1Department of Computer Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen, Thailand
2Department of Mechanical Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen, Thailand
3Department of Chemical Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen, Thailand
*Corresponding author’s email: aapich@kku.ac.th
Received:18 July2025/ Revised:11 October 2025/ Accepted:15 October 2025/ Published Online: 22 October 2025
Abstract
This study investigates the anaerobic co-digestion of thermochemically pretreated pig manure and Napier grass under mesophilic conditions, focusing on kinetic analysis and the effects of total solids concentration and PM/NG ratio on methane production. PM was treated with 5% Ca(OH)2 at 70 °C for seven days, while NG was immersed in 0.6% NaOH at 90 °C for two hours. A series of 30-day batch experiments was conducted using a laboratory-scale setup to evaluate cumulative methane yield (CMY) as the principal performance metric. Experimental conditions included five PM/NG mixing ratios (1:0, 3:1, 1:1, 1:3, 0:1) and three TS levels (3%, 5%, and 7%). Methane production exhibited a typical sigmoidal profile comprising a lag phase (3–10 days), an exponential production phase, and a plateau phase. The average methane content was 64.27%. The highest daily methane production rate (29.27 mL/g VS/day) and maximum CMY (210.47 mL/g VS) were recorded at a 1:1 PM/NG ratio and 3% TS. Four kinetic models (Modified Gompertz, Cone, Logistic, and Richards) were applied to evaluate predictive performance. Among them, the Modified Gompertz and Cone models provided the most accurate fits (R² > 0.995; lowest RMSE), effectively capturing the sigmoidal nature of methane production.
