Experiments on pretreatment and anaerobic digestion of asparagus stalk for biogas production

NaOH pretreatment of asparagus stalk without fluid water and its anaerobic digestion after pretreatment were performed in order to improve biogas production. Effects of pretreatment time, particle size and NaOH concentration on contents of cellulose, hemicellulose and lignin and yield of biogas were investigated in a bench scale anaerobic digester. Results showed that start-up time of test group with pretreatment time of 15-20d was 10d earlier than that of test group without pretreatment. After the asparagus stalk was crumbled and cut, the start-up time of test group without screening was 5-15d earlier than that of groups with different particle size after screening. At the same time, the fermentation time was shortened by 23d. Total biogas yield of test groups using 5% NaOH in pretreatment were 453.82% and 84.58% higher than groups with 10% and 0% NaOH in pretreatment, respectively. After integrated analysis of experimental results, the suitable NaOH pretreatment conditions were determined as follows: NaOH pretreatment of 15-20d, no screening after crumbling and cutting and with NaOH concentration of 5%. Under this kind of pretreatment conditions, methane content of biogas during anaerobic digestion was above 70%, while pH value was above 7.5, which were located in normal range.