This standard specifies the requirements for equipment used in biological wastewater treatment based on the activated sludge process (ASP) and its various modifications. It provides crucial design parameters like F/M ratio, sludge age, and loading rates for aeration tanks and secondary clarifiers, which are fundamental for designing effective sewage and industrial effluent treatment plants.
Requirements for biological treatment end equipment, Part 2: Activated sludge process and its modifications
Quick Reference Values
F/M Ratio for Conventional ASP0.2 - 0.4 kg BOD/kg MLVSS/day
MLSS for Conventional ASP1500 - 3000 mg/l
Hydraulic Retention Time for Extended Aeration18 - 36 h
Sludge Age for Extended Aeration20 - 30 days
Surface Overflow Rate for Secondary Clarifier (Avg Flow)12 - 20 m³/m²/day
Solids Loading Rate for Secondary Clarifier40 - 120 kg/m²/day
Minimum Freeboard in Aeration Tank0.6 m
Key Formulas
F/M Ratio = (Q × S₀) / (V × Xᵥ) — Food to Microorganism Ratio
Sludge Age (SRT) = (V × X) / (Qw × Xw + Qe × Xe) — Solids Retention Time
Surface Overflow Rate (SOR) = Q / A — Clarifier Sizing
Solids Loading Rate (SLR) = (Q + Qr) × X / A — Clarifier Sizing
Practical Notes
The design parameters in Table 1 are typical ranges and should be used with engineering judgment; pilot studies are recommended for large or unconventional wastewater streams.
The performance of the entire ASP system heavily relies on the proper design and operation of the secondary clarifier, not just the aeration tank. Pay close attention to SOR and SLR values from Table 2.
Selection of the ASP modification (e.g., conventional, extended aeration, SBR) depends on factors like influent BOD, land availability, power costs, and required effluent quality.