| With the continuous improvement of people’s living standard,the production of food waste increases year by year.If it is improperly handled,it will breed a large number of bacteria,causing environmental pollution and harming human health.Therefore,the disposal of food waste is particularly important.Anaerobic digestion of food waste can bring well environmental and economic benefits.However,during anaerobic digestion,ammonia concentration in the anaerobic reactor is often increased due to the hydrolysis of food waste,thus affecting the stability of the anaerobic reaction system.Therefore,with food waste as the research object,the effects of different kinds of biochar and modified biochar on the efficiency and microecology of anaerobic reactor were investigated.In addition,the process of strengthening an expanded granular sludge blanket（EGSB）reactor to treat food waste under ammonia nitrogen stress was discussed by adopting three strengthening measures,namely,opening the cycle,adding modified biochar,and circulating and adding modified biochar.（1）The influent and effluent nitrogen compositions of the EGSB reactor employed for treating food waste operated under ambient temperature was evaluated.Additionally,changes of the bacterial community structures and its metabolic functions were investigated.Results show that the COD concentration in the influent increased to about 10000 mg/L and the COD removal rate stabilized at about 95%.In the three dimensional fluorescence spectra（EEM）,the fluorescence peaks of tryptophan-like substances appeared in both the influent and effluent,and the fluorescence peaks of the ultraviolet fulvic acid-like appeared in the effluent,and the intensity of the fulvic acid-like fluorescence peaks increased with the COD concentration in the influent.The dissolved ammonia nitrogen（D-ammonia）content was the largest,accounting for approximately 70-80%of the dissolved nitrogen in the effluent.The amount of particulate organic nitrogen（PON）decreased by about 25-33%.After increasing the organic load,the abundance of Bacteroidetes and Firmicutes increased from 25.50%and 24.07%to 27.52%and25.45%,respectively.While the abundance of Chloroflexi declined from 13.40%to 5.14%.Meanwhile,the abundance of Methanothrix increased from 30.82%to 70.25%,whereas Methanobacterium decreased from 66.14%to 14.49%.Amino acid,carbohydrate and lipid metabolism decreased at high organic loading rate（OLR）.（2）The effects of sewage sludge（SS）,food waste（FW）,corn cob（CC）and bagasse（BG）biochar on the anaerobic biological treatment of food waste were investigated.Meanwhile,the key enzyme activity,microbial community distribution and metabolic pathway of anaerobic sludge were analyzed.The results showed that the average COD removal rate increased by29.49%,23.16%,29.42%,and 40.29%after addition of the four kinds of biochar in the anaerobic reactor,respectively.The activity of acetokinase in the four anaerobic reactors was0.40,0.42,0.96 and 0.98 mmol/（L·g）,respectively.The high acetokinase activity of the anaerobic sludge in the CC and BG group demonstrated that the addition of the CC and BG biochar promoted the hydrolysis and acidification of food waste.EEM spectra of extracellular polymeric substances（EPS）in the anaerobic sludge showed that the intensity of the fluorescence peak of tryptophan proteins-like in the group with CC and BG was higher than that of the other two groups.The addition of CC and BG biochar promoted the formation and structural stability of anaerobic granular sludge.Meanwhile,the fluorescence peaks of fulvic acid-like substances and humic acid-like substances were the weakest in the BG group,indicating that the addition of BG could effectively reduce the microbial death caused by the inhibition of ammonia nitrogen.In the four anaerobic reactors,Bacteroidetes,Proteobacteria and Firmicutes were the dominant phylum,and the addition of BG biochar promoted the growth of Proteobacteria and Firmicutes.As for the archaea,Methanobacterium and Methanothrix were the dominant species.Methanobacterium in the SS group had highest abundance（53.48%）,while Methanothrix in the BG group had the highest abundance（42.72%）.Kyoto Encyclopedia of Genes and Genomes（KEGG）functional analysis showed that archaea and bacteria were mainly metabolized by carbohydrate and amino acids.In addition,the transport level of microbial membrane was improved in presence of BG and SS biochar.（3）Then using bagasse biochar as the substrate,the effects of iron modified（A）,chitosan modified（B）,iron-chitosan modified（C）,iron-magnesium-chitosan modified（D）biochar on the anaerobic digestion process,sludge characteristics and microbial community of kitchen waste were explored.The results showed that the average COD removal rate of the four reactors in the last five days was 86.95%,85.90%,92.22%and 93.29%,respectively.It was demonstrated that adding iron-magnesium-chitosan modified biochar could effectively improve the efficiency of COD removal in anaerobic reactor under ammonia nitrogen stress.When the anaerobic reactor C and D operated at the 10th day,the content of coenzyme F42020 in the sludge reached to 0.44 and0.57 mmol/g,respectively,indicating that the metal-chitosan complex biochar in the early stage of the experiment could promote the production of coenzyme F420.The bacterial community structure in the reactor D was the most abundant.In the four anaerobic reactors,Firmicutes,Bacteroidetes,Proteobacteria and Chloroflexi were the dominant bacteria,and the abundance of the bacteria reached a maximum of 26.24%in the reactor C.As for archaea,Methanobacterium and Methanothrix occupied the main positions,accounting for 44.03%,49.88%,31.29%,52.01%,38.34%,34.52%,50.9%and 35.72%respectively in the A,B,C and D reactors.KEGG functional analysis showed that the energy metabolism of bacteria and archaea in the reactor D was the largest among the four reactors.Meanwhile,the gene abundance of carbohydrate metabolism and membrane transport of microorganisms in the reactor D was greater than that of other groups.Through comprehensive analysis,iron-magnesium-chitosan modified biochar was selected to be added in the anaerobic reactor.（4）The effects of different influenc concentrations of ammonia nitrogen on COD and ammonia nitrogen removal in the EGSB reactor were investigated.The influent COD concentration remained at about 10000 mg/L,and when the ammonia nitrogen concentration increased to 1200 mg/L in the influent,the removal rate of COD reduced to about 75%,and the removal rate of ammonia nitrogen was only about 6%.Then take the opening cycle,adding the modified biochar,adding the modified biochar and opening the cycle these three strengthening measures,the results showed that the average COD removal rate of the anaerobic reactor in the last 5 days of each operating cycle was 85.51%,84.11%and 90.03%,and the average removal rates of ammonia nitrogen were 11.74%,11%and 12.47%,respectively.It was illustrated that adding modified biochar and opening cycle could better improve the removal efficiency of the anaerobic reactor for food waste under ammonia nitrogen stress.At the 30th day of each stage,the protease content in the sludge was 44.61,42.47,46.24 NH2-N（mg）/mg,and the content of coenzyme F42020 was 0.244,0.217,and 0.267 mmol/g,respectively.Proteobacteria,Bacteroidetes and Chloroflexi were the dominant bacteria in the three stages.Proteobacteria was the most abundant phylum in the first stage,reaching 34.36%.It was accounted for 16.68%and 21.38%,respectively,in the second and third stages.Different strengthening measures had a great impact on the archaea,the dominant archaea in the three stages were Methanosaeta,whose abundance was 38.98%in the first stage,and increased to 64.94%and 64.01%in the second and third stages,respectively.KEGG pathway showed that the abundance of membrane transport in the third stage was 6.13%,higher than 5.68%in the first stage and 5.74%in the second stage,indicating that the addition of modified biochar and the opening of the cycle could promote the function of microbial membrane transport in the anaerobic reactor.According to KEGG modules analysis,the abundance of environmental information processing genes in the third stage was 5.63%,higher than 5.00%in the first stage and 4.90%in the second stage.Among the active carbohydrate enzymes,the gene abundance of Glycoside transferases in the third stage was the largest in the three stages. |
