| Under the coupling background of shortage of crude oil and increasingly demand for petroleum in china,Fischer-Tropsch(F-T)synthesis,as representative for novel coal chemical industrial,has been quickly deveolped in recent years.However,wastewater produced from F-T synthesis would become the main restraining factor that suppress the development of this industrial.Therefore,the effective treatment of F-T wastewater was only method to accomplish win-win situation between development of coal-to-liquid industrial and environmental protection.Considering anaerobic treatment of F-T wastewater might face to the problems of operational instability and lower pollutants removal due to high sensitivity of methanogens to environmental changes.Based on those reason describe above,this study was conducted to investigate the enhanced effect of three exogenous source(scrap zero valent iron(SZVI),powder Fe3O4 and micro-current)on anaerobic F-T wastewater treatment.The enhanced effect of SZVI on peformances of anaerobic F-T wastewater treatment were discussed.It was found that the SZVI not only could buffer the reduction of p H value caused by acidification via its corrosion,but also reduce ORP level,resulting in the fact that COD removal efficiency and methane production in system were always 11.2% and 0.42 L/L·d higher than those in parallel test group(without SZVI)at every stage.Fe2+ ions,as by-product of SZVI corrosion,could create cross-bridging effect to interconnect with protein and polysaccharides in extracellular polymeric substances(EPS),resultig in promoting cell aggregation and adhesive ability for biofilm.In addition,the enhanced effect of Fe2+ ions on specific enzyme relating to methanogenesis was depended on increasing coenzyme F420 content,resulting in enhancing its function of electron carriers,and accelerating the interspecies electron transfer rate.Furthermore,the high-throughput 16 S r RNA gene pyrosequencing in this study further confirmed that the presence of Fe2+ ions could promote the enrichment of H2-utilizing methanogens,making their total relative abundance as high as 30.31%.In this case,the H2 produced from acidification phase could be consumed quickly,resulting in enhancing the interspecies H2 transfer(IHT)mechanism between the organics acids oxidizers and H2 utilizing methanogens.Enhanced effect of powder Fe3O4 on performances of anaerobic F-T wastewater treatment was discussed.The results revealed that the COD removal efficiency with the one-off addition of 0.4 g Fe3O4 was as high as 84.3±2.0%,which was higher than COD removal efficiency at addition of 0.2(73.9%±3.7%),0.6(32.5±2.8%)and 0 g(62.6±1.9%).According the results from Fe speciation inner sludge at diffierent test group,the addition of 0.4 g Fe3O4 could induce high abundance of reducible Fe speciation(39.4%)inner sludge,which was higher that of any other test group.In addition,it was found that the higher reducible Fe speciation exhibited a strictly correlation with higher COD removal efficiency and methane production.The highthroughput 16 S r RNA gene pyrosequencing of sludge at the addition of 0.4 g Fe3O4 further confirmed that genera Geobacter and Methanosaeta both exhibited the predomiant role in corresponding community with the relative abundance of 14.04% and 24.11%,further confirming that the Fe3O4-mediated direct interspecies electron transfer(DIET)was dominantly established.More importantly,the Fe3O4-mediated DIET could reduce the interspecies distance,which increased the electron-utilizing efficiency and promoted ?-oxidation of propionic acid and butyric acid,finally facilitated maintaining driving force in continuous methane production.The enhanced effect of DIET induced by micro-current on performances of anaerobic F-T treatment was analysed.By comparing the operational performance at different condition,it was found that the micro-current effect induced by applied voltage of 1.5 V(electrode distance: 2 cm)could exhibit optimum performance.Especially,effect of micro-current could make anaerobic micro-environment become more reducible,which was beneficial to enrichment of obligated anaerobic microorganism.Under this condition,the COD removal efficiency and methane production in BES-UASB were 86.7±1.7% and 2.23±0.15 L/L·d,which were higher than those in UASB(74.4±1.3% and 1.78±0.08 L/(L·d)).The effect of micro-current could promote anaerobic bacteria for secretion of EPS,which increased the protein content in the tightly bound extracellular polymeric substances(TB-EPS),facilitated filamentous bacteria entangling with tiny sludge particles and dispersed bacteria to form stable granules.Together with the result from high-throughput 16 S r RNA gene pyrosequencing and sludge conductivity,it was found that enhanced effect of microcurrent on DIET mechanism was mainly based on creating favorable condition for DIET via reducing interspecies distance,which could facilitate transfering electrons produced from genera Geobacter to genera Methanosarcina for methane production via electrically pili(e-pili),and promoting continuous transformation of propionic acid and butyric acid.Finally,the completely methane production was accomplished.Based on the evaluation of three exogenous source in lab scale,the powder Fe3O4,as the exogenous source,was added in pilot-scale up-flow anaerobic sludge(UASB)to enhance F-T wastewater treatment.One-off powder Fe3O4 addition of 2400 g coupled with anaerobic effluent recycling of 200% not only could effectively reduce loss of Fe3O4,but also make COD removal efficiency as high as 90.6±2.2%.Simultaneously,The influent p H value of 4.94±0.07 still met the threshold value of p H for UASB and reduced alkali addition was achieved with the aid of anaerobic effluent recycling of 200%.In addition,under the combined function of anaerobic effluent recycling(200%)and presence of Fe3O4,DIET mechanism,as predominant electron transfer mechanism with the assistance of IHT,not only promote propionic acid and butyric acid transform into acetic acid,but also maintain the higher effectiveness in pollutants removal.More importantly,due to optimum performance in anaerobic process,the coupled system,composed of exogenously enhanced anaerobic process,multiple-stages aerobic process and advanced treatment process,could maintain effluent COD concentration below than 50 mg/L in pilot scale and meet the national one-level A effluent standard.These findings indicated that anaerobic enhancement induced by exogenous source peformed a positive effect on effectiveness of the whole process,facilitating operational stablility of whole pilotscale process,and suggesting that enhanced anaerobic process with the assistance of exogenous source has the advantage of high effectiveness,which can highlight the important value of full-scale application. |
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