Spiral-Wound Ultrafiltration Membrane Process for Suspended Solids Removal in a Medium-Sized Water Treatment Plant
12 Aug 2025
Design Scale: 10,000–50,000 m³/d
I. Core Objectives
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Effluent Quality:
- Turbidity ≤ 0.1 NTU
- SDI₁₅ ≤ 3.0
- Suspended Solids (SS) rejection >99.9%
- Bacteria removal >6 log
- Complete retention of Cryptosporidium and Giardia.
- System Recovery Rate: ≥90%
- Membrane Lifespan: ≥5 years (chemical cleaning interval ≥60 days)
II. Process Flow Diagram (Three-Barrier Design)
graph TD
A[Raw Water (Surface/Reservoir)] --> B[Pretreatment] --> C[Spiral-Wound UF System] --> D[Disinfection] --> E[Clearwater Tank]
B -->|Coagulant| F[Coagulation Tank]
B -->|Flocculant| G[Flocculation Tank]
C --> H[Chemical Cleaning System]
C --> I[Compressed Air System]
III. Key Unit Technical Specifications
(1) Enhanced Pretreatment System
| Unit | Design Parameters | Function | Control Points |
|---|---|---|---|
| Coagulation Tank | Mixing time: 30–60s; G-value: 500–1000 s⁻¹ | Destabilizes colloids | Online turbidimeter, pH meter |
| Flocculation Tank | Reaction time: 15–20min; G-value: 50–100 s⁻¹ | Forms settleable flocs | Floc camera, particle monitor |
| DAF Flotation Tank | Dissolved air pressure: 0.4–0.6 MPa; Recycle ratio: 8–12% | Removes algae/light SS | Sludge concentration monitor |
| Self-Cleaning Filter | Filtration grade: 100–200 μm; Backwash at ΔP ≥0.05 MPa | Screens large particles | Differential pressure sensor |
Note: Pretreated water must meet SDI₁₅ ≤ 5 to prevent membrane fouling.
(2) Spiral-Wound UF System Design
| Parameter | Specifications |
|---|---|
| Membrane Model | e.g., Hydranautics HYDRAcap 60 (8") / DOW SFP-2660 |
| Material | Hydrophilic modified PVDF (chlorine tolerance >500,000 ppm·h) |
| Pore Size | 0.03 μm |
| Design Flux | 50–70 LMH (L/m²·h) |
| Operating Pressure | 0.1–0.3 MPa (ΔTMP) |
| Module Configuration | 6-element pressure vessels; 6:4 staging (1st:2nd stage); Total area ≥60,000 m² (for 35,000 m³/d) |
| Operation Mode | Dead-end filtration + automatic backwash (every 30–60 min) |
| Backwash Sequence | 3-step cycle: Air scour (0.1 MPa, 30s) → Water backwash (80–120 LMH, 30s) → Forward flush (30s) |
| CEB (Chemically Enhanced Backwash) | 200 ppm NaClO + 500 ppm NaOH (every 24h; contact time: 60s) |
| CIP (Cleaning-in-Place) | Alkaline: 0.1% NaOH + 0.05% NaClO (40°C); Acidic: 0.2% citric acid (pH=2.5–3.0) |
(3) Control & Monitoring System
-
PLC Control Logic:
if TMP ≥ 0.25 MPa or Flux ≤ 85% design: # Fouling warning Initiate CEB if TMP ≥ 0.35 MPa: # Severe fouling Trigger CIP + Alarm if SDI₅ₘᵢₙ ≥ 4.0: # Pretreatment failure Reduce production to 70% + Boost pretreatment dosing -
Critical Instruments:
- Laser turbidimeter (e.g., HACH TL23)
- Pressure transducers (accuracy: 0.5 class)
- Automatic SDI analyzer (sampling every 2h)
- Residual chlorine analyzer
IV. Technical Advantages
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Low Energy Consumption
- Dead-end mode + low ΔTMP → Energy use ≤0.1 kWh/m³.
-
Shock Load Resistance
- Tolerates turbidity spikes ≤50 NTU (vs. ≤10 NTU for submerged UF).
-
Simplified Pretreatment
- Direct filtration viable for reservoir water (turbidity <10 NTU).
-
Modular Expandability
- Pressure vessel "trains" allow phased expansion.
V. Risk Mitigation
| Risk Factor | Countermeasure |
|---|---|
| Low-Temp/Low-Turbidity Water | PAC dosing (5–10 mg/L) + Backwash water ΔT ≤10°C. |
| Membrane Fiber Breakage | Integrity testing (pressure decay every 24h) + 5% redundancy in modules. |
| Biofouling | 0.1% peracetic acid in backwash (weekly) + UV disinfection in clearwell. |
| CIP Chemical Residues | 3-stage rinse (stop when conductivity difference ≤10 µS/cm). |
VI. Economics (35,000 m³/d Scale)
| Item | Cost |
|---|---|
| Membrane OPEX | 0.12–0.18 RMB/m³ |
| Chemical OPEX | 0.05–0.08 RMB/m³ |
| Energy OPEX | 0.08–0.12 RMB/m³ |
| Total OPEX | ≤0.35 RMB/m³ |
VII. Validation & Compliance
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Performance Testing:
- ASTM D4189-07: Membrane flux decline <5%/year.
- ISO 15839: Bacterial retention (MS2 bacteriophage challenge).
-
Certifications:
- NSF/ANSI 61 (material safety).
- GB 5749-2022 (China drinking water standards).
- HY/T 112-2008 (UF membrane industry standards).
Documentation References:
➤ [Spiral-Wound UF Plant Technical Specification Package.pdf]
➤ [HA-7000 Series UF Membrane Performance Whitepaper]
For detailed CAD drawings, Bill of Quantities (BoQ), or membrane lifespan simulation data, contact engineering support.
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