Effect of dosing method and pH on color removal performance and floc aggregation of polyferric chloride–polyamine dual-coagulant in synthetic dyeing wastewater treatment

Two polyferric chloride–polyamine (PFC–EPI–DMA) dual-coagulants with different dosing methods were comparatively investigated in terms of color removal performance and floc aggregation in the treatment of synthetic disperse yellow and reactive red wastewater, and in comparison with PFC and EPI–DMA. The coagulation efficiency was studied by Jar-test, and Photometric Dispersion Analyzer 2000 (PDA 2000) was used to investigate floc aggregation process. The results showed that in two dual-coagulants treatment, PFC dosing followed by EPI–DMA dosing (PFC/EPI–DMA) achieved higher color removal rate for synthetic disperse yellow 201 wastewater, whereas reverse dosing order compared to the former (EPI–DMA/PFC) obtained better color removal performance for synthetic reactive red 24 wastewater. The optimal color removal efficiencies for treating disperse yellow 201 by PFC/EPI–DMA and reactive red 24 by EPI–DMA/PFC were both 97.5% at pH 6.0. The floc aggregation process showed that the floc growth rate of PFC/EPI–DMA was higher than that of EPI–DMA/PFC at the same dosage, whereas both Ratio and the time-weighted ratio variance (TWV) of PFC/EPI–DMA were almost lower than those of EPI–DMA/PFC in the treatment of disperse yellow 201. For reactive red 24 treatment, both floc growth rate and Ratio of EPI–DMA/PFC were higher than those of PFC/EPI–DMA, whereas TWV of EPI–DMA/PFC was lower than that of PFC/EPI–DMA. For disperse yellow 201 treated by PFC/EPI–DMA, the maximums of floc growth rate and Ratio were both reached at pH 6.0, whereas TWV was decreased as the increase of pH. For reactive red 24 treated by EPI–DMA/PFC, the maximums of three parameters were all reached at pH 4.5.