Hydrothermal carbonisation & struvite precipitation from dairy sludge: Evaluating market uncertainties & scale trade-offs

This study presents a techno-economic assessment of Hydrothermal Carbonisation (HTC) and Struvite Precipitation (STR) for dairy processing sludge (DPS), focusing on energy and cost performance across five system scales (2500–50,000 t/year). A dual approach was employed: a deterministic analysis using fixed input values, and a stochastic Monte Carlo simulation to assess uncertainty in key market and operational parameters. The results demonstrate that larger systems benefit from economies of scale, with lower per-unit costs. However, diminishing returns at larger scales highlight the need to balance technology design, processing scale, product valorisation, operational costs, and logistics. A sensitivity analysis reveal that gate fees, market prices for bio-based fertilisers and thermal energy fluctuations are critical variables influencing profitability. For Scale 3 (10,000 t/year) a reasonable balance between energy efficiency, cost-effectiveness, and logistical feasibility was observed. Still, the model showed susceptibility to market volatility, underlying the importance of adaptable strategies to mitigate financial risks and ensure system resilience in HTC systems. This research contributes to the circular economy literature, providing a transparent and adaptable framework for evaluating bio-based technologies under operational and market uncertainties. Future work should explore different reactor configurations, regional feedstock availability, and site-specific conditions to further validate and refine the system feasibility.