Duratherm* HWS Series

February 18, 2020 - Nathan Olszak

Duratherm* HWS Series

Hot Water Sanitization Pure Water Elements

Description and Use

The Duratherm* HWS Series includes RO, NF and UF membrane elements. This Series is specifically designed to maximize the benefits of hot water sanitization for industries relying on chemical free sanitization for product quality and/or industry compliance standard.

Separation system sanitization protocol is performed via periodic exposure to temperature as high as 195°F (90°C) at minimum feed pressure to kill microorganisms by denaturation and coagulation of the proteins chains

The Duratherm HWS RO and HWS NF are suitable for separation systems purifying water at temperature up to 122°F (50°C) in low crossflow environment and no suspended solids.

This Series includes a variety of size 8″, 4″ and 2.5″ diameters. All element constructions include Durasan* Cage outer wrap, Polysulfone ATD and central tube.

Features and Benefits

  • Prevent bio-fouling development
  • No disposal costs
  • 100% wet testing Quality Assurance
  • Durable construction
  • Sanitization on the permeate side


  • Food / Beverage
  • BioPharm
  • Electronics
  • Chemical

Table 1: Element Specification

A-Series, Thin-film membrane (TFM*)a,b
D-Series, Thin-film membrane (TFM*)c
P-Series, Polyethersulfoned

Model Maximum Crossflow gpm (m3/h) Average permeate flow gpd (m3/day) Average salt rejection / MWCO
Duratherm HWS RO25211,4 4 (0.9) 270 (1.0) 99.0%
Duratherm HWS RO2540HR1,4 4 (0.9) 620 (2.3) 99.5%
Duratherm HWS RO4040HR1,4 20 (4.5) 2,250 (8.5) 99.5%
Duratherm HWS RO8040HR1,4 65 (14.8) 9,000 (34.1) 99.5%
Duratherm HWS RO25402,4 4 (0.9) 760 (2.9) 99.0%
Duratherm HWS RO40402,4 20 (4.5) 2,250 (8.5) 99.0%
Duratherm HWS RO80402,4 65 (14.8) 9,000 (34.1) 99.0%
Duratherm HWS SG80402 60 (13.62) 8,600 (32.6) 98.5%
Duratherm HWS NF40403,4 20 (4.5) 2,400 (9.1) 96.0%
Duratherm HWS NF80403,4 65 (14.8) 10,200 (38.6) 10,200 (38.6)
Duratherm HWS UF8040 65 (14.8) 10,000 Da

1. Testing conditions: 2,000ppm NaCl solution at 225psig (1,550kPa) operating pressure, 77°F, pH7.5 and 15% recovery before any hot water sanitization.
2. Testing conditions: 500ppm NaCl solution at 115psig (790kPa) operating pressure, 77°F, pH7.5 and 15% recovery before any hot water sanitization.
3. Testing conditions: 2,000ppm MgSO4 solution at 110psig (760kPa) operating pressure, 77°F, pH7.5 and 15% recovery before any hot water sanitization
4. Average salt rejection after 24 hours operation. Individual flow rate may vary +25%/-15%. Final permeate flow rate is subject to variations in the heat treatments. In most cases, the permeate flow rate after heat treatments will stabilize below nominal flow rate before heat treatment at:
– 25% for the Duratherm HWS RO HR
– 30-50% for the Duratherm HWS RO, NF and UF.
This is taken into consideration in Winflows Database 3.07 and later

Model Active area ft2 (m2 ) Outer Wrap Part Number
Duratherm HWS RO2521 10 (1.0) Cage 1229607
Duratherm HWS RO2540HR 24 (2.2) Cage 1263600
Duratherm HWS RO4040HR 90 (8.4) Cage 1263435
Duratherm HWS RO8040HR 374 (34.8) Cage 1263599
Duratherm HWS RO2540 24 (2.2) Cage 1228430
Duratherm HWS RO4040 90 (8.4) Cage 1228459
Duratherm HWS RO8040 374 (34.8) Cage 1228481
Duratherm HWS SG8040 374 (34.8) Cage 1207613
Duratherm HWS NF4040 90 (8.4) Cage 1263437
Duratherm HWS NF8040 374 (34.8) Cage 1262377
Duratherm HWS UF8040 348 (32.3) Cage 1263602
Figure 1b: Element Dimensions Diagram (Male) – 2540
Figure 1a: Element Dimensions Diagram (Female) – 4040 & 8040

Table 2: Dimensions and Weight

A,B,C Dimensions, inches (cm)

Model 1 A B C Boxed Weight lbs (kg)
HWS 2521 Models 21.0(533) 0.75 (1.90) OD 2.4(6.1) 1.3(0.6)
HWS 2540 Models 40.0(101.6) 0.75 (1.90) OD 2.4(6.1) 4(1.8)
HWS 4040 Models 40.01(101.6) 0.625(1.59) 3.9(9.9) 9(4.1)
HWS 8040 Models 40.0(101.6) 1.125(2.86) 7.9(20.1) 29(13.2)

1 A includes the interconnector.
2 Internal diameter unless specified OD (outside diameter).
3 The element diameter (dimension C) is designed for optimum performance in GE pressure vessels. Other pressure vessel dimension and tolerance may result in excessive bypass and loss of capacity

Table 3: Temperatures

Do not exceed 20 GFD (34LMH) in any circumstances

Model Maximum Operating Temperature Maximum Cleaning Temperature Maximum Sanitization Temperature
Duratherm HWS RO HR 122°F (50°C) 122°F (50°C) 194°F (90°C)
Duratherm HWS RO 122°F (50°C) 122°F (50°C) 194°F (90°C)
Duratherm HWS SG 122°F (50°C) 122°F (50°C) 194°F (90°C)
Duratherm HWS NF 122°F (50°C) 113°F (40°C) 194°F (90°C)
Duratherm HWS UF 122°F (50°C) 122°F (50°C) 194°F (90°C)

Table 4: Pressures and operating parameters

Model Max Operating Pressure
41-122°F (5-50°C
Typical Applied Pressure Rec. Element Recovery Typical Operating Flux
Duratherm HWS RO HR 600psi (4,137kPa) 225psi(1,551kPa) <15% 225psi(1,551kPa)
Duratherm HWS RO 600psi (4,137kPa) 225psi (1,551kPa) <15% 10-18GFD(17-31LMH)
Duratherm HWS SG 600psi (4,137kPa) 225psi(1,551kPa) <15% 10-18GFD(17-31LMH)
Duratherm HWS NF 600psi (4,137kPa) 110psi(760kPa) <15% 10-18GFD(17-31LMH)
Duratherm HWS UF 600psi (4,137kPa) 80psi (552kPa) <15% 10-25GFD (17-40 LMH)

1 Do not operate at T>50°C (Sanitizing only)

Table 5: Operating and CIP parameters

pH range
Continuous Operation Clean-inPlace (CIP)
Chlorine tolerance Feed Water
Duratherm HWS RO HR 4.0-11.0 2.0-11.5 500 ppm-hours1 NTU < 1
SDI < 5
Duratherm HWS RO 4.0-11.0 2.0-11.5 500 ppmhours1 NTU < 1
SDI < 5
Duratherm HWS SG 2.0-10.0 1.0-10.5 500 ppmhours1 NTU < 1
SDI < 5
Duratherm HWS NF 3.0-9.0 2.0-10.5 500 ppmhours1 NTU < 1
SDI < 5
Duratherm HWS UF 4.0-11.0 2.0-11.5 5,000+ ppmhours1 NTU < 1
SDI < 5

Dechlorination recommended


For optimal performance, Duratherm HWS elements should always be cleaned using approved CIP procedures and flushed with fouling free water before the sanitization process. Feed pressure during sanitization should not exceed 40psi (275kPa) and the crossflow should not incur a pressure drop greater than 2psi (14kPa) per element. Heating rate to sanitizing temperature and cool down should not be faster than 5°C (9°F)/minute. Maximum sanitization temperature is 90°C (194°F).


It is almost impossible to exactly predict the percentage of permeate flow rate lost from the high temperature sanitations, which among other factors depends on:

  1. Rate of temperature increase and decrease.
  2. Presence of other species like organics, ionic and metallic compounds that could locally decrease or increase the temperature at the surface of the membrane.
  3. Feed flow rate and specifically the heat transfer rate to the membrane surface.
  4. The thickness and geometry of the feed spacer used.

At optimum conditions measured in controlled environment with deionized water, a loss of flow is observed before the element performance had stabilized after repeated heat treatments (over 90% of this flow reduction occurred during the first heat treatment). This loss of flow represents:

  • maximum 25% for Duratherm HWS RO HR
  • between 30% and 50% for Duratherm HWS RO, HWS NF and HWS UF

With the loss of permeate flow rate, the salt rejection increases. The rate of cooling and heating was not more than 5°C (41°F) per minute, and the differential pressure drop per element did not exceed 2 psi.

Pilot testing based on the criteria noted above will give the best operating parameters for any specific application.

All the graphs below are RO Winflows simulations (Winflows 3.2.1 Database 3.07) which consider a 50% permeate flow loss for the HWS RO and 25% for HWS RO HR.


Figure 2: Simulated NaCl rejections with 2000 ppm NaCl at 15% recovery and 33 LMH
Figure 3: Simulated rejections for HWS NF with: 2000 ppm NaCl at 15% recovery and 33 LMH 2000 ppm MgSO4 at 15% recovery and 33 LMH


Figure 4: Simulated pressure drop for HWS 2540 elements
Figure 5: Simulated pressure drop for HWS 4040 elements
Figure 6: Simulated pressure drop for HWS 8040 elements


Figure 7: Simulated Net Driving Pressure for HWS RO HR with 2000 ppm NaCl and HWS RO elements with 500 ppm NaCl at 15% recovery and 33 LMH


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