Study On Treatment Process For Papermaking Wastewater

In this paper, the merit and demerit of currently domestic and foreign technics used to treat wastewater of regenerate paper and paper-plant mid-stage wastewater is summarized on the basis of fully understanding the process of paper making industry and the characteristics of paper making wastewater. Furthermore the progress trend of these technics and the mechanism of coagulation sedimentation, iron carbon micro electrolytic method, biochemical process and chlorine dioxide oxidation process are analysed. The "coagulation sedimentation-iron carbon micro electrolytic-SBR-chlorine dioxide oxidation" combined treating process was studied to deal with paper-plant mid-stage wastewater. The "hydrolytic acidification-SBR-microfiltration" combined treating process was studied to deal with paper-plant mid-stage wastewater.Iron-carbon micro-electrolysis process combined with coagulation was used to pretreat wastewater of regenerate paper. The types of coagulants, pharmaceutical dosage, coagulation time in coagulation unit and the effect of initial pH of raw water, total iron and carbon, proportion of iron and carbon, hydraulic retention time as well as after the reaction of the pH in micro-electrolysis unit were investigated. The optimal condition of the process were determined. The results show that the best coagulant was Ca (OH)2, the pharmaceutical dosage was4g/L, the coagulation time was40min, the dosage of iron and carbon was20g/L, the proportion of iron and carbon was3:1, the initial pH was3.0, the effluent pH was8.0and the reaction time was40min. Under these conditions, the removal rates of CODCr, ammonia nitrogen, total phosphorus, SS and BOD5were reached to52.88%,43.08%,93.61%,91.64%and33.19%. Biodegradability increased from0.32to0.46at the same time, the pollution load of subsequent biochemical treatment process was reduced. The SBR was used to treat the waste water which was after pretreatment. The reaction time, dissolved oxygen and temperature were investigated. The optimal condition of the process were determined. The results show that the best reaction time was10h, the dissolved oxygen was4mg/L, the reaction temperature was27-38℃. The removal rates of CODCr, ammonia nitrogen, total phosphorus, SS and BOD5were reached to82%,94%,77.22%,100%and98%. The chlorine dioxide oxidation was used to treat the waste water which was after the SBR. The results show that the best reaction time was30min, the pharmaceutical dosage of chlorine dioxide was100mg/L. After the reaction, the COD。ammonia nitrogen, total phosphorus and SS were80mg/L,0.62mg/L,0.45mg/L and0. The operating results showed that quality of the outlet water reached the Discharge Standard of Water Pollutants for Pulp and Paper Industry (GB3544-2008). The "hydrolytic acidification-SBR-microfiltration" combined treating process was studied to deal with paper-plant mid-stage wastewater. After experimental treatment, the total removal rates of CODr, ammonia nitrogen, total phosphorus, SS and TOC were91.8%,93.8%,94.7%,100%and91.4%. The operating results showed that the quality of the outlet water wrer reached the Discharge Standard of Water Pollutants for Pulp and Paper Industry (GB3544-2008). The membrance unit was placed at the back of the biochemical reaction, which reduced membrane pollution and had certain interception effect on the polluted materials.