Solids Separation by Ultrafiltration for Concentrated Activated Sludge

A feasibility study of the use of ultrafiltration as a separation device for a concentrated microbial system was conducted at filtrate flux rates from 35 to 75 psig (2.45 to 5.25 kg/sq m) with cell concentrations of 20 to 30 g/l volatile suspended solids. Increases in water flux rates caused by increases in pressure force were obtained at a sacrifice of solute retention by membranes. Gradual accumulation of cell degradation products occurs in the biological reactor if sludge is not wasted; this may inhibit the viable cell mass. The system showed greater than 98 percent reduction of chemical oxygen demand throughout the study. Dissolved solids of molecular weights greater than 1,000 were retained on the membranes used.