| Food waste is rich in organic matter,which can be used for anaerobic digestion.Anaerobic digestion of food waste could be promoted by thermal pretreatment and alkali pretreatment.However,different results of appropriate temperature and time of thermal pretreatment were reported.Moreover,there are few systemic researches to investigate the effect of alkali pretreatment.This paper mainly focused on anaerobic digestion of food waste.A batch experiment was used to investigate the effect of temperature and time of thermal pretreatment.The impact of alkali pretreatment was studied by a batch experiment.The effect of Ca O pretreatment and organic loading rate on anaerobic digestion was studied by a semi-continuous experiment.The solubility of organic matter of food waste and biogas performance of anaerobic digestion were improved with thermal pretreatment.In this research,the best conduction was to pretreat at 120?for 30 min.After this pretreatment,the solubilization rates of carbohydrate and protein were improved by 24.36%and 212.81%,respectively.The concentration of VFAs?volatile fatty acids?was improved by 35.93%.The accumulative biogas yield during anaerobic digestion was 1073.3 m L/g VS,and the proportion of CH4 was 58.53%.Alkali pretreatment of food waste could decrease the oil content and improve the concentration of soluble organic matter.The best conduction for reduction of oil and solubility of organic matter was to pretreat with 3%Na OH.The oil content reduced by 40.30%and the concentration of soluble chemical oxygen demand?SCOD?increased by 99.63%.The food waste with 1%Ca O pretreatment had the best biogas performance during anaerobic digestion.The accumulative biogas yield was 829 m L/g VS.The content of H2 and CH4 was 806 ppm and65.48%,respectively.The biogas production after Na OH pretreatment was close to the blank.The biogas performance was improved after pretreated by 1%KOH and 2%KOH,while it reduced after pretreated by 3%KOH.It was because of the inhibition of high concentrations of K+.What's more,humic acids were produced after pretreated by high quality fraction of strong alkali,which was difficult to biodegrade and accumulated in the reaction devices.According to the sequence batch experiment,the best dosage of Ca O was 1%?m/m?.A semi-continuous experiment was conducted with 1%Ca O pretreated food waste.The biogas performance and the system operation stability were improved by the pretreatment with 1%Ca O.After organic loading rate was increased to 6 g VS/?L?d?,the biogas production decreased in the blank,associate with the reduction of p H and accumulation of VFAs.However,the biogas production kept increasing in the reactor of Ca O pretreated food waste,and the values of p H and concentration of VFAs were stable.The microbial diversity of sludge decreased after anaerobic digestion.Patescibacteria was the main phylum of bacteria in the inoculum,while Bacteroidetes became the main bacteria in the reactors on day 70.In the reactor of Ca O pretreated food waste,the main archaea stably changed from acetic acid-using methanogens?Methanosaeta?to hydrogen-using methanogens?Methanospirillum?.After organic loading rate was increased to 6 g VS/?L?d?,the relative abundance of Methanosaeta in the blank was increased due to the increasing concentration of VFAs.Therefore,Ca O pretreatment was beneficial for the stable operation of anaerobic digestion of food waste under high organic loading rate. |
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