This paper investigated the application of hydrogen peroxide (H2O2) for achieving partial nitrification in mainstream municipal wastewater treatment process. The investigation was carried out in both bench-scale and pilot-scale sequencing batch reactor systems using primary effluent as feed from municipal wastewater treatment plant. H2O2 played a dual role of: (1) inhibitor for nitrifying microorganisms, and (2) supplemental oxygen source. Bench scale studies were carried out at various doses of initial hydrogen peroxide concentrations (10,25,50,100 mg/L). It was found that at a concentration of 50 mg/L and above ammonia removal reduced by more than 80% implying significant impact on both ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB). After an acclimatization period of 18 days at a dose of 50 mg/L H2O2, complete nitrification was observed with about 30% nitrite accumulation in the effluent which showed NOBs were impacted more significantly than AOBs. It was also observed from the long-term pilot-scale study that the inhibitory impact on NOBs is almost double the impact of on AOBs which facilitated partial nitrification resulting a nitrite accumulation ratio up to 60% in the effluent at 2 mg/L DO and 15 days SRT.Peroxide dosing resulted in an energy savings of 12–15% compared to a control reactor. It was also shown that by reducing the DO from 2 to 1 mg/L, additional power saving of 15% is achievable. Therefore, the proposed approach is an efficient method for aeration energy savings and can be easily implemented in existing wastewater treatment plants.