A novel double-membrane system for simultaneous nitrification and denitrification in a single tank

A novel biological treatment system, which contains two types of membrane modules in a single tank, was developed for simultaneous nitrification and denitrification. Both of the modules were fed with the substrates on the tube side of the silicone tubes by diffusing them to the biofilms which form on the surface of the tubes. One module was fed with methanol for denitrification and the other one was fed with pure oxygen for nitrification. As a result, the interference of organic carbon on nitrification, and that of oxygen on denitrification, were both hindered by the diffusion barriers (biofilms), thereby allowing tyro different niches for nitrifiers and denitrifiers to coexist in a single tank. Besides saving space and the amount of alkalinity required for nitrification, this system also produced low residual chemical oxygen demand (COD) and high nitrogen removal rates (2.9 similar to 3.4 g N m(-2) d(-1) of surface area of membrane).