Mesophilic And Thermophilic Anaerobic Co-Digestion Of Food Waste And Straw

The anaerobic mono-digestion of food waste and straw may easily cause the accumulation of volatile fatty acids and the low degradation of lignocellulose.In this paper,the mesophilic and thermophilic anaerobic co-digestion of food waste and straw was investigated and the life cycle assessment of the anaerobic co-digestion of food waste and straw was carried out.The main conclusions were as follow:(1)The batch co-digestion of food waste and wheat straw were investigated under mesophilic(35?C)and thermophilic(55?C)conditions.The results indicated that for a volatile solid concentration of 3 kg/m~3,the peak accumulated methane production yield of the mesophilic reactors is 272.0 ml/g VS at a food waste-to-straw ratio of 9:1,and is 402.3ml/g for the thermophilic reactors at a food waste-to-straw ratio of 5:5.These amounts are significantly higher than that of food waste or wheat straw digestion alone.(2)The total degradation rate for lignocellulose of the thermophilic reactors was 34.7%-45.8%,higher than that of the mesophilic reactors,12.6%-42.2%,and the degradation rate of cellulose and hemicellulose was obviously increased when the amout of wheat straw was larger.For the mesophilic reactors,the peak degradation rate of lignocellulose is42.4%at a food waste-to-straw ratio of 9:1,and 45.8%for the thermophilic reactors at a food waste-to-straw ratio of 8:2 and 5:5 for the thermophilic reactors.(3)To analyse the microbial communities of mesophilic and thermophilic anaerobic system,16S rRNA gene sequences of bacteria and archaea,and the Internal Transcribed Spacer(ITS)sequences of fungi were tested based on high-throughput sequencing techniques,which showed that the amounts of lignocellulose degrading bacteria and actinomycetes in the thermophilic reactor were both higher than those in the mesophilic reactor.(4)The semi-continuous experiment results indicated that for an organic loading rate of 3kg/m~3·d,the ammonia and volatile fatty acids were found to accumulate obviously after30 days'mono-digestion of food waste in the mesophilic reactor and the biogas production yield decreased significantly.During this period,the amount of hydrolysis and acidogenic fermentation microorganism and hydrogen-producing acetogens was deceasing,and the amount of homo-acetogens was increasing.(5)The mesophilic and thermophilic co-digestion of food waste and straw was very stable.The maximum biogas production yield was 555.4 ml/(g VS·d)at a food waste-to-straw ratio of 9:1 for mesophilic condition and 614.2 ml/(g VS·d)at a food waste-to-straw ratio of 5:5 for thermophilic condition,both were much higher than that of food waste or wheat straw digestion alone.(6)The environmental impact analysis of the anaerobic digestion process of the food waste was carried taking JNSF food waste anaerobic treatment plant for an example.The results showed that the whole life cycle global warming potential(GWP)of the treatment plant was 203.16 kgCO2e,much lower than the GWP of landfill and incineration.The GWP of the thermophilic anaerobic co-digestion of food waste and straw significantly decreased to a negative number which meat the process could bring more environmental benefits.