TREATMENT OF LOW STRENGTH WASTEWATER USING A UASB REACTOR

Abstract

The upflow anaerobic sludge blanket (UASB) technology developed in 1979, has proved to be highly efficient for medium to high strength wastewater. The COD removal efficiency of more than 90% has been observed with granulated seed sludge at low hydraulic retention time (HRT). However, the granulation of seed sludge is not feasible for low strength wastewater. The sludge remains flocculant, COD reduction is not more than 60-80% and OLR cannot be increased beyond a certain limit (5-6 kg COD m-3 d-1). In view of the difficulty observed in microbial granulation in UASB reactor, efforts are being made in this direction with low strength wastewater. The present study is also an attempt to attain granulation with low strength wastewater. In this project a 46 1 UASB reactor was operated with high upflow liquid velocity (ULV) and sludge loading rate (SLR) for 15 days in the 1st-phase. The COD removal efficiency was, however, low probably due to channeling. To tackle this problem, (i) sludge granulation process was carried by feeding high strength wastewater to the reactor and (ii) induce sludge mixing mechanically. The COD removal efficiency 60-70%(with HRT 3-6 hr.) was achieved in reactor. The batch fed continuous reactors was mechanically mixed and there severed indication of sludge granulation with SLR of 0.34 kg COD VSS-iday-1 and OLR of 2.4 kg COD kg VSS-1 day-1.