Effect of Sodium Carbonate Pretreatment and Pretreatment Duration on Total Solids of Maize Stalk: Response Surface Methodology Approach

Maize stalks (MS) are among the most abundant lignocellulosic crop residues in Kenya, offering considerable but under-utilized energy potential. Although cellulose in such biomass releases about 15 kJ g⁻¹ when burned, converting it to methane can raise the energy yield to roughly 50 kJ g⁻¹. The chief obstacle to microbial access is lignin, which shields the cellulose and hemicellulose fractions in municipal solid waste. To generate biogas efficiently from lignocellulosic feedstocks, co‑digestion is often preceded by enzymatic hydrolysis, and the success of that step hinges on an effective pretreatment that opens the biomass structure. This study evaluated sodium carbonate (Na₂CO₃) as a pretreatment agent for MS, focusing on its effect on total solids (TS) and on identifying an optimum pretreatment time. A central composite design (CCD) guided the experimental matrix, combining several Na₂CO₃ concentrations with different exposure periods: 7 % for 8 days, 3 % for 4 days, 7 % for 4 days, 5 % for 6 days, 5 % for 3 days, 2 % for 6 days, 5 % for 6 days, 5 % for 6 days, 7.8 % for 6 days, 5 % for 8.8 days, 3 % for 8 days and 5 % for 6 days. Changes in TS were used as a proxy for improved digestibility. The optimal pretreatment—7 % Na₂CO₃ applied for 4 days—achieved the highest TS value, 15.15 %, corresponding to a 7.26 % increase relative to untreated MS. Statistical analysis confirmed the fitted TS response model was significant at P < 0.05.