FAS stands for Combined Fixed Film Activated Sludge and it indicates a hybrid process where you can achieve all the benefits of a traditional activated sludge process combined with a biological fixed-film system to create a highly efficient wastewater treatment plant in a much smaller footprint.
In the start-up phase, the plastic supports are dispersed in the biological reactor in which the activated sludge process will have already started, while the growth of the biofilm inside the carrier allows for the removal of the majority of the BOD and subsequently the oxidation of the ammonia.
The quantity of air to be supplied for the endogenous respiration of the bacteria must also guarantee the correct movement of the “carriers”, which must remain suspended, in the biological volume. Therefore, it will be necessary to verify the quantity required in order to perform both tasks.
One of the main applications for the CFAS solution is the retrofitting of existing activated sludge plants where it is necessary to implement the nitrification stage and increase the BOD removal yield. However, this technology can also be adopted in the construction of new plants, where a compact and efficient design is needed.