Ultrafiltration or UF is a pressure driven membrane separation process that separates particulate matter from soluble components in the carrier fluid (such as water). UF membranes typically have pore sizes in the range of 0.01 – 0.10 µm and have a high removal cabability for bacteria and most viruses, colloids and silt (SDI). The smaller the nominal pore size, the higher the removal cabability. Most materials that are used in UF are polymeric and are naturally hydrophobic. Common polymeric materials used in UF include: Polysulfone (PS), Polyethersulfone (PES), Polypropylene (PP), or Polyvinylidenefluoride (PVDF). Although these materials can be blended with hydrophilic agents, they can reduce the membranes ability to be cleaned with high strength disinfectants such as hypochlorite that impacts removal of bacterial growth.

The DOW™ Ultrafiltration module utilizes a double-walled hollow fiber (capillary) PVDF membrane which has a very small nominal pore diameter for PVDF material that allows for the removal of all particulate matter, bacteria and most viruses and colloids. Despite the small pore diameter, the membrane has a very high porosity resulting in a flux similar to that of micro-filtration (MF) and can effectively replace MF in most cases.

Systems designed with DOW™ Ultrafiltration use an outside-in flow configuration which allows for less plugging, higher solids loading, higher flow area and easy cleaning. The primary flow design is dead-end filtration but the module can be operated using a concentrate bleed. Dead-end filtration uses less energy and has a lower operating pressure than the concentrate bleed, therefore reducing operating costs.

Typically, DOW™ Ultrafiltration is operated at a constant permeate flow. The transmembrane pressure (TMP) will naturally increase over time and the module can be cleaned periodically by back flushing and air scouring to remove the fouling layer. Disinfectants and other cleaning agents can be used to fully remove and prevent performance loss due to biological growth as well as other foulants.

Operating Specifications

Fiber Physical Properties Operating Conditions SI Units US Units
Configuration (fluid flow) Hollow Fiber (Outside-In) Feed Pressure, Maximum at Inlet 3 bar 45 psi
Base Polymer H-PVDF Operating TMP (Maximum) 2.1 bar 30 psi
Nominal Pore Diameter 0.03 μm Backwash Pressure (Maximum) 2.5 bar 36 psi
Hollow Fiber ID 0.70 mm (0.028″) Filtrate Flux @ 25°C 40-120 L/m2/hr 24-70 gfd
Hollow Fiber OD 1.3 mm (0.051″) Backwash Flux 100-150 L/m2 /hr 59-88 gfd
Temperature (UPVC limited) 1-40°C 34-104°F
Operating pH Range 2-11
NaOCl, Cleaning Maximum 2,000 ppm
Process Conditions Typical Maximum
Turbidity, NTU < 50 300
TSS, mg/L < 50 100
Particle Size, μ < 150 300
TOC, mg/L < 10 40
CODMn, mg/L 60
Oil/Grease, mg/L 0 < 2
pH, Continuous 6-9 2-11
pH, Cleaning 1-12 1-12
Temperature 25°C 40°C
Cl2 Continuous, mg/L 0.5 200
Cl2 Cleaning, mg/L 2000 5000
Backwash Frequency Once every 20-60 minutes
Backwash Duration 40-120 seconds
Chemically Enhanced Backwash Frequency As needed with NaOCl
Typical Cleaning Frequency 1-3 months
Cleaning Chemicals NaOCl, NaOH, HCl, Citric Acid, Oxalic Acid
Air Scouring Frequency 0 times per day to backwash frequency
Module Properties SFX-2660 SFX-2680 SFX-2860
SI units US units SI units US units SI units US units
Length – L 1860 mm 73.2″ 2360 mm 92.9″ 1860 mm 73.2″
Length – L1 1500 mm 59.1″ 2000 mm 78.7″ 1500 mm 59.1″
Length – L2 1610 mm 63.4″ 2110 mm 83.1″ 1630 mm 64.2″
Length – L3 1710 mm 67.3″ 2210 mm 87.0″ 1820 mm 71.7″
Diameter – D 165 mm 6.5″ 165 mm 6.5″ 225 mm 8.9″
Width – W 250 mm 9.8″ 250 mm 9.8″ 342 mm 13.5″
Module Surface Area 33 m2 355 ft2 44 m2 474 ft2 51 m2 549 ft2
Volume per Module 16 L 4.2 gal 20 L 5.3 gal 35 L 9.3 gal
Weight (water filled) 41 kg 90 lbs 53 kg 117 lbs 83 kg 183 lbs
Shipping Weight (w/o packaging) 25 kg 55 lbs 33 kg 73 lbs 48 kg 106 lbs
Fibers per Module 5760 5760 9000

‘X’ in SFX = Application (P = Pretreatment, D = Drinking Water)

Ultrafiltration is used for the separation of suspended solids, colloids, bacteria and virus. This technique uses membranes with pore size between 1-100nm.

Microflitration >105
Ultrafiltration 103-105
Nanofiltration 102-104
Reverse osmosis 102

* MWCO = molecular weight cut-off

There are 4 membranes geometries:

  • Spiral wound module: this design tries to maximize surface area in a minimum amount of space. It is the less expensive but more sensitive to pollution due to its manufacturing process. It consists of consecutive layers of large membrane and support material in an envelope type design rolled up around a perforated steel tube.
  • Plate and frame module: it is normally used for bad quality water. They are set up with a stack of membranes and support plates.
  • Tubular membrane: Generally used for viscous or bad quality fluids. These modules do not need a preliminary pre-treatment of the water. As the feed solution flows through the membrane core, the permeate passes through the membrane and is collected in the tubular housing.
    The main drawback is that the system is not very compact and has a high cost per m2 installed and it is not very compact. Diameter’s tube is generally between 4 and 25mm.
  • Hollow fiber membrane: The modules contain several small (0.6 to 2 mm diameter) tubes or fibers. As the feed solution flows through the open cores of the fibers, the permeate is collected in the cartridge area surrounding the fibers. It can carry out the filtration in two ways, either “inside-out” or “outside-in”

Comparison between the different types of geometry (Source: Water Treatment Handbook, Degrémont Suez, 7th edition):

Tubular Hollow fiber Plate and frame Spiral wound
Reverse Osmosis, Nanofiltration yes yes yes >95%
Ultrafiltration, Microfiltration yes >95% yes yes
Cleaning ease + +++ +
Pre-treatment need +++ + +
Recovery rate + +++ + ++
Module size ++ + ++
Cost per m2 +++ + +++

-: disadvantage

+++: obvious advantage

DOW™ Ultrafiltration Literature

Find information on DOW™ Ultrafiltration.

DOW™ Ultrafiltration (426KB PDF)
Product Manual
DOW™ Ultrafiltration ManualEnglish (1.6MB PDF) Spanish (1.5MB PDF) Portuguese (1.4MB PDF)
Case Histories
Cooling Tower Blowdown Reuse in Gaojing Power Plant [Beijing, China] (168KB PDF)
Pretreatment with DOW™ Ultrafiltration Membranes Beats Challenge of High Turbidity [JiangShu, China] (152KB PDF)
DOW™ Ultrafiltration Membranes Offer Reliable, Economical Answer to High Solids [NingBo, China] (200KB PDF)
DOW™ Ultrafiltration Membranes Ensure Quality RO Feed from Domestic Waste Water [ShanXi, China] (140KB PDF)
DOW™ Ultrafiltration Membranes Meet Challenge of High COD, Oil-Contaminated [Beijing, China] (120KB PDF)
High Turbidity and Temperature Fluctuation No Obstacle for DOW™ Ultrafiltration [HeBei, China] (192KB PDF)
DOW™ Ultrafiltration Modules Protect Reverse Osmosis System from High Iron [ShanXi, China] (152KB PDF)
Qingdao Hengyuan Cogen Plant (501KB PDF)
Shanxi Sanwei Chemical Group (499KB PDF)
Product Data Sheets
DOW™ Ultrafiltration SFP 2660 Pretreatment Module (59KB PDF)
DOW™ Ultrafiltration SFP 2680 Pretreatment Module (59KB PDF)
DOW™ Ultrafiltration SFP 2860 Pretreatment Module (73KB PDF)
DOW™ Ultrafiltration SFP 2880 and SFD 2880 (96KB PDF)
Tech Fact
DOW™ Ultrafiltration Fiber Repair Protocol (48KB PDF)
DOW™ Ultrafiltration Fiber Repair – Air Supply Apparatus Assembly (112KB PDF)
Warranty Information
DOW™ Ultrafiltration Module Three-Year Prorated Limited Warranty (44KB PDF)

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