Growth of Salmonella spp. and Vibrio cholerae in Reconditioned Wastewater ^†

Many food-processing plants are looking to increase the use of reconditioned water beyond the currently approved uses for initial cleaning (vegetables) and scalding water (meat and poultry). The preliminary survey showed that the reconditioned water from a local meat plant could support bacterial growth. The growth potential of Salmonella spp. and Vibrio cholerae (starting level of 3 to 4 log CFU/ml) in the reconditioned wastewater from this plant (with and without added thiosulfate) was studied at temperatures from 5 to 42°C. Bioassays for the assimilable organic carbon and coliform growth response suggest that this reconditioned water contained sufficient nutrients to support bacterial growth. Both pathogens grew in the unchlorinated reconditioned and chlorinated reconditioned water containing 10 mg of sodium thiosulfate per ml to neutralize the residual chlorine. Cell counts declined rapidly in chlorinated water without thiosulfate. The results of this study emphasized the importance of maintaining residual chlorine levels (0.2 mg/liter) in both reconditioned and potable waters to prevent pathogen growth.