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The sludge has low organic matter content, low C/N, and poor biodegradability. The gas production rate and organic matter degradation rate of the sludge are both low. Mixed anaerobic fermentation of high organic content and easily biodegradable food waste and sludge is an effective way to increase the gas production rate of sludge alone. After sludge and food waste are mixed in a certain ratio, the nutrient elements and trace elements of the fermentation substrate can be optimized, and the buffering capacity of the system can be improved, thereby increasing the methane production rate, shortening the fermentation cycle, increasing the removal rate of organic matter and the anaerobic fermentation tank volume utilization rate. This study explores the effect of vegetable oil content on the anaerobic fermentation of sludge and food waste, and the effect of low-temperature heat treatment on the anaerobic fermentation of sludge and food waste. The CSTR reactor is used for dehydrated sludge and food waste mixed anaerobic fermentation. The aerobic fermentation experiment studies the operation of mixed anaerobic fermentation of dehydrated sludge and food waste. Experimental results show that when the vegetable oil content is 0-30%, the methane production rate increases with the increase of the vegetable oil content. When the vegetable oil content is 30%, the methane production rate reaches the highest, which is 449 mL/g-VS. When the vegetable oil content is 40%-50%, the anaerobic fermentation process is completely inhibited, and mixed fermentation can improve its oil tolerance. Low-temperature heat treatment can increase the initial methane production rate of anaerobic fermentation, and after low-temperature heat treatment of the mixed substrate, the methane production rate and the initial methane production rate of anaerobic fermentation increase with the increase of heat treatment time and temperature. In the mixed anaerobic fermentation of dehydrated sludge and food waste, the gas production varies greatly, the start-up period is long, and the gas production rate is low. [ABSTRACT FROM AUTHOR]

In order to study the effect of the different ratios on the anaerobic fermentation rate is investigated, and the rate-limiting factors are preliminarily determined, at mesophilic (38±1)℃ condition, with anaerobic granular sludge as inoculums, different ratios of cow manure and corn straw are used as substrate for mixed anaerobic fermentation. By measuring daily biogas production, the concentrations of CH4 and CO2 in the marsh gas, TC, the concentration of VFAs and pH value, The results show that under the mixture ratio of 2∶1, the hydrolysis rate constants, cumulative biogas yield and biodegradability CH4 reach their high limits, which are 0.043 7 d-1, 271.93 mL/g and 71.59%, respectively. Moreover, it is found that the concentration of acetic acid is proportional to the amount of cow manure at the beginning (the first day) of mixed fermentation, and the concentration of propionicacid is proportional to the amount of corn straw in medium fermentation stage (the fifth day). In addition, rate-limiting step of biogas production is related to the ratio of cow manure and corn in fermentation material. With the increasing of corn straw proportion, on the 1st day, it tends to hydrolysis acidogenesis; from the 2th day to 15th day, it tends to hydrogen-production acetogenisis; and from the 16th day to 30th day, it is hydrolysis acidogenesis. The paper focuses on the relationship between the ratio of cow manure and corn straw and the rate-limiting step for biogas production, which could provide a theoretical and experimental support for improving the efficiency of biogas production in mixed fermentation.

In this study the effect of trace elements on methanogenesis was investigated during mixed anaerobic fermentation using a single-factor experiment in the present study. The most effective concentrations of Fe0, Fe2+, Co2+ and Ni2+ that were added were 1500, 250, 0.3 and 0.6 mg/L, respectively. The optimal trace element combination was 0.58 mg/L Ni2+, 1200 mg/L Fe0 and 0.34 mg/L Co2+ by the ternary quadratic general rotary unitized design method. The degree of influence exerted by trace elements on the cumulative methane yields decreased in the order of Ni2+, Fe0 and Co2+, and the maximum CH4 yield was 241.6 mL/g volatile solids (VS), according to a regression equation. The non-dissolved organic carbon hydrolytic process showed a good fit with the first-order kinetic model. The maximum value of CH4 was 312.87 mL/g VS. Compared to the control, the bioconversion efficiencies of CH4 and CO2 production increased by 36.76% and 74.50%, respectively, at the optimal trace element combination. The obtained results provide new knowledge for improvements in the efficiency of anaerobic fermentation biogas production.

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