INFLUENCE OF BROMIDE ON LOW-PRESSURE MEMBRANE FILTRATION FOR CONTROLLING DBPS IN SURFACE WATERS

As a result of current and anticipated disinfection by-product (DBP) regulations, increased interest is being shown in pressure-driven membrane processes for DBP precursor removal. Pilot studies were conducted with two California surface waters and one in Ottawa, Ont. One ultrafiltration (UF) membrane with a molecular weight cutoff (MWCO) of 100,000 daltons and four nanofilbration (NF) membranes with MWCOs ranging from 200 to 800 daltons were evaluated. Results indicated that UF was ineffective for controlling the formation of DBPs. When little or no bromide was detected in the permeate, hollow-fiber NF membranes with MWCOs of 400-800 daltons effectively controlled DBP formation. In waters containing bromide, higher bromoform concentrations (compared with the raw water) were observed after chlorination of the permeate of these membranes. Use of spiral-wound NF membranes (200-300 daltons) controlled the formation of brominated THMs, but pretreatment of the water was necessary.