Elimination of microcystins and associated toxicitythrough biofiltration processes

摘要

Microcystins are potent hepatotoxins which are produced in water supplies by blue-greenalgae (cyanobacteria). In dissolved (extracellular) form, microcystins are not efficientlyremoved by conventional water treatment processes. This study focussed on the removal ofmicrocystins from drinking water using biological sand and granular activated carbon (GAC)filtration processes. The results indicate that these toxins were effectively removed in a rangeof biological filters and that a specific bacterium was responsible for the degradation throughthe sand filters. Batch degradation experiments were performed using this bacterium toconfirm that it could degrade microcystins. Furthermore, these batch experimentsdemonstrated that no toxic by-products were generated during the biodegradation of themicrocystins, with toxicity assessed by a protein phosphatase inhibition assay and a cellculture cytotoxicity assay. Molecular techniques were also used to detect the presence of agene, mlrA, previously shown to be involved in the degradation of microcystin toxins. Thisgene was detected within the genome of the aforementioned bacterium providing additionalevidence that removal of microcystins was through biodegradation. The isolated bacteriumwas shown to belong to the family Sphingomonadaceae using phylogenetic methods.