Three-dimensional Electrochemical Reactors Coupled With Bioreactors For Coking Wastewater Treatment

Coking wastewater is a typical industrial wastewater with the properties of high concentration,complex components,and strong biological toxicity.The coking wastewater contains abundant ammonia,phenol,cyanide,thiocyanate,and varieties of heterocyclic compounds comprising nitrogen,oxygen,and sulfur,which would seriously threaten the ecological environment and the public health without efficient treatment before discharge.Traditional biological wastewater treatment decomposes the pollutants through the metabolism of microorganisms,thus effectively purifying the wastewater.Coking wastewater is relatively toxic and inhibits the microbial activity significantly,leading to the poor treatment efficiency of biological technologies to coking wastewater.Although physical and chemical technologies,such as coagulation and adsorption,have a good adsorption performance for refractory organic substances in coking wastewater,a use of adsorbents on a large scale will increase costs,and at the same time,generated precipitates adsorb high concentration of organic substances,and secondary pollution will be caused if treatment is not performed in time.Electrocatalytic oxidation technology has the advantages of high removal efficiency,no secondary pollution,and easy automation.The three-dimensional electrochemical reactor(3DER),a novel electrocatalytic oxidation technology,is more efficient compared to the traditional electrolysis in terms of better mass transfer and higher current efficiency.Therefore,unique advantages of 3DER are present in industrial wastewater treatment.In this study,an integrated wastewater treatment system of 3DERs and bioreactors was established based on the laboratory for advanced treatment of coking wastewater.And a pilot scale experiment was further carried out to explore the influences of different process conditions on the coking wastewater treatment effect,to investigate the long-term operation effect of the integrated wastewater treatment system treating coking wastewater and to optimize the operation conditions of the integrated wastewater treatment system.The main findings are as follows:(1)A 3DER-three-dimensional bio-electrochemical reactor(3DBER)-three-dimensional bio-electrochemical reactor for denitrification(3DBER-De)system is established for advanced treatment of coking wastewater.The results show that under the optimal condition(1 h HRT of 3DER,20 h HRT of 3DBER and 46.2 h HRT of3DBER-De),the integrated system obtains COD removal efficiency of 73.1%,NH₄⁺-N removal efficiency of 91.7%,NO₃^--N removal efficiency of 26.7%,and TN removal efficiency of 70.2%,respectively.The integrated system exhibits good treatment performances in ammonia nitrogen and COD of coking wastewater,realizing the simultaneous removal of carbonous and nitrogenous pollutants in the coking wastewater.(2)The pilot scale 3DER is integrated into the anaerobic-anoxic-oxic(A²O)system as a pretreatment unit to improve the treatment efficiency of coking wastewater.The results indicate that 3DER pretreatment increased the biodegradability of coking wastewater,promoting the biodegradation of coking wastewater in A²O system.The integrated 3DER-A²O system can remove 94.4%of COD and 76.2%of TN from raw coking wastewater,and the energy consumption was only 0.22 k Wh/kg COD and 4.69k Wh/kg TN.The biological toxicity of the treated coking wastewater decreased significantly.The acute toxicity of coking wastewater was reduced from over 99%to12%after treatment.The GC-MS test results show that phenol and its homologous compounds,quinolines and other organic substances are the main organic compounds in the raw wastewater.After the treatment of the integrated system,most of the heterocyclic organic compounds in water have been decomposed and removed.The3DER-A²O system can effectively degrade heterocyclic organic compounds in coking wastewater.Comparing with traditional biotechnology,the integration of 3DERs and bioreactors shows a good treatment effect in removing both COD and TN in coking wastewater and the treatment efficiency of coking wastewater is significantly improved,while the energy consumption maintains at a low level.The integration of 3DER and bioreactors treats coking wastewater by means if updating the existed biotechnology and optimizing system operating conditions,which provides a new solution to advanced treatment of coking wastewater.Figure[25]table[15]reference[129]...