Mechanisms of bacteria, virus, and turbidity removal by chitosan coagulation in water

Chitosan is a promising coagulant for bacteria, viruses and turbidity in water, but needs identification of optimal dose-polymer combinations. This research tested chitosans to identify dose range and characteristics that provide highest simultaneous reduction of bacteria, viruses, and turbidity, and possible coagulation mechanisms, including charge neutralization, sweep coagulation, and electrostatic patch. Three molecular weights (MW) and degrees of deacetylation (DD) were tested at doses 1, 3, 10 and 30 mg/L using jar tests in water containing clays, <i>E. coli</i>, and bacteriophage MS2. Turbidity removal was 93-99% at 1 and 3 mg/L, with no significant difference between MW. MW, DD and dose significantly affected viral and bacterial reduction. Across doses, MW 100,000 Da had highest mean log10 MS2 (3.5) and <i>E. coli</i> (3.5) reductions. The 100,000 Da/10 mg combination had the highest mean log10 <i>E. coli</i> (4.5) and MS2 (3.5) reductions simultaneously. Overall, 100,000 Da/3 mg and 1,000,000 Da/3 mg maximize reduction of turbidity and MS2, but not <i>E. coli</i>. 100,000 Da/10 mg maximized <i>E. coli</i> reduction and gave MS2 reductions similar to 100,000 Da/3 mg, but turbidity reduction was lower. Chitosan reduced turbidity, bacteria, and viruses in water, influenced by MW, DD, and dose. Data suggests that there is no single dose/MW/DD combination that produced significantly higher reductions of all three contaminants simultaneously but good removal of all three can be achieved with 100,000 Da at 3 or 10 mg/L. Chitosans can be effective coagulant-flocculants in water at reasonably achievable doses using polymer characteristics that are commercially available.