Effect of Municipal Wastewater Effluent On Arsenic Sorption to Desert Soils.

Chronic low-level exposure to arsenic has been found to increase health risks.  In January 2006, the Environmental Protection Agency lowered the maximum contaminant level for arsenic in drinking water to 10 parts per billion (ppb).  This affected many communities, and forced them to develop procedures for lowering arsenic in their drinking water.  Disposal of arsenic residuals is a problem that must be considered when developing such a procedure.  A simple and low cost solution is to land apply the arsenic concentrates with the municipal wastewater effluent.  To insure the efficacy of this disposal method, experiments were performed to assess arsenic sorption parameters, including retention values, when arsenic is added to soil as part of the wastewater stream.  In this study, the sorption of arsenate [As(V)] on soil was measured in the presence and absence of wastewater effluent.  Kinetic batch experiments were carried out on three diverse soils (sandy loam, clay loam and clay) collected from a land application facility in southern New Mexico.  Arsenate solutions were equilibrated with the soils for 2 to 504 h.  The presence of wastewater effluent decreased the retention of As(V) on all soils at all reaction times.  Thus, it appears that while soil is typically an effective sorbent for As(V) in ‘clean’ aqueous solutions, when the contaminant is added with wastewater effluent the sorption capacity of the soil is decreased.  This work has important implications for land application practices and soil monitoring.