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Stillage reflux fermentation in food waste ethanol fermentation could reduce sewage discharge but exert a harmful effect because of side-product accumulation. In this study, regulation methods based on metabolic regulation and side-product alleviation were conducted. Result demonstrated that controlling the proper oxidation–reduction potential value (−150 mV to −250 mV) could reduce the harmful effect, improve ethanol yield by 21%, and reduce fermentation time by 20%. The methods of adding calcium carbonate to adjust the accumulated lactic acid showed that ethanol yield increased by 17.3%, and fermentation time decreased by 20%. The accumulated glyceal also shows that these two methods can reduce the harmful effect. Fermentation time lasted for seven times without effect, and metabolic regulation had a better effect than side-product regulation. [ABSTRACT FROM AUTHOR]

Raw materials and pollution control are key issues for the ethanol fermentation industry. To address these concerns, food waste was selected as fermentation substrate, and stillage reflux was carried out in this study. Reflux was used seven times during fermentation. Corresponding ethanol and reducing sugar were detected. Accumulation of by-products, such as organic acid, sodium chloride, and glycerol, was investigated. Lactic acid was observed to accumulate up to 120 g/L, and sodium chloride reached 0.14 mol/L. Other by-products did not accumulate. The first five cycles of reflux increased ethanol concentration, which prolonged fermentation time. Further increases in reflux time negatively influenced ethanol fermentation. Single-factor analysis with lactic acid and sodium chloride demonstrated that both factors affected ethanol fermentation, but lactic acid induced more effects. [ABSTRACT FROM AUTHOR]

To solve the inhibition issue caused by volatile fatty acids in two-stage dry anaerobic co-digestion of food waste and distillers grains, microzyme was added into the reactors in the acidification process with different pre-treated times of 12 h, 24 h and 48 h respectively. After pre-fermentation, all groups underwent anaerobic digestion under the same experimental condition. The purpose was to investigate the effects of pre-treated time on methane yield, the changes of parameters such as pH, TVFA, acetic acid, propanoic acid, and ethanol concentration in the methane fermentation process, and to compare them with the control group. The most innovative idea is that of the ethanol pre-fermentation process, food waste was converted into ethanol which decreased the other volatile fatty acids' concentration in the meantime. Since ethanol is neutral and it can convert into acetic acid, which can be directly used by methanogens, this ethanol pre-fermentation process can indeed improve digestion efficiency and methane yield in the following anaerobic system. Moreover, with less volatile fatty acids produced at the beginning of digestion, the acid accumulation issue could be well relieved in the future. This meaningful topic has been focused on by our research team since 2011. Please find more detailed information in our articles if you are interested. According to this experiment, the result showed that the ranks of ethanol concentration and pH (from high to low) of all groups were: pre-treated 48h > 24h > 12h > control. However, the ranks of acetic acid and TVFA concentration were the opposite. This phenomenon is caused by the ethanol pre-fermentation which can force more glucose to degrade into ethanol instead of other volatile fatty acids such as propanoic acid. Besides, the ethanol is neutral, and it can convert into acetic acid more easily than propanoic acid. Therefore, the pre-fermentation process can overcome the acidification issue caused by the accumulation of VFAs. As compared with the control group, the accumulated methane yields of pre-treated groups with 12h, 24h, and 48h were 9.1%, 31.6% and 19.9% higher respectively. The results indicated that the pre-treated group of 24h was the most effective. As well known, methanogens' activity is very sensitive regarding tiny changes of propanoic acid concentration. The ratio of PC/AC is also a warning indicator in anaerobic system. One relevant literature shows that a range of 0∼0.08 has a positive effect on methanogens. Interestingly, we found that there was a difference in the range-width among different groups. The rank of range-width (from high to low) in this result was: pre-treated 24 h>48 h>12 h> control. This result indicated that pre-fermentation could increase the suitable range-width in order to prevent the digestion system from acid accumulation issue. The same situation happened with the relationship between methane yield and initial ethanol concentration. It deeply explained the reason why anaerobic digestion could benefit from pre-fermentation. From another point of view, both the concentration of acetic acid and ethanol, microzyme and methanogen were reaching a dynamic balance. However, this complex mechanism of biology and dynamics should be discussed in future research. [ABSTRACT FROM AUTHOR]

The aim of the present study was to examine ethanol production from concentrated food waste hydrolysates using whole cells of S. cerevisiae immobilized on corn stalks. In order to improve cell immobilization efficiency, biological modification of the carrier was carried out by cellulase hydrolysis. The results show that proper modification of the carrier with cellulase hydrolysis was suitable for cell immobilization. The mechanism proposed, cellulase hydrolysis, not only increased the immobilized cell concentration, but also disrupted the sleek surface to become rough and porous, which enhanced ethanol production. In batch fermentation with an initial reducing sugar concentration of 202.64 ± 1.86 g/l, an optimal ethanol concentration of 87.91 ± 1.98 g/l was obtained using a modified corn stalk-immobilized cell system. The ethanol concentration produced by the immobilized cells was 6.9% higher than that produced by the free cells. Ethanol production in the 14th cycle repeated batch fermentation demonstrated the enhanced stability of the immobilized yeast cells. Under continuous fermentation in an immobilized cell reactor, the maximum ethanol concentration of 84.85 g/l, and the highest ethanol yield of 0.43 g/g (of reducing sugar) were achieved at hydraulic retention time (HRT) of 3.10 h, whereas the maximum volumetric ethanol productivity of 43.54 g/l/h was observed at a HRT of 1.55 h. [ABSTRACT FROM AUTHOR]