Anaerobic digestion (AD) is central to sludge stabilisation and renewable energy recovery in wastewater treatment plants. Increasing organic loading rates (OLRs) can improve throughput but may increase the risk of process instability. Many full-scale AD facilities operate at conservative OLRs to prevent organic overload, undermining energy recovery and process efficiency. This study investigates the effect of osmoprotectant (OP) supplementation on the stability and performance of conventional and thermally hydrolysed (THP) sludge digesters. Four pilot-scale mesophilic continuously stirred tank reactors were operated using conventional and THP sludge, with and without OP supplementation. Conventional digesters were operated at a baseline OLR of 2.0 g.VS/L/d and were increased stepwise to 3.5 g.VS/L/d, while THP digesters were increased from 3.5 to 5.0 g.VS/L/d. Progression between stages requires stable performance over at least two hydraulic retention times. Following baseline operation and the first OLR increase, pH values remained between 7.5 and 7.7, and Ripley ratios were below 0.25, indicating a suitable balance between alkalinity and acidity. THP digesters achieved higher specific biogas yields (439- 451 mL/g.VS added) than conventional digesters (272- 283 mL/g.VS added). No clear performance differences were observed between OP-supplemented and control digesters at the initial OLR increase. This aligns with previous batch studies, which showed biogas enhancements of up to 70% under stressed conditions with OP addition, suggesting that any protective effects may only become apparent as loading rates approach inhibitory levels. Ongoing work evaluates whether OP supplementation improves resilience and extends the maximum sustainable OLR before inhibition.