Optimization Of DMF Wastewater Treatment By Fenton Oxidation

The actual industrial wastewater with N.N-dimethylformamide（DMF）as main pollutant from Shandong chemical company was used as target pollutant and simulated water was studied.Fenton oxidation was selected to treat DMF simulated wastewater and the various factors of influencing removal efficiency were investigated,including pH value,reaction time,dosage of chemicals and inorganic anions.However,there are four problems in the treatment of Fenton oxidation containing large amounts of chemicals,narrow range of pH,lots of iron mud and great influence by inorganic anions,which may be improved by changing oxidants,using heterogeneous catalysts and recycling iron sludge.After being treated by Fenton oxidation,1000 mg/L simulated DMF wastewater（COD=900 mg/L）met discharge standard and COD value was lower than 100 mg/L.Through orthogonal test,the sequence of each factors on affecting oxidative performance followed as H₂O₂ dosage>n（H₂O₂）:n(Fe²⁺)>pH>reaction time.Based on single-factor experiments,the optimum conditions were as follows:the dosage of 30%H₂O₂ =40mL/L（16.5gH₂O₂/g△COD）,pH=2.0,n（H₂O₂）:n(Fe²⁺)=3:1 and reaction time=2.5h.The anionic effect experiments showed that Cl-had a strong inhibition effect on Fenton oxidation:the COD of effluent raised from 90 mg/L to 250 mg/L when Cl-raised from 0 mg/L to 1000 mg/L.The adverse impact can be eliminated by adding more H₂O₂,and the relation between H₂O₂ dosage and concentration of Cl-fitted the equation as follows:30%H₂O₂（mL/L）=0.1451Cl-（mg/L）+27.876.However,S_O4^2-almost had no effect on the reaction,and only when at a high concentration(SO₄^2->10g/L),it can accelerate the reaction to some extent.With the effect of inorganic anions in actual wastewater,the cost of treatment increased by 3 times of simulated wastewater.According to the effect of high concentration of SO₄^2-on degrading DMF,it was inferred that SO_4-·could performed better on treating DMF.So thermal activation of sodium persulfate to treat DMF wastewater was used,which could solve the problem of iron sludge and the range of pH at the same time.The optimum conditions were as follows:S2O82-=17g/L.reaction temperature=70℃,pH can be chosen freely（simulated water without adjustment as well）,reaction time=3 hours.In this condition,the effluent COD met standard,the tolerance of Cl-was 100 times higher than Fenton process,and the reagent cost can be reduced to 1/3 of Fenton process.Five kinds of materials were used in the preparation of ferrous heterogeneous catalysts to treat DMF wastewater,including ion exchange resin,activated carbon,molecular sieve,glass bead and quartz sand.However,these materials were not applicable:ion exchange resin was degraded in the reaction;activated carbon had shown positive effects on treatment,but it had the problems such as high color in effluent,slow reaction rate and high cost;molecular sieve,glass bead and quartz sand had no effect on DMF wastewater treatment.With acid dissolving and reduction,the iron sludge can be reused 2 times,and the discharge amount of iron mud can be reduced by 60%.Through the single-factor experiments,it can be concluded that the optimal pH of acid dissolution was 1.5,the acid soluble iron mud needs to be filtered before discharging into the recovery stage,and the optimum iron powder dosage was 0.75g/L.After recycling,the cost can be reduced to 1/2 of the original system.