Enhanced nitrogen removal in constructed wetlands with a multistage-A/O process

Abstract

In this study, the performance of a multistage-A/O process in constructed wetlands (CWs) was compared with the A/O/A process in terms of its ability for nitrogen (N) and phosphorus (P) removal under carbon-limited conditions. Simultaneous nitrification and endogenous denitrification (SNED) was found to be the predominant nitrogen removal pathway in both systems. The SNED rate for the multistage-A/O system was 92.49%, higher than 65.63% for the A/O/A system. Moreover, partial nitrification and endogenous partial denitrification (shortcut SNED) via nitrite was found to be 59.46% in the multistage-A/O system, which was greater than 41.48% observed in the A/O/A system. Microbial community analysis of the nitrite oxidizing bacteria (NOB) to ammonia oxidizing bacteria (AOB) ratio in the multistage-A/O system showed a value of 2.05 compared to 4.95 in the A/O/A system, presenting the superior advantage of multistage-A/O in NOB inhibition. Additionally, the ratio of glycogen-accumulating organisms (GAOs) to polyphosphate-accumulating organisms (PAOs) was 4.95 in the multistage-A/O system, much lower than 10.17 in the A/O/A system, due to the suppression of aerobic GAOs (AGAOs) in the multistage-A/O system. Thus, the multistage-A/O process in CWs is a promising technology for carbon-limited wastewater treatment.