Research On Process And Effect Of PVA Production Waste Water Treatment

The dramatic increase in the production capacity of polyvinyl alcohol（PVA）has made it difficult to treat production wastewater containing PVA,which has seriously affected the sustainable development of the industry.Considering the high pollutants’concentration,poor biodegradability,and difficulty in meeting the discharge standard of PVA production wastewater,this study used the combined process of"coagulation+Fenton+biochemical"and investigated treatment performance of the process on PVA production wastewater,further clarifying the optimal process parameters to achieve up-to-standard discharge.The research results can provide new technological measures for the treatment of PVA production wastewater,which have promising application prospects.The main findings are as follows:（1）Organic matter in wastewater was removed via coagulation sedimentation process.The commonly used coagulants were screened by comparing the produced flocs and the treatment effect and poly aluminum ferric chloride（PFC）was selected as the coagulant in this study.Meanwhile,polyacrylamide（PAM）was added together with PFC to improve the treatment effect.And we optimized the coagulation sedimentation process conditions.The results showed that the coagulation effect was the best when the dosage of PFC and PAM were 0.7 g/L and 0.07 g/L,respectively,and the coagulation speed kept at 350 r/min with pH at 7.The removal rates of COD,TN,TP,NH₃-N and chroma reached 62.22%,56.30%,45.60%,40.30%and 69.34%,respectively.（2）According to the results of response surface analysis of COD removal rate,it was found that PAM dosage and pH value had a significant impact on COD removal rate,and the interaction of PFC and PAM dosage also had a significant impact on it.Through the optimization analysis of the regression model,the optimal conditions for removing COD in wastewater by coagulation sedimentation process were verified:the dosages of PFC and PAM were 0.74 g/L and 0.07 g/L,respectively,stirring speed was353.73 r/min with pH kept at 7.49.And the model predicted that the COD removal rate could reach 67.69%under the optimal condition.（3）The residual COD concentration in wastewater after coagulation and sedimentation was 2200～2500 mg/L,and the B/C value was 0.26.The Fenton method was employed to treat wastewater subsequently.The results showed that Fenton oxidation effect was the best with the COD removal rate reaching 63.50%when adding13.33 g/L of hydrogen peroxide,6 g/L of ferrous sulfate and keeping the reaction time at 120 min with pH at 3.The influence of various factors on the Fenton treatment effect was determined by orthogonal experiment.The dosage of H₂O₂exhibited the maximum influence,followed by that of Fe SO₄·7H₂O,then pH value and reaction time.The temperature of wastewater had the minimal influence on the treatment effect in the oxidation process.We further analyzed the reaction kinetics of the removal efficiency of Fenton oxidation on COD and founded that it followed the first order reaction kinetics model.（4）After Fenton oxidation process,the COD,TN,and TP in the wastewater were reduced to 800～1200 mg/L,4.0～5.0 mg/L,1.0～1.2 mg/L,respectively,and the value of B/C was risen to 0.6.Then,wastewater was further treated by SBR reactor to explore the influence of temperature（T）,pH,aeration time,sludge concentration,and dissolved oxygen（DO）on the performance of SBR reactor.Whilst,we changed the influent COD concentration to test the impact load capacity of the reactor.The results showed that the performance was the best with the removal rates of COD,TN and TP all above 89%when sludge concentration was 3000 mg/L and operating mode of the reactor followed the proceeding"instantaneous water inflow-anoxia stirring 2 h-aeration 7 h-sedimentation 2 h-instantaneous drainage-idling 1 h"（T=25℃,pH=7,DO>3.0mg/L）.（5）The effluent quality changes during 30 operating cycles were monitored in order to study the treatment effect of the combined process"coagulation-Fenton oxidation-SBR reactor"on treating PVA production wastewater.The results showed that this combined process had excellent and stable treatment effect with the effluent COD,TN,TP,NH₃-N concentrations and chroma reduced to 80～100 mg/L,4.0～4.5mg/L,0.3～0.5 mg/L,0.003～0.005 mg/L and 5～6 times,respectively.We further analyzed the economics of the combined process for PVA wastewater treatment,comprehensively considering the costs of electricity,pharmaceuticals,operation and maintenance.and the calculated cost of treating PVA production wastewater per ton was about 28.13 yuan.Compared with other treatment methods,this combined process has advantages of better treatment effect and low operating cost,thus,having a good industrial application prospect.