This paper examines the ability to produce biogas for two mixtures of cow dung with water and cow dung with vegetable and fruit waste, using a single digester for each mixture. The microbiological activity and digestion are optimized at a pH of 7, and departures in either direction adversely affect the process. Both mixtures showed near-optimal pH in the first days; however, pH decreased and stabilized at lower values on the 15th day, reducing biogas production on the 30th day due to the accumulation of short-chain fatty acids, inhibiting methanogen activity. Methane generation from the cow dung–water mixture enhanced from 20 to 75% by the 30th day, while the cow dung-vegetable/fruit mixture measured 30% to hold on the 30th day. The results show that the regulation of pH is an important factor in biogas production since either too acid or alkaline conditions limit the efficiency of species and, therefore, methane production and global biogas production efficiency.