Technical revolution of biological nitrogen removal from municipal wastewater: Recent advances in Anammox research and application

Abstract

The eutrophication of a body of water is a globally serious water-polluting problem caused by the excess discharge of nutrients. Nitrogen and phosphorus removal from wastewater is extremely necessary. The biological method is the major technology used for nitrogen removal. With the increasingly strict discharging standard worldwide, the problems of insufficient efficiency, considerable energy consumption, and secondary pollution involved in the traditional nitrogen removal process have become increasingly apparent, resulting in an urgent need for an economic, efficient, and sustainable technology. The widely investigated anaerobic ammonium oxidation (Anammox) process discovered in the 1990s is regarded as the most energy-efficient technology for nitrogen removal without aeration and organic carbon demand. However, it has not been widely adopted because for a long time now, it has faced bottlenecks in stable substrate nitrite (NO2-) acquisition. Recent studies have demonstrated that the NO2--produced partial denitrification (PD) process provides a completely novel concept for solving this problem. China takes the lead in the investigation and practice of the discovery, development, and microbial mechanism of this process. A novel technology combining PD and Anammox is opening a new window for the low-carbon and high-efficiency treatment of municipal wastewater, which has been regarded as a hot and cutting-edge topic in this field. Compared with the conventional nitrification/denitrification process, it could save aeration energy by 100% and organic carbon source by 80% and reduce the sludge production and greenhouse gas (CO2, N2O) emission in the simultaneous treatment of municipal wastewater and nitrate (NO3-) contained in wastewater. In comparison with the present Anammox process, it is little affected by the substrate concentrate, temperature, and other environmental factors, could break the top limit of nitrogen removal efficiency by Anammox (89%), and reach up to 100% of the total nitrogen removal efficiency, thereby exhibiting great significance and applicable value. In the future, the separation, purification, and molecular metabolic mechanism of the PD and Anammox bacteria should be focused on. Furthermore, the engineering application of the novel technology should also be promoted.