Determining the optimal transmembrane gas pressure for nitrification in membrane-aerated biofilm reactors based on oxygen profile analysis

The goal of this study was to investigate the effect of transmembrane gas pressure (P (g)) on the specific ammonium removal rate in a membrane-aerated biofilm reactor (MABR). Our experimental results show that the specific ammonium removal rate increased from 4.98 to 9.26 gN m(-2) day(-1) when P (g) increased from 2 to 20 kPa in an MABR with a biofilm thickness of approximately 600 mu m. However, this improvement was not linear; there was a threshold of P (g) separating the stronger and weaker effects of P (g). The ammonium removal rate was improved less significantly when P (g) was over the threshold, indicating that there is an optimal threshold of P (g) for maximizing ammonium removal in an MABR. The change in oxygen penetration depth (d (p)) is less sensitive to P (g) in the ammonia-oxidizing active layer than in the inactive layer in membrane-aerated biofilm. The location of the P (g) threshold is at the same point as the thickness of the active layer on the curve of d (p) versus P (g); thus, the active layer thickness and the optimal P (g) can be determined on the basis of the changes in the slope of d (p) to P (g).