Adsorption of Phosphorus Using Water Treatment Sludge

Abstract

In line with global sustainable development the search for cost effective and eco-friendly disposal options for water treatment sludge continues to be an urgent priority. In this study, the phosphate adsorption potential of three types of water treatment sludge, namely; alum sludge, lime sludge and lime-iron sludge were investigated through a series of batch experiments. All three sludges exhibited potential for phosphate removal however; lime-iron sludge produced the highest adsorption capacity which was 34 and 52% higher than that for lime sludge and alum sludge, respectively. Phosphate adsorption using alum sludge favoured slightly acidic conditions (pH 4) while lime sludge and lime-iron sludge favoured slightly basic conditions at pH 8. Mathematical simulation of the adsorption process was conducted using linear and non-linear regression. Adsorption kinetics was analyzed using the pseudo-first-order, pseudo-second-order, intraparticle diffusion and diffusion-chemisorption models. The goodness of fit was assessed using the coefficient of determination (R2), the Relative Percent Error (RPE) Marquardt’s Percent Standard Deviation (MPSD) and Hybrid Error Function (HYBRID). The diffusion-chemisorption model produced the highest correlation to reaction variables for all sludges tested. It was successfully used to predict process kinetics which can aid in the eventual development of full-scale design.