| The food wastewater contained a lot of organic matter,which had the characteristics of high nutrient,good biodegradation,etc.However,untreated food wastewater would cause serious water pollution,its harmlessness and enrgy resource treatment have been attracted widely concerned.Anaerobic digestion technology was a common method to treat food wastewater,it could generate biogas while treating wastewater.Biogas could replace traditional energy to realize energy recovery and resource utilization.However,the untreated biogas had the low calorific value,which limited its application.Biogas biological upgrading based on the metabolism of hydrogenotrophic methanogens was an environmentally friendly treatment method that could be used to purify biogas,but the source of hydrogen（H2）was the main limiting factor for biogas biological upgrading.Based on this,this paper studied the effect of in-situ hydrogen supply from nano-zero-valent iron（nZVI）on biogas biological upgrading and anaerobic digestionperformance,and the optimal nZVI dosage and buffering conditions were determined.In order to further increase the content of methane（CH4）,three gas types of direction-flow,reciprocating-flow and circulating-flow were adopted to improve the degradation rate and conversion rate of food wastewater,H2 and carbon dioxide（CO2）,and the best gas recirculation type was indicated.However,the agglomeration and passivation of nZVI was affected the H2 generationprocess.Therefore,sodium lauroyl sarcosine（SLS）was added to optimize the biogas upgrading system,improve the hydrogen generation from nZVI,the effects of SLS on nZVI and anaerobic microorganisms were evaluated.The main conclusions of this study were as follows:（1）The effects of different concentrations of nZVI and buffering conditions on anaerobic digestion and biogas biological upgrading were indicated.In-situ hydrogen evolution of nZVI provided a feasible way for hydrogen supply and biogas biological upgrading.Different doses of nZVI（0,2,4,6,8,10 g/L）were added to the anaerobic digestion systems containing HEPES(2-[4-（2-hydroxyethyl）piperazin-1-yl]ethanesulfonic acid,C8H18N2O4S)and Na HCO3 buffers.The results showed that the addition of nZVI improved the stability of the anaerobic digestion system,the hydrogen supply from nZVI promoted the conversion of H2 and CO2,and the content of CH4 was increased.In HEPES buffer system,the highest CH4 content was 90.51%with 10 g/L nZVI addition,which was 32.25%higher than that of the control.Microbial community analysis showed that the abundance of Methanobacterium and Methanolinea increased after the addition of nZVI.However,in Na HCO3 buffer systems,the CH4 content was lower than that in the control after 10 g/L nZVI addition.The effect of biogas biological upgrading with nZVI may be related to the buffering conditions of anaerobic system.（2）Study ofgas recirculation types to promote biogas biological upgrading,H2 gas-liquid mass transfer efficiency and CH4 content.The results showed that direction-flow,reciprocating-flow and circulating-flow methods could all improve CH4 content,and the circulating-flow method was the best,the maximum CH4 content and yield were 93.87%and 157.18 mL/g VS,respectively.In addition,gas recirculation improved the gas-liquid mass transfer efficiency and the solubility of H2,gas recirculation promoted the conversion of H2 and CO2 into CH4 by microorganisms.Microbial community structure showed that the relative abundance of Methanobacterium and Methanolinea was the maximum,which was increased from 28%to38%～51%,indicating that gas recirculation promoted the succession of methanogens from acetic acid and methyl methanogens to hydrogenotrophic methanogens.（3）Study on the sodium lauryl sarcosine（SLS）to improve the hydrogen release from nZVI and the CH4yield.The concentration of 0,10,30,50 and 70 mg/L SLS was added to the anaerobic digestion system,the result showed that the content and yield of CH4 all increased in the experimental groups.The maximum CH4 content（96.23%）and yield（1193 mL）was obtained by 30 mg/L SLS addition,the gas production lagged in SLS additionof 50 and 70 mg/L,which may be due to the degradation product of lauric acid.In addition,hydrogen release time from nZVI was prolonged,hydrogen production was increased,the dissolution rate of H2was accerlerated after SLS addition.The maximum hydrogen enrichment value was 5.62 mg/L when 30 mg/L SLS was added,which was more than 3 times higher than that of anaerobic digestion system.The enzyme activity of 30 mg/L SLS addition group was the maximum,the ratio of protein to polysaccharide in extracellular polymeric substances was increased,and the microbial flocculation ability was enhanced.Microbial community analysis showed that the relative abundance of Methanobacterium,Methanomicrobiales and Methanolinea increased,and the total amount was 18.57%～32.10%higher than that in the initial sludge,and hydrogenotrophic methanogens became the dominant microorganism. |
