Q-240. Extending Water Supplies through Treatment of Impaired Rio Grande River Water

E. L. Espinoza1, N. F. Garcia1, A. J. Tarquin2, G. D. Di Giovanni1;
1Texas AgriLife Res., Texas A&M Univ., El Paso, TX, 2Univ. of Texas, El Paso, TX.

The Rio Grande River is the primary surface water resource for the El Paso, Texas and Juarez, Mexico region. It is heavily utilized for agriculture and as a drinking water supply, but has been poorly characterized for its microbiological quality. Winter return flows during the non-irrigation season (November through April) contain significantly higher levels of pathogens due to agricultural return flows and wastewater treatment plant effluents. However, nanofiltration is being assessed as a treatment method for these impaired winter return flows in an attempt to increase the area’s limited drinking water supply. To evaluate microbial removal, samples of raw winter return flow water and nanofiltration pilot-plant treated water were analyzed for the presence of Cryptosporidium, Giardia, E. coli, fecal coliforms, and somatic bacteriophage. Water sample types included raw, nanofilter feed (after microfiltration), and nanofilter permeate. E. coli was detected using USEPA Method 1603, fecal coliforms using mFC agar, somatic phage by USEPA Method 1602, and Cryptosporidium and Giardia using USEPA Method 1623. Naturally occurring pathogens were only detected in the raw water and the feed and permeate waters tested negative for pathogens. To date, the pilot plant appears to be capable of 3-logs or greater physical removal of these naturally occurring pathogens and indicator organisms. In addition a somatic phage challenge of the pilot-plant was performed resulting in 5.7-log, but not absolute, removal. In conclusion, nanofiltration appears useful for treatment of Rio Grande winter return flows. However, phage challenge results stress the importance of a multiple barrier approach to water treatment, including the use of a disinfectant.