| The process is performed in fixed-bed open filters with pre-aerated water. Common silica sand covered with manganese oxides is used as a filtration material. Manganese oxides layer serves as a rough support for the biofilm of nitrifying bacteria that are not thus removed from the packing during backwashing. Ammonia is under controlled conditions biologically oxidized to nitrate. The process was applied in several water treatment plants in central Bohemian region in full scale. Long term operational results showed that concentration of ammonia up to 3 mg.l-1 can be removed with higher than 90 % efficiency. For a concentration of ammonia higher than 3 mg.l-1 in raw water two step technology has to be applied (1st aeration ® 1st filtration ® 2nd aeration ® 2nd filtration). Practicability of the two-step arrangement was also successfully verified in full scale. Key contact: V. Janda, Institute of chemical technology, Prague, Dept. of water technology and environmental engineering, Technická 5, 166 28 Prague 6, Czech Republic, e-mail: vaclav.janda@vscht.cz. |
