A Framework for Evaluating Large-Scale Resource Recovery Strategies to Achieve Compliance with Directive (EU) 2024/3019

This study proposes an integrated experimental and modeling framework to evaluate the feasibility and impact of utilizing volatile fatty acids (VFAs) derived from primary sludge as a sustainable carbon source to enhance biological nitrogen removal under Directive (EU) 2024/3019. The directive imposes strict nitrogen effluent limits and emphasizes resource recovery, necessitating innovative strategies in wastewater treatment plants (WWTPs). While VFA-based strategies demonstrate potential, real-scale implementation faces significant challenges, particularly due to variability in fermentate production caused by fluctuations in sludge composition, operational conditions, and environmental factors. These inconsistencies can compromise VFA quality and denitrification performance. Scenario analyses conducted at 15°C, a critical low-temperature condition, were used to assess effluent TN concentrations under different operational strategies. Compliance with the 10 mg/L TN target was demonstrated by maintaining an optimized sludge retention time (SRT) of 25 days and a fermentate flow rate of approximately 75 m³/d, albeit with increased energy costs of 600 kWh/day (60 Euros/day) to achieve a 12% improvement in denitrification efficiency. We highlight the complexity of implementing resource recovery strategies at scale and the need for further research and operational adaptations to align with regulatory goals.