Research On The Enhanced Process And Performance During Anaerobic Digestion Of Tetracycline Wastewater By Redox Mediator

In the anaerobic biological treatment process, the slower degradation rate and lower efficiency are characterized due to the limited electron transfer and the toxicity of compounds which even collapsed the reactor.As the intermediate of electron transfer, redox mediator could simplify the complex processes of electronic carrier transfer, therefore increase the anaerobic biodegradation rate.Currently, more research was focused on quinones redox mediator, whereas less works was devoted to carbon-based and metal-based redox mediator, and little was known about the antibiotic wastewater treatment strengthened by redox mediator.In this research, the typical antibiotic wastewater-tetracycline wastewater was used to investigate the effect of single and combined redox mediator species on its anaerobic digestion process. The optimal concentration of redox mediator will be determined, and the strengthened mechanisms by redox mediator will be interpreted preliminary. Based on the batch experimental results, the effect of redox mediator on performance of EGSB that treated tetracycline wastewater in continuous mode and community structure was tested.Based on the COD, TOC, VFA, gas volume, CH4 volume, SO42-and TC removal, the efficiency of anaerobic digested tetracycline wastewater was evaluated by adding different concentrations of CNT, PAC, GR, ZVI, Fe3O4,Fe2O3 and combination to anaerobic sludge to determine the optimal concentration.Different concentrations and types of redox mediator promoted anaerobic digestion of tetracycline wastewater with various degree.Redox mediator could promote degradation and transformation of organic substance as well as reduction of SO42-, whereas it had no significant influence of tetracycline removal. In addition,the effect of redox mediator was more superior to CH4 accumulation compared to COD degradation and SO42-reduction.The better anaerobic digestion of tetracycline wastewater was obtained when PAC and ZVI were used than the other four kinds of redox mediator, and the optimal concentration was 0.25 g/g MLVSS and 0.5 g/g MLVSS, respectively which generated CH4 volume of 49.0 m L and 56.6 m L. Orthogonal test determined the best combination was PAC 1200 mg/L and ZVI 1000 mg/L.The effect of redox mediators on properties of anaerobic sludge including the surface morphology, structure, conductivity and extracellular polymers, electrochemical activity of the supernatant of the reaction system and degradation process of tetracycline was investigated to preliminarily explain the possible strengthening mechanism. The introduction of redox mediator into anaerobic system could promote the direct electron transfer between species by tightening connection between bacteria and improving the conductivity of anaerobic sludge; at the same time, it also enhanced the indirect electron transfer between species by accelerating secretion of extracellular polymeric substances and endogenous mediator. It may also increase the CO2 reduction by H2 to CH4. Redox mediator could promote the removal of degradation products of refractory tetracycline significantly, therefore provided favorable conditions for the efficient degradation which enhanced the anaerobic digestion of tetracycline wastewater. There was a slightly difference of mechanism between iron and carbon materials: in addition to the above reasons, the iron materials may also strengthen the effect of anaerobic digestion of tetracycline wastewater by increasing the activity of anaerobic microorganisms and the role of dissimilation iron reduction.The performance of EGSB reactor,properties of anaerobic sludge and microbial community structure were compared before and after adding PAC and ZVI in situ,together with the adsorption property of the complex of PAC / ZVI / anaerobic sludge and the loss of ZVI, the feasibility of the enhanced anaerobic digestion by redox mediator was verified. Competing substrate was the main relationship between MPB and SRB in EGSB reactor, and the anaerobic degradation products of tetracycline significantly inhibited HPA and MPB with effluent circle.Although the adsorption capacity of the complex of PAC / ZVI / anaerobic sludge was not significant after adding PAC and ZVI to EGSB reactor, the performance of EGSB reactor and methane production could be improved, while the loss of ZVI during the operation of EGSB was not serious.Treponema, Klebsiella, Levilinea, Desulfovibrio, Syntrophomonas and Syntrophus were the most prevalent genes of bacterium in EGSB reactor which ensured the stable performance of the system. Methanobacterium and Methanosaeta were the most prevalent genes of archaea.PAC and ZVI could not only promote interspecies electron transfer by strengthening direct contact between HPA and MPB and secreting endogenous mediator, but also improved the interspecies electron transfer between HPA and MPB by enhancing the proportion, thus the anaerobic digestion of tetracycline wastewater was strengthened.