 | This articleneeds additional citations forverification. Please helpimprove this article byadding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Upflow anaerobic sludge blanket digestion" – news ·newspapers ·books ·scholar ·JSTOR(November 2020) (Learn how and when to remove this message) |
Upflow anaerobic sludge blanket (UASB) technology, normally referred to as UASB reactor, is a form ofanaerobic digester that is used forwastewater treatment.
The UASB reactor is amethanogenic (methane-producing) digester that evolved from theanaerobic clarigester. A similar but variant technology to UASB is theexpanded granular sludge bed (EGSB) digester.
UASB uses ananaerobic process whilst forming a blanket of granular sludge which suspends in the tank. Wastewater flows upwards through the blanket and is processed (degraded) by theanaerobic microorganisms. The upward flow combined with the settling action ofgravity suspends the blanket with the aid offlocculants. The blanket begins to reach maturity at around three 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 create 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".[2]
Biogas with a high concentration ofmethane is produced as a by-product, and this may be captured and used as an energy source, to generateelectricity for 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.[3] 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).
Over time, the UASB model has been upgraded, pain points have been addressed, and design has been optimized - ultimately resulting in the following types of systems.
With UASB (but also EGSB and ECSB), the process of settlement and digestion occurs in one or more large tank(s). The effluent from the UASB, which has a much reducedbiochemical oxygen demand (BOD) concentration, usually needs to be treated further, for example with theactivated sludge process, depending on the effluent quality requirements.[citation needed]
