- Upflow anaerobic sludge blanket digestion
Upflow Anaerobic Sludge Blanket (UASB) technology, normally referred to as UASB reactor, is a form of
anaerobic digesterthat is used in the treatment of wastewater.
The UASB reactor is a
methanogenic(methane-producing) digester that evolved from the anaerobic clarigester. A similar but variant technology to UASB is the expanded granular sludge bed( EGSB) digester. A diagramatic comparison of different anaerobic digesters can be found [http://www.fao.org/docrep/t0541e/T0541E02.gifhere] .
UASB uses an anaerobic process whilst forming a blanket of granular sludge which suspends in the tank. Wastewater flows upwards through the blanket and is processed (degraded) by the
anaerobic microorganisms. The upward flow combined with the settling action of gravitysuspends the blanket with the aid of flocculants. The blanket begins to reach maturity at around 3 months. Small sludge granules begin to form whose surface area is covered in aggregations of bacteria. In the absence of any support matrix, the flow conditions creates a selective environment in which only those microorganisms, capable of attaching to each other, survive and proliferate. Eventually the aggregates form into dense compact biofilms referred to as "granules" [ [http://www.uasb.org/discover/granules.htm#granules What are sludge granules? UASB Homepage] ] . A picture of anaerobic sludge granules can be found [http://www.uasb.org/discover/granules.htm#figure1 here] . Biogaswith a high concentration of methaneis produced as a by-product, and this may be captured and used as an energy source, to generate electricityfor export and to cover its own running power. The technology needs constant monitoring when put into use to ensure that the sludge blanket is maintained, and not washed out (thereby losing the effect). The heat produced as a by-product of electricity generation can be reused to heat the digestion tanks.
The blanketing of the sludge enables a dual solid and hydraulic (liquid) retention time in the digesters. Solids requiring a high degree of digestion can remain in the reactors for periods up to 90 days [ [http://www.alexmarshall.me.uk/index_files/documents/HarrogateProceedings.pdf ArrowBio Process] Finstein, M. S., Zadik, Y., Marshall, A. T. & Brody, D. (2004) The ArrowBio Process for Mixed Municipal Solid Waste – Responses to “Requests for Information”, Proceedings for Biodegradable and Residual Waste Management, Proceedings. (Eds. E. K. Papadimitriou & E. I. Stentiford), Technology and Service Providers Forum, p. 407-413 ] . Sugars dissolved in the liquid waste stream can be converted into gas quickly in the liquid phase which can exit the system in less than a day.
UASB reactors are typically suited to dilute waste water streams (3% TSS with particle size >0.75mm).
Anaerobic digester types
Expanded granular sludge bed digestion
Hybrid reactor(combination of UASBand an anaerobic filter(AF))
Fluidized bed reactor
Mechanical biological treatment
* [http://www.austep.com/ Austep: Anaerobic Granular Sludge Bed Technology supplier]
* [http://www.uasb.org/ Anaerobic Granular Sludge Bed Technology Pages] - a site about anaerobic bioreactor systems for wastewater treatment and sustainable environmental technology.
* [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12397675&dopt=Abstract Upflow anaerobic sludge blanket reactor--a review.] - (highly technical)
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