Promotion of biogas production of wheat straw by controling composting pretreatment temperature

Abstract: Composting pretreatment has been widely used in biogas plant of agricultural straw for improving biotransformation rate of lignocellulosic materials. However, the mechanisms on composting pretreatment of agricultural straw for biogas production need more research. In this study, two experiments were conducted to evaluate the impacts of composting pretreatment on biogas production of wheat straw. In the first experiment, the wheat straw was directly used for composting and then composted straw was used in the biomethane potential (BMP) test. For the second one, wheat straw was sterilized by gamma ray radiation pretreatment and treated under different temperature with different time. Then the treated straw was used for the BMP test. The results of experiments indicated that large percentage of organic matter in wheat straw was degraded during composting process. The total solid (TS) loss rate of wheat straw was only 4.06% when composting pile temperature was less than 55℃. When composting pile temperature was set up at 55℃, the TS loss rate of wheat straw increased 22.45% after 10 days' composting treatment. Gas data showed that biogas production rate of wheat straw was not improved obviously. The TS biogas yield of wheat straw increased with composting pile temperature and then decreased. The highest TS biogas yield of wheat straw of 349.92 mL/g was observed at 55℃ of composting pile temperature, which is 7.56% higher than that of uncomposted wheat straw. There was no significantly improvement in biogas production between composted and uncomposted wheat straw during composting process for organic matter loss of wheat straw. However, longer composting time led to lower biogas yield of wheat straw. When composting pile temperature was kept at 55℃ for 9 days, The TS biogas yield of composted wheat straw was only 66.58%. When the content of organic matter and material composition of wheat straw were changed, content of hemicellulose of wheat straw was decreased by 28.10%. Results of gas data of simulated composting experiment showed the same trend as the first experiment. The highest TS biogas yield of wheat straw of 342.36 mL/g was obtained at 55℃ with 8.35%, which is higher than that of control. Therefore the high temperature from composting process is an important factor of destruction of lignocellulose structure and improving biotransformation rate of wheat straw. When the composting pile temperature was set up at 55℃, anaerobic digested inoculums was added into straw pile and can be used for biogas production.