Copyright © Philip M. Parker, INSEAD. Terms of Use.
| Domain | Definition |
Environment | The process to which wastewater is subjected in order to remove or alter its objectionable constituents and thus render it less offensive or dangerous. Source: European Union. (references) |
Weather | (primary) Mechanical treatment of sewage in which large solids are filtered out by screens and suspended solids settle out as sludge in a sedimentation tank. (references) |
Source: compiled by the editor from various references; see credits. | |
(From Wikipedia, the free Encyclopedia)
This article essentially describes sewage treatment as practiced in the USA. Other countries practices might be quite different.
Originally, cities had no sewers. Waste water simply ran down the streets, which had stepping stones to keep pedestrians out of the muck, and eventually drained as runoff into the local watershed. The next significant development was to move to a single set of sewers that accepted both storm runoff as well as blackwater and industrial waste, which improved conditions on the streets significantly but which still usually just dumped the untreated waste water into the local watershed.
Common practice in the U.S. and Canada at this time (2002) is to have two systems: storm sewers, and sanitary sewers. Storm sewers in some wealthy areas (like southern California) might get some processing to remove waste such as automobile oil. Sanitary sewers are processed to clean up human waste. In some areas there is a clear movement advocating dedicated industrial sewers as well, to handle chemical wastes and solvents. In the ultimate case, perhaps automatic delivery vehicles should visit every waste point, and pick up pure wastes for precise forms of recycling.
In many other countries, including many quite-wealthy ones, untreated sewage is released directly to surface water. A rule of thumb is that if a city's tapwater is not considered potable, the country does not perform sewage treatment. In many such countries, the legislature would have to allocate money to such treatment were it to mandate outfall levels, and the legislators find other priorities more pressing.
Although there are many methods for coping with human excreta, generations of sewage engineers have refined the following processes, which are the least expensive known mass processes to separate people from pathogens in their excreta.
It consists of several stages:
This begins with a collection network of sewer pipes. Most sewers are arranged so that gravity moves the sewage. Pumps are problematic in a sewer system because people often flush foreign objects such as socks, tampons, condoms and disposable diapers down their toilets. Even so, in a very flat area, sewer pumps and regional sumps are a practical necessity.
The pipes can also be blocked by the growth of biofilms. The flow has to exceed 3/4 of a meter at least once per day to keep slime from building up and blocking the pipes. Even so, most systems have problem spots that have to be cleaned periodically. Sewage pipes are cleaned with pressurised water.
The first step in the plant is foreign-object protection: The incoming sewage pipes go up in a hump, usually about six feet high. This helps keep very large foreign objects in the pipes from damaging the bar grid. There are valves to divert the flow, and manholes to remove these objects. Every sewage plant has stories about objects found in the pipes: toilets, children's tricycles and toys, and the staple: very large round rocks.
The valves divert the sewage directly to the outfall. The hump hall's drain also leads directly to the outfall. If the plant goes off-line, this is where the spill occurs.
If the plant is for a single-pipe system that processes storm runoff as well as sewage, there will be provision for diverting storm flows to holding tanks. Often the first flush of a storm flow will be terribly dirty, and require treatment, while the rest will be more than 5/6 rain water and can be safely diverted to the outfall.
A treatment plant measures the incoming volume from major pipes in order to track and charge customers. The measurement area is usually at the top of the hump. Generally the sewage charge is actually paid as a surcharge on customers' water bills. The difference between incoming sewage and outgoing water is used to establish the sewage rate fees as a percentage of water use. The metering also gives administrators a means to measure water waste and irrigation of lawns and other diversions to the storm sewers.
The measurement area is also where chemists monitor the incoming sewage for industrial chemicals such as heavy metals and toxic solvents. If these become too high in concentration, the plant (in the U.S., anyway) becomes unable to sell its sludge, which must then be placed in toxic land-fills.
To keep the sludge salable, when toxic waste is detected, the sewage engineers begin tracing the toxic waste to its source. At this point, the polluter is at least notified. In some areas, he is charged with fines large enough to motivate him to change his ways.
The next step is a bar grid. A bar grid is supposed to remove foreign objects from the sewage. It generally has strap-shaped stainless-steel bars, edge to the flow, a half-inch apart. Every few minutes, a mechanical claw scrapes foreign objects up the bar grid, onto a conveyor, and out to a dumpster. The dumpster contents are usually placed in a landfill.
The next step is a grit settling tank, or in smaller systems, a series of finer grids. These take out things between a half inch and sand-sized. These also go to the landfill.
The next step is usually a sedimentation basin or an Imhoff tank. At this point, the sewage separates into sludge and waste water.
At this point, primary treatment is complete. In poor countries, the water goes to the outfall, and the sludge goes to the farms.
Secondary treatment removes bacteria and offensive smells from the sludge and water. It generally employs bacteria to consume the available nutrients and organic compounds. What remains are inorganic salts, carbon dioxide and water.
The basic treatment for the sludge is digestion. The sludge is pumped to concrete digesters where anaerobic bacteria eat the sludge and produce methane. The digesters usually run quite hot, near 100°F, just from the bacterial action. Sludge may also be processed and thickened in aerobic digesters kept oxygenated by the same power source that supplies the secondary treatment aeration.
The sludge is then run through another settling tank, or in some plants, pressed between mesh conveyor belts to wring out the water.
The result of the digester is reduced sludge, methane, and water.
The reduced-volume, bacterially-safe sludge can then be sold to farmers, gardeners and nurseries, who use it as an organic amendment for soil.
The plant doesn't make any money on sludge. The fee is usually just enough to keep the users from abandoning the sludge. Other organic amendments are cheap, so the chief cost advantage of sewage sludge is that it is local.
In some countries, sludge is incinerated. This is far too polluting for most locations in the U.S. Some of these plants use the heat to generate electricity. It's theoretically possible to scrub the stack gases if pure human waste were being processed, but in practice, the chemicals in sludge and human waste are too unpredictable to be safely burned in an urban area.
If the sludge has too many solvents or heavy metals to be sold, it has to be trucked, or hauled by railway to a toxic landfill. This is much more expensive than selling it.
The methane is usually burned in large internal combustion engines to generate power. These are usually diesel (compression ignited), although some plants have adapted natural gas turbines (natural gas is mostly methane). If the plant is efficient enough, it can generate enough electricity from the methane to run itself.
The heat from the engine exhaust is usually recycled as process heat. In some plants, it preheats sludge going into the digesters.Historical sewage treatment
Modern sewage treatment
Traditional plants use massive installations with large concrete tanks. Recent trends are to use plastic pool liners in dirt pools, or small mass-produced plastic or metal tanks in small systems that run themselves automatically. (See septic tanks.)Primary treatment
Secondary treatment
Sludge treatment
Source: adapted by the editor from Wikipedia, the free encyclopedia under a copyleft GNU Free Documentation License (GFDL) from the article "Sewage treatment."
Synonym: SEWAGE TREATMENTSynonym: Sewage purification. (additional references) |
Crosswords: SEWAGE TREATMENT |
| English words defined with "SEWAGE TREATMENT": extensively ♦ sludge. (references) |
| Specialty definitions using "SEWAGE TREATMENT": biodisc, biological disc, biological disk ♦ Clean Water Act ♦ INSPECTOR, WATER-POLLUTION CONTROL ♦ Polyelectrolytes ♦ rotating biochemical filter, rotating biological contactor, rotating biological disc, rotating disk filter ♦ Significant Municipal Facilities. (references) |
| Domain | Title |
References | |
Books | |
Source: compiled by the editor from various references; see credits. | |
| Thumbnail | Description & Credit | Thumbnail | Description & Credit |
 | Sewage treatment plant settling tank at the southern tip of Clarks Point. The facility is now gone. Credit: NOAA Restoration Center. |  | The sewage treatment plant at the southern tip of Clarks Point, now gone. Credit: NOAA Restoration Center. |
 | Coney Island Sewage Treatment Works, Ave. Z, Sheepshead Bay, Brooklyn. Chemical house from northwest. Credit: Library of Congress. | ||
Source: pictures compiled by the editor from various references; see picture credits. | |||
| Subject | Topic | Quote |
Health | The Environmental Protection Agency is working with water and sewage treatment operators in the United States to prevent contamination of water with the cholera bacterium. (references) | |
Business | The project, known as Bajagua is a private project to build a US$63 million sewage treatment plant in Tijuana, Mexico. (references) | |
Authorities on both sides of the U.S. and Mexican border are supporting the construction of a sewage treatment plant in Tijuana, Mexico. (references) | ||
Provide a heating system in the Swinoujscie port, a facility for the collection of waste from ships and a sewage treatment plant in Peninsula Katowicki. (references) | ||
Economic History | Yemen | In addition to the electricity sector, the World Bank and other donors are financing road, water and sewage treatment projects. (references) |
West Bank | USAID's projects focus primarily on basic infrastructure (water, sewage treatment, roads, etc.) and supporting the private sector through investment and policy interventions. (references) | |
Honduras | Drinking water access and service quality still need to be improved in both rural and urban areas, and a high percentage of the population is still not connected to sewage treatment facilities. (references) | |
Minorities | Greece | Most Romani camps have no running water, electricity, garbage disposal, or sewage treatment. (references) |
Political Economy | PARAGUAY | Efforts to improve weak infrastructure, especially in power transmission and distribution; telecommunications; road, river, and civil aviation systems; postal system; potable water; and sewage treatment provide potential markets for United States' goods and services. (references) |
Trade | Mauritius | These sources fund a broad portfolio of projects, including port and airport upgrades, sewage treatment, road, bridge and dam construction, energy, telecommunications, and hospital and housing construction. (references) |
Source: compiled by the editor from ICON Group International, Inc.; see credits. | ||
Expression using "SEWAGE TREATMENT": sewage treatment plant. Additional references. | |
| Source: compiled by the editor from various references; see credits. |
| The following statistics estimate the number of searches per day across the major English-language search engines as identified by various trade publications. Hyperlinks lead to commercial use of the expression at Amazon.com. |
| Language | Translations for "SEWAGE TREATMENT"; alternative meanings/domain in parentheses. | ||||||||||||||||||||||
Danish | spildevandsrensning (sewage purification, wastewater purification, wastewater treatment), vandrensning (sewage purification, wastewater purification, wastewater treatment). (various references) | ||||||||||||||||||||||
Dutch | waterzuivering (sewage purification, wastewater purification, wastewater treatment), rioolwaterzuivering (sewage purification, wastewater purification, wastewater treatment), afvalwaterzuivering (sewage purification, wastewater purification, wastewater treatment). (various references) | ||||||||||||||||||||||
Finnish | jäteveden puhdistus (sewage purification, wastewater purification, wastewater treatment). (various references) | ||||||||||||||||||||||
French | épuration des eaux usées (sewage purification), épuration des eaux résiduaires (sewage purification), épuration des eaux d'égout (sewage purification). (various references) | ||||||||||||||||||||||
German | Reinigung von Abwasser (sewage purification, wastewater purification, wastewater treatment), Abwasserreinigung (sewage purification, wastewater purification, wastewater treatment). (various references) | ||||||||||||||||||||||
Greek | καθαρισμός των λυμάτων (sewage purification, wastewater purification, wastewater treatment), επεξεργασία λυμάτων (sewage purification, wastewater purification, wastewater treatment). (various references) | ||||||||||||||||||||||
Italian | trattamento delle acque (sewage purification, wastewater purification, wastewater treatment), depurazione delle acque (sewage purification, wastewater purification, wastewater treatment), depurazione dei liquami di fogna (sewage purification, wastewater purification, wastewater treatment). (various references) | ||||||||||||||||||||||
Pig Latin | ewagesay eatmenttray purificação das águas dos esgotos (sewage purification, wastewater purification, wastewater treatment). (various references) depuración de aguas residuales (sewage purification, wastewater purification, wastewater treatment). (various references) avloppsvattenrening (sewage purification, wastewater purification, wastewater treatment). (various references) | ||||||||||||||||||||||
Scrabble® Enable2K-Verified Anagrams | |
| Words within the letters "a-a-e-e-e-e-g-m-n-r-s-t-t-t-w" | |
-4 letters: restatement. | |
-5 letters: agreements, termagants, treatments, wattmeters. | |
| Source: compiled by the editor from various references; see credits. SCRABBLE® is a registered trademark. All intellectual property rights in and to the game are owned in the U.S.A and Canada by Hasbro Inc., and throughout the rest of the world by J.W. Spear & Sons Limited of Maidenhead, Berkshire, England, a subsidiary of Mattel Inc. Mattel and Spear are not affiliated with Hasbro. | |
| 1. Synonyms 2. Crosswords 3. Usage: Commercial 4. Images: Slideshow | 5. Images: Photo Album 6. Quotations: Non-fiction 7. Expressions 8. Expressions: Internet | 9. Translations: Modern 10. Anagrams 11. Bibliography |
Copyright © Philip M. Parker, INSEAD. Terms of Use.
