Hybrid chitosan/FeCl₃ coagulation-membrane processes: Performance evaluation and membrane fouling study in removing natural organic matter

Coagulation is the most common process used to remove the natural organic matter (NOM) for clean water supply and safe consumption. However, most of the time, the supernatant water quality produced did not meet the drinking water standard and several dispute issues currently exist about the impact of conventional inorganic coagulants on the environment and living organisms. In this study, hybrid coagulation-membrane processes were implemented for NOM treatment using chitosan as a natural coagulant. Its performance in terms of turbidity and humic acid (HA) removal was tested and compared with inorganic ferric chloride (FeCl₃) coagulant. It was discovered that both coagulants were capable to remove 90% of the HA and produce supernatant water with acceptable quality for membrane processes; both nanofiltration (NF) and reverse osmosis (RO) membrane processes managed to remove nearly all of the turbidity and HA in the water. However, a hybrid process using chitosan had a more severe effect on membrane fouling compared to FeCl₃ coagulation pre-treatment processes due to the smaller and neutral particles produced by chitosan coagulation, forming a compact foulant layer on the membrane surface. Therefore, the wise selection of a coagulant for the hybrid coagulation-membrane process is crucial for attaining high removal efficiency and low fouling propensity.