Effect of fresh aluminum hydroxide gels on algae removal from micro-polluted water by polyaluminum chloride coagulant

摘要

Polyaluminum chloride (PAC) coagulant, a most commonly used inorganic coagulant, was prepared using fresh aluminum hydroxide gels under the low energy consumption. The aim of this study was to investigate the influence of fresh aluminum hydroxide gels on the characteristics of PAC and the algae removal from micro-polluted water. The results suggested that PAC with the basicity values (OH/Al) of 2.5 and 2.0 synthesized by this method possessed the high content of middle polymeric aluminum (Al-b2). And fresh aluminum hydroxide gels contributed to the formation of Al-b2. Adding fresh aluminum hydroxide gels in the aging period temporarily increased the small/middle polymeric aluminum (Al-b) content that rapidly reduced with the time extending since fresh aluminum hydroxide gels accelerated the aluminum hydrolysis. The excessive fresh aluminum hydroxide gels would aggravate the decrease of Al-b content. The presence of fresh aluminum hydroxide gels in PAC slightly reduced the coagulation efficiency, but the performance deterioration resulted from overdosing was weakened in the cases. Besides, the residual aluminum concentrations in the treated water were always low as fresh aluminum hydroxide gels induced the generation of colloidal aluminum hydroxide particles. Charge neutralization was not the only coagulation mechanism in this treatment. (c) 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.