MICROBIAL QUALITY DEGRADATION OF TREATED EFFLUENT DURING DISTRIBUTION FOR CROP IRRIGATION

Authors: JERMAN, J - ASU, TEMPE, AZ; SPENCER, L - ASU, TEMPE, AZ; Duran, Norma

Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Proceedings
Publication Acceptance Date: 6/15/2003
Publication Date: 12/15/2003
Citation: Jerman, J.D., Spencer, L.K., Duran, N.L. Microbial quality degradation of treated effluent during distribution for crop irrigation. American Society for Microbiology Annual Meeting. Abstract 03:GM-A-1764-ASM

Interpretive Summary: It has been estimated that crop irrigation accounts for up to forty-one percent of all fresh water withdrawals, including wells and surface water. Consequently, use of municipal wastewater for irrigation has great potential to reduce reliance on surface water and help prevent groundwater depletion. Despite attempts by several states to utilize treated effluent for irrigation purposes, conventional wastewater treatment serves to reduce microbial numbers but does not eliminate them from the finished water. Thus, the effluent may possibly deteriorate during transport to the point of use by loss of disinfectant residual and growth of biofilm along pipe walls as well as other processes. The purpose of this study was to evaluate bacterial survival and potential for microbial regrowth in tertiary-treated effluent as it passed through a model water distribution system. The treated effluent utilized in this study serves as irrigation water for agricultural purposes in the Southwestern United States. It was found that total coliforms increased exponentially within one week of passage through the distribution system with a steady increase of E. coli. Heterotrophic plate counts similarly increased exponentially, however, decreasing by the end of the experiment. Changes in pH and conductivity were not found to be significant. Phosphorous and total organic carbon concentrations showed a general decrease over time. These results indicate that although the treated wastewater may maintain a uniform level of quality while at the WWTP, it does not secure microbial quality in the distribution system. Hence, care should be taken to prevent deterioration in microbial quality of effluent used for crop irrigation so that risks to public health and the environment are minimized.

Technical Abstract: It has been estimated that crop irrigation accounts for up to forty-one percent of all fresh water withdrawals, including wells and surface water. Consequently, use of municipal wastewater for irrigation has great potential to reduce reliance on surface water and help prevent groundwater depletion. Despite attempts by several states to utilize treated effluent for irrigation purposes, conventional wastewater treatment serves to reduce microbial numbers but does not eliminate them from the finished water. Thus, the effluent may possibly deteriorate during transport to the point of use by loss of disinfectant residual and growth of biofilm along pipe walls as well as other processes. The purpose of this study was to evaluate bacterial survival and potential for microbial regrowth in tertiary-treated effluent as it passed through a model water distribution system. The treated effluent utilized in this study serves as irrigation water for agricultural purposes in the Southwestern United States. It was found that total coliforms increased exponentially within one week of passage through the distribution system with a steady increase of E. coli. Heterotrophic plate counts similarly increased exponentially, however, decreasing by the end of the experiment. Changes in pH and conductivity were not found to be significant. Phosphorous and total organic carbon concentrations showed a general decrease over time. These results indicate that although the treated wastewater may maintain a uniform level of quality while at the WWTP, it does not secure microbial quality in the distribution system. Hence, care should be taken to prevent deterioration in microbial quality of effluent used for crop irrigation so that risks to public health and the environment are minimized.