Coagulation of low temperature and low turbidity water: Adjusting basicity of polyaluminum chloride (PAC) and using chitosan as coagulant aid

This study evaluated the feasibility of integrating high-basicity polyaluminum chloride (PAC) and high-viscosity chitosan for the coagulation of low-temperature and low-turbidity water. The effects of PAC basicity on coagulation performance and residual Al control were also investigated. It was found that higher-basicity PAC with a larger proportion of Al-c (colloidal Al species in PAC) and smaller proportion of Al-a (monomeric Al species in PAC) was beneficial for removing turbidity and natural organic matter (NOM), as well as controlling the residual Al content. Further, the integration of PAC with a high basicity (90.3%) and chitosan with a high viscosity (500 mPa.s) realized the efficient removal of turbidity and NOM, with removal efficiencies of approximately 87%, 63%, and 82% for turbidity, dissolved organic matter (DOC) and UV254, respectively. It was speculated that larger and more settleable flocs tended to form via the synergistic effect of charge neutralization by Al-b (polymeric Al species in PAC) and interparticle bridging by both the Al-c species and chitosan, consequently leading to excellent coagulation performance. This study may provide a useful option to drinking water treatment operators for dealing with low-temperature and low-turbidity water in practice.