The aim of study was confirm isopropyl alcohol(IPA) as an external carbon source in municipal sewage with low C/N ratio. For the above experiment, it was tried to batch test(denitrification rate test) and continuous operation(MLE process). The results of denitrification rate test, it was showed that activated sludge could not use IPA which are not pre-adapted substrates in the experiment. However IPA pre-adapted sludge could use IPA as well as acetate. The results of continuous operation, it was more than 90% at HRT 8 hr, 6 hr, regardless of the C/N ratio in ammonia nitrogen removal rate. In case of nitrate nitrogen, the average concentration was 1.29 mg/L after 34 days of MLE operating days. In case of TN, the average removal efficiency was 83.1% at HRT 6 hr. The removal rate of TN was increased after 34 days. Because the denitrification rate was increased by using the artificially injected IPA which is a substrate of the denitrifying microorganism. In operating periods, SCOD removal efficiency was shows more than 90%.