Anaerobic Bacteria for UASB Systems

Upflow Anaerobic Sludge Blanket (UASB) is a mature wastewater treatment technology since the 1980s. India and Brazil are among the leaders in the adoption of this anaerobic method for sewage treatment. UASB system offers a number of benefits such as compactness of the plant, negligible energy consumption, potential for methane generation, energy recovery, etc. The tropical climate of India makes it an attractive method for wastewater treatment.

However, UASB is primarily an anaerobic digestion system. And anaerobic biological systems by nature are very delicately balanced. A drop in temperature during winters, or a sudden shock-load, can throw the system off track. UASB operation requires skill and a really good microbial culture. UASB systems work well only with mixed biocultures with bacteria that can form a compact sludge blanket. Methanogenic bacteria and Acetogenic bacteria play a key role in successful effluent treatment with UASB. Along with that, the degradation profile of bacteria and the ability to degrade fat, oil and grease in water is also an essential criterion in selecting the bioculture for UASB systems. Inability to degrade FOG often leads to rising sludge and biomass wastage. If the sludge blanket is not compact, if the bacteria fail to form dense granular aggregates, biomass washout is imminent.

In this example, a CETP in Mumbai was facing two challenges typical to UASB systems. Sludge floatation and washout of active biomass. This was a pilot UASB constructed to evaluate the possibility of setting up multiple larger UASB systems. The Pilot Plant was supplied with organic loading of 5 Kg COD/m³/day. The HRT was at 10 to 12 hours on average, (maximum velocity of 6 hours at peak flow.) Upflow velocity was maintained at 0.5m/h. Although the operational parameters for UASB were in order, the results were not encouraging. The COD reduction was less than 40% while BOD reduction was around 60%. Besides, the treated water had a dark brown colour and high levels of suspended solids.

The consultant engaged in the designing and commissioning of the plant tried Evolon Biotech's Evobac ANB (anaerobic bacteria) for treatment. Soon enough, the sludge blanket got compacted to less than one-third of the tank height. COD reduction of 80 - 85% and BOD reduction of 90 - 95 % was achieved. One of the high COD streams diverted to the pilot plant was from a textile unit. Along with high COD, it imparted a dark maroon-brown colour to the effluent. The colour was significantly reduced anaerobically in the UASB system. The system further demonstrated the production and recovery of 60% methane gas from sludge digestion.