Biologically Enhanced Coagulation–Ultrafiltration Process for Healthy Water Production with Low Fouling Propensity

Abstract

Coagulation combined with ultrafiltration (UF) is an effective drinking water treatment process. However, inefficient removal of natural organic matter (NOM) and membrane fouling problems, especially those initiated by the adhesion of biopolymers, greatly restrict the practical application of the UF process. Here, we investigated a biologically enhanced coagulation–ultrafiltration (CUF) process treating samples of a natural surface water, which demonstrated a superior NOM removal and antifouling performance. The membrane flux (under 1.0 bar constant pressure) of the biologically enhanced CUF [using polyaluminum chloride (PACl)] process scheme was approximately 4.4 and 8.4 times higher than that of a conventional CUF and direct UF process, respectively, and PACl was found to perform better than AlCl3. Characterization of the NOM showed that the biological pretreatment combined with the coagulation process significantly contributed to the reduction of hydrophobicity, aromaticity, and molecular weight of the dissolved organics. Analyses of biopolymers showed that the combined process can remove over 99% of the biopolymers (represented by proteins and polysaccharides), which are considered to be the main cause of membrane fouling. Results of X-ray photoelectron spectroscopy and FTIR analyses further elucidated the transformation and reduction of biopolymers during the combined process. With respect to the disinfection byproduct formation potential (DBP-FP), the results showed that the conventional CUF process had a limited impact on the DBP-FP, while the biologically enhanced CUF process had a substantial impact consistent with meeting the current EPA DBP standards. Overall, this study has highlighted the potential advantages of using a biologically enhanced CUF process for producing higher quality drinking water with a simultaneous low membrane fouling propensity.