Biodegradation of an Organophosphate Chemical Warfare Agent Simulant by Activated Sludge with Varying Solid Retention Times

This study examined the fate of malathion, a surrogate compound for VX studies, in bench-scale sequencing batch bioreactors being operated under varied solid retention times (SRTs) to simulate the activated sludge process in wastewater treatment facilities. Results show that a constant influent of the malathion will largely be removed. However, the heterotrophic bacteria undergo a stress response which temporarily inhibits malathion removal, the extent of which increases with increasing SRTs. After this stress response takes place, the activated sludge is able to resume a high degree of malathion removal, even with increased influent concentration; however, this is done so at the expense of acceptable COD removal in the effluent, suggesting malathion may be toxic to the heterotrophic bacteria in activated sludge