Effect Of Inoculation Proportion On The Biochemical Methane Potential Of Pig Manure Under Mesophilic And Low Temperature Conditions

Greenhouse effect has a serious impact on human and the earth’s ecological environment.Scientific and accurate evaluation of greenhouse gas emissions from livestock and poultry manure management is one of the prerequisites for the aquaculture industry to achieve "carbon peaking and carbon neutralization".The aim of this study was to investigate the effect of different manure to inoculum ratios(S/I)on the Biochemical Methane Potential(BMP)of pig manure at medium(35±0.5℃)and low(23±0.5℃)temperatures,with a view to providing a scientific basis for the development of a standardised and uniform BMP test method in pig manure.The methane production experiment was carried out using a fully automated methanogenic potential meter.The daily methane production was continuously monitored,and the p H,ammonia nitrogen,total nitrogen,glucose and reducing sugars of the supernatant of the fermentation broth were sampled regularly.According to the analysis of the data of moderate temperature experiment,when the initial vs was 3%,the BMP of pig manure was 250.59±1.28 m L/g VS,and there was no significant difference in the BMP of pig manure with different inoculation ratios(P>0.05).Anaerobic digestion reaction cycle and maximum daily methane production were significantly positively correlated with S/I(P<0.05).In the first 6 days of anaerobic digestion,the daily methane production growth and ammonia nitrogen growth in the same period between different pig manure treatment groups were negatively correlated,and after 6 days,the daily methane production growth and ammonia nitrogen growth in the same period between groups were positively correlated.Firmicutes,Bacteroides and Cloacimonadota are the three kinds of bacteria with the highest relative abundance in the anaerobic digestion system of pig manure.The addition of pig manure reduced the bacterial richness and increased the bacterial diversity after anaerobic digestion.The decline of bacterial richness was positively correlated with S/I,and the increase of bacterial diversity was negatively correlated with S/I.The abundance and diversity of methanogenic archaea decreased,and the decline of abundance was negatively correlated with S/I,while the decline of diversity was positively correlated with S/I.In addition,the homogeneity of bacteria and methanogens was negatively correlated with S/I.Halobacterota was the most dominant methanogenic archaea.The addition of pig manure reduced the relative abundance of Methanobacterium,and the degree of decline was negatively correlated with the inoculation ratio.In addition,by analyzing the low-temperature experimental data,it can be seen that when the initial vs was 3%,the BMP of pig manure under low temperature was 188.11 ±4.31 ml/g VS,and there was no significant difference in the BMP of pig manure with different inoculation ratios(P>0.05);.Anaerobic digestion reaction cycle and maximum daily methane production were significantly positively correlated with S/I(P<0.05).The degree of carbohydrate hydrolysis was significantly positively correlated with S/I(P<0.05).For volatile fatty acids(VFAs),the proportion of acetic acid in VFAs was positively correlated with S/I,the proportion of isobutyric acid and isovaleric acid in VFAs was negatively correlated with S/I,and the occurrence time of the maximum concentration of propionic acid was positively correlated with S/I.As for microorganisms,Firmicutes and Bacteroides are the dominant bacteria in bacteria,while the dominance of Synergistota and Chloroflexi changes due to S/I;Halobacterota is the most dominant methanogenic archaea,and its relative abundance is lower than that of the same treatment group under moderate temperature.There was a negative correlation between bacterial richness and S/I.When S/I was 1.0,bacterial diversity was the lowest.The abundance of methanogenic archaea was negatively correlated with S/I.When S/I was 1.0,the diversity of methanogenic archaea was the highest.Furthermore,the results of the kinetic model fitting showed that the modified Gompertz model was more accurate than the Logistic model and was more suitable for predicting BMP in pig manure.The results showed that there was no significant difference in the BMP of pig manure with different inoculation ratios(P>0.05),and the inoculation ratio was not the limiting factor of the BMP test of pig manure.In order to save the amount of pig manure and shorten the BMP test time,it is suggested that the ratio of pig manure to inoculated sludge should be 1:2.