Experiment and calculation on the biochemical methane potential of typical livestock and poultry manure in anaerobic digestion

Abstract: The purpose of this study was to acquire the biochemical methane potential (BMP) of livestock manure in practical production at the present stage. BMP tests of chicken manure (CM), dairy manure (DM), and swine manure (SM) were also conducted using the automatic methane potential test system at (37±0.5)℃. The first-order kinetic model and modified Gompertz model were selected to fit the BMP curve of CM, DM, and SM, thereby estimating the kinetic constant and the maximum BMP. The experiment results showed that the accumulated methane yields of CM, DM, and SM were measured to be 0.33, 0.17, and 0.38 m3/kg VSadded which extremely differed from the default value of 0.24, 0.13, and 0.29 m3·kg-1VSadded given by IPCC. Furthermore, BMP was also an important parameter to evaluate anaerobic digestion. The default value was offered by the IPCC suitable for regional inventory and the average level of all different livestock farms. As such, the livestock manure varied dramatically in composition, due mainly to the different factors, including livestock breeds, diet, and breeding structure. Meanwhile, the BMP depended only on the characteristic of livestock manure, such as organic carbon content. Two kinetic models presented a better fitting to the experimental data, suitable for the simulation of anaerobic digestion. A scientific estimation was made on the BMP value in the anaerobic digestion of livestock manure from different farms in various regions. Although the experiment was given a highly accurate BMP value, the BMP test required relatively complicated conditions, high cost, and long testing time, where the finishing time relied mostly on the subjective judgment of an experimenter. The BMP1% (the cumulative methane production when the present methane production reached 1% of cumulative methane production) was raised in German guideline VDI4630. The standardized way was used to define BMP value corresponding to necessary experiment time, in order to avoid subjective judgment during evaluation. The accumulated methane production all reached more than 90% of the ultimate accumulated methane production, and the test period was reduced by 45.3%-76.6% when the BMP1% was taken as a judging index. The BMP value (using BMP1%) of three livestock manures (CM, DM, and SM) were 0.32, 0.16, and 0.35 m3/kgVSadded, respectively. The introduction of BMP1% improved the efficiency to estimate the methane emission reduction potential of livestock manure. Consequently, the specific BMP was calculated for the three typical manure of livestock and poultry, according to the Bo obtained from the BMP test. The finding can provide much more scientific data for the parameter selection in the biogas plant, thereby determining the methane emission coefficient of livestock manure. In addition, a great contribution can be made to greenhouse gas emissions and the decision-making in livestock manure management in various livestock farms.