Biodegradation of Organophosphate Chemical Warfare Agents by Activated Sludge

Organophosphates (OPs) have been widely used as Chemical Warfare Agents (CWAs) as well as pesticides since World War II and still remain a threat to national security. While efforts have been taken at military installations and civilian communities to secure these chemicals and prevent their misuse, a determined adversary could still obtain and deploy them to injure, kill, or instill terror. The lethal properties of this group of compounds are primarily owed to their irreversible inhibition of the enzyme acetyl cholinesterase (AChE) and thus may alter the human nervous system or affect the hormonal balance of children in particular. In the event of a chemical incident, standard operating procedures dictate that contaminated personnel be decontaminated. Often times, decontamination is accomplished with water. Many communities plan for this decontamination water to be sent to the local municipal wastewater treatment plant. However, the fate of these compounds in a municipal wastewater treatment plant is largely unknown. If the compounds cannot be degraded, they will enter surface water bodies with plant effluent or waste sludge. This study investigated the fate of ethyl methylphosphonic acid (EMPA), a hydrolysis product of VX, in a single sludge laboratory-scale sequencing batch reactor (SBR) that simulated a municipal activated sludge wastewater treatment plant. The reactor was fed peptone and sodium acetate to simulate wastewater. Sorption kinetics, sorption equilibrium isotherm, and degradation batch experiments demonstrated that EMPA did not sorb to the biomass. Degradation results showed that approximately 28% of the initial concentration of 1 mg L-1 EMPA was degraded. In addition, the results suggest that the nitrifying bacteria may be responsible for the degradation via cometabolism. Therefore, CWA may pass through an activated sludge wastewater treatment plant completely unchanged