Secondary Treatment: The Heart of Biological Purification & Process Diversity

SHANGHAI - Dec. 19, 2025 - PRLog -- Secondary Treatment: The Heart of Biological Purification & Process Diversity

This stage utilizes microbial communities (activated sludge) to degrade pollutants, representing the most technically complex and energy-intensive unit in wastewater treatment.

4. Biological Reactor Systems
AAO Series Processes and Variants:
Standard AAO: Achieves simultaneous nitrogen and phosphorus removal through a series configuration of anaerobic zone (phosphorus release), anoxic zone (denitrification for nitrogen removal), and aerobic zone (nitrification, phosphorus uptake, and BOD removal). The key lies in mixed liquor recirculation and return activated sludge.

Modified AAO: Such as the UCT process, which modifies the recirculation pathway to minimize nitrate interference with anaerobic phosphorus release, further enhancing phosphorus removal efficiency.

Oxidation Ditch: A closed-loop channel reactor that uses surface aerators to propel water flow and provide oxygenation, creating alternating aerobic and anoxic zones within the ditch. It combines the characteristics of both plug flow and complete mix systems, delivering excellent nitrogen removal performance.

SBR (Sequencing Batch Reactor): Completes five sequential phases—fill, react, settle, decant, and idle—within a single tank on a time-controlled basis. Variants such as CASS/CAST incorporate a biological selector at the front end of the tank, effectively preventing sludge bulking.

MBR (Membrane Bioreactor): Integrates biological degradation with membrane separation technology, using ultra/microfiltration membrane modules (hollow fiber or flat sheet membranes) to completely replace the secondary clarifier. It offers superior effluent quality (suitable for direct reuse), high sludge concentration, and reduced footprint, though it presents management challenges related to membrane fouling and energy consumption.

💡 Understanding these diverse biological treatment options is essential for selecting the optimal process configuration based on your specific effluent requirements, site constraints, and operational considerations.

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