Biomethane production and physicochemical characterization of anaerobically digested teff (Eragrostis tef) straw pretreated by sodium hydroxide

• This is the first report of using teff straw for biomethane production.
• Anaerobic digestion of teff straw was conducted with altering solid loadings at 35 °C.
• Teff straw was treated to improve hydrolysis and biodegradability.
• Improvement of biomethane yield can be achieved after NaOH pretreatment.
• The highest biomethane yield was 248.8 mL/gTS for 4% NaOH concentrations.

The biogas production potential and biomethane content of teff straw through pretreatment by NaOH was investigated. Different NaOH concentrations (1%, 2%, 4% and 6%) were used for each four solid loadings (50, 65, 80 and 95 g/L). The effects of NaOH as pretreatment factor on the biodegradability of teff straw, changes in main compositions and enhancement of anaerobic digestion were analyzed. The result showed that, using 4% NaOH for pretreatment in 80 g/L solid loading produced 40.0% higher total biogas production and 48.1% higher biomethane content than the untreated sample of teff straw. Investigation of changes in chemical compositions and physical microstructure indicated that there was 4.3–22.1% total lignocellulosic compositions removal after three days pretreatment with NaOH. The results further revealed that NaOH pretreatment changed the structural compositions and lignin network, and improved biogas production from teff straw.