Proceedings

Membrane Aerated Biofilm Reactors (MABR) are an emerging technology, mainly known for its aeration energy efficiency. However, the unique biology obtained in IFAS mode (Integrated Fixed-film Activated Sludge) presents great advantages in nutrients removal. The basic principle of an IFAS MABR is holding two different biomasses in the same tank to complement each other’s functionality. More specifically: there is an aerobic autotrophic nitrifying biofilm, and there are the suspended solids denitrifying in anoxic conditions.

The IFAS MABR is preferably arranged as a staged process, typically having 3 MABR stages followed by an aerated volume. The membranes are installed at the upstream side of the tank to make the most of the installed surface area at higher concentrations, or local volumetric loading rates. The most common standard process of this type is a marine-container based MABR (figure 1), but the process can be installed I a concrete basin as well (figure 2).

Recently it has been found that at high enough influent COD/TP ratio, there is significant phosphorous release in the first MABR stage of a multi-stage process, and that this leads to TP removal of up to 90% along the process. Concentration profiles along the process show that TP concentration of less than 8 mg/l increases to more than 20 mg/l ortho-phosphate in the first stage, then gradually decreases along the reactor to less than 1 mg/l in the effluent (figure 3). Similarly, ammonia and nitrate concentration profiles along the process show simultaneous nitrification and denitrification (figure 4).

The system treating 120 m3/d in a single marine container has been operating for more than a year. It demonstrates that high quality effluent can be sustained at small scale through application of a suitable technology.

Biological nutrients removal & Innovation, optimization and process modelling