The Study Of Highly Efficient Fermentation Of Food Waste For Vfas Production And Its Preliminary Mechanism

This paper examined the effects of inoculated sludge and pH on food wastes acidogenic fermentation. Food wastes were pretreated by hydrothermal method to study the promoting effect of fermentation acid production. Also, a liquid-liquid extraction method was applied to recover VFAs from fermentation broth. At last, through the single substrate acidogenic fermentation based on food wastes, the VFAs production and composition of each carbon source were studied. And the produced acid pathways were analyzed. This article mainly obtains the following conclusion:(1) Compared to aerobic sludge, anaerobic sludge is more conducive to the food wastes fermentation for VFAs production. The optimal pH was6. The highest VFAs yields of aerobic and anaerobic sludge were0.482g/g VSSremoval and0.918g/g VSSremoval, respectively. And acetic and butyric acid were the major part in the produced VFAs. Lower pH condition could promote the hydrolysis of food wastes, but due to the microbial activity was inhibited, VFAs production was limited. After4d fermentation, the ammonia nitrogen release rate kept constant. When pH was6, butyric acid was the dominating acid, followed by acetic acid and propionic acid.(2) Hydrothermal pretreatment could decompose the recalcitrant part in food waste, thus lead an increase of soluble organic content. The optimal hydothermal temperature for organic dissolving was180℃. After hydrothermal pretreatment, VFAs production from food wastes fermentation was significantly improved, which got a VFAs yield of0.908g/g VSSremovai after160℃pretreated. Acetic and burytic acids accounted for70%of VFAs, and were still the main acids. However, once the hydrothermal temperature was more than180℃, the by-products would be formed which could inhibit the food wastes fermentation process.50-70%VFAs can be recovered by a liquid-liquid extraction method. Thus,0.294-0.411g VFAs could be obtained per gram of hydrothermally pretreated FW (in dry weight) by this method.(3) Hydrothermal pretreatment with phosphoric acid could enhance the organics dissolution of food waste in a short time. And the soluble organics quality was increased with the amount of Phosphoric acid addition. But the subsequent VFAs production from food wastes fermentation was only10%higher than unpretreated foo wastes. The most reson was the high salinity in phosphoric acid addition food waste.(4) The utilization rates of different carbon sources by acid-forming bacteria in sludge system were as followed, Glucose>Peptone>Glycerol. The highest VFAs yields of glucose, peptone, glycerol and mixture fermentation were38.2,32.2,31.1and38.5g COD/L. The main VFA component of glucose fermentation was burytate, and acetate for peptone, propionate for glycerol, propionate and burytate for mixture. By calculating, the ratio of acetate, propionate and burytate producing pathways of glucose is1:0.6:1.1. However, the VFAs producing pathway of glycerol was most likely through the realization of "glycerin--lactic acid--VFAs" approach.