Study On Electrochemical Control Of Sulfur Cycle To Enhance Anaerobic Reduction Of Nitrobenzene

Fine chemical wastewaters such as pharmaceuticals,dyes,explosives,etc.are complex in composition and contain large amounts of nitroaromatic compounds（NACs）and sulfates.Sulfate will be reduced to produce H₂S in the anaerobic biological treatment section,thereby inhibiting the reduction of NACs and methane production.How to reduce the impact of the sulfate reduction process on the anaerobic reduction of nitrobenzene and improve the efficiency and stability of anaerobic treatment is a key issue that needs to be solved urgently in the field of fine chemical wastewater treatment.This thesis intends to use potential to realize the oxidation of sulfate reduction product sulfide at the anode,reduce the toxicity of H₂S and release electrons to promote the reduction of nitrobenzene.A diaphragm-free upflow bioelectrochemical reactor（UBER）was constructed to strengthen the anaerobic reduction of nitrobenzene around the electrochemical regulation of sulfur cycle,and the effect of key parameters on the reduction performance of sulfate and nitrobenzene in the bioelectrochemical system was studied;Construct anaerobic treatment systems with different operating modes,combine microbial community structure analysis and function prediction,and explore the mechanism of electrochemical regulation.The main research conclusions are as follows:When the cathode potential is reduced from-400 m V to-800 m V,the current density increases,and the reduction rates of nitrobenzene and sulfate are improved.The conversion rate of sulfide decreases with the decrease of cathode potential.When the cathode potential drops to-800 m V,the conversion rate of sulfide is only about 20%.The bioelectrochemical system promotes the conversion of S^2-produced by the reduction of SO₄^2-in the cathode area to elemental sulfur or polysulfides,and relieves the accumulation of sulfides from inhibiting microorganisms.For ordinary anaerobic reactors,the COD/SO₄^2-ratio is an important factor affecting the reduction of nitrobenzene and sulfate.When the COD/SO₄^2-ratio decreased from 11.2:1 to1.67:1,the anaerobic reduction process was severely inhibited.In the UBER system,the reactor processing efficiency is less affected by COD/SO₄^2-.When COD/SO₄^2-is in the range of 11.2:1 to 1.67:1,both nitrobenzene and sulfate maintain high reduction rates,and Sulfide is maintained at a relatively low concentration,only about 20 mg L^-1.Compared with sodium acetate and glucose,when sodium propionate is used as an electron donor,the removal rate of nitrobenzene and sulfate is higher.The nitrobenzene reduction performance of the bioelectrochemical system with the participation of the sulfur cycle is better than that of the anaerobic reduction system and the bioelectrochemical system with the participation of the sulfur-free cycle.In the UBER system,the abundance of anode Desulfobulbus is as high as 7.6%,replacing Geobacter as the main electroactive microorganism.Sulfate reducing bacteria were detected in the system:Desulfobulbus,Desulfovibrio,etc.At the same time,there is a certain abundance of sulfur-oxidizing bacteria in the system—Chlorobaculum.The PICRUSt2function predicts the abundance of genes encoding yellow cytochrome c sulfur dehydrogenase on the anode,implying that the oxidation of sulfide to elemental sulfur may have occurred at the anode.The nitrobenzene removal rate,aniline generation rate and sulfate removal rate under long-term stable operation of the UBER system can reach 97.12%,70.67%,and 82.12%,respectively,and the sulfide concentration is maintained at about 20 mg L^-1.It is feasible to use electrochemical regulation of sulfur cycle to enhance the anaerobic treatment of nitrobenzene.