One of the most commonly used BNR processes is the modified Ludzack Etinger( MlE) process. Bamar(1973)in wdrock-Ettinger design by providing the internal recycle nitre bo the anoxic zone directly from the aerobic zone. Both t ore denitrification role and overall nitrogen removal efficiency are increased The inernal recyde flow ratio(recycle flowrate divided by influent RowTate)typically ranges from 2 bo 4. with sufficient infuent BOD and anoxic contact time, these recycle ratios result in ON concentration from 4 to 7 mg/ when treating domestic wastewater. The MlE process is very adaptable to exishing activate <10mg/L total nitrogen A BOD/KN rtio of 4: I in the infuent wastewater is usually sufficient for nitrate reduction by preanoxic processes. Typical anoxic tank anoxic zone is divided into 3 to 4 stages in series, denitrification kinet tes are increased and the tolal detention time needed may then be 50 to 70 percent of the single -soge design. Another modification of the MLE process, termed'eMLEuses on additional set of anoxic/aeration basins Aerobic Erens Retum activated sludge13