Optimization Of Coagulation Process For Heavy Metals From Wastewater Using Uniform Design And Response Surface Methodology

As the water environment is not optimistic in nowadays, pollution abatementcan’t be an effective way to solve the water resource shortages’ situation at present,and the wastewater reuse have become a trend. Heavy metals pollution problem hascaused wide attention of the whole society in recent years. Because of the migrationbehavior of heavy metals in the environment and the hard degradation characteristics,as well as the migration of heavy metals between the soil environment and the waterenvironment, leading to the spread of the pollution, has caused a serious threat onhuman activities. This research based on flocculation method treating lowconcentration of manganese (Ⅱ), zinc (Ⅱ), arsenic (Ⅴ) from wastewater，and tooptimize the flocculation process use uniform design and response surfacemethodology.Using oxidant and flocculant polymeric aluminum chloride (PAC) to enhancedcoagulation treatment of low concentration of Mn (Ⅱ) from wastewater. Oxidant kindand wastewater pH value, oxidant dosage and flocculant dosage, and other singlefactors influence on the removal rate of Mn were considered, respectively; Combiningthe uniform design and response surface methodology investigate the influence ofmain factors on removal rate, the quadratic polynomial model was establishedbetween the main factors and the removal rate of Mn, optimal experimental resultsshow that wastewater pH value is7.53, oxidant sodium hypochlorite dosage is0.37ml/L, flocculant dosage is182.01mg/L, removal rate was98.96%, and the residualMn (Ⅱ) concentration is0.052mg/L.Flocculants was used to treat low concentration of zinc (Ⅱ) from wastewater,Flocculant kind and wastewater pH value, flocculant dosage, stirring rate and otherfactors influence on zinc removal rate were considered, respectively; Combining theuniform design and response surface methodology investigate the influence of mainfactors on removal rate, the two factor interaction model was established between themain factors and the removal rate of zinc, optimal experimental results show thatwastewater pH value is8.85, flocculant PAC dosage is65.00mg/L, removal rate is88.58%, zinc residual concentration is0.571mg/L.Using flocculants polymeric ferric sulfate (PFS) and polyaluminium ferricchloride (PAFC) to treat low concentration of As(Ⅴ) from wastewater,respectively.wastewater pH value, As(Ⅴ) initial concentration, flocculant dosage andother factors influence on As removal rate were considered; Combining the uniformdesign and response surface methodology investigate the influence of main factors onremoval rate, the quadratic polynomial model was established between the mainfactors and the removal rate of both flocculants, optimal experimental results showthat using PFS as the coagulant, the range of wastewater pH is7.5~8.5, the range offlocculant dosage is190~260mg/L, the removal rate is over96%and the As residues are less than0.05mg/L; using PAFC as the coagulant, the range ofwastewater pH is7.1~7.3, the range of flocculant dosage is170~290mg/L, theremoval rate is over95%, if the As(Ⅴ) initial concentration is about1.0mg/L，theresidues are less than0.05mg/L.Using the combination of uniform design and response surface methodology tooptimize the flocculation process of wastewater containing Mn (Ⅱ) treatment, zinc(Ⅱ) and As (Ⅴ). Optimization scheme of oxidants NaClO dosage is0.40ml/L aroundor about0.15ml/L,corresponding wastewater pH value is controlled in7.5or9.0, andflocculant PAFC dosage is between240~300mg/L, At the above condition, thetreated wastewater can achieve the Mn (Ⅱ), zinc (Ⅱ) and As (Ⅴ) requirement of Thereuse of urban recycling water-Water quality standard for groundwater recharge(GB/T19772—2005).