Dec. 22, 2000—A study available for review on the Internet covers the use of urban sewage for irrigation in the water-scarce Guanajuato River Basin of Mexico.
There are significant trade-offs associated with irrigation using untreated urban sewage. From a river-basin perspective, wastewater irrigation is an important form of water and nutrient reuse, wrote authors Christopher A. Scott, J. Antonio Zaraz�a, and Gilbert Levine in their paper. However, there are important water quality, environmental, and public health considerations.
The report explores the advantages and risks of this wastewater reuse for crop production. Through a literature review, the authors demonstrate how common this practice is throughout the world and in Mexico specifically.
The report also applies and validates the Interactive River Aquifer Simulation (IRAS) model, developed by Cornell University and Resource Planning Associates, and evaluates the outcomes of several alternative water management scenarios for water and soil quality in the study area.
The 140 hectares of land irrigated with raw wastewater downstream of the city of Guanajuato serve as de facto water treatment with significant retention of contaminants.
However, recycling does tend to concentrate salts in the flows leaving the study area. Measured coliform levels where high did not, however, show significant evidence of direct health impacts of wastewater irrigation, the authors wrote.
Heavy metal concentrations in bed sediments and in irrigated fields are within Mexican, EU, and U.S. norms. Under current irrigation practices, the buildup of heavy metals in soils is within EU and U.S. norms. Based on simulation modeling of flow and nutrient transport, the annual gross values of the wastewater and wasteload to farmers in the Guanajuato river basin, Mexico were estimated at U.S.$252,000 and $18,900, respectively.
To see the report, visit http://www.cgiar.org/iwmi/pubs/pub041/images/PUB041.htm.
