Effects of natural organic matter removal by integrated processes: alum coagulation and PAC-adsorption

Abstract

This paper presents the results of bench-scale research into the efficiency of NOM removal by integrated processes—alum coagulation and PAC-adsorption. Experiments were conducted using riverine water samples (collected from the Odra River, Poland) and commercial powdered activated carbon. It has been shown that a PAC-enhanced coagulation process reduces the coagulant dose required and increases the process efficiency at the same time. For example, a coagulant dose of 2.0 mgAl/L and a PAC dose of 5 mg/L have produced results comparable to those of a coagulation process with no adsorbent aid but with a coagulant dose increased by 54%. The coagulation-adsorption tests were carried out at a pH of 6.0, which was lower than the pHIEP of the adsorbent. This procedure yielded a high extent of DOC and UV-254 removal, at 90% and 77%, respectively. The drop observed in the SUVA value after the process implied a decrease in reactive DOC forms and consequently a diminished risk that disinfection by-products might form. HPSEC analyses made it possible to describe the changes in the molecular weight distribution for the organic substances persisting in the water both after coagulation and after PAC-aided coagulation, and to evaluate their propensity to removal by the two methods. The coagulation process was effective as far as the removal of high-molecular-weight fractions is concerned. An increase in the removal of the low molecular weight NOM was achieved when the PAC-adsorption process had been combined with coagulation.