Research On Methane Production Performance During Anaerobic Digestion Of Shell Wastes

With the improvement of human living quality,the consumption of fruit is increasing,producing more and more shell waste.Fruit waste is perishable due to the high organic matter.Improper treatment will pollute the environment and waste natural resources.Anaerobic digestion(AD)technology is suitable for the treatment of wastes rich in organic matter,which can not only effectively alleviate environmental pollution,but also produce clean energy.Therefore,this research mainly focuses on the AD of six kinds of wastes,and makes an in-depth study on the promotion of the methane yield performance of durian shell and jackfruit shell.Firstly,the properties and methane potentials of six kinds of wastes including coconut fiber,coconut shell,durian shell,jackfruit shell,grapefruit peel,and rubber seed shell were studied.Results showed that the jackfruit shell obtained the highest cumulative methane yield(CMY),which was 240.2 mL/gVS.The CMY of durian shell was 158.5 mL/gVS.The results of kinetic analysis illustrated that the modified Gompertz model could well simulate the methane production process of AD for these six kinds of wastes.Secondly,durian shell,jackfruit shell,coconut shell,and coconut fiber,with high lignocellulose contents and methane potentials,were pretreated by alkalis(NaOH,KOH,Ca(OH)2 and alkaline H2O2(alkaline hydrogen peroxide,AHP).Then,the effects of pretreatments on methane yields of AD were studied.Results showed that the CMY of coconut fiber pretreated by 7%NaOH reached 85.8 mL/gVS,which increased by 143.9%in relation to that of untreated froup.After 3%KOH pretreatment,the CMY of coconut shell was 25 mL/gVS.The CMY of durian shell pretreated by 7%NaOH reached 317.2 mL/gVS,which was 99.5%higher than that untreated of durian shell.5%AHP was the best pretreatment condition for jackfruit shell,and the CMY was 304.0 mL/gVS,which was 69.8%higher than that of raw materials(179.1 mL/gVS).The compositional and structural analyses of lignocellulose showed that NaOH and AHP pretreatment could effectively remove lignin and might increase the accessibility of microorganisms to cellulose.Finally,in order to gain higher methane yield,the durian shell pretreated by 3%KOH and the jackfruit shell pretreated by 5%AHP were co-digested with cow manure and pig manure in different proportions under the condition of total organic loading of 20 gVS/L and feed to inoculum ratio of 1.The methane yield performances of anaerobic co-digestion was studied.The results showed that durian shell showed synergistic effect with cow manure and pig manure,which was suitable for anaerobic co-digestion.The CMY of durian shell with cow manure and pig manure were 252.0 mL/gVS and 263.3 mL/gVS,respectively.The synergistic effect on the methane production was shown in all co-digestions of jackfruit shell and cow manure,while it detected in the co-digestions of jackfruit shell and pig manure at the ratio of 1:1 and 1:3.The synergistic effect on the methane production was shown in all co-digestions of jackfruit shell pretreated by 5%AHP and cow manure,while it detected in the co-digestions of jackfruit shell pretreated by 5%AHP and pig manure at the ratio of 3:1 and 1:3.This study improved the efficiency of recycling shell wastes into methane through pretreatment and co-digestion with manures,which provided data support and laid a theoretical foundation for the rational use of shell wastes in the future.