Q-238. Regrowth of Opportunistic Pathogens and Indicators in Reclaimed Water Systems

P. K. Jjemba1, L. A. Weinrich1, W. Cheng1, E. Giraldo2, M. W. LeChevallier2;
1American Water, Delran, NJ, 2American Water, Voorhees, NJ.

Acceptance of reclaimed water is challenged by concerns for the potential of pathogens to growth in distribution systems. To address this concern, microorganisms in four different reclaimed water distribution systems in California, Florida, Massachusetts, and New York were examined over a one year period. For two of the systems, the reclaimed water was stored in open ponds, where algal growth significantly affected its quality. Results showed that organic carbon, particularly assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC) had the strongest relationship to bacterial growth. The disinfectant residuals dissipated rapidly in the reclaimed systems. In treated effluents, indicator bacteria (total coliforms and E. coli) were generally absent, but typically regrew in the distribution system. Heterotrophic bacteria densities in the distribution systems were as high as 106 cfu/mL. The occurrence of Mycobacterium and Legionella spp. were correlated and were detected even in instances when bacterial indicators were absent. Mycobacterium spp. were detected in the effluents from all four plants and at all points in the reclaimed water systems with densities as high as 103 organisms/100mL. Legionella spp. were detected most commonly in the summer and fall samples at densities of 105 per 100 mL, and were strongly associated with high AOC levels and loss of disinfectant residuals. Generally, fecal coliform and E. coli levels were low, but total coliform bacteria could grow to levels exceeding105 cfu/100 mL. Other organisms detected at various densities included Pseudomonas, Enterococci, Aeromonas, iron-related bacteria, and sulfur bacteria. The choice of treatment technology, storage reservoir, as well as the maintenance and operation of the distribution - including the choice of disinfectant residual, can all have significant impacts on the quality of reclaimed water. The study concludes that the biostability of reclaimed water is an important parameter that can affect the microbial quality and risk of reclaimed water at the point of use.