混凝去除五价砷中试研究及絮体回流的强化效果

Pilot Study on Pentavalent Arsenic Removal by Coagulation and the Strengthening Effect of Flocs Recycling

采用中试和小试结合的方式研究了混凝去除地表水中五价砷的机制及絮体回流的强化效果.结果表明,砷在常规水处理流程各段的形态变化及去除率分配显示,原水中的As(Ⅴ)主要以溶解态存在,占总量的95%.溶解态的砷和总砷在快速混合、一级絮凝、二级絮凝、沉淀、过滤个单元去除率分别为87.92%、6.18%、2.38%、1.55%、1.23%以及1.10%、1.83%、2.20%、86.42%、7.38%,因此,混凝效果的好坏直接决定溶解态的砷向颗粒态砷的转化率以及含砷絮体的沉降性能.絮体对As(Ⅴ)表现出很强的吸附性能,其吸附速率符合拟二级反应动力学模型,以化学吸附为主.吸附等温线符合修正的Freundlich模型.当絮体回流点位于快速混合处时,回流比为50%时,絮体回流能很好地起到减少混凝剂投量,促进混凝除As(Ⅴ)的作用.

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%.