Alternative cost-effective preparation method of polyaluminium chloride (PAC) coagulant agent: Characterization and comparative application for water/wastewater treatment

Abstract

An alternative preparation procedure for polyaluminium chloride (PAC), a common inorganic coagulant, is presented in this paper. The proposed procedure is based on the use of granular aluminium metal, a common by-product of several aluminium-processing secondary industries, instead of using Al2O3 (or of using a mineral containing Al2O3) which is commonly applied by most industrial producers, and exhibits important benefits such as energy and time saving during the preparation procedure. Several efforts have been made to produce the pre-polymerized coagulant with properties, similar to the properties of a commercially available PAC solution, using appropriate, commonly found laboratory equipment and without the application of extreme conditions (in terms of temperature or pressure). The laboratory prepared PAClab was characterized mainly by means of aluminium content, basicity, density and aluminium species distribution. Furthermore, the coagulation performance of PAClab was evaluated for the treatment of contaminated tap water and of wastewater samples and it was compared with the performance of a commercially available PAC solution. Finally, the coagulation–flocculation kinetics was examined with the use of Photometric Dispersion Analyzer instrument (PDA) and the floc growth rates between the two coagulants were compared. The results suggest that PAC can be alternatively produced under mild conditions, resulting in a product with better properties than the commercial PAC used for comparison. Additionally, if the preparation takes place in industrial scale, a greater improvement is further feasible, due to the common equipment used, instead of using e.g. autoclaving.