Bioacclimation versus bioaugmentation: efficacy, mechanisms, applications, and optimization of biological nitrogen...

Bioaugmentation and bioacclimation are two strategies to enhance nitrogen removal from hypersaline wastewater. Using Web of Science literature (2016-2026), this review systematically summarizes advances in improving salt tolerance via these two strategies and conducts a bibliometric analysis of 758 publications to identify research hotspots and trends. The key conclusions are as follows: (1) Research on hypersaline wastewater treatment has grown rapidly, yet existing studies focus mainly on applications; microbial mechanisms should be prioritized. (2) Lab-scale bioacclimation tolerates salinity up to 10%, outperforming bioaugmentation. By contrast, pilot-scale bioaugmentation tolerates up to 9% salinity, exceeding pilot-scale bioacclimation. Sequential coupling of bioaugmentation and bioacclimation exhibits practical potential. (3) Bioacclimation enriches halotolerant genera Candidatus Kuenenia, Thauera and Halomonas, while bioaugmentation enriches Halomonas, Paracoccus and Truepera. Both strategies confer salt tolerance through these mechanisms: remodeling nitrogen metabolic pathways to promote compatible solute secretion, upregulating ion transporters, increasing extracellular polymeric substance production, and strengthening synergistic electron transfer within microbial communities. (4) Salinity can trigger N₂O emissions, which can be mitigated by constructed wetlands optimized with the two biostrategies. Appropriately tailored stacked ensemble machine learning models help optimize treatment performance. (5) Major limitations involve low operational efficiency, unclear microbial synergies and underestimated greenhouse gas risks. Future work should optimize inoculum propagation, salinity gradients and maximum salinity limits. Controlling greenhouse gas emissions and developing predictive models are critical for clean biotreatment of hypersaline wastewater. This review clarifies the enhancement mechanisms of bioaugmentation and bioacclimation, proposes targeted optimizations, and provides theoretical support for sustainable large-scale biotreatment.