Study On The Process And Mechanism Of Biochar Enhanced Anaerobic Treatment And Degradation Of Aromatic Compounds

Aromatic compounds are a kind of organic compounds with aromatic ring structure that exist in large quantities in production and life,and have strong toxicity and"three causes"effects.Aromatic compounds have a stable structure.In industrial production,it is inevitable to enter the aquatic environment through various channels.Such pollutants will not degrade and disappear after entering the environment,and will eventually cause serious pollution to the environment.Therefore,how to efficiently treat aromatic wastewater to reduce its potential harm has attracted the attention of many scholars.The effects of aromatic compounds on the removal of organic matter and the characteristics of anaerobic granular sludge were investigated.Bisphenol A（BPA）and 2,4-dichlorophenol（2,4-DCP）were selected as the treatment objects.Using biochar to enhance the anaerobic system,exploring the energy efficiency of organic matter degradation,and then analyzing the physical and chemical properties of the sludge and microbial community,in order to investigate the strengthening mechanism of biochar on the anaerobic treatment of BPA and 2,4-DCP.The conclusions were drawn as follows:（1）The effects of BPA and 2,4-DCP on the physical and chemical properties of anaerobic granular sludge and microbial communities were investigated.The average removal rates of chemical oxygen demand（COD）in the BPA and 2,4-DCP experimental groups were 62%and35%,respectively,which were reduced by 31%and 58%compared with the blank control group.The electron transport system（ETS）activities of the blank control group,experimental group BPA,and 2,4-DCP were 57.11,86.53,46.79 mg/INTF·（g TTS·h）^-1,respectively.It shows that2,4-DCP can inhibit electron transfer.The content of loosely-bound extracellular polymeric substances（LB-EPS）protein（PN）in the control group and experimental group BPA and2,4-DCP were（0.23±0.011）mg·g^-1,（0.13±0.016）mg·g^-1 and（0.04±0.008）mg·g^-1.The content of polysaccharide（PS）was（0.46±0.017）mg·g^-1,（0.98±0.079）mg·g^-1,（0.66±0.011）mg·g^-1,respectively.It shows that 2,4-DCP would strongly inhibit the generation of PN in LB-EPS as the experiment progresses.The analysis of the excitation-emission matrix（EEM）spectra of tightly-bound EPS（TB-EPS）showed that the fluorescence peak intensity of coenzyme F₄₂₀ in the experimental group was weaker than that in the control group.BPA and 2,4-DCP would reduced the diversity of microbial communities in the anaerobic granular sludge,in which the relative abundance of Actinobacteria increases.High performance liquid chromatography mass spectrometry（LC-MS）analysis showed that the degradation path of BPA was the cleavage of carbon chain bridges,forming 2-hydroxyphenylacetic acid and methyl benzoate.At the same time,the hydroxylated BPA was further oxidized to form 4-hydroxybenzoic acid and benzoic acid.These intermediate products further react to form allyl vinyl ether,which was finally mineralized into CO₂ and H₂O.2,4-DCP was degraded to p-chlorophenol.It was speculated that most of the final product was mineralized into CO₂ and H₂O,and there was still a small amount of p-chlorophenol and undegraded 2,4-DCP in the rest.（2）Taking benzoic acid（BA）,phthalic acid（PA）,hemimellitic acid（HA）and 1-naphthoic acid（1NA）as research objects,the effects of different aromatic acids on the physicochemical properties and microbial community of anaerobic granular sludge were investigated.The results showed that in the 40-day exposure experiment,the COD removal rate of the group added with1NA was 86.09%,decreasing by 7%compared with the control group.The PS content of LB-EPS and TB-EPS of anaerobic granular sludge in the four experimental groups was0.30-1.28 mg·g^-1 and 0.19-1.03 mg·g^-1 higher than that in the control group,respectively.Meanwhile,the PN content was 0.025-0.326 mg·g^-1 and 0.007-0.171 mg·g^-1 higher than the control group,respectively.In the LB-EPS of EEM fluorescence spectra,the humic acid-like substance fluorescence peaks mostly appeared in the experimental group containing HA and1NA,and the intensity of the coenzyme F₄₂₀ peak decreased.For enzyme activity,the relative activity of acetate kinase（AK）in the experimental group containing HA and 1NA decreased by65.26%and 6.93%compared with the control group.Through high-throughput sequencing technology,the dominant abundant bacteria in the control and experimental groups were Proteobacteria,Chloroflexi,and Firmicutes.The relative abundance of Actinobacteria decreased,while the relative abundance of Bacteroidetes and Synergistetes increased in the presence of HA and 1NA.For archaea,Methanothrix was dominated in the control group and the experimental groups,accounting for 49.95%-80.40%.However,the relative abundance of Methanothrix in the experimental group decreased by 10.69%-30.45%,especially in the experimental group with1NA.While the relative abundance of Methanospirillum increased to 34.08%in the presence of1NA.The function prediction of bacterial and archaea genes indicated that the main functional groups were metabolism,genetic information processing,environmental information processing and cellular processes.Meanwhile,the amino acids metabolism bacteria in the anaerobic granular sludge was enhanced in the presence of aromatic acids.（3）Three types of biochar were prepared,namely biochar prepared from corn cob（CB）,ferric chloride modified biochar(CB+Fe³⁺)and chitosan modified biochar（CB+Chitosan）.In the Fourier Transform infrared spectroscopy（FTIR）analysis,CB+Chitosan significantly changed the chemical groups of the original biochar.X-ray diffraction spectroscopy（XPS）after biochar-enhanced anaerobic granular sludge treatment of BPA shows that oxidation-reduction reactions have occurred on the surface of the biochar modified by ferric chloride.FTIR analysis of anaerobic sludge enhanced by surface biochar could provide more adsorption sites.Characterization and analysis after biochar-enhanced sludge treatment of 2,4-DCP,it could be seen from XPS analysis that C-C and C-H were the main forms of C on the sludge surface.There was no difference in the composition of carbon and oxygen functional groups between the biochar-enhanced sludge and the unenhanced sludge after treating 2,4-DCP wastewater.In the FTIR analysis,the intensity of the peak at 1406 cm^-1 of the sludge enhanced by the modified biochar was reduced,which corresponds to the C-O-C tensile vibration of polysaccharides or polysaccharide-like substances.（4）The process and mechanism of BPA removal by biochar-enhanced anaerobic granular sludge system were discussed through pollutant degradation rate,sludge EPS composition,key enzyme activity and microbial community.The biochar-enhanced anaerobic treatment showed a good pollutant removal effect when treating BPA wastewater.The average COD removal rate of the control sludge without biochar was 84%.The average COD removal rates of sludge enhanced by CB,CB+Fe³⁺and CB+Chitosan were 89%,91%and 91%,respectively.Compared with CB enhanced anaerobic system,CB+Fe³⁺and CB+Chitosan have a better effect on removing BPA,and the removal rate of BPA was between 92%-96%.The EEM spectra of TB-EPS showed absorption peaks of tryptophan protein,aromatic protein,and coenzyme F₄₂₀.The intensity of the three peaks of anaerobic sludge enhanced by biochar was greater than that of the control group.With the increase of BPA dosage,the content of coenzyme F₄₂₀ keeps increasing.When biochar-enhanced sludge was exposed to BPA,the abundance and diversity of bacteria were increased.At the phylum level,the abundance of Proteobacteria and Fimicutes decreased after the removal of BPA by the biochar-enhanced anaerobic granular sludge.Among them,the Proteobacteria abundance of the sludge enhanced with CB+Fe³⁺and CB+Chitosan modified biochar decreased the most,with a decrease of 7.95%and 10.75%respectively.（5）In the study of the degradation of 2,4-DCP by biochar-enhanced anaerobic granular sludge,it was found that when the dosage of 2,4-DCP was 200 mg·L^-1,the removal rate of COD in the control group was 72.4%.The COD removal rate of the experimental group after CB,CB+Fe³⁺and CB+Chitosan enhanced sludge were 83.7%,86.7%and 85.6%,respectively.When the dosage of 2,4-DCP was 200 mg·L^-1,the removal rate of 2,4-DCP in the anaerobic system enhanced by modified biochar was 13.8%-15.3%higher than that of the control group.When the dosage of 2,4-DCP was 200 mg·L^-1,the PN and PS content of the control group were（1.01±0.10）mg·g^-1,and the PN content of the experimental group enhanced by modified biochar was（3.50±0.38）mg·g^-1 and（3.32±0.49）mg·g^-1.The analysis of the archaea community at the genus level found that the relative abundance of Methanothrix in the sludge enhanced by biochar was higher than that of the unenhanced sludge after 2,4-DCP treatment,while the relative abundance of Methanobacterium was reduced.At the bacterial phylum level,the experimental groups B,C and D after the CB,CB+Fe³⁺and CB+Chitosan enhanced sludge were compared with the unenhanced sludge control group A,the abundance of Euryarchaeota increased by 17.47%,2.37%,and 3.07%,respectively.