shafts carried the waste away into cesspools.
In the Middle Ages the sewer systems built by the Romans fell into disuse and waste was collected into cesspools that were periodically emptied by workers known as 'rakers' who would often sell it as fertilizer to farmers outside the city.
Modern sewage systems were first built in the mid-nineteenth century as a reaction to the exacerbation of sanitary conditions brought on by heavy industrialization and urbanization. Due to the contaminated water supply, cholera outbreaks occurred in , and in London , killing tens of thousands of people.
This, combined with the Great Stink of , when the smell of untreated human waste in the River Thames became overpowering, and the report into sanitation reform of the Royal Commissioner Edwin Chadwick ,  led to the Metropolitan Commission of Sewers appointing Joseph Bazalgette to construct a vast underground sewage system for the safe removal of waste.
Contrary to Chadwick's recommendations, Bazalgette's system, and others later built in Continental Europe , did not pump the sewage onto farm land for use as fertilizer; it was simply piped to a natural waterway away from population centres, and pumped back into the environment. One of the first attempts at diverting sewage for use as a fertilizer in the farm was made by the cotton mill owner James Smith in the s. He experimented with a piped distribution system initially proposed by James Vetch  that collected sewage from his factory and pumped it into the outlying farms, and his success was enthusiastically followed by Edwin Chadwick and supported by organic chemist Justus von Liebig.
The idea was officially adopted by the Health of Towns Commission , and various schemes known as sewage farms were trialled by different municipalities over the next 50 years. At first, the heavier solids were channeled into ditches on the side of the farm and were covered over when full, but soon flat-bottomed tanks were employed as reservoirs for the sewage; the earliest patent was taken out by William Higgs in for "tanks or reservoirs in which the contents of sewers and drains from cities, towns and villages are to be collected and the solid animal or vegetable matters therein contained, solidified and dried These tanks had to be manually de-sludged periodically, until the introduction of automatic mechanical de-sludgers in the early s.
The precursor to the modern septic tank was the cesspool in which the water was sealed off to prevent contamination and the solid waste was slowly liquified due to anaerobic action; it was invented by L. H Mouras in France in the s. Donald Cameron, as City Surveyor for Exeter patented an improved version in , which he called a 'septic tank'; septic having the meaning of 'bacterial'. These are still in worldwide use, especially in rural areas unconnected to large-scale sewage systems.
It was not until the late 19th century that it became possible to treat the sewage by biologically decomposing the organic components through the use of microorganisms and removing the pollutants. Land treatment was also steadily becoming less feasible, as cities grew and the volume of sewage produced could no longer be absorbed by the farmland on the outskirts. Edward Frankland conducted experiments at the sewage farm in Croydon , England, during the s and was able to demonstrate that filtration of sewage through porous gravel produced a nitrified effluent the ammonia was converted into nitrate and that the filter remained unclogged over long periods of time.
From to filters working on this principle were constructed throughout the UK and the idea was also taken up in the US at the Lawrence Experiment Station in Massachusetts , where Frankland's work was confirmed.
In the LES developed a ' trickling filter ' that gave a much more reliable performance. Contact beds were developed in Salford , Lancashire and by scientists working for the London City Council in the early s.
According to Christopher Hamlin, this was part of a conceptual revolution that replaced the philosophy that saw "sewage purification as the prevention of decomposition with one that tried to facilitate the biological process that destroy sewage naturally.
Contact beds were tanks containing the inert substance, such as stones or slate, that maximized the surface area available for the microbial growth to break down the sewage. The sewage was held in the tank until it was fully decomposed and it was then filtered out into the ground.
This method quickly became widespread, especially in the UK, where it was used in Leicester , Sheffield , Manchester and Leeds. The bacterial bed was simultaneously developed by Joseph Corbett as Borough Engineer in Salford and experiments in showed that his method was superior in that greater volumes of sewage could be purified better for longer periods of time than could be achieved by the contact bed.
The Royal Commission on Sewage Disposal published its eighth report in that set what became the international standard for sewage discharge into rivers; the '