Drinking water treatment residual as a ballast to sink Microcystis cyanobacteria and inactivate phosphorus in tropical lake water

• Published in: Water research (Oxford) Vol. 207; p. 117792
• Main Authors: Kuster, Anthony C., Huser, Brian J., Thongdamrongtham, Somjate, Padungthon, Surapol, Junggoth, Rittirong, Kuster, Anootnara T.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.12.2021
• Subjects: Alum; Cyanobacteria; Drinking Water; Drinking water sludge; Environmental Sciences; Eutrophication; Flocculation; Geoengineering; Internal phosphorus loading; Lake restoration; Lakes; Microcystis; Miljövetenskap; Phosphorus - analysis; Geoengineering; Flocculation; Lake restoration; Drinking water sludge; Internal phosphorus loading; Alum; Eutrophication
• ISSN: 0043-1354; 1879-2448; 1879-2448
• DOI: 10.1016/j.watres.2021.117792

•A drinking water treatment residual (DWTR) was washed and heated without oxygen.•The DWTR sank Microcystis colonies in lake water more effectively than a local soil.•Ballast dose, alkalinity, pH, and chlorophyll-a affected sinking efficacy.•Leaching of metals and nutrients from the pre-treated DWTR was low.•The DWTR had a high P sorption capacity, sufficient for inactivating P in lake sediment. The combination of a low dose of coagulant with a ballast that can inactive phosphorus (P) in lake sediment—a technique known as “flock and lock”—is one method for restoration of eutrophic lakes. The effectiveness of a drinking water treatment residual (DWTR) as a ballast in flock and lock was assessed using assays of eutrophic lake water from Thailand dominated by Microcystis aeruginosa cyanobacteria colonies by measuring changes in chlorophyll-a, pH, and zeta potential. P sorption isotherms were developed from long-term batch equilibrium experiments; desorption of nutrients and metals was assessed via leaching experiments; and morphological changes to cellular structure were assessed using scanning electron microscopy. Results showed that combining DWTR with a low dose of aluminum sulfate (0.6-4.0 mg Al/L) effectively sank 74-96% of Microcystis, with DWTR dose (50-400 mg/L), initial chlorophyll-a concentration (92-976 µg/L), pH (7.4-9.3), and alkalinity (99-108 ppm CaCO3) identified as factors significantly associated with sinking efficacy. P sorption capacity of the DWTR (7.12 mg/g) was significantly higher than a local soil (0.33 mg/g), enabling the DWTR to inactivate P in lake sediment. Desorption of Al, Fe, Ca and N from the DWTR was estimated to contribute to a marginal increase in concentrations of those compounds in the water column of a small shallow lake (1.2, 0.66, 53.4, and 0.07 µg/L, respectively) following a simulated application. Therefore, pre-treated DWTRs may be a viable alternative ballast in the flock and lock approach to lake restoration, supplementing or replacing modified local soils or lanthanum modified clays. [Display omitted]