Assessment of the use of wastewater for irrigation in Mexico City

Abstract

The Mexico City Metropolitan Area generates as much as 56.6 m3/s of wastewater (Conagua, 2009b). For over a 100 years this untreated wastewater (predominantly from domestic sources) has been used to irrigate over 85 000 hectares of crops in the Mezquital Valley. Although several studies have shown the harmful effects on health and the environment from the direct application of untreated water, little research exists to evaluate its use in irrigation while taking into account salinity and sodicity. This study evaluated wastewater from the three main drainage channels (Grand Drainage channel, Central Outlet Tunnel and El Salto River) using quality criteria for irrigation water. The results indicate that the water does not comply with current Mexican guidelines for electric conductivity, total dissolved solids, turbidity and bicarbonate and sodium ions. Regarding salinity and sodicity, these waters can be directly used as long as the characteristics of the soil to which it is going to be applied are taken into account (such as the use of salt-tolerant crop species) and certain management practices are performed (such as leaching). Since prolonged irrigation with this water over time could affect the soil, treating the water before its direct use is recommended.