Direct delivery of CO₂ into a hydrogen-based membrane biofilm reactor and model development

A new hydrogen-based hollow fiber membrane biofilm reactor (MBfR) with double membrane technique was developed in this work and systematic research was conducted. A mathematical model was built up to predict pH and Langelier Saturation Index (LSI) in the hydrogen-based autotrophic denitrification system with minimal error. The model tested with varied CO₂ pressures identified that increasing CO₂ pressure resulted in pH decrease and prevention from precipitation. Long-term performance of the new MBfR was also evaluated. When CO₂ was delivered at 0.05 MPa, 99% nitrate was removed with a constant neutral pH in the reactor. In the long-term experiment, misdistributions of H₂ and CO₂ caused disparity of biomass communities on the H₂ and CO₂ modules, but functional bacteria existed on both modules; this suggested that despite of misdistribution, bubbleless H₂ was still able to be transported by recirculation to the CO₂ module and became available for the bacteria on the module.