Organic Micropollutant Removal by a Nanofiltration Pilot Plant used to Treat Spring Water from a Wastewater-Irrigated Valley

Abstract

The abundance of freshwater springs in the Tula Valley is well documented. Large quantities of untreated wastewater from Mexico City are used for irrigation purposes, with the resultant emerging springs. Studies are needed to assess how safe water is to be supplied to the community. Comparative membrane studies were done on lab-scale, from which NF270 membrane was selected for a pilot plant in situ (critical flux 185Lm^-2h^-1). The system was successful at removing natural organic matter, hardness and pathogenic content. On-site membrane pretreatment using microfiltration and softening allowed moderate recoveries (60%) and slow permeate flux losses (124-90Lm^-2h^-1). Micropollutant (MP) removal was greater than 90% for most of the pharmaceuticals, hormones and phthalates using spiked spring water. However, moderate and variable removals were found when the concentrations of MPs were very low. Molecular structure and hydrophobicity were loosely related to the removal rates of the compounds evaluated, however an accumulating effect on the membrane might be key for higher MP removals. A threshold of concentration could have to be overcome to allow the removal process to achieve a better performance. In consequence, optimization of a large-scale process is the next step to take.