| According to the UN Food and Agriculture Organization,about 16 x 108 tons of food waste is generated each year globally,causing a large number of unnecessary global environmental impacts such as greenhouse gas emissions,water use,land use and unnecessary natural and biological diversity on land and water.The Reduction,harmlessness,resource utilization and energyization of kitchen waste has become a hot spot in scientific research in recent years,and it is also an urgent problem to be solved in the world.Dark fermentation usually refers to anaerobic fermentation to produce hydrogen and acid.It refers to the process of converting organic matter into biological hydrogen in three steps by using the bacterial group multi-enzyme system.Hydrogen and volatile fatty acids?VFAs?have great economic value.There are many factors affecting dark fermentation.The existence of organic matter is based on a delicate balance,which may affect the stability of digestion in the treatment of food waste.The raw materials in the food waste are complex and diverse,which has a great impact on the fermentation process.In this study,two main components of food waste,protein and glucose,were selected to change the headspace factors in fermentation bottles in different ways to explore the fermentation process.This paper objectively analyzed the influence of each treatment on fermentation process,and provided the mechanism for the treatment of food waste in the future.Firstly,the effects of headspace pressure,protein concentration and HRT on VFAs were investigated by using protein as fermentation material.When the concentration of protein is less than 12.50 g/L and HRT is less than 36 h,VFA concentration is higher.Negative pressure conditions can significantly increase the concentration of VFAs,and the production rate of acid has similar results.By response surface analysis,the influence of three factors was obtained,and the optimal parameters were obtained when the maximum response values were VFA concentration and yield.Then,when glucose and protein were used as substrates and different headspace conditions?carbon dioxide with hydrogen,hydrogen with nitrogen,nitrogen sparging?were used for fermentation,the main factors affecting the fermentation process were partial pressure of hydrogen,partial pressure of carbon dioxide and homoacetogenesis.When protein is used as substrate,hydrogen partial pressure can only promote acid production at very low conditions.When hydrogen partial pressure is greater than 0.268atm,homoacetogenesis begins to play a major role in the fermentation process.Nitrogen sparing can reduce the acid yield,and carbon dioxide with hydrogen is more conducive to acid production.When glucose was used as substrate,nitrogen was propitious to gas production.At 40 L/d,the yield of hydrogen was the highest,which was 0.350 mol/mol glucose.In terms of VFAs,the main factors affecting the whole fermentation process are still partial pressure of hydrogen,partial pressure of carbon dioxide and homoacetogenesis.In carbon dioxide with hydrogen group,the concentration of VFAs fluctuates with the increase of H2 level,while in hydrogen with nitrogen group,the concentration of VFAs increases with the increase of H2 level to a certain extent,while in nitrogen sparing group,the concentration of VFAs decreases first and then increases.The trend of VFAs production rate is similar to that of concentration.In general,hydrogen and carbon dioxide mixtures are more suitable for acid production.When the flux balance analysis was carried out with glucose as the substrate,acetic acid and hydrogen were concerned.According to the model,yhe homoacetogenesis occupy a high position in the metabolic network,and its flux R21=0.147,which is much larger than other hydrogen-consuming pathways,had a significant impact on the hydrogen production process.Protein is a complex macromolecule structure whose composition varies greatly due to different amino acids.Therefore,it is not suitable for flow equilibrium analysis. |
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