Biogas is increasingly recognized as a key renewable energy source for decentralized power generation, particularly in rural and agricultural communities worldwide. However, the direct use of raw biogas, typically containing high levels of carbon dioxide (CO₂), results in low heating value, reduced thermal efficiency, and operational problems such as equipment corrosion and clogging. Enhancing biogas quality through cost-effective CO₂ removal is therefore essential for maximizing energy output and improving system reliability, especially in resource-limited settings. This study proposes a simple, low-cost, and practical upgrading process suitable for decentralized biogas systems by employing adsorption and absorption techniques using readily available materials. Experiments were conducted with a fixed-bed adsorption column and a packed-column scrubber using wood chips, diatomite, activated carbon, sodium hydroxide solution, calcium carbonate, ethylamine, and water. The fixed-bed adsorption system using sodium-hydroxide-coated wood chips at a flow rate of 10–15 L/min achieved a CO₂ removal efficiency of 68%, increasing methane concentration to 79.6 (±0.9)%. The packed-column scrubber using 0.5 M NaOH demonstrated a comparable CO₂ removal efficiency of 66%, yielding upgraded biogas with 85 (±3)% methane. The NaOH solution remained effective for 50–60 minutes before reaching saturation. The resulting upgraded biogas exhibited a methane content exceeding 80% and an average heating value of 29.11 MJ/m³. Moreover, increasing NaOH concentration further enhanced CO₂ removal and methane purity. The findings highlight the potential of simple, locally sourced adsorption and absorption systems to deliver significant improvements in biogas quality, offering a viable pathway for boosting energy efficiency, extending equipment lifespan, and supporting sustainable energy development in rural and off-grid communities worldwide.