Elucidating prioritized factor for mainstream partial nitritation between C/N ratio and dissolved oxygen: Response surface methodology and microbial community shifts

Abstract

Recently, C/N ratio is suggested as a promising control factor with dissolved oxygen (DO) achieving mainstream partial nitritation (PN); however, their combined effects on mainstream PN are still limited. This study evaluated the mainstream PN with respect to the combined factors, and investigated the prioritized factor affecting the community of aerobic functional microbes competing with NOB. Response surface methodology was performed to assess the combined effects of C/N ratio and DO on the activity of functional microbes. Aerobic heterotrophic bacteria (AHB) played the greatest role in oxygen competition among functional microbes, which resulted in relative inhibition of nitrite-oxidizing bacteria (NOB). The combination of high C/N ratio and low DO had a positive role in the relative inhibition of NOB. In bioreactor operation, the PN was successfully achieved at ≥ 1.5 of C/N ratio for 0.5–2.0 mg/L DO conditions. Interestingly, aerobic functional microbes outcompeting NOB were shifted with C/N ratio rather than DO, suggesting C/N ratio is more prioritized factor achieving mainstream PN. These findings will provide insights into how combined aerobic conditions contribute to achieve mainstream PN.