Removal of organic contaminants from river and reservoir waters by three different aluminum-based metal salts: Coagulation adsorption and kinetics studies

Surface waters from two different sources, river and reservoir, with different dissolved organic matter (DOM) concentrations and characters were investigated for removals using three metal coagulants, alum, a high performance aluminum polymer (HPAC) and polyaluminum chloride (PACl). Jar tests were conducted with coagulation pH ranging between 5.5 and 8.5 and doses between 5 and 16 mgAl/L. The adsorption mechanisms of DOM onto Al hydroxide precipitates of the three coagulants were investigated based on Freundlich, Langmuir and BET isotherm models. Coagulation kinetics and floc formation were studied using a photometric dispersion analyzer (PDA). For the three coagulants tested, optimum DOM removal was achieved at a coagulant dose of 11 mgAl/L and pH 6 for both waters. The lowest coagulant dose (5 mgAl/L) removed most organics with apparent molecular weights of between 2000 and 10,000 Da for both waters. DOM adsorption is best described by the BET isotherm model, indicating that DOM sorption occurred through multilayer formation in an arbitrary distribution of adsorbed particles. PACl showed the highest DOM adsorption capacity, determined by the Freundlich model. By PDA analyses, the flocculation index, average growth rate and variance values from the use of HPAC were highest in comparison with alum and PACl. The study of the coagulation kinetics suggested that HPAC produced the largest and most heterogeneous floc sizes with highest settling rates. (c) 2013 Elsevier B.V. All rights reserved.