HIGH-RATE AND COMPACT SINGLE SLUDGE PRE-DENITRIFICATION PROCESS FOR RETROFIT

For the sewage treatment plants near rivers and closed water bodies in urbanized areas in Japan and European countries, there is a growing d emand for introduction of advanced treatment processes for nitrogen an d phosphorus from the viewpoints of water quality conservation and env ironmental protection, In order to remove nitrogen by the conventional biological treatment techniques, it is necessary to make a substantia l expansion of the facility as compared with the conventional activate d sludge process, In such urbanized districts, it is difficult to secu re a site and much capital is required to expand the existing treatmen t plant, To solve these problems, a compact single sludge pre-denitrif ication process using immobilized nitrifiers was developed, Dosing the pellets, which are suitable for nitrifiers growth and physically dura ble, into the nitrification tank of single sludge pre-denitrification process made it possible to perform simultaneous removal of BOD and ni trogen in a retention time equal to that in the conventional activated sludge process even at the low water temperature of about 10 degrees C, The 3,000 m(3)/d full-scale conventional activated sludge plant was retrofitted and has been successfully operated