Trading-off greenhouse gas emissions and 741/2020 European Union water reuse legislation: An experimental MBR study

A trade-off between greenhouse emissions (direct and indirect) and operational costs in the water treatment sector is of great importance, although only few literature studies exist. The paper presents a comprehensive experimental study on a Membrane Bioreactor (MBR) pilot plant at the Water Resource Recovery Facility of Palermo University (Italy). The MBR pilot plant was aimed at reducing carbon footprint while producing water suitable for water reuse in agriculture. Multiple scenarios were assessed to unveil the best operational variables including the assessment of the reclaimed water quality index for water reuse. Results showed the lowest operational costs for the MBR of 5.05 € cent/m³ with Class B according to 741/2020 European legislation. Results revealed optimised values, in terms of airflow rate and backwash frequency, of 0.8 m³/m²/h and 12 times/h, respectively. The highest N₂O emission was measured in correspondence of scenario S5 (airflow rate of 1.6 m³/m²/h) with 0.40 mg N₂O-N/m²/h in agreement with previous literature studies. The obtained results could effectively address the operators to find a trade-off between operational costs and water quality.