Enhancement of biogas production by anaerobic co-digestion of leather waste with raw and pretreated wheat straw

Abstract

This work investigated the effect of the addition of wheat straw on the anaerobic co-digestion of leather waste regarding biogas production. In an attempt to improve biodegradability, wheat straw was pretreated using (i) acid pretreatment with HCl 2% at 90 °C for 2 h, (ii) alkaline pretreatment with NaOH at 30 °C for 24 h and (iii) thermal pretreatment by autoclaving the straw at 121 °C (1 atm) for 15 min. In addition, the combination between the pretreatments (iv) acid + thermal and (v) alkaline + thermal was tested. Pretreatment with alkali seems to affect the wheat straw more with a significant increase in cellulose content and a decrease in hemicellulose and lignin content. However, methanogenesis appears to have been inhibited in these cases, resulting in the lowest biogas production among all the tested issues (8.84 mL/gVSS for alkaline pretreatment and 4.01 mL/gVSS for the combination between alkaline and thermal pretreatments). The highest cumulative biogas yield of 43.15 mL/gVSS was obtained for wheat straw pretreated with HCl, 59% higher than untreated wheat straw (27.12 mL/gVSS) and almost 167% higher than that without wheat straw (16.17 mL/gVSS), indicating that the codigestion studied in this condition is a promising alternative.