Resilient High-Rate Sulfidogenesis in a Hydrogen-Based Membrane Biofilm Reactor: Mechanistic Analysis of...

Copper mining industry generates water with high sulfate (SO₄ ^2-) concentrations. The hydrogen-based membrane biofilm reactor (H₂-MBfR) is a promising sulfidogenesis solution, using H₂ as a clean electron donor. An H₂-MBfR was operated for 209 days treating synthetic mining-influenced water under varying conditions (HRT, H₂ pressure, SO₄ ^2- loadings). The system proved highly resilient, achieving stable SO₄ ^2- removal (> 90%) and fully recovering from a severe shock load (4500 mg S L^-1). To identify the governing mechanisms, a transient pseudoanalytical biofilm model was developed. A Global Sensitivity Analysis (Sobol) showed performance is dominated by the maximum specific growth rate ( ${\mu }_{\max }$ ), detachment coefficient ( $b_{\text{det}}$ ), and H₂S inhibition ( $K_{H2S}$ ). The model was calibrated on Stages 1-3 (Days 0-169, n = 44), achieving R² = 0.962 (calibration) and R² = 0.572 (blind validation, Stage 4). Crucial findings from the model calibration ( ${\mu }_{\max }$  = 0.344 d^-1) and a diagnostic analysis using the Thiele Modulus (mean $\varphi$  = 0.224) strongly indicate that the system operated in a kinetically-limited regime. Performance was governed by the delicate balance of slow growth and high detachment, not by mass transfer (H₂ supply or SO₄ ^2- diffusion). This research validates the H₂-MBfR for high-rate applications and correctly shifts the bottleneck for future optimization from mass transfer to biofilm retention kinetics.