The mainstream process of sewage treatment—A/O process


Introduction to A/O Process

The A/O process was produced in the 1970s. Because of its simultaneous degrading of organic matter and denitrification, and its convenient operation and management, it has been widely used. Since the sewage treatment process is determined according to various factors such as the amount of sewage, water quality, effluent requirements and local actual conditions, small and medium-sized urban sewage treatment stations generally choose A/O and other processes.

Process characteristics


1. High efficiency

This process has a high removal effect on organic matter and ammonia nitrogen in wastewater. When the total residence time is greater than 54h, the effluent after biological denitrification is coagulated and sedimented, which can reduce the COD value to below 100mg/L, and other indicators also meet the emission standards, and the total nitrogen removal rate is above 70%.

2. Simple process, low investment and low operating cost

The process uses organic matter in wastewater as a carbon source for denitrification, so there is no need to add expensive carbon sources such as methanol.


1. Since there is no independent sludge return system, sludge with unique functions cannot be cultivated, and the degradation rate of refractory substances is low.

2. To improve the denitrification efficiency, the internal circulation ratio must be increased, thus increasing the operating cost. In addition, the internal circulating liquid comes from the aeration tank and contains a certain amount of DO, which makes it difficult for the A section to maintain an ideal anoxic state, which affects the denitrification effect, and the nitrogen removal rate is difficult to reach 90%.