Unique characteristics of Candidatus Nitrosoglobus-driven acidic partial nitritation: critical review and potential applications

• Unique physiology and kinetics of Ca. Nitrosoglobus are clarified. • Stable acidic PN and Ca. Nitrosoglobus enrichment mechanisms are discussed. • Acidic PN uses in N removal, sludge treatment and metal bioleaching are summarized. • Key challenges, future research directions and application prospects for acidic PN are outlined. Acid-tolerant ammonium-oxidizing bacteria (AOB) Candidatus (Ca.) Nitrosoglobus challenge the long-standing view that efficient bacterial ammonium oxidation is restricted to neutral pH. Driven by low pH and free nitrous acid (FNA), Ca. Nitrosoglobus mediates an acidic partial nitritation (PN) pathway that achieves stable, high nitrite accumulation while strongly suppressing nitrite-oxidizing bacteria (NOB). This review synthesises current knowledge on its discovery, physiology and kinetics, emphasises its broad pH range, extraordinary FNA tolerance, distinct growth and affinity traits relative to traditional AOB and discusses emerging applications, including downstream anammox support, acidic aerobic digestion for sludge reduction, ammonium-based bioleaching, and other potential application perspective. This review summarised key challenges in application and proposed future research priorities, including advancing selective enrichment strategies, optimizing control windows, and identifying potential research and application directions enabled by products generated through acidic PN, aiming to advance Ca. Nitrosoglobus -centred acidic PN toward new insight into the practical wastewater treatment