I. Characteristics of Wastewater and Treatment Challenges

1. Water Quality Features:

• High Concentration of Organic Matter: COD 12,000~15,000 mg/L, containing antibiotic residues (e.g., Mevastatin, Salinomycin), fermentation by-products, and solvents (e.g., ethyl acetate).
• Biological Inhibition: Some antibiotics inhibit microbial activity, requiring enhanced pretreatment.
• Color and Odor: Raw water color >500 times, containing sulfides and volatile organic compounds (VOCs).

2. Treatment Objectives:

• Effluent COD ≤150 mg/L (in accordance with the "Emission Standard of Water Pollutants for Mixed-Formulation Pharmaceutical Industry" GB 21908-2008).
• Color ≤30 times, no odor, no residual biological toxicity.

II. Process Design

1. Physical-Chemical Pretreatment

• Equalization Tank (HRT=8 h): Homogenize water quality and quantity, reduce shock load, with aeration stirring to prevent sedimentation.
• Coagulation and Sedimentation (Optional): If raw water SS >500 mg/L, PAC/PAM is added to remove suspended solids and colloids (COD removal rate of about 10%).

2. Composite Catalytic Micro-Electrolysis System

• Equipment Parameters:
  • Reactor: 2 parallel units, filled with iron-carbon packing (Fe/C mass ratio 3:1, particle size 2~5 mm) + catalyst (Cu/Fe oxides).
  • Retention Time: 2~3 h, pH adjusted to 2~3 (with sulfuric acid).
• Treatment Effect:
  • COD removal rate ≥35% (reduced to 7,800~9,750 mg/L), color removal rate 80%, VOCs reduction by over 60%.
  • Chain-breaking and ring-opening: Degradation of large-molecule antibiotics into small organic molecules (B/C increased from 0.2 to 0.35).

3. Biological Treatment System (A²/O Process)

• Process Configuration:
  • Anaerobic Tank (A1) (HRT=12 h): Hydrolysis and acidification to further degrade refractory organic matter, with packing for biofilm.
  • Anoxic Tank (A2) (HRT=8 h): Denitrification for nitrogen removal, sodium acetate added as a carbon source (C/N=4~6).
  • Aeration Tank (O) (HRT=24 h): Two-stage series activated sludge method (MLSS=4,000~5,000 mg/L), using high-efficiency aerators (DO=2~4 mg/L).
• Treatment Effect:
  • COD removal rate ≥85% (effluent COD reduced to 1,200~1,500 mg/L), ammonia nitrogen ≤15 mg/L.

4. Advanced Treatment

• Fenton Oxidation (H₂O₂/Fe²+):
  • Add H₂O₂ (0.5~1.0 kg/m³) and FeSO₄, pH=3~4, react for 1~2 h, oxidize residual antibiotics and refractory COD.
  • COD removal rate ≥50% (effluent COD ≤300 mg/L).
• Coagulation and Sedimentation:
  • Add PAC/PAM to remove oxidation products, further reduce COD by 20~30% (effluent COD ≤150 mg/L).
• Disinfection Tank (Sodium Hypochlorite):
  • Add 5~10 mg/L to kill pathogens and decolorize.

III. Key Equipment and Operating Parameters

IV. Operating Effect and Economic Viability

• Investment Cost: Approximately 8~10 million yuan (including civil construction, equipment, and installation).
• Operating Cost:
  • Electricity: 1.2~1.5 yuan/m³ (mainly for micro-electrolysis + aeration);
  • Chemicals: 0.8~1.0 yuan/m³ (acids, Fenton reagents, PAC, etc.);
  • Sludge Disposal: 0.3~0.5 yuan/m³.

V. Precautions

• Biological Inhibition Control: Micro-electrolysis effluent should be adjusted to neutral pH (6~8) before entering the biological system to avoid acid inhibition of microorganisms.
• Sludge Acclimatization: Initially add special bacteria (e.g., white rot fungi, salt-tolerant bacteria), gradually increase antibiotic load to design value.
• Safety Protection: The micro-electrolysis unit should be equipped with explosion-proof devices, and VOCs gases should be collected and treated with activated carbon adsorption.
• Water Quality Monitoring: Daily detection of antibiotic residues (by HPLC) to ensure no biotoxic substances enter the biological system.

VI. Optimization Suggestions

• Alternative Solution: If COD in the biological section fluctuates significantly, an MBR membrane bioreactor (replacing the secondary clarifier) can be added to increase sludge concentration and resistance to shock loads.
• Resource Recovery: High-concentration waste acid (from micro-electrolysis stage) can be recycled to produce ferrous sulfate for the Fenton oxidation unit.