Bean curd wastewater treatment by membrane separation

Wastewater from a preserved bean curd manufacture was treated using the mem brane separation method. The wastewater had chemical oxygen demand (COD) of about 10 000 mg/l. Chemical coagulation was rejected due to its poor effic iency in COD removal. Biological oxidation was not considered because of it s requirement of large space which is not available in the factory. Microfi ltration and ultrafiltration were tested but found inadequate for COD remov al to meet the government foul sewer discharge permit, 3000 mg/l. Nanofiltration was found to be a feasible technology for treating this kind of wastewater. The permeate flux and COD were investigated in relation to the transmembrane pressure drop, temperature, and;feed solution COD concent ration. The permeate flux was found to increase significantly with transmem brane pressure drop and to decrease with feed concentration. The permeate C OD for all the conditions tested meets the discharge permit. The permeate C OD decreases with the increase of transmembrane pressure drop and increases with the operation temperature, which is consistent with the theory. The p ermeate can be reused in the bean processing and the concentrate may be ret urned to the production line. This method has been adopted by a bean curd m anufacturing factory in Hong Kong. (C) 1999 Elsevier Science B.V. All right s reserved.