A Thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1988

Feasibility of . hollow fiber microfiltration for solid liquid separation from the aeration tank of an activated sludge process was investigated. The study was divided into short term experiments and a long term experiment. From the short term experiments results. cyclic operation was found effective against inter' module clogginq and hence resulting in stable membrane flux. Out of three different organic loadings given in the long term experiment. 3 kg/Cm3. d) was found to be the critical one. concerning solid liquid separation. 2 kg/( m3. d) was the most suitable loading. Membrane permeate was free of turbidity, free of bacteria, completely nitrified, partially denitrified and very low in effluent COD concentration. The process operated at very high MLSS concentration without sludge wastage. Low values of kinetic coefficients (kd and Y) and F/M ratio were obtained showing little sludge production at steady state. 0. 45 æm membranes operated at '1ower suction pressures than 0.1 æm membranes. The · highest pressure requirement during, around 4 months of operational period was within 0. 5 m head of water employing O'. 45 æm membranes. This idea motivated the use of elevation difference as a · driving force for membrane separation, precluding the pump suction. The proposed system showed better quality of effluent with much lower HRT. and high enough organic 1oading, when compared with the extended aeration process, in context of sludge production.