Role of algae in the formation of water chlorination byproducts

Summary

For many years the precursors and mechanisms of water chlorination byproducts formation in the process of water purification at the surface water intake of Ufa city have been investigated. The main task of the study was evaluating the contribution of the representatives of the three phytoplankton species typical for the Ufa River to the trihalomethanes formation: diatomic (Bacillariophyta), green (Chlorophyta) and blue-green algae (Сyanophyta). Initially phytoplankton cells were isolated from the river water samples by concentrating, then in laboratory conditions algae were cultured on substrata. The chlorination experiments were carried out both with water samples with algae biomass and with the sample filtrates. The model samples were chlorinated with 1; 2; 3 mg/l chlorine dosages, exposure time – 2 hours. The concentration of trihalomethanes was measured by gas chromatographic vapor-phase analysis with electron-capture detection. The results of the studies revealed the following specific features. The samples with high concentration of blue-green algal biomass (13.6 mg/l – 96%) after chlorination with 3 mg/l dosage showed significant increase of the total trihalomethane concentration– 131.6 µg/l. In the samples with dominant green algal mass (26.19 mg/l – 99.8%) or with green (0.07 mg/l – 53%) and diatomic algae (0.059 mg/l – 47%) only the lowest total trihalomethane concentrations were detected – 3.69 and 2.62 µg/l, respectively. The similar situation was observed in the process of chlorinating filtrates of these samples. This suggests that blue-green algal metabolites or products of the algal mass decay are most probable precursors of trihalomethanes.

Key words

chlorination , potable water quality , phytoplankton , total trihalomethanes , algae , Chlorophyta (green) , Bacillariophyta (diatomic) , Сyanophyta (blue-green)