Research On Enhanced Production Of Volatile Fatty Acid From Food Waste: Effects Of Salt And Grease

As we known, landfill of food waste usually coast lots of land. Thus using food waste to produce volatile fatty acids by anaerobic method can resolve this problem. The VFAs can be used as carbon sources in the biological removal of nitrogen in municipal or industrial wastewater treatment plants. Additionally, VFAs can be used to produce not only polyhydroxyalkanoates(PHA), which are biodegradable and used in the production of bioplastics, but also VFAs can be used to generate hydrogen via steam reforming on alumina-supported platinum catalysts, such as Pt/Al2O3. So we studied the effect of salt and grease on VFAs production from food waste:Under laboratory condition, we examined the effects of salt and grease on food waste acid genesis, investigating their impact on the concentration and yield of VFAs, component proportions of VFAs, SCOD/NH4+, TS/VS, and concentration of alkali ions. The results show that, Na Cl can inhibit VFAs production, when Na Cl content exceeds 6.0g/L, the inhibition of acid production increase rapidly. If it reach to 12.0g/L, food waste almost stop producing acid. But Na Cl don’t effect anaerobic fermentation type, and all the batch fermentation is butyric acid type fermentation. Besides, grease also have obvious effect on VFAs production, which are reduction of acid production and the lag of the acid production. When grease content is 35g/L, the maximum VFA concentration decreased by 68%, and acid production lagged 39.4h. Grease will also change anaerobic fermentation type from butyric-acid-type to propionic-acid-type.Additionally, we reveal a weak antagonism between the inhibitory effects of Na Cl and grease. That is, the inhibition of VFA production by the combination of salt and grease is intermediate between that of salt and grease independently. Besides, the change of VFAs component in each fermentation shows the same pattern, and the main component are acetic, propionic and butyric acid. Proportion of butyrate increases rapidly in early fermentation, and then tends to be stable. But proportion of acetic and propionic acid have little change in the fermentation process. In addition, Na + concentration in fermentation will rise gradually, synchronized with VFAs production. So, when we use actual food waste to produce VFAs, we should conduct pretreatment to make sure Na Cl content less than 6.0g/L with grease content less than 15.0g/ L, and harvest VFAs in the 2-3 days of fermentation.Based on the lab tests, we construct a 3.5t/d pilot project. In this pilot project, fermentation substrate is a mixture of the food waste and anaerobic sludge, and TS and VS of the substrate is 128.2 and 107.4g/L. In the fifth days of fermentation, the yield of VFAs achieved maximum at 21.8g/L, which is close to the results of laboratory experiment. This suggested that using food waste to produce VFAs by anaerobic method is suit for large-scale production.