Utilizing Water Treatment Residuals for Phosphorus Removal: Batch Trials,Column Trials and Effects of Three Low-Molecular-Weight Organic Acids

Phosphorus（ P） has been recognized as a major limited nutrient responsible for the eutrophication of surface waters. Water treatment residuals（ WTRs） are safe by-products of water treatment plants and are cost-efficient adsorbents. In this study, batch experiments and column experiments based on WTRs were employed to study the characteristics of P adsorption and the effects of lowmolecular-weight organic acids（ LMWOAs）（ citric acid, oxalic acid,and tartaric acid） on P adsorption. Different models of adsorption were used to describe equilibrium and kinetic data. The adsorption data were fitted well by a pseudo-second order kinetic model. The adsorption process was determined to be controlled by three steps of diffusion mechanisms through the intra-particle model.The adsorption equilibrium was well described by the Langmuir,Freundlich,Redlich-Peterson,and Sips isotherm models. Batch and continuous flow experiments indicated that the LMWOAs exhibited inhibitory action,and as pH increased,the inhibitory action became weaker for all the three acids. The effect of LMWOAs concentration was not significant on inhibition. The effects of LMWOAs were closely related to reaction time.