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'''Activated Sludge is a multi-chamber reactor unit that makes use of (mostly) aerobic microorganisms to degrade organics in wastewater and to produce a high-quality effluent. To maintain aerobic conditions and to the keep the active biomass suspended, a constant and well-timed supply of oxygen is required.'''
To achieve specific effluent goals for BOD, nitrogen and phosphorus, different adaptations and modifications have been made to the basic Activated Sludge design. Aerobic conditions, nutrient-specific organisms (especially for phosphorus), recycle design and carbon dosing, among others, have successfully allowed Activated Sludge processes to achieve high treatment efficiencies.
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{{procontable | pro=
- Good resistance against shock loading. <br> - Can be operated at a range of organic and hydraulic loading rates. High reduction of BOD and pathogens (up to 99%). <br> - Can be modified to meet specific discharge limits. | con=
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===Adequacy===
Activated Sludge is only appropriate for a centralized treatment facility with a well-trained staff, constant electricity and a highly developed centralized management system to ensure that the facility is operated and maintained correctly.
Treatment efficiency can be severely compromised if the plant is under- or over- designed. An Activated Sludge process is appropriate for almost every climate.
===Health Aspects/Acceptance===
Because of space requirements, Centralized treatment facilities are generally located away from the densely populated areas that they serve. Although the effluent produced is of high quality, it still poses a health risk and should not be handled directly.
===Maintenance===
The mechanical equipment (mixers, aerators and pumps) must be maintained constantly. As well, the influent and effluent must be monitored constantly to ensure that there are no abnormalities that could kill the active biomass and to ensure that detrimental organisms have not developed that could impair the process (e.g. filamentous bacteria).
===References===
* Crites, R. and Tchobanoglous, G. (1998). [http://books.google.com/books/about/Small_and_decentralized_wastewater_manag.html?id=yx9SAAAAMAAJ Small and Decentralized Wastewater Management Systems]. WCB and McGraw-Hill, New York, USA. pp 451–504. Comprehensive summary including solved problems.
* Tchobanoglous, G., Burton, FL. and Stensel, HD. (2003). [http://books.google.com/books/about/Wastewater_Engineering_Treatment_and_Reu.html?id=L1MAXTAkL-QC Wastewater Engineering: Treatment and Reuse, 4th Edition]. Metcalf & Eddy, New York.
===Acknowledgements===
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