Hi all…with the 2016 cyanobacteria season now occurring I suspect that many of you have wondered what happens to cyanobacteria when they are trapped/settled out in drinking water treatment plants/reservoirs. An article has recently been published reporting that unfortunately “it was shown that cyanobacteria can proliferate in the conditions manifest in a sludge treatment lagoon, and that cyanobacteria can survive and produce metabolites for at least 10 days in sludge.”
The paper was generated from a study on the impact to sludge from cyanobacteria (WaterRA 1073/WaterRF 4523). The study found that sludge treatment facilities offer a suitable environment for the persistence and proliferation of cyanobacteria, and confinement in the sludge may not result in rapid cell death as previously believed. The executive summary is available at http://www.waterrf.org/Pages/Projects.aspx?PID=4523
Bill
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Fate of cyanobacteria in drinking water treatment plant lagoon supernatant and sludge
Carlos J. Pestana, Petra J. Reeve, Emma Sawade, Camille F. Voldoire, Kelly Newton, Radisti Praptiwi, Lea Collingnon, Jennifer Dreyfus, Peter Hobson, Virginie Gaget, Gayle Newcombe
Science of The Total Environment
Volume 565, 15 September 2016, Pages 1192–1200
http://www.sciencedirect.com/science/article/pii/S0048969716311032
ABSTRACT:
“In conventional water treatment processes, where the coagulation and flocculation steps are designed to remove particles from drinking water, cyanobacteria are also concentrated into the resultant sludge. As a consequence, cyanobacteria-laden sludge can act as a reservoir for metabolites such as taste and odour compounds and cyanotoxins. This can pose a significant risk to water quality where supernatant from the sludge treatment facility is returned to the inlet to the plant. In this study the complex processes that can take place in a sludge treatment lagoon were investigated. It was shown that cyanobacteria can proliferate in the conditions manifest in a sludge treatment lagoon, and that cyanobacteria can survive and produce metabolites for at least 10 days in sludge. The major processes of metabolite release and degradation are very dependent on the physical, chemical and biological environment in the sludge treatment facility and it was not possible to accurately model the net effect. For the first time evidence is provided to suggest that there is a greater risk associated with recycling sludge supernatant than can be estimated from the raw water quality, as metabolite concentrations increased by up to 500% over several days after coagulation, attributed to increased metabolite production and/or cell proliferation in the sludge.”
