Heavy Metals & Wastewater Reuse

Abstract

Water shortages in the Western United States have intensified the search for new sources. Wastewater reuse is being increasingly called upon to augment existing supplies. One potential impediment to the continued expansion of wastewater reuse efforts is the accumulation of toxic heavy metals and other salts in the recycled water. Conventional and advanced wastewater treatment effect the removal of a portion of the heavy metals added during use. Removal is by chemical precipitation and adsorption and disposed of with the sludges. Potential uses of treated wastewater effluents include irrigation and groundwater recharge. Care must be taken to prevent contamination of groundwater, especially since existing wells have been reported to have concentrations of heavy metals in excess of drinking water standards. Percolation of wastewaters through soils (especially fine soils) results in a reduction in heavy metal concentrations. It is postulated that removal of these metals is by a combination of chemical precipitation with filtration of the precipitates, and adsorption on soil particles (thus the effectiveness of fine soils). Long term saturation of the soils with heavy metals may result in a "breakthrough" contamination of the groundwater. A predictive model of heavy metal-wastewater-soil interactions is proposed to aid in the design and regulation of wastewater reuse systems to eliminate or minimize this problem.