Introduction to Wastewater Treatment Equipment and General Process Flow

I. Classification of Wastewater Treatment Equipment

1. By Wastewater Source

• Domestic Wastewater Treatment Equipment:
  Processes household sewage (e.g., toilet, kitchen, and laundry wastewater), focusing on organic matter (COD, BOD₅) and suspended solids (SS) removal.
• Industrial Wastewater Treatment Equipment:
  Customized for specific industries (e.g., chemical, textile, food processing), addressing contaminants like heavy metals, oils, and high-concentration organics.
• Municipal Wastewater Treatment Equipment:
  Handles large-scale urban sewage, integrating pretreatment, biological treatment, and sludge management to meet stringent discharge standards.

2. By Treatment Process

• Physical Treatment Equipment:
  Grilles, sedimentation tanks, clarifiers, filters (sand/activated carbon), and membrane systems (UF, MF) for solid-liquid separation.
• Chemical Treatment Equipment:
  Dosing systems (coagulants, flocculants, disinfectants), pH adjustment tanks, and advanced oxidation processes (e.g., ozone generators).
• Biological Treatment Equipment:
  Activated sludge reactors (e.g., aeration tanks, SBR, MBR), anaerobic digesters, and biofilm systems (trickling filters, moving bed biofilm reactors).
• Advanced Treatment Equipment:
  Reverse osmosis (RO) units, ion exchange columns, UV disinfection systems, and evaporation crystallizers for high-purity water production.

II. General Process Flow

1. Pretreatment

• Screening & Grit Removal:
  • Bar Screens: Remove large debris (e.g., sticks, plastics) to protect downstream equipment.
  • Grit Chambers: Sediment heavy inorganic particles (sand, gravel) through gravity separation.
• Equalization Tanks:
  Buffer flow and concentration fluctuations to stabilize subsequent treatment processes.

2. Primary Treatment

• Sedimentation Tanks:
  Remove settleable solids through gravity, reducing SS by 50-70% and organic load by 30-40%.
• Optional Processes:
  • Dissolved Air Flotation (DAF): For oily wastewater or low-density solids removal.
  • Chemical Coagulation: Enhances particle aggregation for better sedimentation.

3. Secondary Treatment (Biological)

• Activated Sludge Process:
  • Aeration Tanks: Microorganisms degrade organic matter into CO₂ and water under aerobic conditions.
  • Secondary Clarifiers: Separate biomass (activated sludge) from treated water; sludge is partially recycled.
• Variants:
  • A/O (Anaerobic-Oxic) Process: Removes nitrogen and phosphorus through sequential anaerobic and aerobic zones.
  • MBR (Membrane Bioreactor): Combines biological treatment with membrane filtration for superior effluent quality (SS < 10 mg/L).

4. Tertiary Treatment (Advanced Purification)

• Filtration:
  Sand/anthracite filters or membrane systems (UF/RO) remove residual solids and dissolved contaminants.
• Disinfection:
  Chlorination, UV irradiation, or ozone treatment to inactivate pathogens (e.g., E. coli, viruses).
• Nutrient Removal:
  Chemical precipitation (for phosphorus) or biological processes (nitrification-denitrification).

5. Sludge Treatment

• Thickening & Dewatering:
  Reduce sludge volume via gravity thickeners, belt filter presses, or centrifuges (moisture content from 99% to 75-85%).
• Stabilization:
  • Anaerobic Digestion: Convert organic sludge to biogas (methane) for energy recovery.
  • Composting: Aerobic decomposition with bulking agents (e.g., wood chips) to produce biofertilizer.
• Final Disposal:
  Landfill, incineration, or land application (if meeting regulatory standards).

III. Typical Applications & Process Selection

IV. Key Considerations for Equipment Selection

1. Water Quality & Flow:
   Analyze contaminants (COD, heavy metals, pH) and design capacity (e.g., 1,000 m³/day).
2. Regulatory Compliance:
   Adhere to national (e.g., GB standards) or local discharge limits (e.g., coastal areas stricter for nitrogen).
3. Cost-Benefit Analysis:
   • Capital Cost: MBR systems are costlier but save space; conventional activated sludge is more affordable.
   • Operational Cost: Energy (aeration ~50% of total cost), chemical dosing, and sludge disposal.
4. Footprint & Automation:
   • Modular/containerized systems for limited space (e.g., mobile wastewater treatment units).
   • PLC/DCS control for real-time monitoring and remote operation.