Study On Efficiency And Mechanism Of Baffled Three-dimensional Electro-Biological Coupled Reactor For Ni-EDTA Wastewater Treatment

The complex heavy metals represented by Ni-EDTA in metal complexed organic wastewater are difficult to break down and biodegradable.Firstly,the mechanism of breaking the Ni EDTA complex by three-dimensional electrocatalysis technology was studied.Based on this,the three-dimensional electrocatalysis technology and biofilm technology were coupled into a baffled aerated biofilter to further optimize and construct a baffled three-dimensional electro-biological coupling reactor.The start-up characteristics and degradation efficiency of reaction system for simulating Ni-EDTA containing wastewater were analyzed,and the influence mechanism of current density on microorganisms was investigated,and the contribution degree and spatial characteristics of pollutant degradation in different areas within the reaction system were further analyzed,then the coupling mechanism of Ni-EDTA degradation in baffled three-dimensional electro-biological coupling reactor was revealed.Using ruthenium-iridium-titanium plated plate as the anode and stainless steel plate as the cathode,a three-dimensional electrocatalytic system was constructed to break the Ni-EDTA complex.The effects of electrolyte type,electrolyte concentration,current density and initial p H value on the removal of breakage were investigated.The removal rates of Ni-EDTA and COD reached 85.05%and 80.48%respectively at Na Cl concentration of 0.25 g·L^-1,current density of 1.0 m A·cm^-2and initial p H value of 3.0,with the best breaking effect.The breaking process of Ni-EDTA basically conformed to the pseudo-second-order reaction kinetics and the breaking rate constant was 5.3×10^-3min^-1.The breakdown of Ni-EDTA by three-dimensional electrocatalytic system was attributed to the direct oxidation of anode surface and indirect oxidation of hydroxyl radicals and active chlorine components,of which20.15%depended on active chlorine components and 25.52%depended on hydroxyl radicals.Based on the breaking mechanism of three-dimensional electrocatalytic system to Ni-EDTA,a baffled three-dimensional electro-biological coupling reactor was constructed.By analyzing the effect of current density on the degradation of Ni-EDTA wastewater and microorganisms,it was found that the average removal rates of COD,ammonia nitrogen and Ni-EDTA reached 94.06%,94.31%and 69.51%respectively when current density was 0.35m A·cm^-2;The highest microbial biomass and activity were 38.21 mg·g^-1and 177.02μg TF·（g·h）^-1respectively;At the same time,the content of protein and polysaccharide in EPS was the highest,7.33 and 7.85μg·m L^-1respectively.Further analysis on the removal effect of pollutants in different areas of the system under different current densities showed that the anaerobic tank contributed the most to COD removal;At low current density(≤0.35 m A·cm^-2),the front end of the aerobic tank contributed the most to ammonia nitrogen removal,while at high current density(>0.35 m A·cm^-2),the middle end of the aerobic tank contributes the most to ammonia nitrogen removal;The front end of the aerobic tank contributes the most to the removal of Ni-EDTA.The analysis of spatial characteristics of microorganisms and EPS showed that suitable current density improved microbial biomass,microbial activity and EPS composition in different areas.Diversity analysis of microbial communities in the area under the optimum current density(0.35 m A·cm^-2)showed that Trichococcus,desulfurization and dechlorination functional bacteria were gathered in the anaerobic area,Nitrosomonas,Hydrogenophaga and Pherotilus were gathered in the anaerobic tank;Nitrosomonas,Nitrospira,Hydrogenophaga and Pherotilus were gathered in the aerobic tank.The microbial community inside the reactor showed spatial characteristics along the way.Through the change of composition and structure of particle bio-electrode,it was found that the catalytic components,active groups and electro-biofilm in particle bio-electrode could accelerate the electron transfer efficiency and improve the overall treatment efficiency of the system.The analysis of microbial surface morphology showed that the biofilm was closely wrapped on the particle bioelectrode,and the gap and void structure provided the necessary place for the biosorption.According to microbial diversity analysis,Trichococcus was the dominant bacteria in the system,which could combine with Ni-EDTA to absorb,utilize Ni-EDTA as the only carbon and nitrogen source and release nickel ions.At the same time,the coupling mechanism of“electrocatalysis-biosorption-multi-region”biodegradability was proposed by combining intermediates,analysis of heavy metal destinations and electrocatalytic breaking mechanism.