Effect of second coagulant addition on coagulation efficiency, floe properties and residual Al for humic acid treatment by Al13 polymer and polyaluminum chloride (PAG)

摘要

Influence of second dose on coagulation efficiency, floe re-growth, fractal structure and residual Al of the effluent in humic acid (HA) coagulation with Al_(13) polymer ([Al_(13)O_4(OH)_(24)(H_2O)_(12)]~(7+)) and PACl were comparatively investigated in this study. Effects of breakage shear on the floe properties generated in the coagulation with and without additional dose were also investigated. The results indicated that additional dose during breakage could essentially improve the HA removal efficiency and floe re-growth in both Al_(13) and PACl coagulations. Second doses of Al_(13) at 0.5 and 1.0mg/L resulted in better turbidity and UV_(254) removal as well as floe re-growth rather than higher additional dose of 1.5 and 2.0mg/L; while in PACl coagulation, more efficient HA removal and better floe re-growth were obtained at higher additional doses (1.0,1.5 and 2.0mg/L). Small additional Al_(13) could apparently increase the D_f of re-formed floes while the additional PACl displayed inconspicuous effect on floe D_f. The additional coagulant dose could alleviate the further decrease of re-grown floe size with increased breakage shear for both coagulants. The residual Al analysis implied that two-stage addition contributed to lower residual Al in effluent than one-time addition mode with the same total coagulant concentration.