Effect of aging period on the characteristics and coagulation behavior of polyferric chloride and polyferric chloride-polyamine composite coagulant for synthetic dying wastewater treatment

In this paper, a new composite inorganic-organic coagulant (PFC-EPI-DMA) was prepared by polyferric chloride (PFC) and epichlorohydrin-dimethylamine (EPI-DMA) under a given EPI-DMA/Fe and OH/Fe molar ratio. In comparison with PFC, the Fe (III) species and zeta potential of PFC-EPI-DMA were measured. Then their coagulation performance and coagulation kinetics for treating synthetic reactive dying wastewater were investigated. The results showed that the content of Fea and Feb in PFC-EPI-DMA and PFC coagulants decreased with increasing aging period. Compared to PFC, PFC-EPI-DMA had higher content of Fea but lower content of Feb and Fec. The zeta potentials of two coagulants decreased with increasing aging period within all tested pH range. For the treatment of reactive red 24, the color removal efficiency treated by PFC-EPI-DMA decreased, while that treated by PFC remained almost constant with increasing aging period. However, the color removal efficiencies of reactive blue 14 treated by two coagulants both decreased with increasing aging period. The results of floc aggregation process confirmed that with increasing aging period, the orders of floc growth rate, ratio and TWV treated by two coagulants were complicated.