Study on Treatments of Specific Papermaking Effluents Using Electrocoagulation Technology

• Main Authors: Zhen-Zong Xiao, 蕭振宗
• Other Authors: Yuan-Shing Penrg
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/47624917124251237709

碩士 === 大葉大學 === 環境工程學系碩士班 === 98 === In pulp and paper industry, the production processes consisted of 2 major parts of pulping and papermaking. The sources of effluents are also different depending on the raw materials, processes, products genres and discharging units. In the production processes, various chemical additives are often applied, such as sizing agents, fluorescent optical brightening agents (OBAs), starches, alum (aluminum sulfate), dyestuffs etc., which cause water quality of the effluent streams to constantly vary, After several cycles of white water recirculation, the chemical variables of papermaking system wet end tend to increase, and harmful pollutants such as stickies also tend to accumulate, causing white water quality to become even more complicated. In this study, we simulated mill process effluents as the treatment targets and used a bench-top electrocoagulation (EC) unit to treat the effluents and make comparisons to traditional chemical coagulation treatments. We applied a factorial experimental design to investigate the effects of 3 different variables: electrical current density, hydraulic retention time, and types of electrode materials, on the treatment efficacies against pollutants such as OBAs, stickies, and dyestuffs using different treatment methods and variable conditions. Morphology of the various flocs formed in the treatment was also observed with a scanning electron microscope (SEM). The experimental results indicated that compared to traditional chemical coagulation methods, the EC system could effectively enhance the removal of electrical conductivity, SS, COD, true color, turbidity, OBAs, and stickies deposits. EC system treatments of the simulated OBA effluents indicated that for the disulfo-OBA (2S-OBA) effluent, the best results of iron and aluminum electrodes could remove 93.5, 90.5, and 35.7%; and 99.9, 97.4 and 36.8% of OBA, SS, and electrical conductivity, respectively. For the simulated tetrasulfo-OBA (4S-OBA) effluent, the iron and aluminum electrodes were capable of removing 89.0, 98.5, and 39.1%; and 83.6, 96.6, and 40.0% of OBA, SS and electrical conductivity, respectively. Overall, removal efficiency of the 2S-OBA was better than that of the 4S-OBA effluents, mainly because it has a higher hygrophobicity. The aluminum electrode set showed a better treatment results than did the iron one under high current densities. Treatment of simulated stickies-containing effluent with the EC system indicated that iron and aluminum electrodes could remove 41.0, 93.1, 83.3, 99.1, and 80.3%; and 33.9, 99.2, 80.0, 98.3, and 92.1% of the electrical conductivity, SS, COD, turbidity, and stickies deposit, respectively. The aluminum electrodes performed better than did the ctrodes under higher current densities. .As for the treatment of simulated dyestuff effluents, the EC system removed 45.8% electrical conductivity, and 97.4% true color with the iron electrodes; and 22.6% of electrical conductivity and 69.6% true color with the aluminum electrodes. Thus, under higher current densities, the iron electrodes performed better than did the aluminum electrodes. When traditional chemical coagulation methods were applied to treat simulated 2S-OBA effluent, the results indicated that alum could remove 78.8% of OBA; ferric chloride removed 71.0% of the OBA; and ferrous chloride removed 64.4% of the OBA. For the simulated 4S-OBA effluent, the chemicals removed 61.2, 54.7, and 46.6% of the OBA, respectively. In treating the simulated stickies-containing effluent, the 3 chemicals removed 85.1, 83.3, and 79.6% of SS; 54.5, 60.0, and 54.5% COD; and 88.4, 78.9, and 82.5% turbidity, respectively. And in treating simulated dyed effluent, the 3 chemicals were capable of remove 35.8, 64.4, and 31.2% of true color, respectively.