Combined partial denitrification/anammox process for nitrogen removal in wastewater treatment

Recently, the combined partial denitrification and anammox (PD/anammox) has received special attention as a viable alternative for N removal using organic matter present in municipal wastewater. In comparison with conventional nitrification-denitrification, PD/anammox provides enormous opportunities to achieve sustainable wastewater treatment due to the lack of dissolved oxygen (DO) demand, a smaller amount of organic carbon (C) and less excess sludge production and GHG emissions. The PD/anammox process can be widely carried out in different technical systems, including single-or two-stage systems for side-stream and mainstream wastewater. This review focuses on the latest improvements related to the PD/anammox system and discusses the produc-tion/consumption pathways of NO2- as a critical intermediate. The C/N ratio plays a key role in the PD/anammox process; therefore, the concentration of the dosed organic C is important due to its negative influence on the activity of anammox resulting from the overgrowth of denitrifying bacteria in the systems. Understanding microorganism competition in a one-stage PD/anammox is typically the most important key to optimal efficiency of N removal from mainstream wastewater. Therefore, in this review, a comprehensive description of microbial metabolism i.e., autotrophic anammox, denitrifying heterotrophs/autotrophs, DNRA heterotrophs, and the contiguity competition between them in single-stage PD/anammox systems are inclusively explained. The challenge and limitations are described to recognize inhibition mechanisms and performance inhibitors. The combination of PD/anammox with other processes and the development of a self-supporting bacterial system should be the main lines of future research and efficiency development towards further enhancing total nitrogen removal efficiency (TNRE).

Automated summary

Recently, the combined partial denitrification and anammox (PD/anammox) process using organic matter in municipal wastewater has gained attention for sustainable N removal. It offers advantages such as reduced dissolved oxygen demand, lower organic carbon requirement, less excess sludge production, and lower greenhouse gas emissions compared to conventional nitrification-denitrification. This review discusses the latest improvements in PD/anammox systems and focuses on the production/consumption pathways of critical intermediate NO2-. The C/N ratio and concentration of dosed organic carbon are crucial for optimal efficiency, as overgrowth of denitrifying bacteria can negatively impact anammox activity. Microorganism competition in single-stage PD/anammox systems plays a key role in achieving efficient N removal from mainstream wastewater. Challenges and limitations in recognizing inhibition mechanisms and performance inhibitors are also addressed. Future research should explore combining PD/anammox with other processes and developing self-supporting bacterial systems to enhance total nitrogen removal efficiency.