Removal Of Humic Acid In Water By Enhanced Coagulation-dissolved Air Flotation(DAF) Process

The removal efficiency of humic acid in water by coagulation-sedimentation process (CS) and coagulation-dissolved air flotation (CDAF) process was assessed by the static jar test. A series of contrast experiments were carried out to study the chemical and hydraulic effect factors of inorganic polymer flocculant(PAC , PFC) on removing humic acid(HA) in water by enhanced coagulation-dissolved air flotation process with measuring the following water quality index of UV,TOC,CODMn and turbidity. The optimum chemical and hydraulic effect factors scopes were determined.The results showed that the broader dosage scope of stable removal ratio was found in coagulation-sedimentation (CS) process than coagulation-DAF (CDAF) which removed more HA (in un-filtrated water). As to removal of dissolved HA,CDAF process had a better performance than CS one at some low doses,but at doses more than these the trend was opposite.Furthermore,CDAF process retarded 0.5-1.2 pH unit from the initial point of the optimum pH scope 4.5-8.2 in CS.The optimum operational conditions of CDAF were:(1)The optimum dose scopes of PAC are 1.7-2.4mmol/L and that of PFC are 0.19-0.56mmol/L, 0.75mmol/L.(2)The optimum pH scopes of PAC are 6 - 8.1 and that of PFC are 8 -10, 5- 6.5.(3)The optimum ion intensity of PAC and PFC is less than 0.001mol/L.(3)The optimum hydraulic conditions :the optimum coagulation Mixing intensity scopes are 250-750s-1 (as PAC), 250-500s-1 (as PFC),the optimum coagulation Mixing time scopes arel5 - 120s(as PAC and PFC),the optimum flocculation Mixing intensity scopes are 20-200s-1 (as PAC) 20- 100s-1(as PFC),the optimum flocculation Mixing time scopes are 3 - 10min(as PAC), 3- 8min (as PFC) .(5)The optimum recycle ratio scopes of PAC are 10% -15%, The optimum recycle ratio scope of PFC is 10%.(6)The removal efficiency of humic acid was increased indistinctively by co-flocculation.