Study On Anaerobic Digestion Characteristics Of Poplar Fuel Ethanol Distillation Wastewater

Poplar fuel ethanol is a liquid fuel which is produced by saccharification and fermentation with poplar as raw material.Fuel ethanol is a clean high octane fuel and renewable energy.However,wastewater produced in fuel ethanol process had the characteristics of high chemical oxygen demand（COD）,acidity and deep color.It would cause serious environmental problems if the wastewater was directly discharged.Based on these issues,anaerobic digestion technology was used to treat wastewater produced by distillation of poplar fuel ethanol（PFEW）.The influence of the ratio between anaerobic sludge and PFEW on the wastewater treatment efficiency was investigated.The effect of cow dung on anaerobic digestion characteristics of PFEW was explored.The effect of sulfate type on the anaerobic digestion characteristics of PFEW was studied at the optimal ratio of S/W.On this basis,the relationship between the organic compounds and chromaticity at the initial,middle and end of anaerobic digestion of PFEW with the Fe2（SO4）3 was discussed.The main results and conclusions were as follows:The appropriate S/W ratio provided a good living environment for microorganisms.The maximum methane yield was 265.2 mL/gVS when the ratio of S/W was 7.3.The results showed that the methanogenic ability was weakened owing to the less available substrate for microorganisms in anaerobic digestion when the substrate concentration was too small at the higher ratio of S/W.The acid accumulation occurred result from the rate of acid production was greater than the rate of methane production when the substrate concentration was too large at the lower ratio of S/W,and the activity of methanogens was inhibited.The analysis of the microbial community showed that Halobacterota was the dominant bacteria.The cumulative methane productions of mono-digestion were higher than that of co-digestion.The cumulative methane production of mono-digestion was 22.16%higher than that of co-digestion when the substrate concentration of PFEW was 2.58 gVS/L（S/W=7.3）.The volatile fatty acids（VFAs）testing results indicated that the degradation of propionic acid by acetogen was inhibited and the methane process was weakened in anaerobic co-digestion.The analysis of the microbial community showed that norank f Bacteroidetes vadinHA17,Clostridium sensu stricto and Leptolinea were acid-producing bacteria,Anaerolineaceae was acetogen,Methanosarcina and Methanobacterium were methanogens,of which appeared in both co-digestion and mono-digestion.Psychrobacillus which was only found in the co-digestion inhibited the growth of acetogen and affected the methane production,which revealed the exogenous inhibitory effect of cow dung on the anaerobic digestion of PFEW.Fe₂（SO₄）₃,FeSO₄ and Na₂SO4 were added to the PFEW according to the amount of COD/SO42-=20 for anaerobic digestion under the condition of S/W=7.3,respectively.The maximum methane production of Fe2（SO4）3-PFEW was 543.0 mL/gVS,which was 29.72%,35.82%and 104.75%higher than that of FeSO4-PFEW,Na2SO4-PFEW and control group,respectively.The VFAs content was the highest with Fe2（SO4）3,indicating that Fe3+ can enrich dissimilation iron-reducing bacteria which can increase the acetic acid content and enhance methanogenic activity.The sulfur balance analysis showed that the sulfide content in Fe2（SO4）3-PFEW was the lowest at the end of anaerobic digestion,indicating that the addition of Fe3+ promoted the combination of sulfide and metal ion in the system.UV-Vis spectra,fourier transform infrared spectrometer（FTIR）and excitation-emission matrix（EEM）were used to analyze the organic compounds at the initial,middle and end of anaerobic digestion of Fe2（SO4）3-PFEW.The results showed that PFEW was consisted of simple aromatic protein,fulvic acid and humic acid-like matter.Fulvic acid matter was completely degraded at the middle of anaerobic digestion.Esters,ethers,alcohols and phenols were effectively degraded,the content of humic acid-like matter and the chromaticity were reduced at the end of anaerobic digestion.However,there was humic acid-like matter,indicating that the aromatic substance was incompletely degraded,which revealed the presence of humic acid-like matter related to chromaticity of Fe2（SO4）3-PFEW at the end of the anaerobic digestion.