municipal wastewater suspended solids (SS) treatment methods, technical approaches, and their pros and cons:

I. Major Treatment Processes & Technical Methods

1. Physical Interception

• Bar Screens (Coarse/Fine/Ultrafine)
  • Principle: Intercept large particulate matter (>1 mm) via variously sized bars.
  • Application: Preliminary treatment to remove debris (branches, plastics).
  • Types:
    • Coarse screens (20–50 mm gaps), fine screens (1–10 mm), ultrafine screens (0.1–1 mm).
  • Pros & Cons:

    Pros	Cons
    Simple operation, low cost	Limited to large particles; requires downstream processes
    Protects downstream equipment	Frequent cleaning & maintenance required

    

2. Gravity Sedimentation

• Grit Chambers (Horizontal/Vortex Type)

  • Principle: Separate inorganic particles (sand/gravel, density >2.65 g/cm³) via gravity.
  • Application: Protects pumps/valves/piping at preliminary stage.
  • Key Tech: Vortex grit chambers enhance separation via centrifugal force (HRT: 30 s).
  • Pros & Cons:

    Pros	Cons
    High grit removal (>95%)	Ineffective for organic SS
    Reduces equipment wear	Grit requires separate disposal (prevents decay)

• Primary Clarifiers (Horizontal/Radial Flow)

  • Principle: Sedimentation removes 30–50% organic SS and 20–30% BOD.
  • Design Params:
    • Surface loading rate: 1.0–2.5 m³/(m²·h); HRT: 1.5–2.5 h.
  • Pros & Cons:

    Pros	Cons
    Reduces downstream biological load	Low colloidal SS removal (<40%)
    Sludge digestible for biogas	Large footprint; high construction cost

3. Chemical Enhancement

• Chemical Coagulation-Flocculation & Sedimentation
  • Principle: Add coagulants (e.g., PAC, FeCl₃) to neutralize colloids; flocculants (PAM) form flocs.
  • Application: Removes colloidal SS (0.001–1 μm) and phosphorus.
  • Tech Params:
    • Rapid mixing (G-value: 300 s⁻¹) → Slow flocculation (G-value: 50 s⁻¹) → Sedimentation (surface loading: 0.6–1.0 m³/(m²·h)).
  • Pros & Cons:

    Pros	Cons
    SS removal: 85–95%	High chemical cost (+CN¥0.1–0.3/ton)
    Phosphorus removal: >90%	Generates chemical sludge (difficult to dewater; high disposal cost)
    Fast response to shock loads	Overdosing risks biological toxicity

4. Biological Treatment

• Activated Sludge Process (Secondary Clarifier)
  • Principle: Microbes metabolize organic SS; secondary clarifier separates sludge.
  • Key Tech:
    • Sludge recirculation ratio: 50–100%; surface loading: 0.6–1.0 m³/(m²·h).
  • SS Removal: 90–95% (effluent SS typically <20 mg/L).
  • Pros & Cons:

    Pros	Cons
    Simultaneous COD/BOD/SS removal	Efficiency depends on sludge settleability (risk of bulking)
    Lower operating cost	Performance drops under low temp/toxicity shocks

5. Advanced Filtration

• Filter Systems (Sand/Fiber Disc)
  • Principle: Deep-bed filtration traps fine SS (1–100 μm).
  • Type Comparison:

    Type	Precision (μm)	Opex	Use Case
    Sand Filters	>10	Low	Standard SS polishing (<10 mg/L)
    Fiber Filters	1–5	Medium	High standards (<5 mg/L)
    Disc Filters	5–10	Low	Space-limited projects

  • Pros & Cons:

    Pros	Cons
    Effluent SS <5 mg/L	Requires backwashing (3–5% water loss)
    Modular design; easy expansion	Filter fouling requires chemical cleaning

6. Membrane Separation

• Ultrafiltration (UF)/Microfiltration (MF) Membranes
  • Principle: Physical sieving retains particles >0.01–0.1 μm.
  • Application: MBR (Membrane Bioreactor) or tertiary treatment.
  • Tech Params:
    • Flux: 15–30 L/(m²·h); TMP: 0.1–0.3 MPa.
  • Pros & Cons:

    Pros	Cons
    Effluent SS<1 mg/L; bacteria-free	High capex (CN¥2000–3000/m³ capacity)
    High MLSS (8–15 g/L)	Membrane fouling demands frequent cleaning (lifespan: 5–8 yr)
    Footprint reduction: >50%	High energy use (0.4–0.6 kWh/m³)

II. Process Selection Guidelines

III. Key Optimization Strategies

1. Precise Chemical Dosing: Use zeta potential analyzers to cut coagulant use by 30%.
2. Sludge Conditioning: Separate primary and chemical sludge streams for easier dewatering.
3. Smart Controls: MLSS online monitors + secondary clarifier sludge level controllers to prevent sludge loss.
4. Membrane Fouling Control: High-frequency air scouring (SADₘ: 0.5 Nm³/(m²·h)) + alternating NaOCl/citric acid cleaning.

*Note: Final design must weigh influent SS concentration (typically 150–300 mg/L), effluent standards (e.g., Class 1A requires SS ≤10 mg/L), capex, and opex. Chemical/membrane methods suit sensitive water bodies or reuse cases; biological treatment + filtration is the mainstream choice for municipal upgrades.*