A review of the metabolic response of the anammox process to biochar carriers: Performance impacts and mechanisms

Anaerobic ammonium oxidation (Anammox), as an efficient biological nitrogen removal process, has been engineered and applied in the field of side-stream wastewater. Inhibition of nitrite-oxidizing bacteria (NOB) and lack of biomass for anaerobic ammonia oxidation are the core barriers to the scale-up of mainstream PN-A technology. In recent years, biochar has shown broad application prospects in the mainstream anammox field due to its unique ability to reduce nitrates. This review systematically summarizes the role of biochar carriers under different feedstocks and production conditions for the promotion of nitrogen removal performance in anammox reactors and the effective mitigation of pollutant inhibition, and further analyzes the possible mechanisms of action involved in terms of metabolic changes at the microbial molecular level. The structure of biochar optimizes the survival environment of anaerobic ammonium oxidation bacteria (AnAOB), promotes the activity and gene expression of functional bacteria, and synergizes with partial denitrification and anaerobic ammonia oxidation to achieve the degradation of nitrate and the stable supply of nitrite, which enhances the efficiency of anammox for nitrogen removal. In addition, the potential risks of biochar to the environment are summarized, and risk aversion measures are given to promote the anammox reaction and promote the friendly development of the environment. This indicates that the future biochar anammox process can be carried out in the direction of research on biochar harmlessness, compositing and modification strategies, to provide a theoretical basis for biochar in the mainstream anammox.