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United States Department of Agriculture

Agricultural Research Service

Research Project: REUSE OF TREATED MUNICIPAL WASTE WATER FOR IRRIGATION Title: Assessing Environmental Impacts of Treated Wastewater through Monitoring of Fecal Indicator Bacteria and Salinity in Irrigated Soils

Authors
item McLain, Jean
item Williams, Clinton

Submitted to: Environmental Monitoring and Assessment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 7, 2011
Publication Date: May 21, 2011
Citation: Mclain, J.E., Williams, C.F. 2011. Assessing Environmental Impacts of Treated Wastewater through Monitoring of Fecal Indicator Bacteria and Salinity in Irrigated Soils. Environmental Monitoring and Assessment. 184:1559-1572.

Interpretive Summary: As communities seek new sources of water and more efficient ways to use it, recycled wastewater has been increasingly used for municipal irrigation in the Southwest US. Despite the economic benefits of reclaimed water use for irrigation, questions remain about potential public and environmental health risks. This study was performed to assess the potential for bacterial persistence and/or growth in reclaimed water irrigation systems and in irrigated soils, and to quantify the effects of wastewater application on soil salinity. Levels of fecal bacteria (E. coli, Enterococcus) were measured in a reclaimed water holding pond (irrigation source water), water leaving the irrigation system, and in irrigated soils over two years in a municipal parkland in Arizona. Spikes in fecal indicator bacteria in the pond water were found, possibly related to fecal inputs from parkland dogs, birds, and fish, but over two years, no detectable buildup of fecal bacteria was observed in soils. The highest E. coli levels were found in deeper soils during summer, indicating that surface conditions (intense solar radiation and drying) were toxic to bacteria, reducing any potential risk to humans coming into contact with the irrigated areas. No overall increase in soil salinity resulting from reclaimed water irrigation was measured. Studies such as these are important to water managers and municipalities throughout the US for making informed decisions regarding the use of wastewater for irrigation.

Technical Abstract: To assess the potential for bacterial persistence and/or growth in reclaimed water irrigation systems and in irrigated soils, and to quantify the effects of wastewater application on soil salinity, levels of fecal indicator bacteria (E. coli, Enterococcus) and environmental covariates were measured in a reclaimed water holding pond (irrigation source water), water leaving the irrigation system, and in irrigated soils over two years in a municipal parkland in Arizona. Spikes in fecal indicator bacteria in the pond water as high as 250 CFU 100 mL-1 were found, possibly related to fecal inputs from dogs, birds, and fish. Higher E. coli levels were measured in the pond in winter (56 CFU 100 mL-1) than in summer (17 CFU 100 mL-1), but this was not the case in the irrigation system, where levels of E. coli and Enterococcus decreased from summer (20 CFU 100 mL-1) to winter (4 CFU 100 mL-1), possibly resulting from low water use in winter and corresponding declines in residual bacteria within the system. Over two years, no detectable buildup of fecal bacteria was observed in soils, though highest E. coli levels (700 CFU g-1 soil) were found in deeper (20 cm) soils during summer, indicating that irrigation levels were sufficiently high to generate bacterial percolation to deeper soil layers, and that surface conditions (intense solar radiation and drying) were toxic to enteric bacteria. No overall increase in soil salinity resulting from reclaimed water irrigation was measured, but distinct seasonal peaks as high as 4 ds m-1 were found during both summers. The peaks significantly declined in winter when more favorable water balances could be maintained. Studies such as these are important for identifying and minimizing any hazards to environmental and human health associated with the increasing use of wastewater for irrigation.

Last Modified: 12/22/2014
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