Evaluation of the Reuse of Baked-Alum Water Treatment Residual to Adsorb Phosphorous

Abstract

Excess phosphorous in waterways is known to be a cause of harmful algal blooms. This research evaluated if baking water treatment residuals (WTRs) would increase the number of adsorption sites, thereby increasing the WTRs ability to adsorb phosphorous. Initial 24-h sorption studies determined optimal baking temperatures of 175°C for alum based-WTR (Al-WTR) and 150°C for Al-WTR amended with power activated carbon (PAC) (PAC-WTR). Adsorption-desorption isotherm studies for baked Al-WTR (175°C) and PAC-WTR (150°C) found that there was a net desorption of phosphorous when distilled water was used as the background solution. When surface water was used, baked Al-WTR adsorbed more phosphorous at 5°C while baked PAC-WTR adsorbed more at 20°C. Continuous flow column tests were also conducted and found a sorption capacity of 7.91 mg PO4 g−1 WTR for baked Al-WTR that was less than as-is and 16.21 mg PO4 per kg-WTR, which was 83% better than its as-is counterpart. An analysis of all experiments found that as-is WTR performed better (p<0.05) than baked WTR and would be the recommended reuse of the water treatment plant’s WTR for the adsorption of phosphorous.