Step 1: Anaerobic Tank (A2O Only). Raw sewage mixed with return sludge enters the anaerobic zone. In the absence of oxygen and nitrate, Phosphorus Accumulating Organisms (PAOs) release phosphorus into the water. This biological nutrient removal (BNR) step is critical for preventing downstream eutrophication when discharging into natural water bodies. Optimized Hydraulic Retention Time (HRT) ensures maximum phosphorus release.
Step 2: Anoxic Denitrification. The water then flows into the Anoxic tank, mixed with an internal recycle stream from the aerobic tank. Here, heterotrophic bacteria utilize organic carbon to strip oxygen from nitrate (NO3-), converting it to harmless nitrogen gas (N2), effectively reducing Total Nitrogen (TN).
Step 3: Aerobic Nitrification (Oxic Zone). Powered by heavy-duty roots blowers and fine bubble diffusers, oxygen is heavily introduced into the activated sludge bioreactor. Autotrophic bacteria consume the BOD/COD and convert ammonia (NH3) into nitrate. Simultaneously, PAOs uptake excess phosphorus from the water into their cellular mass.
Step 4: Clarifier Settling & Disinfection. Unlike MBRs that use membranes, this packaged conventional sewage treatment plant utilizes a gravity clarifier. Engineered with a conservative surface overflow rate to prevent sludge bulking, the biological sludge settles to the bottom (to be returned as RAS or wasted), while the clear supernatant overflows the weirs. A final dosage of Sodium Hypochlorite ensures the effluent is free of pathogens and safe for discharge.
