Experimental Research On The Pretreatment Of Coking Wastewater By Bipolar Three-dimensional Electrode Reactor

Coking wastewater is a typical, but not readily biodegradable organic industrial wastewater, which is characterized by complicated composition, high concentration of pollutants, great change range of water quality, high colority and toxicity. At present,organic matter and nitrogen pollutants in coking wastewater are mainly treated by biological process but the effluent quality can not achieve ideal performance. Since the electrochemical methods shows many advantages such as high efficiency, less added agents, flexible operation, ease automation control, and no secondary pollution, it has been been extensively studied and used in organic wastewater treatment.Three-dimensional electrode, compared with the traditional two-dimensional electrode,adds the particle electrode, and increases the efficiency of reaction area and mass-transfer efficiency. In this study, three-dimensional electrode was employed to pretreat coking wastewater, and remove ammonia nitrogen and total nitrogen?TN? from coking wastewater, which could reduce the cost of biochemical pool investment, the time of reactions and the load on the follow-up biochemical processing.The self-made bipolar three-dimensional-electrode reactor, which chose DSA as anode, titanium as cathode, and mixture of activated carbon and glass as filled electrode, was employed to treat simulated ammonia nitrogen wastewater and the coking wastewater obtained from Coal-Coking Company of Maanshan Iron. Impact factors and treatment efficiency were studied for the optimal operating conditions, and the degradation process of ammonia nitrogen and COD reaction kinetics were analyzed in order to explore the degradation mechanism of coking wastewater preliminarily.The impact factors for the removal of ammonia-nitrogen included time, voltage,initial concentration of ammonia-nitrogen, dose of NaCl and concentration of conducting medium?Na₂SO₄? during the single factor experiments of simulated ammonia nitrogen wastewater degradation. Experimental results showed that the optimal operating conditions were as follows: ammonia-nitrogen is 300 mg/L, Na₂SO₄ is 0.15mol/L, NaCl is 1g/L, and voltage is 20 V,under these conditions, the removal of ammonia-nitrogen approached 81.4% after 2 hours.After using the reactor for pretreatment of coking wastewater, the removal of ammonium nitrogen and COD, compared with two-dimensional electrode reactor,improved 25.9% and 16.4% respectively, due to the larger specific surface area. During the single factor experiments of coking wastewater degradation, the factors including time, amount of particles, aeration, electrolysis voltage, dose of NaCl, and initial pH,had an impact on the treatment. When voltage is 25 V, dose of NaCl is 1.5g/L, amount of particles is 100 g, and initial pH is 7, the removal of ammonia nitrogen, COD, TN and chromaticity reached 98%, 83.66%, 88% and 87.5%, respectively after 3 hours.During orthogonal experiments of pretreating coking wastewater, the descending order of factors impact level for ammonia nitrogen degradation is time, voltage, dose of NaCl and amount of particles. In COD degradation, the descending order is voltage,time, amount of particles, dose of NaCl. In addition the best conditions obtained were that the voltage, dose of NaCl and amount of particles is 25 V, 1.5g/L, 100 g respectively, which achieved the 98.1% removal of ammonia nitrogen and 83.8%removal of COD respectively. This is consistent with the results of single factor experiments.During the pretreatment of coking wastewater, indirect oxidation achieved by breakpoint chlorination mainly contributed to the removal of ammonia nitrogen. The degradation of COD corresponded to first order kinetic model and the degradation speed rate became faster with voltage increasing.