Optimization of anaerobic fermentation with mixed materials of corn straw and pig manure

Abstract: Rural household biogas fermentation materials are mainly manure in China. Biogas plants cannot run steadily due to shortage of manure. Straw are rich in China, and anaerobic fermentation with mixed materials of corn straw and pig manure can be used to supplement fermentation materials. Thus it is important to study on optimization of mixed material of corn straw and pig manure. In this study, we conducted the experiments through the earlier single factor test. Quadratic regression orthogonal rotating combination design was adopted and the whole gas production was taken as the response value. Effects of four factors on anaerobic fermentation were analyzed. These four factors included ratio of corn straw and pig manure, temperature, pH, and ratio of inoculum and quality of raw fermentation material. The mathematical model for mixed fermentation of corn straw and pig manure was developed. The regression equation was optimized and analyzed when the optimum conditions and interactive effects were exposed. The optimum conditions for mixed-fermentation were determined as follows: the ratio of corn straw to pig manure was 1, pH value was 7.5, the ratio of inoculum volume and quality of raw fermentation material was 50%, the temperature was 30℃, and biogas production obtained is 18.51 L. The order of the influence of four factors on mixed-fermentation of corn straw and pig manure was: ratio of corn straw and pig manure, temperature, ratio of corn straw and pig manure, and pH value. Comparing with interactive effects of corn straw and pig manure raw material ratio, pH, raw material ratio and temperature on biogas yield including corn straw and pig manure raw material ratio and inoculum volume, pH and inoculum volume, pH and temperature, the effect of inoculum volume and temperature was not significant. During the optimum biogas production process in this experiment, the relative error of gas production between model prediction and experiment measurement was less than 5%. This study is expected to provide references for improving biogas production and fermentation efficiency of mixed material of corn straw and pig manure.