AWWA WQTC71437

This study addresses the colonization of a submerged hollow fiber membrane-based water treatment plant by a population of pulmonate snails. Physical shearing of the fiber membranes caused by embedded calcareous shell structures, has created a challenge in meeting membrane integrity testing. Chlorine dioxide (ClO₂) has been successfully used in treating and preventing the proliferation of both bivalve and gastropod mollusks. The biocidal effectiveness of ClO₂ is considered superior to that of chlorine and hypochlorite in penetrating cell wall structure, acting on the colloidal nature of protoplasm, and suspending cellular enzymatic activity. Additionally, ClO₂ has been shown to have added advantages over chlorination by improving the removal of organic carbons and minimizing disinfection byproduct. A definitive bioassay was developed to establish the ClO₂ dose concentration and exposure that would effectively inactivate the life cycle of the resident snail. Results derived from initial bench scale dosing experiments performed on a laboratory propagated snail culture, suggest that continuous dosing at lower concentrations may be most effective by inducing a perpetual moribund state. In contrast, it was found that intermittent dosing at levels tenable for drinking water application, were ineffective at inactivating all of the life stages tested. Microscopic observations of the blastula and embryo stages made it possible to identify the egg bound vitellus content as a major protective barrier against oxidation. Additional chemical dosing trials are scheduled to be conducted in a custom built monitoring chamber stationed at the affected water treatment plant. Concurrent studies will be performed aimed at evaluating the effectiveness of ClO₂ as a pretreatment option to mitigate downstream Total Trihalomethane (TTHM) formation. Includes abstract only.