This study applies the Taguchi method to identify the key factors affecting methane biogas production and to determine optimal operating parameters for maximizing methane yield. The experimental design employed an L4 (2³) orthogonal array with three replications. The investigated factors included the volume-based ratio of organic waste to manure as feedstock, the volume-based dilution ratio between the mixed substrate and water, and the application of pre-treatment through conditioning of chopped organic waste. The levels of organic waste–manure composition and substrate–water composition was set at volume ratios of 30:70 and 70:30, while pre-treatment was evaluated under two conditions: conditioning of chopped organic waste by allowing it to stand for a defined period prior to digestion and no pre-treatment. The experimental results indicate that the organic waste–manure composition and the pre-treatment process have a statistically significant effect on methane biogas production, whereas the substrate–water dilution ratio shows a lower influence. Based on response table analysis, the optimal operating conditions were identified as an organic waste : manure volume ratio of 30:70, a substrate : water volume ratio of 30:70, and the absence of pre-treatment. These findings highlight the importance of clearly defining feedstock preparation and proportioning when optimizing biogas production using the Taguchi approach.