41 Research Report Urban-Wastewater Reuse for Crop Production in the Water-Short Guanajuato River Basin, Mexico Christopher A. Scott J. Antonio Zarazúa, and Gilbert Levine INTERNATIONAL WATER MANAGEMENT INSTITUTE P O Box 2075, Colombo, Sri Lanka Tel (94-1) 867404 • Fax (94-1) 866854 • E-mail [email protected] Internet Home Page http://www.iwmi.org ISBN 92-9090-404-6 ISSN 1026-0862 International Water Management Institute Research Reports IWMI’s mission is to contribute to food security and poverty eradication by fostering sustainable increases in the productivity of water through better management of irri- gation and other water uses in river basins. In serving this mission, IWMI concentrates on the integration of policies, technologies and management systems to achieve work- able solutions to real problems—practical, relevant results in the field of irrigation and water resources. The publications in this series cover a wide range of subjects—from computer modeling to experience with water user associations—and vary in content from directly applicable research to more basic studies, on which applied work ultimately depends. Some research reports are narrowly focused, analytical, and detailed empirical stud- ies; others are wide-ranging and synthetic overviews of generic problems. Although most of the reports are published by IWMI staff and their collaborators, we welcome contributions from others. Each report is reviewed internally by IWMI’s own staff and Fellows, and by external reviewers. The reports are published and dis- tributed both in hard copy and electronically (http://www.iwmi.org) and where possible all data and analyses will be available as separate downloadable files. Reports may be copied freely and cited with due acknowledgment. Research Report 41 Urban-Wastewater Reuse for Crop Production in the Water-Short Guanajuato River Basin, Mexico Christopher A. Scott J. Antonio Zarazúa, and Gilbert Levine International Water Management Institute P O Box 2075, Colombo, Sri Lanka i IWMI thanks the Taiwan Council of Agriculture, the Tao Yuan Foundation for Irrigation Research (Taiwan) and the T. Sao-Jin Memorial Foundation for R&D for Agriculture and Irrigation (Taiwan) for the financial support for this study. IWMI gratefully acknowledges the unrestricted and program support provided by the following Governments, Development Banks, Agencies, and Foundations: Australia, Belgium, Brazil, Canada, China, Denmark, Germany, India, Iran, Japan, Mexico, Netherlands, Norway, Pakistan, Peru, South Africa, Sweden, Switzerland, United Kingdom, United States of America, and European Union (EU); African Development Bank (AfDB), Asian Development Bank (ADB), Ford Foundation and World Bank. The Governments of Nepal, Pakistan, and Sri Lanka provide logistical support for IWMI-related activities in these countries. Authors: Christopher A. Scott and J. Antonio Zarazúa are Research Scientist and Research Assistant, respectively, of the International Water Management Institute (IWMI), Mexico Program, and Gilbert Levine is a Senior Fellow, IWMI, Colombo, Sri Lanka. The authors wish to acknowledge with sincere appreciation the valuable collaboration of our Mexican partners, especially Ing. Marco Antonio Ortíz and Ing. Raúl Silva, Chief of Operations and General Manager, respectively, of the Water and Sewage Authority of the City of Guanajuato; Irene Cano and M. S. Elena Rodríguez of the Chemistry Department, University of Guanajuato, and the farmers in the Guanajuato basin. Finally, we wish to state that field data collection would not have been possible without the support of Francisco Flores, José Jesús Ramírez, and Paula Silva of the IWMI Mexico Program and Victoria Méndez of the University of Guanajuato. Scott, C. A., J. A. Zarazúa, and G. Levine. 2000. Urban-wastewater reuse for crop production in the water-short Guanajuato river basin, Mexico. Colombo, Sri Lanka. Research Report 41. Colombo, Sri Lanka: International Water Management Institute. /wastewater management / water quality / irrigation management / water shortage / legislation / river basins / environmental degradation / crop production / public health / water reuse / recycling / simulation models / field tests / Mexico/ ISBN 92-9090-404-6 ISSN 1026-0862 Copyright © 2000, by IWMI. All rights reserved. Responsibility for the contents of this publication rests with the authors. Please send inquiries and comments to: [email protected] The International Irrigation Management Institute, one of sixteen centers supported by the Consultative Group on International Agricultural Research (CGIAR), was incorporated by an Act of Parliament in Sri Lanka. The Act is currently under amendment to read as International Water Management Institute (IWMI). ii Contents Summary v Introduction 1 Wastewater Irrigation as a Global Practice 2 Wastewater Irrigation in Mexico 6 Field Research Program 10 Methods and Materials 11 Results and Discussion 13 Conclusions 22 Annex 1. Mexican Regulations on Wastewater Irrigation 25 Annex 2. Analytical Methods 30 Literature Cited 32 iii Summary Overview As is the case with most water management river basin in west-central Mexico. Through a practices, there are significant trade-offs selective literature review, we demonstrate how associated with irrigation using untreated urban common this practice is throughout the world and sewage. From a river-basin perspective, in Mexico specifically. Finally, we apply and wastewater irrigation is an important form of water validate the Interactive River Aquifer Simulation and nutrient reuse; however, there are important (IRAS) model, developed by Cornell University water quality, environmental, and public health and Resource Planning Associates, and evaluate considerations. This report explores the the outcomes of several alternative water advantages and risks of urban wastewater reuse management scenarios for water and soil quality for crop production in the water-short Guanajuato in the study area. Summary of Results Wastewater irrigation is a critical component of irrigated fields are within Mexican, EU, and US intensive water recycling in the Guanajuato river norms. Under current irrigation practices, the basin, based primarily on the value of the water buildup of heavy metals in soils is within EU and resource and the nutrients it transports. The 140 US norms. Based on simulation modeling of flow hectares of land irrigated with raw wastewater and nutrient transport, the annual gross values of downstream of the city of Guanajuato serve as de the wastewater and wasteload to farmers in the facto water treatment with significant retention of Guanajuato river basin, Mexico were estimated at contaminants. However, recycling does tend to US$252,000 and $18,900, respectively. As part of concentrate salts in the flows leaving the study its plan to install a wastewater treatment plant area. Measured coliform levels where high did and sell the water to commercial interests, the not, however, show significant evidence of direct city would need to consider how to recover this health impacts of wastewater irrigation. Heavy foregone economic benefit. metal concentrations in bed sediments and in v Urban-Wastewater Reuse for Crop Production in the Water-Short Guanajuato River Basin, Mexico Christopher A. Scott, J. Antonio Zarazúa, and Gilbert Levine Introduction Background reducing the degradation in water quality. This last has been of significant concern to the The need to understand water management from agricultural community for many years, a river basin perspective has been recognized for particularly in relation to salinization. In recent many years, and attempts have been made to years, however, concern has broadened, both in translate this understanding into action. Some of relation to the nature of the contamination, and in these attempts have been successful, and many terms of the communities affected. Within the others failures. Within the past few years, there agricultural community, there is increasing has been a resurgence of interest in regional recognition that agricultural activities contribute to authorities and basin councils, reflecting the degradation of water quality—through erosion increased recognition that it is impossible to and through contamination of surface water effectively manage water resources without aquifers with residues of agricultural chemicals considering management in a basin context and microorganisms. There also is growing (Molden 1997). This context explicitly concern about the quality of water available for acknowledges that the productivity and equity of irrigation (as well as for domestic water in rural water use cannot be understood by considering areas). the various uses and users as if they were This concern has grown, in significant part, independent (Seckler 1996). There also is as a result of the increased importance of increasing recognition that productivity and equity wastewater in the hydrology of many river are functions of the path of use of the water from basins. As urban populations grow, and as its source to a sink, where it is no longer industrial development expands, the volumes of available for use. This sink may be the wastewater produced increase at a rapid rate, atmosphere, a saline water body—subsurface and their composition becomes more complex. aquifer, lake, or the ocean—that cannot be used The waste streams often include industrial for productive purposes (including environmental), wastes, such as heavy metals, acids, and or a level of pollution that