| Cellulosic ethanol is considered as a promising source of substitute energy for fossil fuels,which has been attracting worldwide interest.Diluted sulfuric acid and steam explosion pretreatment are widely used in cellulosic ethanol production by countries around the world.Large quantities of refractory wastewater with high-strength and high sulfate resulting from dilute sulfuric acid pretreatment will be produced during cellulosic ethanol production,which need to be treated urgently.The wastewater is difficult to treat due to its quality,which will affect the activity of microorganisms.Most cellulosic ethanol wastewater could not be discharged on standard by single treatment process.As the primary treatment process,the biological technology could not remove the color and refractory pollutants efficiently,which need multiple processes.Base on these issues,the combined process of anaerobic-aerobic biotreatment and electrochemical oxidation was employed to treat sulfate-rich cellulosic ethanol wastewater in this study.The microbial communities from CSTR-EGSB-SBR combined system was analysed,the characteristics in the biological process for treatment of cellulosic ethanol wastewater was investigated,and degradation mechanism of the organic pollutants in the process of electrochemical oxidation was fully discussed,which provided the basis for the effective treatment of this kind of wastewater.Two-phase anaerobic process combined with aerobic process was employed to treat the sulfate-rich cellulosic ethanol wastewater(diluted acid and steam explosion as pretreatment method),which composed of a continuous stirred tank reactor(CSTR),expanded granular sludge bed(EGSB)reactor and sequencing batch reactor(SBR).The pollutant removal efficiency was investigated.The organic loading rate of the CSTR was 32.4 kg COD/(m3·d),the sludge loading rate was 0.13 kg COD/(kg MLVSS·d)and the average COD of influent was 13497 mg/L,the hydraulic retention time of the combined system was 48 h,the total COD and sulfate removal of the combined system was 94.5% and 89.3%,the yield of methane of the EGSB was 0.327L/g COD.The acidogenic reactor made a positive contribution to volatile fatty acids production and sulfate removal.The produced sulfide can be isolated from the methane production process which reduced sulfide toxicity and represented the excellent and stable performance.High-throughput sequencing based on Illumina Miseq system was applied to study the microbial community structure and functional microbial populations in the CSTR-EGSB-SBR combined system.Acidogenic bacteria(Megasphaera,Parabacteroides and unclassified Ruminococcaceae spp.)and sulfate-reducing bacteria(Prevotella,Butyrivibrio and Megasphaera)were rich in the CSTR.A relatively complicated bacterial communities presented in EGSB.The Methanosaeta with a relative abundance of 77.3% was the predominant methanogenes in EGSB,suggesting a acetotrophic methanogenesis pathway occurred.Syntrophobacter,Thermovirga and unclassified Desulfuromonadales species were also detected in the EGSB reactor,which might facilitate the removal of sulfate from sulfate-rich cellulosic ethanol wastewater.The dominant bacterial genus identified in the SBR were affiliated with Truepera(63.5%).which enhanced the removal of macromolecules of cellulose ethanol wastewater and consequently increased removal efficiency of the combined system.Some microorganisms were found to degrade lignin,cellulose,hemicellulose and aldehydes,phenol compounds and other inhibitory substances,such as Ruminococcaceae,Prevotella,Acinetobacter and Truepera.Excitation-emission matrix(EEM),fourier transform infrared spectrometer(FTIR)and UV-Vis spectra were used to analyze the organic compounds in the biological process for treatment of cellulosic ethanol wastewater.Liquid chromatography and ultrafiltration(UF)fractionation were also employed to investigate the molecule weight distribution in colour.It was showed that cellulosic ethanol wastewater was mainly consist of soluble microbial products,simple aromatic protein and humic acid-like matter.The biological treatment led to an apparent decrease in protein,carbohydrate and other substances,while the aromatic substances was still presented.The color of biologically treated effluent(SBR effluent)was primarily due to the presence of humic acid-like matter,which exhibited a great proportion of 67.1%.The organic materials were mainly distributed in the molecular weight fractions below 3-30 k Da,while the color compounds were 3-10 and 10-30 k Da.Electrochemical oxidation was employed to treat the biologically treated effluent of the cellulosic ethanol wastewater.Current density,initial p H and supporting electrolyte were studied to investigate their influence on hydrolyzation.The mechanism of decolorization,COD and TOC removal were also studied by cyclic voltammograms,indirect electrochemical oxidation analysis,UV-Vis and EEM.Complete decolorization,86.5% COD removal and 69.1% TOC removal were achieved under the optimal conditions(20 mA/cm2,p H 5 and supporting electrolytes of 0.1M Na Cl)after 150 min.Further investigation revealed that the role in the degradation of organic contaminants is hydroxyl radicals > active chlorine > peroxodisulfate > direct anodic oxidation?Finally,with the combined process of anaerobic-aerobic biotreatment and electrochemical oxidation for treating sulfate-rich cellulosic ethanol wastewater,the average COD of influent was 13497 mg/L,the treatment time was 50.5h,total COD and sulfate removal was 99.4%,90.8% respectively.So the effluent can be almost met the discharge standard for fermentation alcohol and distilled spirits industry of China(GB 27631-2011). |
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