Removal of Algal Toxins By Reverse Osmosis

Removal of Algal Toxins by Reverse Osmosis

Abstract

Harmful algal blooms can release a variety of toxins. These include the myriad microcystin variants that are hepatotoxins of which microcystin-LR (MC-LR) is the most common. Conventional water treatment processes such as coagulation, flocculation and sedimentation are not effective at MC-LR removal. Potential techniques to remove MC-LR include activated carbon adsorption, ozonation, biosorption, nanofiltration, reverse osmosis (RO) and chlorination.

The ability of RO to remove MC-LR has raised questions among vendors of home point-of-use systems for drinking water treatment as to the efficacy of removal. This study evaluates the performance of several commercial RO membranes. The water permeability and salt rejection of the membranes are characterized in addition to MC-LR rejection. All membranes remove MC-LR to non-detectable limits.

Membranes are subject to accelerated aging by exposure to elevated chlorine concentrations for various times. Upon exposure to chlorine, the membranes either exhibit a continuous increase in hydraulic permeability or slight decrease followed by an increase. Salt rejection does not change in those membranes which show an initial hydraulic permeability decrease until the permeability starts to increase. AFM imaging indicates membrane surface roughness decreases upon chlorine exposure for the membranes that exhibit an initial permeability decrease.

MC-LR rejection does not change with chlorine exposure for most membranes. Rejection remains nearly 100% despite dramatic increases in hydraulic permeability.