Application of the anammox-based process for nitrogen removal from anaerobic digestion effluent: A review of treatment performance, biochemical reactions, and impact factors

Anaerobic digestion (AD) combined with an anammox-based process is an efficient and energy-saving technology. The key to realizing the wide application of this technology is to deeply understand the anammox-based process, which is the limiting phase of this technology. This study provides an overview of more than 30 reactors from published studies on AD effluent treatment via anammox-based processes. The objective of this review is to evaluate how to achieve stability and high efficiency in the anammox-based process. Therefore, the AD effluent components are critically reviewed, and the appropriate pretreatment procedures for the AD effluent before it is fed into an anammox-based process reactor are summarized. Single-stage and two-stage partial nitration–anammox (PN/A) are two common anammox-based processes for removing autotrophic nitrogen from AD effluent. To reduce the nitrate produced by anammox, a combination of partial denitrification with PN/A is recommended. Nitrogen and carbon removal efficiencies are the basic criteria that are used to assess the performance of existing anammox-based processes for AD effluent treatment. Thus, the strategies for efficiently removing nitrogen and carbon in anammox-based processes are documented in this review. Moreover, the relationships between anammox, ammonium-oxidizing bacteria, nitrite-oxidizing bacteria, and denitrifiers are explored by clarifying the potential biochemical reactions in anammox-based processes for AD effluent treatment. Furthermore, the three primary influencing factors—ammonia and nitrite concentrations, organic concentration, and the operation parameters—are summarized.