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Anaerobic Filter

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'''An Anaerobic Filter anaerobic filter is a fixed-bed biological reactorwith one or more filtration chambers in series. As wastewater flows through the filter, particles are trapped and organic matter is degraded by the active biomass that is attached to the surface of the filter material.'''

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This With this technology consists of a sedimentation tank (or [[Septic Tank]]) followed by one or more filter chambers. Filter material commonly used includes gravel, crushed rockssuspended solids and BOD removal can be as high as 90%, cinder, or specially formed plastic pieces. Typical filter material sizes range from 12 to 55mm in diameter. Ideally, the material will provide but is typically between 90 to 300m2 of surface area per 1m3 of reactor volume50% and 80%. By providing a large surface area for the bacterial mass, there Nitrogen removal is increased contact between the organic matter limited and the active biomass that effectively degrades itnormally does not exceed 15% in terms of total nitrogen (TN).

===Design Considerations=== Pre- and primary treatment is essential to remove solids and garbage that may clog the filter. The Anaerobic Filter majority of settleable solids are removed in a sedimentation chamber in front of the anaerobic filter. Small-scale, stand-alone units typically have an integratedsettling compartment, but primary sedimentation can be operated also take place in either upflow a separate Settler (T.1) or downflow modeanother preceding technology (e.g., existing Septic Tanks). Designs without a settling compartment (as shown in T. The upflow mode is recommended because there is less risk 4) are of particular interest for (Semi-) Centralized Treatment plants that combine the fixed biomass will be washed out. The water level should cover anaerobic filter with other technologies, such as the filter media by at least 0Anaerobic Baffled Reactor (ABR, T.3m to guarantee an even flow regime3).

Studies have shown Anaerobic filters are usually operated in upflow mode because there is less risk that the fixed biomass will be washed out. The water level should cover the filter media by at least 0.3 m to guarantee an even flow regime. The hydraulic retention time (HRT ) is the most important design parameter influencing filter performance. An HRT of 0.5 12 to 1.5 days 36 hours is a typical and recommended. A maximum The ideal filter should have a large surface-loading (iarea for bacteria to grow, with pores large enough to prevent clogging.eThe surface area ensures increased contactbetween the organic matter and the attached biomass that effectively degrades it. flow Ideally, the material should provide between 90 to 300 m2 of surface area per area) rate m3 of 2occupied reactor volume.8m/d has proven Typical filter material sizes range from 12 to be suitable55 mm in diameter. Materialscommonly used include gravel, crushed rocks or bricks, cinder, pumice, or specially formed plastic pieces, depending on local availability. Suspended solids and BOD removal  The connection between the chambers can be as high as 85% designed either with vertical pipes or baffles. Accessibility to 90% but all chambers (through access ports) is typically between 50% and 80%necessary for maintenance. Nitrogen removal is limited The tank should be vented to allow for controlled release of odorous and normally does not exceed 15% in terms of total nitrogen (TN)potentially harmful gases.

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{{procontable | pro=

- Resistant to organic and hydraulic shock loads. <br> - No electrical energy is required. <br> - Can be built and repaired with locally available materials. Low operating costs <br> - Long service life. <br> - High reduction of BOD and solids <br>- Low sludge production; the sludge is stabilized <br>- Moderate capital costs, moderate operating costs depending on emptying; area requirement (can be lowered depending on number of users. built underground) <br> - High reduction of BOD and solids. | con=- Requires constant source expert design and construction <br>- Low reduction of water. pathogens and nutrients <br> - Effluent and sludge require secondary further treatment and/or appropriate discharge. <br> - Low reduction Risk of pathogens clogging, depending on pre- and nutrients. primary treatment <br> - Requires expert design Removing and construction. <br> - Long start up time.cleaning the clogged filter media is cumbersome

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===AdequacyAppropriateness=== This technology is easily adaptable and can be applied at the household level or a , in small neighbourhood (refer to Technology Information Sheet T2: Anaerobic Filter for information about applying an Anaerobic Filter at the community level). An Anaerobic Filter can be designed for a single house neighbourhoods or a group of houses that are using a lot of water for clothes washing, showering, and toilet flushingeven in bigger catchment areas. It is only most appropriate if water use is high, ensuring that the supply where a relatively constant amount of wastewater blackwater and greywater is constantgenerated. The Anaerobic Filter will not operate at full capacity for six to nine months after installation because of the long start up time required for the anaerobic biomass to stabilize. Therefore, the Anaerobic Filter technology should not filter can be used when for secondary treatment, to reduce the need organic loading rate for a subsequent aerobic treatment technology is immediate. Once working at full capacity it is a stable technology that requires little attention. The Anaerobic Filter should be watertight but it should still not be constructed in areas with high groundwater tables or where there is frequent flooding. Depending on land availability and the hydraulic gradient of the sewer (if applicable)step, the Anaerobic Filter can be built above or below ground. It can be installed in every type of climate, although the efficiency will be affected in colder climatesfor polishing.

===Health Aspects/Acceptance===This technology is suitable for areas where land may be limited since the tank is most commonly installed underground and requires a small area. Accessibility by vacuum truck is important for desludging. Anaerobic filters can be installed in every type of climate,although the efficiency is lower in colder climates. They are not efficient at removing nutrients and pathogens. Depending on the filter material, however, complete removal of worm eggs may be achieved. The effluent usually requires further treatment.

Because the Anaerobic Filter unit is underground===Health Aspects/Acceptance=== Under normal operating conditions, users do not come in contact with the influent or effluent. Infectious organisms are not sufficiently removedEffluent, so the effluent should scum and sludge must be further treated or discharged properlyhandled with care as they contain high levels of pathogenic organisms. The effluent, despite treatment, will still contains odorous compounds that may have to be removed in a strong odour and care further polishing step. Care should be taken to design and locate the facility such that odours do not bother community members. To prevent the release of potentially harmful gases, the Anaerobic Filters should be vented. The desludging of the filter is hazardous and appropriate safety precautions should be taken.

===Operation & Maintenance===An anaerobic filter requires a start-up period of 6 to 9 months to reach full treatment capacity since the slow growing anaerobic biomass first needs to be established on the filter media. To reduce startup time, the filter can be inoculated with anaerobic bacteria, e.g., by spraying Septic Tank sludge onto the filter material. The flow should be gradually increased over time. Because of the delicateecology, care should be taken not to discharge harsh chemicals into the anaerobic filter.

Active bacteria must Scum and sludge levels need to be added monitored to start up ensure that the Anaerobic Filter. The active bacteria can come from sludge from a septic tank that has been sprayed onto the filter material. The flow should be gradually increased over time, and the filter should be working at maximum capacity within six to nine monthsis functioning well. With Over time, the solids will clog the pores of the filter. As well, the growing bacterial mass will become too thick and will , break off and eventually clog pores. A sedimentation tank before the filter is required to prevent the majority of settleable solids from entering the unit. Some clogging increases the ability of the filter to retain solids. When the efficiency of decreases, the filter decreases, it must be cleaned. Running This is done by running the system in reverse mode to dislodge accumulated biomass (backwashing) or by removing and particles cleans cleaning the filtersfilter material. Alternatively, the Anaerobic filter material can tanks should be removed and cleanedchecked from time to time to ensure that they are watertight.

===References===

* Morel, A. and Diener, S. (2006). Greywater Management in Low and Middle-Income Countries. Review of Different Treatment Systems for Households or Neighbourhoods. Eawag (Department Sandec), Dübendorf, CH.

:Available at: [http://www.sandec.ch sandec.ch] (Short summary including case studies – p. 28)

* Morelvon Sperling, AM. and Dienerde Lemos Chernicharo, SC. A. (20062005). [http://www.eawag.ch/forschung/sandec/publikationen/ewm/dl/GW_management.pdf Greywater Management Biological Wastewater Treatment in Low and Middle-Income CountriesWarm Climate Regions, Review of different treatment systems for households or neighbourhoods]Volume One. Swiss Federal Institute of Aquatic Science and Technology (Eawag)IWA Publishing, DübendorfLondon, SwitzerlandUK. pp. Short summary including case studies, page 28728-804. * Polprasert, C. and Rajput, VS. (1982). [http://docs.watsan.net/Scanned_PDF_Files/Class_Code_3_Sanitation/323.2-82SE-884.pdf Environmental Sanitation ReviewsAvailable at: Septic Tank and Septic Systems]. Environmental Sanitation Information Center, AIT, Bangkok, Thailand. pp 68–74. * Sasse, L. (1998). [http://www.indiawaterportaliwawaterwiki.org/sites/indiawaterportaliwawaterwiki.org/files/Decentralised_%20wastewater_%20treatment_%20in_%20developing_%20countries_A_%20handbook_%20by_%20BORDA_1998.pdf DEWATS: Decentralised Wastewater Treatment in Developing Countries]. BORDA, Bremen Overseas Research and Development Association, Bremen, Germany. Design summary including Excel-based design program. * von Sperlin, M. and de Lemos Chernicharo, CA. (2005). [http://www.iwapublishing.com/pdf/contents/isbn1843390027_contents.pdf Biological Wastewater Treatment in Warm Climate Regions]. Volume One. IWA, London. pp 728–804. Detailed design instructions.)

* VigneswaranUlrich, A. (Ed.), Reuter, S.(Ed.), Gutterer, et alB. (1986Ed.), Sasse, L. [http://books, Panzerbieter, T.googleand Reckerzügel, T.com/books/about/Anaerobic_Wastewater_Treatment(2009).html?id=NIJJcgAACAAJ Environmental Sanitation Reviews: Anaerobic Decentralised Wastewater Treatment-Attached growth Systems (DEWATS) and Sludge blanket process]Sanitation in Developing Countries. A Practical Guide. Environmental Sanitation Information CenterWEDC, Loughborough University, AIT BangkokLeicestershire, ThailandUK. (Design criteria and diagrams in Chapter 2.summary including Excel spreadsheets for design calculations)

===Acknowledgements===

{{:Acknowledgements Sanitation}}

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