The disinfection by-products precursors removal efficiency and the subsequent effects on chlorine decay for humic acid synthetic water treated by coagulation process and coagulation-ultrafiltration process

摘要

The disinfection by-products (DBPs) precursors removal efficiency and the subsequent effects on chlorine decay of coagulation-ultrafiltration process were studied in a laboratory in comparison with coagulation process. And the relation between flocs properties and the performance of coagulation-ultrafiltration process was investigated by the experiments of flocs size, fractal dimension and the surface charge. The removal efficiency of coagulation-ultrafiltration process showed that turbidity and UV_(254) could be removed efficiently regardless of polyferric chloride (PFC) dosage and solution pH. Even when dosage was 3 mg L~(-1) the turbidity and UV254 removal efficiencies were higher than 90% in coagulation-ultrafiltration process. The chlorine decay showed that under various technological conditions, the difference between chlorine decay curves obtained by coagulation-ultrafiltration process was less than that obtained by coagulation process. According to the analysis by AQUASIM software, the concentration of fast reducing agents (FRA) in coagulation-ultrafiltration process is lower than that in coagulation process, but the concentration of Slow Reducing Agents (SRA) in coagulation-ultrafiltration process was higher than in coagulation process except dosage = 18 mg L~(-1). Comparing the flocs properties to the performance of coagulation-ultrafiltration process, it can be found that when flocs size was small (<200 μm), the HA removal efficiency increased with flocs size increasing, while when flocs size was large (>200 μm), the HA removal efficiency was influenced mainly by flocs structure. The more compact the flocs, the higher the HA removal efficiency.