The application of hydrocyclones within the return activated sludge (RAS) stream offers a promising approach to improving activated sludge process (ASP) performance at wastewater treatment works. Hydrocyclones provide a compact method for selectively retaining dense, well settling biomass (underflow) and wasting lighter, poorly settling solids (overflow). Early operational data from Veolia’s ZeeDENSE system, utilising MABR in combination with hydrocyclones at a United Utilities site, demonstrates clear improvements in sludge characteristics. The underflow has shown greater sludge settleability, with average maximum settling velocities 45% higher than the feed’s and 62% higher than the overflow’s. Consistent with the higher settling velocities, the average SSVI₃₀ for the underflow is 21% lower than the feed’s and 25% lower than the overflow’s, indicating the underflow’s sludge settles more rapidly and compactly. Compared with the site’s design SSVI₃₀ value of 120 mg/L the site is achieving consistently in the low 80's and the technology has helped remove and prevent a filamentous problem from returning. Given the improvement in settleability, hydrocyclone integration can improve ASP capacity by operating at higher mixed liquor concentrations, removing the need for additional FSTs. Overall, hydrocyclones provide a practical enhancement to biological treatment, offering both performance and operational benefits in wastewater treatment.