FATE AND CONTROL OF NERVE CHEMICAL WARFARE AGENTS IN THE DESALINATIONINDUSTRY OF THE ARABIAN-PERSIAN GULF

This paper assesses the impact of chemical warfare agents (CWAs) on dr inking water. The study is focussed on the Arabian-Persian Gulf(APG) a nd the desalination process. Contamination of seawater with nerve CWAs can be naturally alleviated by degradation mainly through hydrolysis. Hydrolysis is a relatively fast pathway as compared to other processe s such as biodegradation and photooxidation. From the review of the op en literature and based on the marine environmental conditions in the A.P.G., the following projections are made: 1) Hydrolysis will affect the soluble fraction of nerve CWAs only; 2) the rate of degradation of insoluble agent is determined by the transport phenomena and the avai lable contact surface between the two phases (water/CWA); 3) higher te mperature will promote degradation of nerve CWAs by increasing their s olubilities and by accelerating their hydrolysis reactions; and 4) hig her pH and divalent metal content (Cu, Ca, and Mg) in the A.P.G. will promote the hydrolysis of nerve CWAs. In general, all the environmenta l factors involved in the aquatic degradation of nerve CWAs in the A.P .G. marine favor the fast degradation process. In case of massive rele ases of nerve CWAs near the A.P.G, western shorelines, turbulence resu lting from tidal cycles will affect the dissolution process and extend the toxicity of the insoluble agent. However, this phenomenon will le ad to a faster elimination of the toxic substance from the aquatic env ironment. The time needed for the transport of the soluble fraction of the agent from the point of release to the intakes of desalination pl ants should be calculated to estimate the likely residual levels of to xic non-hydrolyzed fractions of the agent. Post- and pre-chlorination during the course of seawater desalination will catalyze and significa ntly accelerate the hydrolysis processes of the nerve CWAs. The heat e xerted on CWAs during the power generation-desalination processes is n ot expected to thermally decompose them. However, the steam heat will augment the agents' rate of hydrolysis with subsequent acceleration in their rate of detoxification. Available data indicate that breakthrou gh of nerve agents into the thermally desalinated water is conceivable and that their remnants can pose a serious life threat to consumers. Conventional pretreatment of feed seawater for RO desalination is theo retically capable of reducing the concentration of nerve CWAs by copre cipitation and adsorption on flocs formed during coagulation. Prechlor ination and prolonged detention time in pretreatment units will simult aneously promote hydrolysis reactions. However, nerve CWAs can breakth rough RO tight membranes into the permeate at levels higher than the a ccepted tolerance posing a potential life threat to the public. Sugges ted control measures include boosting of pre- and post-chlorination do ses, discarding the yield collected from the first stage in MSF, apply ing high doses of activated carbon, extending detention time, and util izing water treatment devices at point of use or boiling the water by consumers.