Prediction of methane production from straw using thermodynamic electron equivalents model

Abstract: The prediction of anaerobic digestion methane production is still rough. The Biochemical Methane Potential (BMP) test is one of the most relevant tests for assessing the methane production of waste materials, but it is time consuming. Considering microbial metabolism, nitrogen source, the degradation of the raw materials as well as the operation of the reactor, a prediction model of anaerobic fermentation is proposed. The method is based on the thermodynamic electron equivalents model (TEEM), which was proposed by McCarty. In the TEEM, the electron flow is divided into two fractions: the fraction of electron donor associated with cell synthesis fs and the fraction associated with energy metabolism fe, in the whole biochemical reaction process electron flow will maintain the conservation. Compared with traditional stoichiometry, the model considered cell synthesis and energy metabolism system, is more scientific and reasonable, and is highly useful for determining mass balance and productions of byproducts from the biological reactions. The quantities of different compounds and anaerobic biodegradability are also important information required to characterize waste. Ingredients of straw analysis methods that draw on traditional animal feed science, the ingredients of straw are divided into lignin, crude fiber, crude fat, crude protein, nitrogen-free extract, crude ash.The method is applied to predict straw methane potential. Validated by different kinds of data in literature, the minimum error is 0.3% and the average error is 10.2%, suggesting that the prediction model is accurate. Further, the paper estimated the potential anaerobic gas production as well as projected anaerobic methane production of the main three straws in china. The country's three major straw production methane potential are as following: corn stalks 295ml/gVS, rice straw 283ml/gVS, and wheat straw 293ml/gVS. The prediction values in the actual biogas project methane production ??are: corn stalks 252ml/gVS, rice straw 248 ml / gVS, and wheat straw 239 ml / gVS, for an average of 246 ml / gVS. Basic research about thermodynamic electron equivalents model in this article such as the important parameters fs and fe study, especially in the field of anaerobic fermentation, is relatively low, so further research is needed. There are still some problems with methane production predictions for the actual biogas project; the biogas project methane production performance, also related to digester structural parameters and anaerobic fermentation operating parameters is very complex. Because the paper is based on the assumption that straw maximum degradation rate and assumes that the type of reactor, the calculation result is relatively large, the prediction model requires further validation and refinement. However, this method undoubtedly provides a new way to forecast the material methane production potential and methane production in the biogas project, and is more convenient and accurate.