Active Sludge Treatment Process

Definition of Activated Sludge

Activated sludge is a flocculent biomass formed through artificial aeration during active sludge treatment. It comprises diverse microorganisms (bacteria, fungi, protozoa, metazoans) and suspended organic/inorganic substances. These microbial communities create an ecosystem capable of adsorbing and oxidizing organic pollutants, serving as the core of active sludge treatment for sewage purification.

Key Properties

• Settling Performance: Forms alum-like biological flocs (100–500 μm) that rapidly agglomerate and settle, enabling efficient solid-liquid separation in active sludge treatment.
• Color & State:
  • Normal: Yellow-brown (aerobic conditions).
  • Black (anaerobic, oxygen-deficient).
  • Off-white (excessive oxygen, nutrient-deficient).

Composition

1. Active Microbes (Ma): Core degraders of organic pollutants (bacteria, fungi, protozoa).
2. Microbial Residues (Me): Cellular debris from self-oxidation.
3. Refractory Organics (Mi): Adsorbed recalcitrant compounds partially treated during active sludge treatment.
4. Inorganics (Mii): Minerals/particles affecting physical properties.

Types of Activated Sludge

By Source

1. Municipal Sludge:

   • Origin: Urban sewage plants (domestic + industrial wastewater mix).
   • Properties: 60–75% organic content; 78–85% moisture post-dehydration.
   • Handling: Requires disinfection for pathogen control.

2. Industrial Sludge:

   • Printing/Dyeing: High dyes/heavy metals; difficult dehydration.
   • Petrochemical: Oily, viscous, contains PAHs.
   • Papermaking: High fiber/ash content; easier dehydration.
   • Custom treatment methods are essential for each type in active sludge treatment.

Filtration Equipment in Active Sludge Treatment

Critical for solid-liquid separation and sludge management:

Chamber Filter Press

• Pros: Simple structure; handles high-viscosity sludge; clean filtrate reuse.
• Cons: Limited dewatering (e.g., 68% moisture in Ni-sludge post-FeCl₃ treatment).
• Role: Foundational step in active sludge treatment chains.

Membrane Filter Press

• Pros: Diaphragm extrusion achieves ≤60% moisture (e.g., Shenzhen plant: 80% → 58%, saving ¥3M/year); auto-discharge.
• Cons: Higher upfront cost.
• Application: Landfill-compliant dewatering in large-scale active sludge treatment.

Belt Filter Press

• Pros: Continuous operation; low energy (0.5 kWh/ton); high automation.
• Cons: Moisture >75% (needs further treatment); daily filter-belt washing.
• Scale: Handles 40 m³/h sludge in 100k-ton/day plants with PAM dosing.