In the wastewater treatment process, the removable of undesirable organic impurities is achieved through biological treatment in Aerobic or Anaerobic modes. In this section, we will discuss the Aerobic systems which we can provide for oxygen supply in water which is achieved mostly through supply of air into wastewater. As the oxygen solubility in water is limited, the driving force is small and this necessitates improving the conditions for mass transfer at the interface of air and wastewater. This is achieved either by optimizing the operating conditions of the biological reactor at different dissolved oxygen levels or by maximizing the air - wastewater interface area by deploying different Aeration Devices as suited best for a specific process requirement. To achieve these objectives, we provide various options for the Biological Reactors which can be based on suspended growth or attached growth. In the suspended growth option, we can offer one of the largest range of Reactors for achieving the objectives of conventional activated sludge process or any of its process modifications including those where sludge recycling may not be required like in Aerated lagoons. These systems can be provided with or without nutrient removal considerations. In the attached growth option, we can provide both systems i.e. with moving bed like RBC or fixed bed like Bio-Filter.