A two‐phase anaerobic digestion system with a completely mixed acid reactor was studied using a 2 percent synthetic glucose substrate. The steady‐state performance of the acid phase was studied at pH 4.3 and a hydraulic retention time (HRT) of 4.5 hours for 117 days. Separation of phases was noted under these conditions as methane production in acid reactor was initially less than 10 percent of the total gas. The effects of pH and HRT on the acid phase were observed by adjusting pH levels to A.3 and 6.5 and HRT to 2, 4.5 and 8 hours.