Parameter optimization of corn staw anaerobic digestibility pretreated by biogas slurry

Abstract: Under natural conditions, corn staw take a long time to start anaerobic digestion and decomposition due to its compact structure. Therefore, many studies have focused on the pretreatment of corn straws. At present, biogas slurry is difficult to treat after anaerobic fermentation. Pretreatment of corn straws with biogas slurry can reduce pollution and reduce the cost of pretreatment. The biogas slurry contains a large number of microorganisms, among which there are many degradable lignocellulose components. Pretreatment of corn straws with biogas slurry has become a research hotspot. This study aimed to optimize the parameter of pretreatment of corn straw with biogas slurry and to improve its anaerobic digestion gas production. The cellulose, hemicellulose, lignin content before and after pretreatment of biogas slurry and gas production were selected as indicators. According to the design principle of CCD (central composite design) experiment, the biogas slurry addation ratio (TS%), temperature and time were selected as factors. When the temperature was from 20 to 40 ℃, the biogas slurry addition ratio was 20% (based on total solid content) and the pretreatment time was 6 d, the cellulose degradation rate was 3.82%-9.27%, and the hemicellulose degradation rate was 13.05%-18.66%. At the same time, the lignin degradation rate was between 5.10% and 7.44%. The content of lignocellulose decreased from 72.41% to 63.44% at 30 ℃, and the degradation rate was 12.39%. When the temperature was set to 30 ℃ and the pretreatment time was 6 d, the addition of biogas slurry was set between 10% and 30%(based on TS content). The cellulose degradation rate was from 6.72% to 9.68%, and the lignin degradation rate was between 1.91% and 7.75%. The degradation effect of hemicellulose was most obvious, ranging from 8.26% to 20.55%. The degradation rate of lignocellulose was ranged from 6.67% to 13.41%. Similarly, when the pretreatment time was between 2 and 10 d the temperature was 30 ℃, the biogas slurry addition ratio is 20%, the total degradation rate of lignocellulose is 8.19% to 13.44%.The test results showed that with the decrease of pretreatment TS and the prolongation of pretreatment time, the degradation rate of lignocellulose is higher. But the degradation rate of lignocellulose reached the maximum at 30℃. From the gas production, the higher the degradation rate of lignocellulose does not mean that the gas production is higher, and the excessive pursuit of degradation of lignocellulose will affect the gas production. After optimizing the gas production by the response surface method, the optimal pretreatment process were: Biogas slurry addition (TS) 19.08%, pretreatment temperature (30±1) ℃, pretreatment time was 5 d, and total gas production can be increased by 30.76%. Pretreatment of corn straws with biogas slurry can effectively hydrolyze cellulose and hemicellulose. Meanwhile, it could reduce the lag time of corn straw anaerobic fermentation digestion and increase gas production. This economical and effective pretreatment method can improve the gas production efficiency of corn straw and provide a comprehensive utilization of biogas slurry.