How should we interpret biochemical indicators in wastewater treatment?
In the wastewater treatment process, biochemical indicators primarily reflect the content and biodegradability of organic pollutants in water, and are key to determining whether wastewater can meet standards through biological treatment. Common biochemical indicators and their interpretation methods are as follows:
1. COD (Chemical Oxygen Demand)
Definition: Indicates the amount of oxygen consumed by strong oxidants to oxidize organic matter in water.
Significance: The higher the COD, the more severe the organic pollution in the water.
Purpose: Reflects the total organic pollutant load in the wastewater, but does not distinguish between biodegradable and unbiodegradable substances.
2. BOD (Biochemical Oxygen Demand)
Definition: The amount of dissolved oxygen consumed by microorganisms when decomposing organic matter under aerobic conditions. BOD₅ (5 days) is commonly used.
Significance: Directly reflects the amount of biodegradable organic matter in water.
Purpose: An important indicator for determining whether wastewater is suitable for biological treatment.
3. COD/BOD Ratio (Biodegradability Index)
General Rules:
BOD₅/COD ≥ 0.4: Good biodegradability, suitable for biological treatment.
0.2 ≤ BOD₅/COD < 0.4: Moderate biodegradability, usually requiring combined physicochemical and biochemical treatment.
BOD₅/COD < 0.2: Poor biodegradability, poor biological treatment results, requiring pretreatment or advanced oxidation.
4. SS (Suspended Solids) and TN/TP (Nitrogen and Phosphorus Index)
SS (Suspended Solids): Excessively high levels can affect dissolved oxygen and sedimentation in the biological pond.
TN (Total Nitrogen) and TP (Total Phosphorus): Biological nitrogen and phosphorus removal requires a reasonable carbon, nitrogen, and phosphorus ratio (generally C:N:P ≈ 100:5:1).
5. Practical Application Interpretation
Influent Indicators: Determine the biodegradability of wastewater and whether physicochemical pretreatment is necessary. During-operation monitoring: Evaluate biological treatment efficiency through changes in COD, BOD, ammonia nitrogen, and other indicators.
Effluent indicators: Compare with discharge standards to ensure compliance for discharge or reuse.