| COD and ammonia nitrogen are common and major pollutants in industrial wastewater, and have been included in the total pollutant reduction targets by the national "12th Five-Year plan" for environmental protection. Electro-oxidation is a green technology that can effectively remove COD and ammonia nitrogen in wastewater and has great application prospects.In this paper, the research on simultaneous removal of COD and ammonia nitrogen in biochemical effluent by electro-oxidation was carried out. Firstly, the labscale experiment was conducted to discuss the effect of current densities and initial p H values on the removal of COD and ammonia nitrogen. Then, on the basis of the lab-scale experiment, the technical and economic evaluation of the industrial scale electro-oxidation device which could treat 300 m3 wastewater per day to remove COD and ammonia nitrogen simultaneously was carried out, which laid a foundation for the wide application of electro-oxidation.The lab-scale experiment results showed that the removal of COD conformed to the first order kinetics(ln[COD]t=ln[COD]0-8.31×10-4·J1.27t) and the removal of ammonia nitrogen conformed to the second order kinetics(ln[NH4+]t=ln[NH4+]0-8.47×10-6·J1.94t2) during the electro-oxidation process.COD and ammonia nitrogen oxidation rate increased significantly with the current densities increasing from 7.5 mA/cm2 to 15 mA/cm2, but the increasing trends slowed down when the current density increased to 17.5 mA/cm2. The effect of initial pH values on the removal of COD and ammonia nitrogen was not obvious with initial pH values less than 10, but the COD and ammonia nitrogen removal rate decreased significantly with the initial pH values higher than 10. Therefore, there is no need to add extra reagents to adjust the pH values of the influent.The industrial scale results showed that the COD and ammonia nitrogen concentration were reduced to 39 mg/L and 3 mg/L, respectively, under the conditions that current density is 15 mA/cm2, and electrolysis time is 40 min. During the electrolysis process, the pH value of the wastewater was relatively constant, and the total current efficiency decreased with the increase of electrolysis time. The operation stability of the electro-oxidation device was evaluated and found that when the influent fluctuations of COD and ammonia nitrogen was up to 20%, the electrooxidation effluent could still reach the "Discharge standard of pollutants for municipal wastewater treatment plant"?GB 18918-2002?, first level A criteria.Finally, the economic assessment of the industrial scale electro-oxidation device was carried out. The total investment was about 1.73 million yuan, and the operating cost for one ton wastewater was about 3.52 yuan. Moreover, the operating cost of electro-oxidation was compared with reverse osmosis, ozone oxidation and sodium hypochlorite oxidation, and the treatment cost for one kilogram COD by electrooxidation was the lowest. In addition, annual COD and ammonia nitrogen reduction can achieve 8.58 tons and 6.93 tons, respectively. |
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