A critical review of anammox processes: Evaluation of their energy and carbon neutrality potential in wastewater treatment

Autotrophic anaerobic ammonium oxidation (anammox) processes are considered better alternative to conventional biological approaches for nitrogen removal from wastewater. Nevertheless, a critical assessment of their potential for energy efficiency, self-sustainability, and carbon neutrality is yet to be presented. To fill this gap, the current review evaluates the anammox processes using a set of criteria, including emissions, chemical and energy consumption, and removal efficiency and provide insights into their self-sustainability. Findings suggest that even with significant advancements, the anammox processes as they stand now are efficient at eliminating nitrogen, but in some cases, they are chemically demanding and neither carbon nor energy neutral. Substituting external chemical carbon sources with sludge fermentation liquid (SFL) and developing glycogen accumulating bacteria (GAB) are two possible approaches that can lower chemical requirements and also lower sludge production and related energy consumption as sludge treatment accounts for a loin share of the overall energy consumption of a wastewater treatment plant (WWTP). Integrating anammox with other systems like membrane bioreactors, denitrifying anaerobic methane-oxidation, anaerobic fixed-film reactors, and bio trickling filters could be an effective approach to reduce sludge production, energy consumption, and carbon emissions. The implementation of digital twin technologies and the development of predictive models through artificial intelligence (AI) and machine learning (ML) would be essential to attaining energy and carbon neutral anammox-based wastewater treatment. Making the anammox process carbon and energy neutral would assist achieve multiple sustainable development goals (SDGs) and reflect climate action, while also making the technology more competitive in the real-world applications.