Development of a novel periodic venting-controlled membrane biofilm reactor for hydrogenotrophic denitrification: Process performance and microbial mechanism

Abstract

The performance of anaerobic membrane biofilm reactor (MBfR) has long been underexploited due to the limited delivery of active gas to the biofilm on the close-end hollow fiber membranes (HFMs). Here, to establish a valid scheme for overcoming this obstacle, we coupled a denitrifying H2-based MBfR to an automatic venting unit for intermittently updating intramembrane gas, and a microsensor unit for investigating the H2 diffusion behavior. In short-term experiments, at the HFM length of 60 cm and H2 supplying pressure of 1.2 atm, the periodic venting strategy, in which the venting time and interval were set as 30 s and 17 min, respectively, was validated to be capable of improving the denitrification performance of H2-based MBfR. The results of long-term experiment show that compared to the conventional close-end operation, the around 50% increase in denitrification flux was achieved in the periodic venting-controlled system, which was found to be associated with the increased biofilm thickness and the evolution of denitrifying bacteria (DNB) and functional genes in the biofilm at the HFM distal end. Model outputs manifest that regardless of the HFM length, the biofilm regions with high DNB activity at the distal end were much narrower than those at the proximal end of the close-end HFMs; owing to the improved H2 delivery, the active biofilm region at the distal end of 60 cm HFM was significantly enlarged from 0–225 µm in the case of close-end operation to 0–450 µm in the venting-controlled system. The proposed periodic venting strategy opens a new avenue for the management of anaerobic MBfR.