| The treatment of pesticide wastewater, which contains toxic and harmful non-biodegradable material, has always been a hotspot and difficulty for environmental protection workers. In recent years the electrochemical technology which was known as "environmentally friendly" technology has attracted people's attention. This paper focused on the herbicides wastewater produced by Heilongjiang Li Min agrichemicals technology Co., LTD, and the electrocoagulation-electrocatalytic oxidization-biological contact oxidation combined process system was built with electrochemistry for core technology, biochemical method for auxiliary on the basis of the feasibility studies in order to provide the technical support for practical wastewater treatment. PAC and electrocoagulation were compared in the stage of the feasibility study.The results showed that electrocoagulation was better than PAC in regard to the treatment effect, while the cost of chemical coagulation was 0.66yuan per ton wastewater less than the electrocoagulation. The quartz ceramic ring particle electrodes loaded with Sb doped SnO2 which were prepared by dip coating and heat treatment method has the characteristics of three-dimensional particle electrode requirements after detected by SEM and XRD method. The relationship among particle electrode stimulate voltage, conductivity of the solution and electrode separation was determined by the RSM method. In certain conductivity and electrode separation conditions, there were U=1.38+2.92D+5.0×10-3P-1.48×10-3D·P+0.19D2-1.85×10-6P2. Through the above feasibility study, the electrocoagulation and 3d electrocatalytic oxidization technology was determined as the herbicides wastewater pretreatment process. The treatment effect, quantity of hydroxyl radicals, energy consumption and current efficiency were compared between the two-dimensional and three-dimensional electrode system. It showed that the COD removal rate, energy consumption and current efficiency were 68%, 24.3kWh/kg COD,140% and 40%, 44.5kWh/kg COD, 52.2% respectively between the two-dimensional and three-dimensional electrode system.The electrocoagulation-electrocatalytic oxidization-biological contact oxidation combined process system was constructed and the process parameters were optimized. Through three levels of four factors of orthogonal experiment, the optimization parameters of electrocoagulation device system listed as follows: water upper speed 4L/h, current density 15mA/cm2, the number of electrode nine, the blackouts time of power 4+1.The 3d fixed bed electrochemical system was optimized through single factor experiment method. They were slot voltage 30V, amount of aeration 50ml/min, particles of filling layer filling quantity of volume 2/3, pH=7.69, electrolysis time 120min. The biodegradable performance of the herbicides wastewater after electrolysis for 120min was determined by microbial oscillation training experiment method. The results showed that it was appropriate to treated by biological method. The biological contact oxidation device system has been started-up and domesticated for 65 days in order to treat the herbicides wastewater. The bio-film of which thickness was 2mm showed good and was rich in biological communities in the system with the HRT 12hours and amount of aeration 0.8 m3/h.The combined process system has been dynamic operated for 20days in these optimized parameters and the treatment effect was analyzed comprehensively. The results showed that the COD removal rate was 95%, pH value was 7.02 which was appropriate for biological method after electro-catalytic oxidization process. The conductivity of the wastewater was increased after electrocoagulation while decreased after electro-catalytic oxidization. The B/C was 0.38 after electro-catalytic oxidization which was increased effectively compared with the raw wastewater. Other water quality analysis project test indicated that the treatment of herbicides wastewater could achieve the integrated wastewater discharge water secondary standard. The water with different reactor was analyzed by GC-MC. The results showed that the macromolecular organic matters in wastewater could be decomposed into several small molecular organic after the electrocatalytic oxidization processing. And then the species of organic was reduced to the lowest and relevant substrates could not be detected after biological contact oxidation treatment. The operation cost was preliminary calculated on the process of electrochemical pretreatment in the combined system. The main operating cost in the aluminum consumption and power consumption. And the aluminum consumption cost was 0.35 yuan and power cost 7.48yuan and total cost was 7.83 yuan for the treatment of per ton wastewater. |
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