In water and wastewater treatment, COD (Chemical Oxygen Demand) is a critical water quality parameter that measures the amount of oxygen required to chemically oxidize organic and inorganic pollutants present in water.
It indicates the total concentration of oxidizable contaminants (both biodegradable and non-biodegradable).
It helps assess the pollution strength of raw wastewater.
It is used to monitor treatment efficiency—a significant drop in COD from influent to effluent shows effective removal of pollutants.
It supports process control, regulatory compliance, and design of treatment systems.
Influent Monitoring: High COD in incoming wastewater may require pretreatment or process adjustments.
Treatment Performance: Engineers compare COD levels before and after treatment (e.g., in primary clarifiers, biological reactors, or chemical coagulation units) to evaluate removal efficiency.
Discharge Compliance: Environmental regulations often set maximum allowable COD levels in treated effluent to protect receiving waters.
Industrial Wastewater Management: Industries (e.g., food processing, textiles, pharmaceuticals) use COD to track waste loads and optimize treatment.
Faster results (2–3 hours vs. 5 days for BOD₅).
More comprehensive, as it oxidizes substances that microbes cannot break down.
Reproducible and reliable under lab conditions.
Does not distinguish between biodegradable and non-biodegradable matter.
Uses toxic chemicals (like chromium), requiring careful handling and disposal.
May overestimate actual oxygen demand in natural environments (since nature relies on biological processes).
A municipal wastewater plant might receive influent with COD = 500 mg/L and discharge effluent with COD = 30 mg/L, indicating >90% removal—meeting environmental standards.
In summary: In water treatment, COD is a fast, robust indicator of overall organic/inorganic pollution load, essential for designing, operating, and regulating treatment processes.
