Cross-flow filtration of synthetic electroplating wastewater by ceramic membranes using high frequency backpulsing

Cross-flow microfiltration (MF) was investigated as a viable option for separating colloidal particles from electroplating wastewater. Filtration experiments with Cr(OH)₃ suspension as synthetic electroplating wastewater were performed on a pilot filter unit equipped with a backpulse device using porous alumina ceramic membranes of various pore sizes (0.2-5.0 µm). The membranes were characterized by nitrogen and clean water permeation. In filtration with Cr(OH)₃ suspension, water permeate flux decreases with decreasing membrane pore size and increasing solute concentration in suspension. All membranes are fouled in filtration primarily due to the cake formation. With backpulse in operation, a constant water permeate flux can be maintained using membranes with pore size smaller or larger than the size of solid aggregates in the suspension. The rejection coefficient of suspended solid is about 100% for the smaller pore membranes but drops to only 70% for the larger pore membrane. The backpulse is not effective in maintaining a constant water permeate flux for filtration using membranes of pore size close to the suspension aggregate size due to entrapment of fine aggregates in the membrane pores. The fouled membranes could be completely regenerated by a chemical rinsing method with NaOH and HNO₃ solutions.