title: Effect of water treatment additives on lime softening residual trace chemical composition--implications for disposal and reuse.
abstract: Drinking water treatment residues (WTR) offer potential benefits when recycled through land application. The current guidance in Florida, US allows for unrestricted land application of lime softening WTR; alum and ferric WTR require additional evaluation of total and leachable concentrations of select trace metals prior to land application. In some cases a mixed WTR is produced when lime softening is accompanied by the addition of a coagulant or other treatment chemical; applicability of the current guidance is unclear. The objective of this research was to characterize the total and leachable chemical content of WTR from Florida facilities that utilize multiple treatment chemicals. Lime and mixed lime WTR samples were collected from 18 water treatment facilities in Florida. Total and leachable concentrations of the WTR were measured. To assess the potential for disposal of mixed WTR as clean fill below the water table, leaching tests were conducted at multiple liquid to solid ratios and under reducing conditions. The results were compared to risk-based soil and groundwater contamination thresholds. Total metal concentrations of WTR were found to be below Florida soil contaminant thresholds with Fe found in the highest abundance at a concentration of 3600 mg/kg-dry. Aluminum was the only element that exceeded the Florida groundwater contaminant thresholds using SPLP (95% UCL = 0.23 mg/L; risk threshold = 0.2 mg/L). Tests under reducing conditions showed elevated concentrations of Fe and Mn, ranging from 1 to 3 orders of magnitude higher than SPLP leachates. Mixed lime WTR concentrations (total and leachable) were lower than the ferric and alum WTR concentrations, supporting that mixed WTR are appropriately represented as lime WTR. Testing of WTR under reducing conditions demonstrated the potential for release of certain trace metals (Fe, Al, Mn) above applicable regulatory thresholds; additional evaluation is needed to assess management options where reducing conditions may develop.
authors: Department of Environmental Engineering Sciences, University of Florida, P.O. Box 116450, Gainesville, FL 32611-6450, USA.
authors: Weizhi
authors: W
authors: Cheng
authors: Department of Environmental Engineering Sciences, University of Florida, P.O. Box 116450, Gainesville, FL 32611-6450, USA.
authors: Justin
authors: J
authors: Roessler
authors: Department of Environmental Engineering Sciences, University of Florida, P.O. Box 116450, Gainesville, FL 32611-6450, USA.
authors: Nawaf I
authors: NI
authors: Blaisi
authors: Department of Environmental Engineering Sciences, University of Florida, P.O. Box 116450, Gainesville, FL 32611-6450, USA. Electronic address: ttown@ufl.edu.
authors: Timothy G
authors: TG
authors: Townsend
mesh_terms: D000534:Alum Compounds / Q000032:analysis; D017610:Calcium Compounds / Q000032:analysis; D005290:Ferric Compounds / Q000032:analysis; D005431:Florida; D060587:Groundwater / Q000032:analysis*; D010087:Oxides / Q000032:analysis; D059027:Recycling; D012989:Soil Pollutants / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*; D018508:Water Purification; D014880:Water Softening / Q000379:methods*
chemical_list: D000534:Alum Compounds; D017610:Calcium Compounds; D005290:Ferric Compounds; D010087:Oxides; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; C041524:aluminum sulfate; C016538:lime
keywords: Leaching; Metals; Recycling; Reducing condition; Sludge; Solid waste; Waste management