Fate of cyanobacteria and their metabolites during water treatment sludge management processes

• Published in: The Science of the total environment 2012-05, Vol.424, p.232-238
• Main Authors: Ho, Lionel, Dreyfus, Jennifer, Boyer, Justine, Lowe, Todd, Bustamante, Heriberto, Duker, Phil, Meli, Tass, Newcombe, Gayle
• Format: Article
• Language: English
• Subjects: Anabaena - metabolism; Anabaena circinalis; Applied sciences; Backwashing; Bacterial Toxins; Chromatography, High Pressure Liquid; Coagulation; Cyanobacteria; Cylindrospermopsin; Cylindrospermopsis - metabolism; Cylindrospermopsis raciborskii; Drinking water and swimming-pool water. Desalination; Enzyme-Linked Immunosorbent Assay; Exact sciences and technology; Filtration; Geosmin; Management; Metabolites; Naphthols - metabolism; Pollution; Saxitoxin; Saxitoxin - metabolism; Sedimentation; Sewage - microbiology; Silicon Dioxide - chemistry; Sludge; Uracil - analogs & derivatives; Uracil - metabolism; Waste Disposal, Fluid; Water Microbiology; Water treatment and pollution
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2012.02.025

Cyanobacteria and their metabolites are an issue for water authorities; however, little is known as to the fate of coagulated cyanobacterial-laden sludge during waste management processes in water treatment plants (WTPs). This paper provides information on the cell integrity of Anabaena circinalis and Cylindrospermopsis raciborskii during: laboratory-scale coagulation/sedimentation processes; direct filtration and backwashing procedures; and cyanobacterial-laden sludge management practices. In addition, the metabolites produced by A. circinalis (geosmin and saxitoxins) and C. raciborskii (cylindrospermopsin) were investigated with respect to their release (and possible degradation) during each of the studied processes. Where sedimentation was used, coagulation effectively removed cyanobacteria (and intracellular metabolites) without any considerable exertion on coagulant demand. During direct filtration experiments, cyanobacteria released intracellular metabolites through a stagnation period, suggesting that more frequent backwashing of filters may be required to prevent floc build-up and metabolite release. Cyanobacteria appeared to be protected within the flocs, with minimal damage during backwashing of the filters. Within coagulant sludge, cyanobacteria released intracellular metabolites into the supernatant after 3d, even though cells remained viable up to 7d. This work has improved the understanding of cyanobacterial metabolite risks associated with management of backwash water and sludge and is likely to facilitate improvements at WTPs, including increased monitoring and the application of treatment strategies and operational practices, with respect to cyanobacterial-laden sludge and/or supernatant recycle management. ► Coagulation removed cyanobacteria without an additional exertion on coagulant demand. ► During a stagnation period in direct filtration intracellular metabolites were released. ► Cyanobacterial cells were not damaged during backwashing of the filters. ► In coagulant sludge, cyanobacteria released intracellular metabolites into the supernatant.