Phosphorus Retention Mechanisms of a Water Treatment Residual

Water treatment residuals (WTRs) are a by-product of municipal drinking water treatment plants and can have the,capacity to adsorb tremendous amounts of P. Understanding the WTR phosphorus ad-sorption process is important for discerning the mechanrism and tenac-ity of P retention. We studied P adsorbing mechanism(s) of an alumi-num-based [A12(SO 4),14H 2O] WTR from Englewood, CO. In a laboratory study, we shook mixtures of P-loaded WTR for 1 to 211 d followed by solution pH analysis, and solution Ca, Al, and P analysis via inductively coupled plasma atomic emission spectroscopy. After shaking periods, we also examined the solids fraction by X-ray diffrac-tion (XRD) and electron microprobe analysis using wavelength dis-persive spectroscopy (EMPA-WDS). The shaking results indicated an increase in pH from 7.2 to 8.2, an increase in desorbed Ca and Al concentrations, and a decrease in desorbed P concentration. Th