Using a novel coagulant as a practical and sustainable approach for cyanobacterial bloom control

Abstract

Excessive cyanobacterial growth, cyanobacterial blooms, occurs in eutrophic water bodies, and coagulants are used to settle down or float up cyanobacterial cells for their removal. In this study, we developed a novel inorganic coagulant, MC, and investigated its practical applicability by treating three water samples from natural reservoirs and compared its efficiency with loess which is a commonly used cyanobacteria-controlling material. To understand how the coagulated cyanobacterial flocs induce water quality changes, each treated-column was exposed to various abiotic environmental conditions (water temperature, pH, dissolved oxygen, light, and water cycle). The chlorophyll-a reduction efficiency of MC was 88%–95% whereas loess showed 37%–57% efficiency. Nutrient concentration increased over time following exposure to environmental conditions. From microcystin and cell integrity tests, MC-treated cyanobacterial cells were damaged two days after the addition, regardless of the conditions, whereas loess-treated cells were damaged only at 40 °C, pH 11, and under aerobic conditions (dissolved oxygen >5 mg L−1). However, the results from an additional experiment revealed that no microcystin was detected from the coagulated cyanobacterial floc removed column, while total nitrogen and total phosphorus concentrations were reduced by 90% and 80%, respectively, than the initial values. On the other hand, in the column with the remaining coagulated cyanobacterial floc, the microcystin started to increase from day 2 of the coagulation and reached almost 1 ppb on day 12. Our study suggests that the use of MC is a practical and sustainable approach for removing cyanobacteria and managing eutrophication in natural water bodies and immediate removal of coagulated cyanobacterial flocs should be accompanied to avoid water contamination via cell damage.