Removal of microcystin from lake water using an internal airlift loop ceramic honeycomb support bioreactor

Abstract

Cyanobacterial microcystins (MCs) are becoming a threat to human health around the world. They are resistant to conventional water treatment processes hence it is pertinent to look to biological remediation, using bacterial degradation. This study reports on the use of the bacterium Sphingomonas isolate NV-3 to develop a small scale bioreactor for biodegradation of [Dha7]MC-LR. A coupon biofilm formation assay was used to determine optimal surface for bacterial attachment. The NV3 isolate attached most effectively to ceramic followed by PVC, polystyrene, stainless steel, and finally glass coupons. It was demonstrated that the biomass of the bacterium increased steadily over time from 24 to 72 hours on the ceramic surface. A ceramic surface was therefore chosen as the carrier in the small scale bioreactors. In this study an internal airlift loop ceramic honeycomb support bioreactor (IAL-CHS bioreactor), was used for removing MCs. In the batch experiment, NV-3 degraded [Dha7]MC-LR at an initial concentration of 25 µg/ml at 30oC in 30 hours whereas in the continuous-flow experiment, NV-3 degraded the same concentration of [Dha7]MC-LR in 36 hours with hydraulic retention time (HRT) of 8 hours.