[Pilot study on pentavalent arsenic removal by coagulation and the strengthening effect of flocs recycling]

The pilot and bench scale studies on pentavalent arsenic removal by coagulation and the strengthening effect of flocs recycling were performed. The results show that above 95% As (V) in the raw water exists in the form of dissolved As (V). Furthermore, the removal efficiencies of dissolved arsenic and total arsenic by mixing, first flocculation, second flocculation, sedimentation, filtration units were 87.92%, 6.18%, 2.38%, 1.55%, 1.23% and 1.10%, 1.83%, 2.20%, 86.42%, 7.38% respectively. Therefore, conversion rate of dissolved As(V) into particulate As(V) and the settlement performance of flocs were strongly dependent on the coagulation effect, which determined the As(V) removal efficiency in the whole system. Flocs have a strong adsorption capacity for As(V) and the adsorption obeys a second order reaction kinetics and well fits the modified Freundlich model. Flocs recycling can obviously promoted the As(V) removal by enhanced coagulation and reduce the dosage of coagulant with recycling point set at rapid mixed site and recycling ratio at 50%.