Nitrogen removal by algal-bacterial consortium during mainstream wastewater treatment: Transformation mechanisms and potential N2O mitigation
Qi Li, Yifeng Xu, Chuanzhou Liang, Lai Peng, Yan Zhou
Abstract
This work investigated nitrogen transformation pathways of the algal-bacterial consortium as well as its potential in reducing nitrous oxide (N 2 O) emission in enclosed, open and aerated reactors. The results confirmed the superior ammonium removal performance of the algal-bacterial consortium relative to the single algae ( Chlorella vulgaris ) or the activated sludge , achieving the highest efficiency at 100% and the highest rate of 7.34 mg N g MLSS −1 h −1 in the open reactor with glucose. Enhanced total nitrogen (TN) removal (to 74.6%) by the algal-bacterial consortium was achieved via mixotrophic algal assimilation and bacterial denitrification under oxygen-limited and glucose-sufficient conditions. Nitrogen distribution indicated that ammonia oxidation (∼41.8%) and algal assimilation (∼43.5%) were the main pathways to remove ammonium by the algal-bacterial consortium. TN removal by the algal-bacterial consortium was primarily achieved by algal assimilation (28.1–40.8%), followed by bacterial denitrification (2.9–26.5%). Furthermore, the algal-bacterial consortium contributed to N 2 O mitigation compared with the activated sludge, reducing N 2 O production by 35.5–55.0% via autotrophic pathways and by 81.0–93.6% via mixotrophic pathways. Nitrogen assimilation by algae was boosted with the addition of glucose and thus largely restrained N 2 O production from nitrification and denitrification. The synergism between algae and bacteria was also conducive to an enhanced N 2 O reduction by denitrification and reduced direct/indirect carbon emissions.