Water treatment residuals amended soils release Mn, Na, S, and C

Drinking water treatment facilities remove impurities from raw water sources using various chemicals. The by-product produced from the purification process is called water treatment residuals (WTR). If WTR contain residual chemicals from the purification process, soluble elements may be released potentially causing chemical imbalances in soil and groundwater systems. The study objectives were to: (i) examine Mn, Na, S, and total organic carbon (TOC) released from soil and deionized water leachate from a Norfolk soil (fine-loamy, kaolinitic, thermic Typic Kandiudult) incubated for 60 days with 0 (untreated) and 60 g kg(-1) of three different WTR; and (ii) assess effects of oxidation-reduction potential on Mn stability and solubility. The WTR were obtained from a North and South Carolina drinking water treatment facility that treated raw water using alum [Al(2)(SO(4))(3)], caustic soda (NaOH), and potassium permanganate (KMnO(4)). During incubation, treatments were maintained between 5% and 10% moisture, and oxidation-reduction potential was measured using a pit electrode. After 60 days, treatments were leached with 1.2-pore volumes of deionized water. Soils were then analyzed for Mn, Na, and S, and leachates were analyzed for TOC and similar elements using inductively coupled plasma spectroscopy. At this time, WTR-treated soils were slightly acidic, moderately reduced, and enriched in extractable Mn, Na, and S concentrations. Water leachates from WTR-treated soil were also enriched with Mn, Na, S, and TOC. Divalent Mn was the dominant oxidation state, making Mn more susceptible to leaching. One WTR enriched with Mn caused Norfolk soil Mn concentrations to exceed crop sensitive stress threshold levels. It is recommended that a prescreening procedure should be used to determine if WTR applied to soil will release elements that may cause plant growth problems.