Research Of The Performance Of The Anaerobic Co-digestion Of Wasted Fat And Animal Manures

With the development of China’s social economy and the improvement of people’s living conditions,the amount of wasted fat produced is increasing year by year.Disposing of wasted fat will cause pollution to the environment and is also a waste of resources.On the other hand,the scale of livestock breeding in China is also expanding,and the amount of livestock manure produced is also increasing year by year.The harmful components such as pathogenic bacterium contained in the manure are also a threat to the surrounding people’s health if they are not treated properly.This study selected wasted swine fat as typical fat waste and cattle manure,swine manure,chicken manure as substrates,methane production and organic acid production as two different ways to study the synergistic transformation of oil and manure,in order to efficiently utilize the two waste resources,increase the added value,broaden the product range,and realize the win-win of environmental protection and economic value.Main research contents of this study are as follows:Firstly,this study investigated the methane production performance of wasted fat and three kinds of animal manures at a mixing ratio of 4:1,3:2,2:3 and 1:4.The results showed that the co-digestion performance of cattle manure and wasted fat was the best at the mixing ratio of 1:4,and the cumulative methane production reached 802.5 mL/gVS with the synergistic effect index(SEI)of 5.53%.The cumulative methane yield of swine manure and wasted fat reached the highest value of 777.9 mL/gVS with the SEI of 7.82%at the mixing ratio of 2:3.Methane production performance was also the best for chicken manure and wasted fat at the ratio of 2:3,whose cumulative methane production reached 767.4 mL/gVS with the SEI of 9.09%.Kinetic analysis results showed that the modified Gompertz model could well fit the methane production process of the co-digestion of wasted fat and animal manures.The co-digestion could increase methane production and shorten the lag phase.Secondly,the volatile fatty acid(VFAs)production performance of wasted fat and animal manures at different mixing ratios was studied.The results showed that under the organic loading ratio of 40 gVS/L,the maximum concentration of total VFAs obtained in the co-digestion of cattle manure,swine manure and chicken manure with wasted fat were 8025.6 mg/L,5535.2 mg/L and 6659.2 mg/L at mixing ratios of 1:1,1:3 and 3:1,respectively.Although the concentration of VFAs increased at the early stage of the reaction,methane was still detected,which indicated that the inhibition effect on methanogens was not obvious by merely heating the inoculum shortly.Finally,the effects of adding methane-producing inhibitors,extending the heating time of the inoculum,and increasing the organic loading ratio on the performance of VFAs production in the co-digestion of wasted fat and animal manures were explored.The results showed that VFAs production in codigestion of cattle manure and wasted fat was increased by 30.9%compared with control at BES concentration of 2 g/L.Adding BES did not significantly enhance the VFAs production in the co-digestion of swine manure and wasted fat while inhibited the co-digestion of chicken manure and wasted fat.Prolonging the heating time of inoculum increased the total VFAs yield of cattle manure and chicken manure by 14.1%and 16.0%,respectively.For monodigestion of swine manure,VFAs production performance was not significantly improved.However,the VFAs production from mono-digestion of wasted fat and co-digestion of wasted fat with animal manures decreased by extending the heating time.In addition,longer heating time would increase the proportion of butyric acid in the system.Increasing organic loading ratio could significantly increase the total production of VFAs in the co-digestion of animal manures and wasted fat.The total VFAs production of cattle manure,swine manure,and chicken manure at the stable stage under the organic loading of 100 gVS/L were 16405.2 mg/L,18527.0 mg/L,and 21769.2 mg/L,respectively.The total VFAs production of the co-digestion of cattle manure,swine manure,chicken manure with wasted fat during the stable stage were 10276.8 mg/L,6883.7 mg/L,and 16138.9 mg/L,respectively.This paper provides basic data for the synergistic transformation of wasted fat and animal manure,and lays a foundation for making full use of the two waste resources to produce biogas and organic acids in the future.