Resilient High-Rate Sulfidogenesis in a Hydrogen-Based Membrane Biofilm Reactor: Mechanistic Analysis of Kinetic-Limited Performance Under Variable Loading.

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 ( μ max ), detachment coefficient ( b det ), and H2S inhibition ( K H 2 S ). 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 ( μ max  = 0.344 d-1) and a diagnostic analysis using the Thiele Modulus (mean ϕ  = 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.