Nitrous oxide (N₂O) emissions from biological nitrogen removal remain a major challenge for achieving Net Zero wastewater treatment. The OFWAT Catalysing a Net Zero Future project investigates biocatalyst-based strategies to suppress N₂O formation while maintaining high treatment performance. Initial laboratory studies evaluated two complementary immobilised biocatalysts: Pseudomonas stutzeri for denitrification and the nitrifying biocatalyst AEROVI™ for ammonia oxidation. Immobilised P. stutzeri achieved rapid, near-complete N₂O removal in municipal wastewater, with optimal performance at a 20% filling ratio and carbon-to-nitrogen ratios of 3.5–6.1, reaching removal rates up to 1.72 mg N₂O·L⁻¹·h⁻¹, supported by enhanced nitrous oxide reductase activity. In parallel, AEROVI™ consistently achieved >90% ammonia removal across loading rates of 0.08–0.43 kg N·m⁻³·d⁻¹ while reducing dissolved N₂O and emission factors by up to 50% compared with conventional systems. Building on these results, a pilot-scale Integrated Microvi Activated Sludge (IMAS) system combining anoxic and aerobic processes with both nitrifying and denitrifying biocatalysts was deployed at Severn Trent’s Resource Recovery and Innovation Centre (R2IC) at Spernal STW (UK). Ongoing monitoring of nitrogen species, N₂O, carbon availability, and operational conditions will demonstrate ammonia and nitrogen removal efficiency, N₂O mitigation, and system resilience, highlighting the potential of biocatalyst-based processes to enable low carbon, energy efficient wastewater treatment.