A mass balance framework to evaluate the new pathways of biological nutrient removal in wastewater treatment

Innovative wastewater treatment technologies, such as partial nitrification (PN), simultaneous nitrification-denitrification (SND), and denitrifying phosphorus removal (DPR), are intensively studied for biological nutrient removal (BNR). However, the implementation of such techniques in practice is still a challenge due to the insufficient engineering experience. Here, we proposed a mass balance framework to quantify the contributions of PN, SND, and DPR for nitrogen and phosphorus removal in a modified anaerobic-anoxic-oxic (AAO) process. The process data were acquired for 8 months in a pilot-scale plant, which was parallel to a full-scale plant with the same process. As the result, SND via nitrite and DPR via nitrate were found dominant among the six pathways of nitrogen removal, which contributed 22% and 15% removal of total influent nitrigon, respectively. Phosphorus accumulation organisms using free oxygen, nitrite, and nitrate contributed 60%, 25%, and 9% removal of total influent phosphorus, respectively. Due to the coupled PN, SND, and DPR pathways, the pilot-scale plant increased 6.3% removal of total influent nitrogen from the full-scale plant and saved one-third oxygen demands at the same time. Mass balance analysis can help quantify the contributions of different BNR pathways in wastewater treatment processes, and thus can support the improvement of process operation in practice.