Under the AMP 7 WINEP programme, the total phosphorous permit limit at a trickling filter works with a PE of 6,400 was tightened from 1 mg/l to 0.25 mg/l, with a stretch target of 0.1 mg/l. This ultra-low stretch target is challenging to achieve reliably with conventional two-point coagulant dosing and tertiary solids removal processes. To meet the stretch target the trickling filter works was upgraded with a new tertiary solids removal process; a high-rate ballasted sand clarifier, which has been proven to achieve < 0.1 mg/l at activated sludge plants in the UK. The implementation of this technology required significant process upgrades at the site, including secondary coagulant dosing, polymer makeup and dosing, micro-sand dosing and online instrumentation for precise dosing control. This presentation will discuss the key elements of the design, review performance data from the first 18 months of operation, and share lessons learnt to inform future applications of this technology. As progressively lower phosphorous limits are being introduced across the industry, ballasted sand clarification is expected to play a critical role in achieving compliance and improving water quality in receiving watercourses.