Effect of additional polyaluminum chloride and polyacrylamide on the evolution of floc characteristics during floc breakage and re-growth process

Effect of additional coagulant on floc breakage and re-growth process was investigated regarding coagulation performance and floc properties. Polyaluminum chloride (PACl) and cationic polyacrylamide (PAM) were used as additional coagulants and dosed at half way of the first breakage stage. The results indicated that additional coagulant was conductive to floc re-growth after first breakage regardless of coagulant type. Moreover, additional PACl still facilitated floc re-growth after second breakage. Compared to PACl, additional PAM couldn't enhance floc re-growth after second breakage. Results of different additional dosages showed that floc recoverability after first breakage was elevated with increasing additional PACl dosage, but presented initially increasing and then decreasing trend when higher PAM dosage was added. In addition, floc recoverability after second breakage was elevated at higher dosages of additional PACl, whereas floc recoverability after second breakage with additional PAM was nearly same as that without additional PAM. It seems likely that the inactive surface points and coverage extent of broken flocs were dominant parameters for PACl addition and PAM addition, respectively.