Development Of A Three-dimensional Electro-biological System And Its Application In The Advanced Treatment Of Coking Wastewater

The treatment of refractory industrial wastewater is a major problem restricting economic development and environmental protection.With the proposed"double carbon"goal,industrial wastewater treatment technologies of energy-saving and efficient are highly desired.Hence,efficient treatment of industrial wastewater has long been a thorny problem in the field of wastewater treatment.In light of the current"double carbon"goal,advanced treatment of industrial wastewater containing refractory organics is particularly challenging.To adapt to the water quality of industrial wastewater,a novel three-dimensional biofilm electrode reactor（3D-BER）is developed by cultivating electro-active biofilm on the surface of particle electrodes based on the three-dimensional electrochemical reactor（3D-ER）.Subsequently,a three-dimensional electro-biological wastewater treatment system is established,which is then combined with biological treatment processes to treat coking wastewater.The influences of various operating conditions on the performance of 3D-ER and 3D-BER are investigated.Furthermore,the functional positioning and pollutants degradation mechanisms for each reactor in the integrated system are identified.The performance of the integrated system in eliminating carbonaceous and nitrogenous contaminants from coking wastewater is evaluated,as well as its energy consumption.The main finding are as follows:（1）Conventional biological nitrification processes are susceptible to temperature,resulting in poor nitrification performance at lower temperatures.To address this issue,a 3D-BER was operated under aerobic conditions to achieve nitrification function at a low temperature（12^oC）to remove ammonia nitrogen（NH₄⁺-N）pollutants in coking wastewater.The results show that when the current is set to 1 m A,the NH₄⁺-N in the coking wastewater is primarily converted into NO₂^--N,with significant ammonia oxidation.When the current is increased to 2 m A or 3 m A,the process of ammonia oxidation is inhibited,resulting in a reduction in NO₂^--N and a significant accumulation of NH₄⁺-N.When the current reaches 5 m A,almost all of the NH₄⁺-N is converted to NO₃^--N,with no accumulation of NO₂^--N.When the hydraulic retention time（HRT）is shortened from 48 h to 24 h at 5 m A current,NO₃^--N decreases rapidly in response to NH₄⁺-N accumulation,indicating that the nitrification of microorganisms in the reactor is gradually weakened.（2）To improve nitrogen removal,a three-dimensional biofilm electrode reactor for denitrification（3D-BER-De）was developed under anoxic conditions and integrated with a biological aerated filter（BAF）,whose performance was evaluated in the denitrification of coking wastewater.The results show that BAF,as a front-end treatment,achieves stable accumulation of NO₂^--N,and the subsequent 3D-BER-De realizes stable denitrification.At 10 m A current,TN and COD removal efficiencies of the BAF/3D-BER-De integrating system are 96.64%and 54.38%,respectively,which are significantly higher than those of BAF/3D-BER-De（0 m A）（2.20%and 49.45%）and single 3D-BER-De（10 m A）（75.19%and 21.51%）.Current intensity has a significant impact on the dominant microbial communities in the 3D-BER-De.At 0m A,potential nitrite oxidizing bacteria（e.g.Hyphomicrobium and Thauera）and potential nitrate reducing bacteria（e.g.Thauera）were enriched.At 10 m A,potential nitrite oxidizing bacteria（e.g.Nitrospira）and potential nitrate reducing bacteria（e.g.Thauera,Hydrogenophaga,Gemmobacter）were effectively enriched,hence significantly improving the performance of nitrogen removal.（3）To improve organics removal in coking wastewater,a 3D-ERs/BAFs/3D-BER-De integrating system was developed by setting 3D-ERs in front.The results show that 3D-ERs remove 73.21%of COD,38.02%of NH₄⁺-N,and 91.46%of NO₃^--N.BAFs mainly converts NH₄⁺-N to NO₃^--N through microbial nitrification.In BAFs,bacteria with potential nitrification function（e.g.Hyphomicrobium,Rhodanobacter,Nitrosospira）and bacteria with potential capability of degrading phenol,biphenyl and other organic pollutants（e.g.Aquabacterium,Dyella）are enriched.The residual NO₃^--N is removed by bio-electrochemical denitrification in the 3D-BER-De.The organics and electro-generated hydrogen gas collaborate to provide electron donors for denitrification,allowing residual organics and NO₃^--N to be removed simultaneously.In 3D-BER-De,bacteria with potential nitrification function（e.g.Candidatus＿Nitrotoga）,bacteria with potential denitrification function（e.g.Thiobacillus,Thauera）and bacteria with potential capability of degrading organic pollutants such as phenol（e.g.Aquabacillus）have been effectively enriched.During continuous operation,the integrating system can remove 74.72%-83.27%of COD,99.38%-99.74%of NH₄⁺-N,and 69.64%-99.83%of TN from coking wastewater,as well as significantly reducing the toxicity of the wastewater.（4）A novel 3D-ERs/3D-BERs/3D-BER-De system was developed by converting BAF into 3D-BER for the advanced treatment of coking wastewater rich in NH₄⁺-N.The results show that 3D-ERs primarily degrade COD and NH₄⁺-N through electrochemical redox reactions,whereas 3D-BERs convert residual NH₄⁺-N to NO₃^--N via bioelectrochemical nitrification.The genera Cupriavidus with potential nitrification function is abundant in 3D-BERs.Furthermore,the 3D-BER-De eliminates NO₃^--N via bio-electrochemical denitrification.The genera Geobacter,Thauera,and Denitratisoma with potential denitrification function are enriched in 3D-BER-De.The integrating system can remove 70.66%of TN and 55.79%of COD with a low energy consumption of 1.29 k Wh m^-3.As the coking wastewater passes through the integrating treatment system,the biological toxicity of the effluent is significantly reduced.In this work,a novel three-dimensional electro-biological system is developed and combined with biological treatment technologies to achieve efficient degradation of coking wastewater.The findings provide a theoretical foundation and technical support for advanced treatment of industrial wastewater containing refractory organics,as well as progressing industrial wastewater treatment technology toward the“dual-carbon”goal.