Optimal Ratio for Anaerobic Co-Digestion of Lignocellulosic Biomass using Cow Manure and Azolla Aquatic Ferns to Enhance Biogas Production.
Abstract
Rice straw (RS), a lignocellulosic biomass, poses challenges in anaerobic digestion (AD). Due to its high lignin content, which restricts biodegradability and methane production. Therefore, this research aims to improve and enhance RS digestion and biogas production by co-digesting RS with cow manure (CM) and azolla aquatic ferns (AZ). Four experimental sets were conducted. 1st trial of mono-substrate digestion [T1 (100% RS), T2 (100% CM), T3 (100% AZ)]; 2nd trial of RS-CM mixtures [T4 (75% RS + 25% CM), T5 (50% RS + 50% CM), T6 (25% RS + 75% CM)]; 3rd trial of RS-AZ mixtures [T7 (75% RS + 25% AZ), T8 (50% RS + 50 % AZ) and T9 (25% RS + 75% AZ)]; 4th trial is a ternary mixture[T10 (RS:CM:AZ = 1:1:1)]. The performance was evaluated based on daily and cumulative biogas production, methane percentage, calorific value, digestate chemical analysis, and statistical analysis. Notably, T10 yielded superior biogas production compared to treatments T1 through T9, with increases of 49.04%, 43.87%, 28.16%, 23.00%, 15.05%, 18.38%, 9.83%, and 6.28%, respectively, except for T3, which exceeded it by 1.64%. Among all treatments, T3 showed the highest methane concentration, while others ranged between 44.72% and 73.14%. The ANOVA results (R² = 1.000, F = 28,428,240.610, p < 0.001) confirmed that the digestion mixtures had a highly significant and reliable effect on biogas production (daily and cumulative), while the results for methane percentage (R² = 0.915, F = 23.894, p < 0.001) likewise indicated a highly significant and reliable effect.