Oxidative chemical pretreatment by piranha solution for enhanced methane yield of wheat straw: mechanism and kinetic study

The present research work aims to explore the potency of piranha solutions at the best-optimized concentrations, i.e., 40% and 30% to reduce the recalcitrant and heterogeneous structure of wheat straw, and the treated wheat straw was denoted as WS40 and WS30. The effect of pretreatment on wheat straw was determined by anaerobic digestion (AD) in a batch mode, followed by the analysis of soluble chemical oxygen demand (sCOD) and volatile fatty acids (VFAs). After pretreatment, the surface fibers shattered and detached, showing a distorted surface of wheat straw. An increase in the crystallinity of wheat straw after pretreatment was also observed due to the removal of amorphous cellulose and lignin. Enhancement in methane yield was obtained on the 9th day, which was 103±6.92 and 99.33±0.57 mL/d for WS40 and WS30, respectively. Displaced water measurement revealed that the pretreatment of wheat straw minimized the hydrolysis period by 14 days. It also improved the methane yield by 2.65 (WS40) and 2.45 (WS30) fold in comparison with the control which yielded 35.66 mL/d methane on the 23rd day. The modified Gompertz model (MGM), logistic function model (LFM) and transference function model (TFM) adequately described the degradation process and explained the kinetic behavior of the cumulative methane yield. Among the three models, MGM was found to fit best for the methane yield of WS40 and WS30.

Graphical abstract