Research On The Methane Production Performance During Anaerobic Digestion Of Different Kinds Of Fruit Residues

Huge amounts of fruit residues are produced annually.Different with the traditional agricultural biomass waste such as crop straw,owing to their properties of high moisture and organic contents,fruits residues will easily deteriorate even for short-term disposal,which will breed mosquitoes,spread disease,and cause other environmental complications.Anaerobic digestion is quite suitable for reusing fruit residues,which could not only effectively degrade the waste,but also generate clean energy-biogas.Until now many researchers worldwide have made a thorough study of anaerobic digestion using agricultural,breeding,and municipal wastes.For fruit waste as a single substrate,it also deserves further studying.This study comprehensively investigated the methane production performance and the relative characteristics of different kind of fruit residues,and then carried out the research on optimizing the parameters focusing on durian shell and evaluated the anaerobic co-digestion condition with manure.First,the biomethane conversion performances of a 17 kinds of fruit residues were determined and compared using batch anaerobic digestion.The results showed that some fruit residues containing high contents of lipids and carbohydrates,such as loquat peels and rambutan seeds,were well fit for anaerobic digestion.Contrarily,residues with high lignin content were strongly recommended not to be used as a single substrate for methane production.Multiple linear regression model was adopted to simulate the correlation between the organic components of these fruit residues and their experimental methane yields,through which the experimental methane yield could probably be predicted for any other fruit residues.Four kinetic models were used to predict the batch anaerobic digestion process of different fruit residues.It was shown that the modified Gompertz and Cone models were better fit for the fruit residues compared to the first-order and Fitzhugh models.Second,based on above,according to the practical output and utilization value,deeper research on durian shell was performed.This part systematically investigated the anaerobic digestibility of durian shell and focused on maximizing the methane yield under different F/I and organic loading using response surface methodology.Results showed that in the F/I range of 0.2 to 2,a lower value was preferred,meanwhile the methane yield showed a sharp rise at first followed by a decline as the organic loading increased from 3 to 27 gVS/L.The highest EMY was calculated to be 170.6 ml/gVS at F/I of 0.2 and organic loading of 20.45 gVS/L based on the experimental result.In order to make the combination of F/I and OL more practical,0.5 was set as the optimum F/I,when the highest EMY was obtained to be 165.0 ml/gVS at the OL of 20.45 gVS/L.Characteristics of final effluent implied the anaerobic system was stable in this case.In addition,based on the results of RSM,the anaerobic co-digestion performance of durian shell and chicken,dairy,and pig manure with different ratios was investigated under the organic loading of 20 gVS/L,F/I=0.5.Results showed that chicken manure and dairy manure were not suitable as a co-substrate with durian shell during anaerobic digestion.While pig manure could enhance the methane production performance of the co-digestion system.When the organic loading between durian shell and pig manure was 50:50,the experimental methane yield was 224.8 ml/g VS,higher than the methane yield of durian shell or pig manure as a single substrate.The groups of durian shell:pig manure at 50:50 and 25:75 by organic loading showed synergetic effect.The difference of the actual methane yield and the weighted methane yield were 27.5 and 10.3 ml/g VS for these 2 groups respectively.The synergetic effect was more obvious for the group of 50:50,which was also found with a high methane yield.