Primary treatment is not required in which modified activated sludge process?

In the context of wastewater treatment processes, the extended aeration activated sludge process is designed to provide both aeration and secondary treatment in a single step, significantly enhancing the degradation of organic materials. This method employs a longer detention time and operates at a lower F/M (food-to-microorganism) ratio, allowing for the effective breakdown of waste without the need for prior primary treatment.

By extending the aeration phase, this method not only promotes the growth of microorganisms that can efficiently treat the wastewater but also naturally separates solids through the extended contact with oxygen and bacteria. This results in improved clarification and digestion of solids directly within the aeration tank. As a result, primary treatment—which typically involves the removal of larger solids and screening—becomes unnecessary.

In contrast, processes like step aeration, complete mix aeration, and tapered aeration typically require primary treatment to remove larger particulates before finer biological processes can effectively treat the wastewater. Therefore, the extended aeration activated sludge does not need primary treatment because it inherently allows for sufficient organic matter reduction during its extended aeration phases.