| 其他摘要 | Waste disposal is a big problem during construction of new urbanization in China. Among all these wastes, domestic waste and straw are two important types of wastes in urbanization area, that's why we chose them as the substrates for anaerobic fermentation in this paper. The effects of the TS (Total Solid), the period of HP (Hydrogen production Phase), the mixing ratio of organic domestic waste to corn straw, and the thermal and micro-aeration pretreatments were studied. The micro-aeration was applied in the HP of these experiments to improve the performance of two-phase anaerobic fermentation. These studies help us to establish efficient two-phase anaerobic fermentation to solve the problem of waste disposal. The main contents of this dissertation are as the followings:
Firstly, the mixed substrate of organic domestic waste, dewatered sludge, livestock manure and kitchen waste was used for two-phase fermentation at TS of 4% and 6%, and results were compared with that of single substrate with only organic domestic waste. Results showed that the hydrogen production of single substrate was higher than those of the mixed substrate. Hydrogen production, VFA (Volatile Fatty Acid) production, VS (Volatile Solid) reduction and methane production with 4%TS were all higher than those with 6%TS. The methane production rate and cumulative methane yield of the two-phase fermentation were significantly higher than those of the single phase fermentation. Among all the experiment groups, 4%TS with a 1.5 d HP reached the maximum methane production of 441.96 mL/gVS, which was 42.04% higher than that of single phase fermentation.
Secondly, in order to investigate the effect of micro-aeration on the co-production of hydrogen and methane from domestic organic waste, different concentrations of oxygen (0,5,10,20 mL/gVS) were supplied at the initial stage of the two-phase fermentation. Results showed that the maximum hydrogen yield (72.23 mL/gVS) was obtained at the oxygen load of 5 mL/gVS, which was 45.51% higher than that of sample without micro-aeration. Though the maximum methane yield (380.35 mL/gVS) was also obtained at the oxygen load of 5 mL/gVS, it had no significant difference with other groups. Overall, the highest VS degradation (75.66%) and energy recovery (72.76%) were simultaneously obtained at the oxygen load of 5 mL/gVS, which were (5.70±0.85)% and (5.33±0.66)% higher than those of sample without oxygen. Micro-aeration (5 mL/gVS O2) at the initial stage of the two-phase fermentation was an effective approach to improve the performance of the two-phase fermentation.
Thirdly, the organic domestic waste and corn straw were mixed with the ratios of 0:1, 1:1, 2:1, 4:1 and 1:0 based on TS, to evaluate the effect of mixing ratios on the two-phase fermentation. Results showed that the mixing ratio of 2:1 got the best performance of VFA production and got the second highest methane production, which indicated that 2:1 is an appropriate mixing ratio that benefited the fermentation performance. Furthermore, the 2:1 mixed substrate was pretreated at 150℃ for 2 h, it was found that the soluble carbohydrate, soluble protein and SCOD (Soluble Chemical Oxygen Demand) were improved by 36.28%, 29.44% and 69.75%, respectively. The thermal pretreatment lead the pH and the propionic acid concentration of HP both lower than the unpretreated experiment, which meant that it make the substrate more digestable and the fermentation more stable. Although thermal pretreatment delayed the production of hydrogen, it improved the hydrogen yield by 92.16%.
At the end, intermittent micro-aeration pretreatment was investigated for improving the performance of two-phase fermentation with corn straw as substrate. Total oxygen loads of 0, 1, 2, 4, 8 mL/gVS were injected in the 5 days HP step at the same time of each day. Results showed that the group with oxygen load of 1mL/gVS got the highest VFA production(2454.01 mg/L), the highest hydrogen yield(10.34 mL/gVS), and the highest methane yield(284.51 mL/gVS), which were 15.09%, 14.25% and 12.55% higher than the group without oxygen, respectively. The methane production data was fitted by the modifed Gompertz equation model and results showed that the methane production rate is improved under intermittent micro-aeration process with oxygen load of 1mL/gVS, while excess oxygen inhibited the methane production rate. The intermittent micro-aeration process has no significant effect on the lag phase of fermentation, but the optimum oxygen load significantly shortened the fermentation period. Experiment results showed that the intermittent micro-aeration could effectively improve the performance of two-phase fermentation. |
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