Removal of the cyanobacterial toxin microcystin -Lr by biofiltration: Identification of toxin-degrading bacteria and effects of backwashing

The removal of the cyanobacterial toxin microcystin-LR by slow and rapid drinking water biofilters, the presence of the microcystin-degrading bacteria in operating biofilters, the impact of backwashing on the removal of microcystin by biofiltration, and the prediction of microcystin-LR removal using a nonsteady-state biofilm model were investigated. A newly recognized microcystin-LR degrader, Morganella morganii, exists in Lake Mead and operating active biofilters. The results of the biodegradation tests indicated that addition of a carbon source, in the form of biodegradable NOM, significantly delayed the degradation of microcystin-LR. The biofiltration experiments demonstrated that at steady-state, biofiltration may be a potential technology for the removal of microcystin-LR under slow and rapid conditions. However, the impact of backwashing on microcystin removal, points out some limitations for this treatment process. The results of biofilm model prediction using estimated biofilm thickness indicated a better agreement with the TOC experimental data than with the microcystin\u27s data

Biodegradation Studies and Sequencing of Microcystin-LR Degrading Bacteria Isolated from a Drinking Water Biofilter and a Fresh Water Lake

The presence of microcystin-LR -degrading bacteria in an active anthracite biofilter and in Lake Mead, Nevada was investigated. Four bacterial isolates from enrichment culture were identified using 16S rRNA analysis. Microcystin biodegradation tests were performed with both, the enrichment cultures and the respective isolates, using microcystin alone and acetate as carbon sources. A newly recognized microcystin-degrading bacterium, Morganella morganii, was isolated from the biofilter and from Lake Mead. The results of the biodegradation tests indicated that addition of a carbon source (acetate), significantly repressed the degradation of microcystin-LR. The findings of this study inform on the prevalence of microcystin-degrading bacteria in the environment indicating bioaugmentation may not be needed, if biofiltration is used to remove microcystin from waters. The results also imply that, in a biofilter, biodegradable naturally organic matter (NOM) and microcystin will compete and therefore lower toxin removals are likely in waters with higher NOM content. The feasibility of removing microcystin by biofiltration depends on the toxin concentration and the concentration of biodegradable carbon sources in the biofilter