Kinetics Analysis of Anaerobic Digestion of Wheat Straw Pretreated by Freezing-Thawing

Abstract

Anaerobic digestion, which can convert agriculture residues into biogas under the anaerobic condition, has rate limited step in its hydrolysis stage. Various pretreatment methods have been used to improve the hydrolysis rate of anaerobic digestion. In this study, freezing-thawing pretreatment was performed on wheat straw, freezing time was studied in terms of methane production. Kinetic models were used to predict the efficient of anaerobic digestion. Three kinetic models which are modified Gompertz model, logistic function model and transfer function model were conducted by Origin Pro 9.1 to find whether the freezing-thawing pretreatment has a positive effect on anaerobic digestion of wheat straw. The fitness of three models were estimated by correlation coefficients (R²) and Root Mean Square Error (RMSE). The results show that, modified Gompertz model and logistic function model conducted on wheat straw are satisfactory with high R² values. Logistic function model has best fit the result from experiment among three models with a lower RMSE value. All these three kinetic models show that freezing-thawing pretreatment shortens the start-up time of anaerobic digestion significantly. The short of lag phase time of methane production proves that this green pretreatment can be used in anaerobic digestion of wheat straw, while still needed for further study.