Separation Of Cellulose Decomposing Strains And Study On The Methane Production From Fermentation Of Food Waste With These Strains

Pretreatment of food waste can change the raw material structure and increase the potential of methane production.The difficulty of cellulose degradation is one of the factors that limit the rate of hydrolysis.In order to change the raw material structure of food waste and improve the capacity of methane production,three cellulose degradation strains were disolated in this paper,which were labeled as Z1,Z2 and Z3 respectively.Using cell culture,morphological characteristics and 18sr DNA sequence analysis,it was determined that the three strains belonged to Rhizopus oryzae,Aspergillus Niger and Aspergillus oryzae,respectively.They were named as Rhizopus oryzae Z1,Aspergillus Niger Z2 and Aspergillus oryzae Z3.It was found that the three strains could produce high activity cellulase.Rhizopus oryzae Z1 also had high activity of mashing enzyme and Aspergillus oryzae Z3 had high activity of protease.The growth characteristics and enzyme production conditions of the three strains were studied.According to the results of single factor experiment,the enzyme production conditions of different strains were optimized by using design-expert software.The cellulolytic activities of strains Z1,Z2 and Z3 were increased by 54.00%,11.80%and42.60%,respectively.Cabbage(Brassica oleracea L),celery(Apium graveolens)and chinese cabbage(Brassica rapa pekinensis)are common cellulose rich vegetables in food waste.In order to verify the cellulose degradation ability of the three strains,the cultures of three cellulose decomposing strains were inoculated into several different vegetables containing rich cellulose at certain proportions.Taking TS as the evaluation index,the optimal degradation conditions of different strains on different vegetables were determined through experiments.Infrared spectroscopy showed that the structural of these vegetables changed significantly after degradation.The infrared spectra of the celery showed that the transmissibility at all peaks was higher than that of the celery after degradation by strains of Z1,Z2,Z3 and Z1+Z2+Z3,respectively.Many new absorption peaks appeared range the wave number numbers from 1070cm^-1to 1380cm^-1.The transmissibility from Z1+Z2+Z3 experienced the biggest growth.The infrared spectra of the chinese cabbage showed that many new absorption peaks appeared at the wave number 1250cm^-1 after degradation by strain Z2.The transmissibility from strain Z2 experienced the biggest growth.The kinetic model was used to study the degradation process of different strains on several vegetables.It was showed that the strains Z1,Z2 and Z3 had better fitting effect on the cabbage,celery and chinese cabbage after 12h degradation than 18h.For Z1,the degradation process of the cabbage and celery were in line with the flaky model and the degradation process of the chinese cabbage was in line with the columnar model.For Z2,the degradation process on the cabbage,celery and chinese cabbage conforms to flaky model,columnar model and flaky model,respectively.For Z3,the degradation process of on the cabbage,celery and chinese cabbage conforms to the flaky model,column model and spherical model,respectively.The synergistic effect of the three strains on the anaerobic fermentation of the co-digestion of food waste and cow dung was studied.The changes in the daily methane rate,TVFA(Total volatile atty acids,p H,coenzyme F₄₂₀ and propionic acid concentration were determined and the results showed that the biological pretreatment from the strains can promote the process of the anaerobic fermentation of the co-digestion to produce more methane.Compared with the control group,the time of the first peak of daily methane production rate of the pretreated groups of strains Z1,Z2 and Z3 were all 5 days earlier than that of the control group,and the daily methane production rates were increased by 60.00%,40.00%and 23.00%respectively.Rhizopus oryzae Z1 had more obvious promoting effect at the early stage of fermentation,while the Aspergillus Niger Z2 had stronger promoting effect at the later stage.The concentrations of TVFA in the pretreatment groups were all higher than that in the control group.The TVFA accumulated before three peaks of methane production appear,however,the TVFA concentration did not exceed 30.00g/L.The concentration of F₄₂₀ was consistent with that of daily methane rate.For Aspergillus oryzae Z3,the concentration of F₄₂₀ was fluctuated greatly.Compared with the control group,the VS(Volatile solid)removal rates were higher in the pretreatment groups.In the pretreatment stage,the VS removal rates were increased by 375.00%,300.00%and 325.00%respectively.In the whole anaerobic digestion stage,they were increased by 15.00%,13.70%and 17.50%respectively.The concentrations of propionic acid in the pretreatment groups were significantly decreased than that of the control group.The?G₀ of the propionic acid is greater than the butyric acid,acetic acid and formic acid.From the thermodynamics view,it was confirmed that pretreatment group has high methane production rate than the control group.The methane production rates and the methane potentials were all higher than those of the single food waste and cow dung group.After pretreatment by strains Z1,Z2,Z3,the methane potentials were increased 173.00%,177.00%and 119.00%respectively,The methane production rates were increased 193.00%,158.00%,134.00%respectively.The dynamic fitting results showed that the methane production demurrage times of co-digestion after pretreatment by the strains Z1,Z2,Z3 were ahead of the 1.74d,1.74d,1.91d,respectively.Compared with control group,the synergistic effect of biological pretreatment groups was obvious.Among them,Z1 had the most obvious promoting effect.High-throughput sequencing was used to analysis the bacterial communities of the cellulose degradation strain Z2,Z3 and Z1 pretreated groups.The group containing food waste and cow dung without addition of the strains but hydrolysis for 12h and the group of food waste and cow dung were used as the control groups.They were labeled as A,B,C,D,E groups respectively.The relative bacterial abundances in the pretreatment groups were higher than that of the control groups.The C pretreated group has the highest relative abundance,with higher species diversity and evenness.The abundance of dominant bacteria in the pretreatment groups was higher than that in the control group.There were seven dominant phyla with the abundance greater than 1%in different groups.The abundance of the dominant phyla changed in the pretreatment groups.Thermotogae and Proteobacteria had the highest abundance in group A,Synergistetes and Euryarchaeota had the highest abundance in group B.Firmicutes and unclassified bacteria had the highest abundance in group C,the abundance of Bacteroidetes was the highest in group E.Lactobacillus,Clostridium,Bacillus and Defluviitoga were the most abundant dominant genus in all the pretreatment groups,but the abundances were changed in the different pretreated groups.The abundance of Defluviititoga was 42.51%in group A.The abundance of Aerobaculum was the highest in B group.Compared with the control group,the abundance of Coprothermobacter in pretreatment groups was obviously decreased,and the abundance of Methanocytoleus was obviously increased.