What is BOD in STP Plant.

 

BOD in Sewage Treatment Plants (STPs)

BOD (Biochemical Oxygen Demand) is a critical parameter in wastewater treatment that measures the amount of oxygen required by microorganisms to biologically decompose organic matter in water over a specific period, typically 5 days at 20°C. It is a key indicator of organic pollution and the efficiency of sewage treatment processes.

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Role of BOD in STPs

1. Assessing Pollution Load:
   • Higher BOD levels indicate a significant organic load, requiring intensive treatment.
2. Designing STP Processes:
   • BOD data helps determine the capacity and type of biological treatment processes (e.g., Activated Sludge Process, MBR, MBBR).
3. Evaluating Treatment Efficiency:
   • Comparing BOD levels in influent (untreated wastewater) and effluent (treated water) indicates how effectively the STP removes organic matter.

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Stages in STPs and BOD Reduction

1. Preliminary Treatment:
   • Removes large solids, reducing physical debris but not significantly impacting BOD.
2. Primary Treatment:
   • Settling tanks remove suspended solids, slightly reducing BOD (around 20-30%).
3. Secondary Treatment:
   • Biological processes like Activated Sludge, MBBR, or RBC degrade dissolved and suspended organic matter, reducing BOD significantly (up to 90% or more).
4. Tertiary Treatment (if needed):
   • Further removes residual organic and inorganic pollutants to meet strict discharge or reuse standards.

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BOD Standards for STP Effluent

• The permissible BOD level in treated effluent depends on local regulations and discharge requirements. Common standards:
  • For discharge into water bodies: ≤ 30 mg/L
  • For water reuse (e.g., irrigation): ≤ 10 mg/L

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Importance of BOD Monitoring

1. Environmental Protection:
   • Reducing BOD prevents oxygen depletion in receiving water bodies, protecting aquatic life.
2. Compliance with Regulations:
   • Ensures the STP meets legal discharge limits to avoid penalties.
3. Process Optimization:
   • Helps operators adjust treatment processes to handle fluctuating organic loads efficiently.

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Conclusion

BOD is a fundamental parameter in STP operations, reflecting the organic pollution load and the treatment plant's performance. By efficiently reducing BOD, STPs protect the environment, ensure regulatory compliance, and enable safe wastewater reuse.