Prechlorination of algae-laden water: the effects of ammonia on chlorinated disinfection byproduct formation during long-distance transportation

ABSTRACT Prechlorination can cause algal cell damage and lead to the formation of disinfection byproducts (DBPs). This study investigates the impact of ammonia (NH4+) concentration on the formation of carbon disinfection byproducts (C-DBPs) and nitrogenous disinfection byproducts (N-DBPs) in algae-laden water during long-distance transportation. It was found that lower chlorine-to-ammonia (Cl2/NH4+) ratios resulted in less algal cell damage and lower DBP levels compared to higher ratios. Surprisingly, after 360 min of transport, C-DBP levels were consistently lower in samples with a Cl2/NH4+ ratio of 1:0 compared to those with a ratio of 1:0.05, despite similar algal cell damage. This difference is attributed to the varying release of algal organic matter (AOM) between the groups, with the 1:0 ratio group releasing more AOM. The presence of NH4+ appears to play a significant role in reducing algal cell damage, influencing AOM release and DBP formation. Dissolved organic carbon, mainly from proteins and polysaccharides, is the primary source of C-DBPs and is absorbed by dead algal cells, indicating a link between algal biomass and DBP formation. Therefore, when using prechlorination for algae-laden water treatment, both chlorine dosage and transport distance should be adjusted based on NH4+ concentration to minimize algal cell damage.