Simultaneous Partial Nitrification, Anammox and Denitrification (SNAD) – A review of critical operating parameters and reactor configurations

Abstract Nitrogen removal is an important aspect of wastewater treatment. Conventional biological nitrogen removal process is widely adopted for its reliable and effective nitrogen removal. However, its high operational and capital costs have led to the development of more cost-effective solutions. The discovery of anaerobic ammonium oxidation (ANAMMOX) bacteria and its integration with shortcut nitrogen removal processes has proved to be a sustainable solution. However, the requirement of carbon-free feed and discharge of high nitrate concentration in the effluent limit their practical applications. To overcome these challenges, an innovative nitrogen removal process, the simultaneous partial nitrification, anammox and denitrification (SNAD) process, has been studied. SNAD involves a synergistic relationship among ammonia oxidizing bacteria (AOB), ANAMMOX and denitrifers for high nitrogen removal efficiency. This study provides a focused review of the recent developments in SNAD process, specifically covering the critical process parameters for efficient operation and different reactor configurations. A detailed assessment of the process parameters such as carbon/nitrogen ratio, substrate type, free ammonia, free nitrous acid and hydraulic retention time is provided to identify the factors affecting the SNAD efficiency and required control measures. A comparison of different suspended and attached growth reactor configurations is also provided to understand the process reliability and potential for full-scale operation. This review will provide guidance for future engineering applications for high efficiency and cost-effective nitrogen removal via SNAD process.