Abstract
Experimental study on biological denitrification of a municipal sewage has been performed without chemicals, applying a pilot plant of a modified activated sludge process. In this plant, a denitrification tank whose volume is about 1.69 m3 and retention time is about 34 minutes is installed at the head part of the aeration tank. The retention time of the aerated part of the aeration tank is kept to around 2.44 hrs. The sludge return eturn ratio is ranged from 0.5 to 2.0.
The removal of organic materials measured by CODcr is successful and the removal efficiency is in the range of 78.6-89.5%. The denitrification reaction takes place in the denitrification tank and the final sedimentation tank. The total removal efficiency of nitrogenous compounds increases with the increment of the sludge return ratio. The oxidized nitrogen removal efficiency in the denitrification tank is in the range of 66.8-84.9%. The alkalinity necessary for the nitrification of ammonium nitrogen is successfuly supplied from that of influent and the product of denitrification reaction without the addition of special alkalinity.
