Knowledge Base
Resources & Technical FAQ
Deepen your understanding of wastewater treatment fundamentals and industry best practices. Verified by our senior engineering team.
BOD (Biochemical Oxygen Demand) measures oxygen used by microorganisms to decompose organic matter over 5 days. It indicates biodegradable organic pollution.
COD (Chemical Oxygen Demand) measures oxygen equivalent of all organic matter that can be oxidized chemically. It includes biodegradable and non-biodegradable organics.
The BOD/COD ratio indicates biodegradability. Ratios >0.5 suggest readily biodegradable wastewater suitable for biological treatment.
Biological reaction rates increase with temperature. Nitrification is particularly sensitive: rate halves at 10°C compared to 20°C. Design must account for winter temperatures.
Sludge bulking is excessive growth of filamentous bacteria that interfere with settling. Indicators: high SVI (>150 mL/g), cloudy effluent.
Control: maintain DO >2 mg/L; install selectors; chlorinate return sludge; improve screening.