Combined Chitosan Quaternary Ammonium Salt and Activated Carbon Technique for Simultaneous Algae Removal and Disinfection Byproduct Control: Efficiency and Mechanisms

Algal blooms not only lead to significant water pollution but also produce algal organic matter (AOM) from algal cells, which serves as precursors for disinfection byproducts. To address the inefficiency of existing algae removal technologies in eliminating AOM, this study investigates the feasibility of a combined technique utilizing chitosan quaternary ammonium salt (HTCC) and activated carbon (AC) for simultaneous algae removal and AOM elimination. First, the release of AOM during algae removal by standalone HTCC was examined. Second, AC with optimal AOM removal efficiency was selected, followed by evaluating the performance of the HTCC–AC combined technique in algae removal and AOM elimination. The disinfection byproduct formation potential before and after treatment was analyzed. Mechanism insights were elucidated through characterization techniques including Zeta potential, scanning electron microscope, Brunauer–Emmett–Teller, and FT-IR. Results indicated that standalone HTCC treatment poses a risk of AOM release, with released AOM originating from both intracellular and extracellular algal components. Wood-based activated carbon exhibited the highest AOM adsorption capacity at 6.43 mg/g. The HTCC–AC combined technique achieved removal efficiencies of 97.32%, 96.11%, and 91.13% for algal density, turbidity, and dissolved organic carbon, respectively. Notably, trihalomethane formation decreased by 94.56% compared with the control group, resulting in a posttreatment THM ratio of 0.15, significantly below the 1.0 limit specified in drinking water standards. The mechanisms of algal removal through the combined technique involve adsorption bridging and charge neutralization, while the removal of AOM occurs via π–π conjugation and hydrogen bonding interactions.