AEROBIC GRANULATION IN BAFFLED REACTOR

Abstract

Biosolid —liquid separation in the conventional activated sludge process is one of the critical operations. Poor separation can lead to the problem of bulking, foaming, or rising of sludge. The problem of poor settling causes deterioration in effluent water quality and increases dewatering cost. Sludge settling characteristics can significantly be improved via proper granulation in the reactor. Granulation is a process where loose floe gets converted into compact granule, so that the sludge formed has lower SVI. The formation of compact dense biomass also prevents the problem of sludge washout. A laboratory scale baffled reactor was used to study the sludge settling characteristics during biological decomposition of synthetic medium strength sewage under various operating conditions. Dried crushed sludge from an activated sludge process plant was added initially in order to improve the settling characteristics of the sludge formed in the reactor. During the early days of operation of the reactor its performance was studied at different HRT's. The HRT was decreased in a step manner from 16 h to 8h. Pseudo-steady state was attained at each step before changing HRT to next lower level. A high COD removal efficiency of 86-90% was observed. The NH4tN removal efficiency was also found to be high i.e. 96-97%. Low SVI of about 33 ml gwas observed on day 49. Settling was found to improve further to 18.83 ml g'. Sequence of aerobic-anaerobic conditions each for 12 h was provided after day 127. MLSS was the found to decrease due to these conditions and slight increase in SVI was observed .COD removal efficiency was not much affected. Nitrogen removal improved further as denitrification was improved. Finally 50 mg/L calcium chloride was added in feed to reactor, making calcium concentration including hardness of water used for making substrate feed to 100 mglL and no significant improvement in settling properties of sludge was observed.