Last Updated: August 2026 | Reading Time: 12 minutes
Introduction
Understanding the difference between COD (Chemical Oxygen Demand) and BOD (Biochemical Oxygen Demand) is essential for selecting the right wastewater treatment method. The COD/BOD ratio indicates biodegradability and guides treatment selection.
Recommended Treatment Chemicals
| Chemical | Role | Typical Dosage |
|---|---|---|
| Poly Aluminium Chloride | Coagulant | 50-300 mg/L |
| Poly Ferric Sulfate | Coagulant | 30-200 mg/L |
| Polyacrylamide | Flocculant | 0.5-5 mg/L |
| Activated Carbon | Adsorbent | 50-500 mg/L |
Treatment Process & Chemical Selection
The treatment process typically involves multiple stages:
- Primary treatment: Coagulation with PAC (50-300 mg/L) and PAM (0.5-5 mg/L) for suspended solids and colloidal removal
- Secondary treatment: Biological process (activated sludge, MBBR, or UASB) for biodegradable COD removal (70-95% efficiency)
- Tertiary treatment: Advanced oxidation (Fenton, ozone) or activated carbon for refractory COD polishing
- Disinfection: TCCA or UV for pathogen control before discharge
Chemical Dosing Guide
| Treatment Stage | Chemical | Dosage | pH Range | Removal Efficiency |
|---|---|---|---|---|
| Coagulation | PAC (30% Al2O3) | 50-300 mg/L | 5.5-8.0 | 30-55% COD |
| Coagulation | PFS | 30-200 mg/L | 4.5-8.0 | 40-60% COD |
| Flocculation | PAM (anionic) | 0.5-5 mg/L | 6.0-9.0 | Improves settling |
| Oxidation | H2O2 (Fenton) | 0.5-2x COD | 3.0-4.0 | 50-80% COD |
| Adsorption | PAC/PAC | 50-500 mg/L | 5.0-9.0 | 20-80% COD |
| Disinfection | TCCA | 5-20 mg/L | 6.0-8.0 | 99.9% bacteria |
Cost Analysis
| Treatment Method | Capital Cost (USD/m3/day) | Operating Cost (USD/m3) | Notes |
|---|---|---|---|
| Coagulation-sedimentation | $50-$150 | $0.10-$0.30 | Simple, fast results |
| Activated sludge | $100-$250 | $0.05-$0.20 | Cheapest for biodegradable COD |
| UASB anaerobic | $150-$350 | $0.02-$0.08 | Best for high COD, produces biogas |
| Fenton oxidation | $80-$200 | $0.30-$1.00 | For refractory COD |
| Activated carbon | $50-$150 | $0.20-$0.80 | Polishing, broad-spectrum |
| MBR membrane | $200-$500 | $0.15-$0.40 | Highest quality effluent |
Frequently Asked Questions
What is cod vs bod?
cod vs bod refers to the process of reducing Chemical Oxygen Demand (COD) in wastewater using chemical, biological, or advanced oxidation methods. The goal is to meet discharge limits (typically < 300 mg/L COD) while minimizing treatment cost and chemical usage.
Which chemicals are best for cod vs bod?
The most effective chemicals for cod vs bod include PAC (Poly Aluminium Chloride) at 50-300 mg/L for coagulation, PFS for higher efficiency, PAM as flocculant aid at 0.5-5 mg/L, hydrogen peroxide for Fenton oxidation, and powdered activated carbon for adsorption. The optimal choice depends on COD concentration and wastewater composition.
How much does cod vs bod cost?
Cost of cod vs bod varies by method: coagulation $0.10-0.30/m3, biological treatment $0.05-0.20/m3, Fenton oxidation $0.30-1.00/m3, activated carbon $0.20-0.80/m3, and membrane treatment $0.50-1.50/m3. Combined biological + chemical treatment typically costs $0.15-0.50/m3.
What COD removal efficiency can be achieved?
COD removal efficiency depends on the method: PAC coagulation achieves 30-55%, biological treatment 70-95%, Fenton AOP 50-80%, activated carbon 20-80%, and MBR 90-98%. Combined treatment trains can achieve 95-99% total COD removal.
Optimization Tips
- Conduct jar tests: Always determine optimal coagulant dosage through laboratory jar testing before full-scale implementation
- Maximize biological treatment: Biological processes are the most cost-effective for biodegradable COD removal
- Optimize pH: Coagulation and AOPs are highly pH-sensitive; maintain optimal pH for maximum removal
- Combine processes: Use PAC + PFS blend for coagulation, biological + chemical for combined COD
- Monitor continuously: Real-time COD monitoring enables dosing optimization and early detection of process upsets
Conclusion
Effective treatment requires matching the right chemical and process to your specific wastewater characteristics. For most industrial applications, a multi-stage approach combining biological treatment with chemical coagulation and advanced oxidation provides the best balance of cost and performance. The key is to maximize low-cost biological removal first, then use chemical methods only for remaining refractory compounds.
Need expert guidance on chemical selection for your wastewater? Contact our technical team for a free evaluation and treatment recommendation.