Anaerobic oxidation of methane coupled to denitrification (AOM-D) in a membrane biofilm reactor (MBfR), a platform used for efficiently coupling gas delivery and biofilm development, has attracted attention in recent years due to the low cost and high availability of methane. However, experimental studies have shown that the nitrate-removal flux in the CH4-based MBfR (<1.0 g N/m(2)-day) is about one order of magnitude smaller than that in the H-2-based MBfR (1.1-6.7 g N/m(2)-day). A one-dimensional multispecies biofilm model predicts that the nitrate-removal flux in the CH4-based MBfR is limited to <1.7 g N/m(2)-day, consistent with the experimental studies reported in the literature. The model also determines the two major limiting factors for the nitrate-removal flux: The methane half-maximum-rate concentration (K-2) and the specific maximum methane utilization rate of the AOM-D syntrophic consortium (k(max2)), with k(max2) being more important. Model simulations show that increasing k(max2) to >3 g chemical oxygen demand (COD)/g cell-day (from its current 1.8 g COD/g cell-day) and developing a new membrane with doubled methane-delivery capacity (D-m) could bring the nitrate-removal flux to >= 4.0 g N/m(2)-day, which is close to the nitrate-removal flux for the H-2-based MBfR. Further increase of the maximum nitrate-removal flux can be achieved when D-m and k(max2) increase together.