| Based on their particular characteristics of using food waste for butanol production and composting, the food waste was centrifuged after saccharification in this study and the supernatant (saccharification liquid) was used for butanol production and the solid phase (saccharification residue) for composting. This combined process not only broadened the source of substrate for butanol production, but also solved the resourcelization problem of the residue that could not be utilized by butanol-producing bacteria.Based on the thermal analysis, the butanol production with food waste saved the gelatinization and liquefaction processes as well as the processing cost in comparison with traditional substrates. Furthermore, the bacteria C. beijerinckii NCIMB 8052 was selected for butanol production. When the saccharification liquid was used as fermentation substrate and no extra nutrients was added (unregulated condition), butanol concentration, total solvent concentration, and butanol productivity were 5.95 g/L,8.23 g/L, and 0.139 g/L/h, respectively.The phenomenon of "acid crash" may occur under unregulated conditions during butanol fermentation with saccharification liquid, leading to slower fermentation starting, delayed phase shift, and lower butanol production. Therefore,0.3%(w/v) CaCO3 was used to improve the pH buffering capacity of the saccharification liquid and also relieve the inhibition of "acid crash". Further addition of 5 g/L yeast extract could positively stimulate the conversion of glucose. The butanol concentration, total solvent concentration, and butanol productivity were 11.7 g/L,16.7 g/L and 0.308 g/L/h, respectively, which were 96.6%,102.9% and 121.6% higher than those under unregulated condition.The dynamic model of butanol fermentation revealed that the higher biomass concentration is, the much higher butanol productivity is. Therefore, a batch butanol fermentation model with high cell density and a continuous butanol fermentation model with high cell density by cell recycling system were established in this study. The butanol concentration, total solvent concentration, and butanol productivity were 13.2 g/L,19.0 g/L and 0.746 g/L/h, respectively, under the batch model. Though the butanol and total solvent concentration were lower under the continuous model, the total amount of butanol and total solvent produced was higher. Moreover, the continuous model achieved a high biomass concentration up to 21.2 g/L and a butanol productivity of 1.37 g/L/h, which were 1.94 and 1.84 times that of the batch model. Therefore, the continuous butanol fermentation model with high cell density by cell recycling system established in this study was proved to be high efficient.In order to make full use of the food waste, the saccharification residue was used for aerobic composting and the community structure of the ammonia-oxidizing bacteria (AOB) was investigated. The community structure of AOB changed significantly with the increase of the pile temperature, and the Nitrosomonas-like and Nitrosospira-like lineages dominated through the whole composting process. The Nitrosomonas europaea/eutropha were the dominant strain in thermophilic stage and played an important role in the ammoxidation during food waste composting. Based on the Redundancy analysis and variation separation, N03"-N and pH had significant effect on the dynamics of AOB community (p<0.05). N03--N solely explained 27.3%(p=0.012) of the variation on the AOB species data, whereas pH explained 21.7% (p=0.024). These parameters were of great significance in regulating the activities of AOB community during food waste composting.The results in the current study have proved the feasibility of using the saccharification liquid of food waste for butanol production and the saccharification residue for composting. This combined technology has provided a new approach to realize energy and resource utilization of food waste. |
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