| The livestock and poultry breeding industry in China is developing rapidly,and the amount of livestock manure is large.However the utilization rate of resources is relatively low,the problem of environmental pollution is serious.Biotechnological methods such as anaerobic digestion can effectively absorb aquaculture waste and realize the resource utilization of agricultural waste.Compared with liquid anaerobic digestion,solid state anaerobic digestion(SS-AD)has the advantages of high organic load,low energy consumption and convenient utilization of fermentation residues,and has broad development prospects.Although SS-AD has many advantages,the inhibitory effect of volatile fatty acids(VFAs)and other intermediate products often causes problems such as slow fermentation start-up and low biogas production efficiency.This thesis uses pig manure as the main fermentation substrate,and focuses on the study of VFAs inhibition,ammonia stress and VFAs-ammonia interaction in SS-AD of pig manure,and proposes methods for adding auxiliary materials to reveal inhibition mechanism of VFAs and ammonia nitrogen in SS-AD,explore the technological measures of inhibition and regulation,and provide theoretical basis and technical support for the energy utilization of livestock and poultry farming manure.The main findings are as follows:(1)The results of the study on the law of VFAs inhibition in SS-AD of pig manure showed that with the increase of the concentration of exogenous VFAs,the cumulative specific methane yield(SMY)gradually decreased,and the lag period was prolonged.When the addition amount of acetic acid and propionic acid was 6 mg/g,the cumulative SMY was 32.21 and 17.46 mL/g,which were reduced by58.24% and 77.37% compared with the control group,and the corresponding lag periods were 16.53 and 18.51 d,respectively.It is 2.63 times and 2.95 times that of the control group.The increase in the concentration of exogenous VFAs promoted the increase in the richness and diversity of the archaeal community in the system.Methanosarcina had an absolute advantage in each treatment group,and its relative abundance was negatively correlated with the concentration of exogenous VFAs.In this experiment,the inhibition thresholds of acetic acid and propionic acid were 9.30～11.24 mg/g and7.59～7.98 mg/g,respectively.(2)The results of the study on the characteristics of ammonia stress in SS-AD of pig manure show that different exogenous nitrogen sources have significant effects on the performance of SS-AD of pig manure straw.When ammonium chloride is used as exogenous nitrogen,the efficiency of methane production is inhibited to varying degrees under each addition amount,and the cumulative SMY is reduced by 13.60%～57.74% compared with the control group;compared with the control group,the addition of 1 mg/g-N urea,the cumulative SMY increased by 29.00%;when 1 mg/g-N and 3 mg/g-N ammonia were added,the cumulative SMY increased by 12.08% and 3.90%,respectively.The occurrence of ammonia suppression is accompanied by the accumulation of VFAs.The accumulation of VFAs in the ammonium chloride group showed propionic acid accumulation;the accumulation of VFAs in the urea group showed the accumulation of acetic acid;the accumulation of VFAs in the ammonia group was dominated by the accumulation of acetic acid in the early stage,and the concentration of propionic acid continued to increase in the later stage of fermentation.As the fermentation progressed,the diversity of bacteria in different nitrogen sources added groups gradually increased,and the community abundance gradually decreased.High ammonia nitrogen content leads to different degrees of ammonia inhibition.Due to various factors such as nitrogen form and system buffering capacity,the total ammonia nitrogen(TAN)(free ammonia nitrogen(FAN))threshold for system inhibition in this study is quite different.(3)The results of the study on the synergistic effect of VFAs-ammonia in the SS-AD of pig manure show that the combined action of 1 mg/g-N urea and different concentrations of acetic acid can improve the biogas production performance of SS-AD,of which 1 mg/g-N urea+5 mg/ g acetic acid of cumulative SMY was the highest,reaching 97.15 mL/g,which was an increase of 18.17% compared with the control group.When 5 mg/g-N urea is combined with different concentrations of acetic acid,anaerobic digestion is severely inhibited,and the cumulative SMY is reduced by 65.62% to 69.88%compared with the control group.Firmicutes has an absolute advantage at the bacterial phylum level in each test group,and its relative abundance gradually decreases with the progress of fermentation.The diversity of the archaeal community is positively correlated with the concentration of exogenous urea,but has no obvious relationship with the concentration of exogenous VFAs.(4)The results of the study on the regulation of the inhibition in the SS-AD of pig manure showed that the mass concentration of total VFAs decreased with the increase of the added proportion of vermiculite and biochar.Compared with biochar and vermiculite,there was no significant difference in TVFAs concentrations for different proportions of added sepiolite.Compared with SS-AD of pig manure without any additive,the lag phase of different biochar addition ratio could be shortened by31.23% to 83.90%.At a 10% addition ratio of addivite,vermiculite,sepiolite and biochar increased the cumulative SMY rate by 98.97%,76.78% and 93.06% respectively.When the addition ratio increased to 20%,the SMY reached at 3.62 mL/g,2.87 mL/g and 3.15 mL/g,and the cumulative SMY were106.38 mL/g,106.68 mL/g and 126.23 mL/g,respectively.The addition of vermiculite,sepiolite and biochar could alleviate the acid inhibition and increase the methane yield in SS-AD process with pig manure as substrate,and the effect of biochar was superior to that of vermiculite and sepiolite. |
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