Optimization of ammonia pretreatment of wheat straw for biogas production

BACKGROUND Agricultural residues such as straw are abundant and low-cost feedstocks for biogas production. However, these lignocelluloses evolved naturally to be recalcitrant to microbial and enzymatic degradation. Ammonia pretreatment has been seen as a potential treatment method to enhance the hydrolysis of biomass, as it selectively removes the lignin and preserves most of the fermentability. This study investigated ammonia pretreatment of wheat straw for biogas production. Biogas yields were determined by standardized batch digestion tests. Additionally, lignin removal, hemicellulose retention and cellulose retention were determined. RESULTS The highest biogas yield of ammonia pretreated straw reached 625 mLNg-1VS, compared with 400 mL from untreated straw. The optimal pretreatment condition was 51.0 °C, 14.8% ammonia concentration and 27.0 h residence time. Corresponding lignin removal, hemicellulose retention, cellulose retention and cumulative biogas yield values were 25.2%, 60.6%, 96.6% and 573 mLNg−1VS, respectively. In addition, different response modes of lignin removal and biogas yield related to the same pretreatment condition were revealed. CONCLUSION Ammonia pretreatment significantly improved cumulative biogas yield, biogas production rate and volatile solid (VS) reduction of wheat straw. Lignin removal was positively related to biogas yield.