UASB (Suspenede Growth System)

UASB (SUSPENDED GROWTH SYSTEM)

Upflow Anaerobic Sludge Blanket.

(High Rate Anaerobic System).

• The UASB reactor maintains a high concentration of biomass through the formation of highly settleable microbial sludge aggregates.

• Waste water flows upwards through a layer of very active sludge (Sludge Bed) to cause anaerobic digestion of organics of the waste water.

• At the top of reactor, three phase separation between gas-solid-liquid takes place.

• This process is suitable for both soluble waste water as well as waste waters containing particulate matter.

• The waste water enters the tank from the bottom and flow upwards through the sludge bed, which is formed during the process itself.

• The sludge bed consists of anaerobic and facultative micro-organisms capable brb of flourishing in a oxygen deficient environment.

• The sludge bed (blanket) traps the suspended organics from the upflowing sewage which are degraded by anaerobic and facultative bacteria, which produce methane (CH₄) and carbondioxide (CO₂) (Biogas).

• The bidog notebi of boyaging sol al beril biogas produced helps in gentle mixing and stirring of biomass thereby increasing the efficiency of decomposition and reducing the BOD and suspended solids concentration of the waste water.

• The gas produced is sufficient to keep the sludge fully mixed.

• The biogas consists of 65 to 70% CH₄ and 30 to 35% CO₂.

•  The methane (or) biogas is collected at at the top of the t

• The water sludge mixture is made to enter a settling tank, where the sludge settles down and flows back into the bottom of the reactor.

• The sludge has good settling properties.

• There is no packing material. The microbes attach to each other or to small particles, agglomerate, granulates to form sludge bed or blanket.

• Retention time is about 6-8 hours with continuous bacterial presence.

• The treated effluent is collected in gutters and discharged out of the reactor.

• The methane generated can be used for generating electricity to run the plant.

• The sludge is dewatered in drying beds and used as soil enricher.

Advantages:

(i) Space required is less compared to ASP/Oxidation pond/Aerated lagoons.

(ii) bn Capital cost is less.

(iii) System requires lesser/simpler electromagnetic parts.

(iv) Low operation and maintenance cost.

(v) Electricity consumption is low and can withstand power failures.

(vi) Quicker sludge digestion.

(vii) Low sludge production. Sludge has quick dewatering properties.

(viii) Biogas produced as by-product is used for electricity generation.

(ix) Used for treatment of high strength waste waters like those from municipalities and industries like food processing, distilleries, dairies, etc.

Disadvantages:

(i) System lowers only two parameters of waste water.

(a) BOD

(b) Suspended solids.

It does not remove heavy metals and toxic pollutants.

(ii) Require larger quantity of organic matter (20 to 30 times) for growth of anaerobic bacteria.

(iii) Acids produced by breakdown of organic matter in UASB - may cause corrosion of reactor.

(iv) Efficiency of BOD/SS removal is low.

(v) Pretreatment (Screening/Grit Removal) is necessary.