UF membranes are widely utilized in water and wastewater treatment processes, employing two primary filtration methods: inside-out (internal pressure) and outside-in (external pressure) filtration. These operation modes differ in membrane module design, flow direction, and fouling control strategies, each offering distinct advantages depending on the application.
Internal Pressure Filtration Principle
- Technical Features: Feed water flows through the lumen of hollow fibers (0.7-1.3 mm inner diameter), adopting an “inside-out” permeation path. Operating pressure ≤0.3 MPa, maximizing the tensile strength of membrane fibers.
- Applicable Scenarios: Suitable for low suspended solids (TSS <50 mg/L) water sources. For example, stable flux at 60 LMH when treating lake water with turbidity <15 NTU.
- Limitations: Retained substances accumulate inside the fibers, requiring cross-flow filtration and high-frequency CEP (every 12 hours).
Advantages of External Pressure Filtration
- Anti-Fouling Design: Open flow channel structure (0.5-1 mm gap between fibers) increases scrubbing efficiency by 40% . The external pressure modules maintain 80 LMH flux even when treating high turbidity water (300 NTU).
- Cleaning Mechanism: Unique air-water combined scrubbing program (0.1 MPa compressed air + 300 LMH backwash flow) removes particles ≥10 μm. For example, the external pressure UF modules achieve a transmembrane pressure recovery rate of 98% in coking wastewater treatment.
- Economic Performance: Compared to internal pressure, energy consumption is reduced by 38% and chemical consumption by 45% for the same treatment capacity.
Comparison of Filtration Methods
| Indicator | Internal Pressure | External Pressure |
| Maximum Feed Particle Size | ≤150 μm | ≤300 μm |
| TSS Tolerance | ≤50 mg/L | ≤100 mg/L |
| pH Tolerance Range | 2-13 | 1-14 |
| Chemical Cleaning Cycle | 7-15 days | 90-180 days |
| Unit Energy Consumption | 0.15-0.3 kWh/m³ | 0.08-0.15 kWh/m³ |
Learn More About FiltMem Internal & External Pressure Products
