Study On Single Substrate Of Food Waste Anaerobic Degestion And Co-degestion With Lawn Grass

Developing research in anaerobic co-digestion of various substrates is an important way to transform municipal residues into resources and to reduce environmental pollution. Food waste is a kind of municipal residues with high fat content, for which it contained a high potential of biogas production. However, food waste was added into the anaerobic digestion system, long chain fatty acids which made the digesting substrate to produce the inhibitory effects on methane production during the anaerobic digestion process. Wet-based thermal treatment on food waste could achieve the purpose of food waste oil removal and collection, the oil collected could be used to converse into biodiesel and other high value-added products. On the other hand, wet-based thermal pretreatment would give physical and chemical properties changes of food waste, and then greatly improved the biodegradability of food waste and its biogas production efficiency of anaerobic digestion. Mono raw biomass anaerobic digestion of food waste may bring in unstability of anaerobic system, like acidification. Lawn grass was a rich biomass of a garden waste, the addition of it to food waste could play a role in maintain nutrients ratios, C/N balanced in anaerobic digestion, and then to increase the stability of the anaerobic digestion system.To study wet-based thermal pretreatment on the oil remove of food waste, several experiments were carried out. Three different temperature treatments(65 oC, 80 oC, 95 oC) and four different processing time(30 min, 60 min, 90 min, 120 min and 150 min) on food waste. The results showed that 95 oC, pretreatment for 90 min turned out to be the best wet-based thermal removing oil pretreatment, under the optimal treatment floating oil content reaches 4.22%, oil removal rate reaches 2.21%. The three different temperatures(65 oC, 80 oC, 95 oC) pretreatment of food waste were used for anaerobic disgestion experimental study, the largest actual biogas amount of food waste, 413 m L·g-1VS was produced by pretreatment of 95 oC, while 65 oC and 80 oC pretreatment had little effect on the amount of biogas production. Meanwhile, 95 oC pretreatment cause the p H of digesting culture stablily between 6.5 ~ 7.5, VFAs conversion rate of 74.31%, significantly higher than the other two groups preprocessing, TS and VS removal rate rised with treatment temperature increased, the removal rate was 56.2%, which was 8.1% higher than unpretreatment group.To compare the food waste and lawn grass performances on methane fermentation, food waste alone and lawn grass alone anaerobic digestion had been conducted, food waste alone digestion bring a total highest biogas production rate, 253.27 m L·g-1VS, while lawn grass alone for 25.58 m L·g-1VS. These two kinds of biomass resources both had the potential of biogas production, with easy degradation characteristics, food waste was more feasible to produce biogas, and lawn grass with pretreatment can shorten the time of acidification and then a gas production period is prolonged. In order to explore the food waste and lawn grass co-digestion performance, the same amount of mixing of food waste and lawn grass for preliminary exploration was carried out, the co-digestion resulted in a final cumulative gas production rate for 130.79 m L·g-1VS, compared with the mono-digestion of food waste, the p H in co-digetion system is in a more normal range, at the same time gas production is more stable.In order to determine the best ratio of food waste and lawn grass, seven different ratios,10:0, 8:2, 6:4, 5:5, 3:7, 1:9 and 0:10 were designed for researching the optimal. Ratio of 3:7 showed a maximum cumulative gas production rate of 268.78 m L·g-1VS, which were 1.44 times and 2.63 times than raw material only for food waste and raw material only for lawn grass. When the C/N ratio was 24.45, the largest total biogas production rate and the removal rate of VS showed out, which also illustrated that the best C/N in the anaerobic digesting system was around 25. The ratio of 5:5 and 3:7 were stable in p H changes, which is conducive to the stability of efficient anaerobic system.This paper focused on the existing problems that food waste anaerobic fermentation for biogas, whose system prone to be acidificated and producing inhibitions, through the thermal pretreatment on the oil remove of food waste and lawn grass addition to food waste system, such methods were to gradually strengthen the stability of the anaerobic digestion system. The results of this study can provide the basis for the combined raw biomass anaerobic digestion for biogas and the pretreatment of different raw biomass.