Field assessment of wastewater treatment facilities in the Oaxaca Valley, Mexico

Latin America and the Caribbean is the most urbanized region in the developing world. However, less than 10 percent of domestic and industrial wastewater is properly treated, causing severe environmental, health, social and economic problems. Over the past several years, Mexico has undertaken significant sanitation projects including wastewater treatment projects. State and federal water agencies have assisted both semi-urban and rural communities construct over 80 municipal wastewater treatment plants in the State of Oaxaca in southern Mexico. From July 2006 through February 2008, an investigation was conducted to evaluate ten (10) wastewater treatment systems in Oaxaca, Mexico. Nine (9) systems utilized vegetated gravel bed treatment systems and the tenth system used wastewater stabilization ponds. The objectives of the investigation were to understand the factors that motivated the communities to install wastewater treatment systems, select the type of systems, costs of the systems, and to review the design and construction of the projects. The evaluation also evaluated the social, political, economic and technical factors affecting the performance, operation and maintenance of the plants. The study found that the majority of the systems were in poor operating condition. The poor operating systems resulted from various factors including engineering designs using dated and inaccurate design criteria, inadequate operation and maintenance, and in some instances substandard construction practices.