Degradation Pathways Analysis Of Organics In MBR And Study On Organics Removal Efficiency Of Coagulation For Food Waste Fermentation Wastewater

The concentration of organic pollutions in food waste fermentation wastewater（FWFW）is high,and the organic components of FWFW are unknown,all of which lead to the difficulty of FWFW treatment.Besides,the degradation pathway and microbial action of these organic components in MBR（A/O+ultrafiltration）,which is the main technology for FWFW treatment,are also unclear.Furthermore,the operational cost for MBR is high when treating FWFW.Aiming at these problems,this study firstly used three-dimensional excitation-emission matrix fluorescence（3D-EEM）,molecular weight cutting,Fourier transform infrared spectroscopy（FTIR）,and solid phase microextraction-gas chromatography/mass spectrometry（SPME-GC/MS）to deeply analyze the components of organic pollutants in the FWFW.After that,combining with the FWFW treatment projects,the degradation pathways and microbial actions for organic pollutants of FWFW in MBR（A/O+ultrafiltration）were revealed.Based on these results,this study developed a high-efficiency and low-cost A/O-coagulation treatment technology for FWFW treatment,and focused on the effects of coagulant type,pH and temperature on the efficiency of coagulation in the removal of organic pollutants in the FWFW.The key parameters of A/O-coagulation treatment technology for efficient treatment of FWFW were obtained.Besides,the coagulation mechanisms were revealed through the method of PARAFAC-3D-EEM and the analysis of Zeta potential.This study reached the following main conclusions:The in-depth analysis of the degradation pathway of organic pollutants in the combined FWFW treatment project showed that the values of influent BOD₅/COD of hydrolytic acidification,A/O,and ultrafiltration units were 0.2,0.43 and 0.04,respectively.The sharing rates of COD removal by these units were 17.95%,62.37%,and12.90%,respectively.The analysis of PARAFAC-3D-EEM showed that after the treatment of two-stage A/O unit,the removal rate of tryptophan-like,UVC+UVA marine-derived humic acid-like and UVC+UVA humic acid-like were 96.97%,78.86%and22.48%,respectively.Besides,the ultrafiltration unit had poor removal effect on the refractory UVC+UVA humic acid-like（only a removal rate of 4.29%）.The results of SPME-GC/MS showed that after the treatment of hydrolysis and acidification,a total of28 organics in the influent cannot be detected,and a total of 28 new organics were added,and the total chromatographic peak area was only reduced by 6.60%.Besides,a total of14 organics were detected from the effluent of two-stage A/O unit,which was 76%less than that of the influent,and the total chromatographic peak area was reduced by 99.10%.The analysis of the refractory organics in the effluent of ultrafiltration unit showed that the macromolecular aromatic UVA humic acid-like was the main component of the refractory organics,and its molecular weight was mainly distributed between5k Da～500Da.In addition,the results of 16S r RNA high-throughput sequencing showed that the organics-degrading functional bacteria in the hydrolytic acidification unit mainly included Desulfobulbus,Comamonas,Advenella,Fastidiosipila,Eubacterium,Sedimentibacter,and the organics-degrading functional bacteria in the A/O unit were mainly Ruminococcaceae＿NK4A214＿group,Lactobacillus,Unclassified＿f＿Clostridiaceae＿1.The in-depth analysis of the degradation pathway of organic pollutants in the separate FWFW treatment project showed that the values of influent BOD₅/COD of first-anoxic and first-aerobic 1a unit,first-aerobic 2a unit,second anoxic and second-aerobic unit,and ultrafiltration unit were 0.34,0.08,0.08,and 0.06,respectively.The sharing rates of COD removal by these units were 95.48%,-0.3%,0.6%,and 2.61%,respectively.The COD removal was mainly completed by the first-anoxic and first-aerobic 1a unit.The analysis of molecular weight cutting and PARAFAC-3D-EEM showed that the most main component of organics in the separate FWFW was protein-like substances（including tryptophan-like and tyrosine-like）,and their molecular weights were mainly distributed in<500Da.After the treatment of the first anoxic and first-aerobic 1a unit,protein-like substances were basically completely removed,and the residual organic component in the effluent were mainly UVC+UVA marine-derived humic acid-like.The subsequent biological unit and the ultrafiltration unit had poor removal effect on the refractory UVC+UVA marine-derived humic acid-like.The analysis of SPME-GC/MS showed that after the treatment of first-anoxic and first-aerobic 1a unit,the number of organics types had been reduced by 72.4%,and the total chromatographic peak area was reduced by 96.10%,which dropped from 156683021 to 6079199.In addition,the results of 16S r RNA high-throughput sequencing showed that the organics-degrading functional bacteria in the A/O unit were mainly Rubrivivax,unclassified＿f＿Saprospiraceae,Amaricoccus,unclassified＿f＿Hyphomonadaceae,Thermomonas,Dokdonella,and Thauera.The effects of coagulant type,pH,and temperature on the removal of the refractory organics by the coagulation in the FWFW was significant.Compared with Al Cl₃ and Al₂（SO₄）₃,FeCl₃ had a higher removal efficiency for the refractory organics in the FWFW,because FeCl₃ was more likely to complex with chromogenic organics on the surface such as UVC humic acid-like,UVA marine-derived humic acid-like,and UVA humic acid-like substances to make it easier to remove the refractory organics.Compared with FeCl₃+neutral PAM,the synergetic coagulant FeCl₃+PDADMAC had a higher removal efficiency for the refractory organics in the FWFW.The analysis of PARAFAC-3D-EEM showed that the addition of flocculant PDADMAC could significantly improve the removal efficiency of UVC+UVA humic acid-like.When decreasing the initial pH of the FWFW,the refractory organics removal efficiencies of FeCl₃,Al Cl₃ and Al₂（SO₄）₃ were significantly improved,and the dosage of coagulants could be reduced.The analysis of Zeta potential showed that the change of the initial pH of the FWFW was linearly and negatively correlated with the change of the initial Zeta potential.The analysis of PARAFAC-3D-EEM showed that lowering the initial pH of the FWFW could improve the removal ability of the coagulation for UVC+UVA marine-derived humic acid-like.The refractory organics removal efficiency of the coagulation significantly reduced when increasing the FWFW temperature,and the temperature influence had an ordered.For metal salt coagulant,the order was FeCl₃≈Al Cl₃>Al₂（SO₄）₃,and for the polymerization coagulant,the order was PAC>PFC≈PAC.In the two-stage A/O-coagulation（FeCl₃）combined system,the COD concentration of the FWFW was 7310 mg/L,and the sharing rates of COD removal by the first-anoxic unit,the first-aerobic unit,the second-anoxic unit,the second-aerobic unit,and the coagulation unit were 42.68%,28.18%,14.91%,4.89%,and 5.48%,respectively.The cumulative removal efficiency of COD reached 96.14%,and the effluent COD met the requirement of the three-level standard in Integrated Wastewater Discharge Standard（GB-8978-1996）.Compared with the MBR system of the FWFW treatment project,the operating cost of the combined system was reduced by 28.52%.