PERFORMANCE EVALUATION OF A PLUNGING LIQUID JET BIOREACTOR WITH CROSS-FLOW FILTRATION FOR SMALL-SCALE TREATMENT OF DOMESTIC WASTE-WATER

Activated sludge treatment of wastewater was successfully carried out by a plunging liquid jet bioreactor with crossflow filtration. The TOC removal efficiency was above 95% in the continuous treatment in which influent BOD concentration was increased in steps from 150 to 1200 g/ m(3). Removal function of cake layer largely contributed to the overal l treatment performance and stability of the bioreactor system. Cake l ayer was found to act as a dynamically formed ultrafiltration membrane . The observed rejection of poly(ethylene glycol) having a molecular w eight of 20000 by the cake layer was about 40%. The removal function o f cake layer was explained by both biodegradation in and solute reject ion by the cake layer. The rejection by the cake layer played a major role in the removal function of cake layer. Performance of the bioreac tor system was simulated based on a mathematical model. A case study f or the treatment of small-scale gray-water was carried out using the m odel. The required working volume was reduced to about one half compar ed to that of the conventional activated sludge process when the cake layer had an observed rejection of only 20%. The cake layer also contr ibuted to treatment performance and operation. Design and operational considerations were also discussed. It was concluded that the bioreact or system has a high potential for small-scale treatment of domestic w astewater.