Process Research On High-temperature Dry Anaerobic Digestion Of Restaurant Garbage

Dry anaerobic digestion refers to the anaerobic digestion process that the total solid content of the digested substrate within 20-40%. It demands less water which can significantly reduce energy costs. And the low construction cost and its high added-value digestive products bring broad prospects to dry anaerobic digestion technology.First of all, the characteristics of restaurant garbage were analysed, the results showed that restaurant garbage was rich in biomass components, containing most nutrients that micro-organisms need, and heavy metal elements was tiny. It meant that restaurant garbage was a kind of high organic solid that typically suitable for anaerobic biological treatment.It was investigated that the effect of inoculation content, soild content, oil content, salt content and hydrolytic acidification on dry anaerobic digestion of restaurant garbage. The results showed that at thermophilic condition(55 ℃), the maximum gas production rate was obtained at inoculation content of 30%, solid content of 20%, which was 180.14 mL/g TS; and compared to the other digestion system, the maximum value of gas production rate reached the maximum at salt content of 3% and oil content of 6%, which were 208.06mL/g TS and 217.05 mL/g TS, respectively. From the comparison with the dry anaerobic digestion under mesothermal condition(35℃), it could learn that at 55℃ the digestion system was more stable, digestive cycles was 1-2 days shorted, TS and VS removal rate were increased by more than 10%. Results showed that the production rate of the restaurant garbage after 1d hydrolytic acidification was 109.77mL/g TS, just 60.88% of the0 d hydrolytic acidification system. So in order to reduce resources waste, timely treatment and disposal were recommended.In order to improve the gas production rate, the effect of hydrothermal pretreatment on dry anaerobic digestion of restaurant garbage was investigated. Orthogonal test L9(33)was employed to determine the effects of the three factors including water addition ratio,temperature and time. The result showed that the maximum value of SCOD was obtained at water addition ratio of 50%, 120 ℃ and 80 min, increased by 5.65 times compared with the untreated group. The gas production rate also reached the maximum at this pretreated condition, which was 269.10 mL/g TS, increased 40.51% compared with the untreated group. The effects of temperature and time of hydrothermal process on restaurant garbage digestion were evident, while the effect of water addition ratio was less evident.The effect of hydrothermal pretreatment time on dry anaerobic digestion of restaurant garbage, when the temperature was 100℃ and the addition ratio was 0, was investigated.The results showed that physical and chemical properties of restaurant garbage changed significantly. When the heating time was 15 minutes, the value of SCOD reached maximum and up to 59.49 g/L, which was 3.33 times more than that of the untreated group.The gas production rate was also reached the maximum at this pretreated condition, which was 219.11 mL/g TS, increased 48.62% compared with the untreated group.Finally, the effects of two additives on dry anaerobic digestion of restaurant garbage were investigated. Results showed that the active carbon of 22.5g/kg TS worked best, its first peak value increased by 30.9% compared with the control group, digestive cycles was1-2 days shorted than the control group, and the gas production rate were also reached the maximum at this condition, which was 231.02 mL/g TS, increased 27.77% compared with the control group. The effect of nutrient addition on anaerobic biogas digestion was "make good effect at low concentration, inhibitory effect at high concentration" trend. The optimum quantity of nutrient solution was 22.5 mL/kg TS, when its gas production rate was 226.10 m L/g TS, 24.94% higher than control group.