Drinking Water Treatment Residuals: A Reveiw of Recent Uses

Coagulants such as alum, [Al2(SO4)3X14H2O], ferric chloride [FeCl3], or ferric sulfate [Fe2(SO4)3] are commonly used to remove particulate and dissolved constituents from water supplies in the production of drinking water. The resulting waste product, called water-treatment residuals (WTR), contains precipitated Al and Fe oxyhydroxides resulting in a strong affinity for anionic species. Recent research has focused on using WTR as cost-effective materials to reduce soluble phosphorus (P) in soils, runoff, and land-applied organic wastes (manures and biosolids). Studies show P adsorption by WTR to be fast and nearly irreversible, suggesting long-term stable immobilization of WTR-bound P. Because excessive WTR application can induce P deficiency in crops, effective application rates and methods remain an area of intense research. Removal of other potential environmental contaminants [ClO4, Se(+IV and +VI), As(+III and +V), Hg] by WTR has been documented, suggesting potential use of WTRs in environmental remediation. While creation of Al plant toxicity and enhanced Al leaching are concerns expressed by researchers, at circumneutral soil pH conditions these effects are minimal. Radioactivity, trace element levels, and enhanced Mn leaching have also been cited as potential problems in WTR usage as a soil supplement. However, these issues can be managed so as not to limit the beneficial use of WTRs in controlling off-site P losses to sensitive water bodies or reducing soil-extractable P concentrations