A Study on the Behaviour of Polyaluminum Chloride/chitosan Composite Coagulant for Water Treatment Process

The aim of this study is to develop novel composite coagulants that are versatile and effective in removing natural organic matter from water. Herein, novel polyaluminum chloride-chitosan composite coagulant was prepared by combining the two reagents at different chitosan/aluminum ratio. The coagulation performance was tested using two different water sources (synthetic water containing 10 mg.L dissolved organic carbon (DOC) and water samples from Myponga reservoir) in a conventional jar test apparatus. Test using synthetic water showed that DOC removal was more favourable at pH ≤ 6 while opposite behaviour was observed for natural water. For synthetic water samples, both polyaluminum chloride (PACl) and PACl-chitosan composite coagulant demonstrated similar maximum DOC percentage removal of approximately 80±5 % whereas the best DOC removal efficiencies for water samples from Myponga reservoir was approximately 40±5% at 4.32 mg Al.L. For synthetic water sample, the composite coagulant was able to achieve the same removal efficiency as PACl at a lower Al dose. Sizing analysis shows that chitosan aids in polymer bridging which leads to an increase in the floc size, thereby improving its removal. Further analysis using resin fractionation and high performance size exclusion chromatography were performed to elucidate how differences in the organic character of the two water samples affects their removal. The results showed that NOM in synthetic water was easier to be removed by coagulation in comparison to natural water. This is because of the different sizes and constitution of NOM between synthetic (contains high aromatic content and large molecular weight) and natural (contains higher aliphatic content and lower molecular weight) water.