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CASE STUDY

RO | UF | MBR

Power Plant
Xiwu, China

Industrial Wastewater Reuse Using Toray UF Membranes
at Xiwu Thermal Power Plant
PROJECT BACKGROUND
A thermal power plant operated by Xiwu in the Inner Mongolia regionof China started up in 2011 with the following treatment scheme:

Groundwater

Manganese Greensand Filter

Heat Exchanger

Ultrafiltration

Double-pass Reverse Osmosis

Heat Exchanger

The ultrafiltration (UF) system was comprised of two trains, eachwith 28 modules, using inside-out capillary type UF membrane
modules to produce a permeate flow of 60 to 80 m3/hr. The UF
membrane material was a polyethersulfone (PES) with a nominal
pore size of 0.025 µm.
CHALLENGES
China's national policy for energy conservation and emissions
reduction heavily scrutinized groundwater extraction by thermal
power plants, and in 2015, the local government restricted theXiwu power plant's withdrawal of freshwater. As a result, the plantbegan evaluating the reuse of secondary effluent reclamationfrom a nearby sewage treatment plant as an alternate source
for raw water. The end-user compared the water quality ofgroundwater and reclaimed water (Table 1).

Table 1 — Water Quality
Parameters

Units

Groundwater

Reclaimed Water

Turbidity

NTU

<12–5

Conductivity

µS/cm

500

2,000

COD

mg/L

<220–50

Oil & Grease

mg/L

ND

1–6

Furthermore, between July and August, during the slaughteringpeak season of livestock in this region, the sewage treatment
plant's effluent quality often exceeds the plant design. Pilot tests
using the reclaimed secondary effluent as the feed revealed thatthe permeate flow in the capillary UF decreased rapidly, and thetransmembrane pressure (TMP) rose quickly. The graph in Figure
1 shows both results.
After one day of operation, the permeate flow of the UF systemdecreased by 40%. M aintenance cleaning by chemicallyenhanced backwash (CEB) and recovery cleaning by clean-inplace (CIP) could not restore the permeate flow to its originalvalues. After resuming operations, the membrane quickly fouledin just a few hours. The plant concluded that inside-out capillarytype UF membrane modules were unsuitable for reclaiming
wastewater due to rapid fouling.

03-CN-MB2-Xiwu-202108

1 of 2Figure 1: TMP and permeate flow of the capillary UF system

C A S E S T U DY
RO | UF | MBR

Industrial Wastewater Reuse Using Toray Ultrafiltration Membraneat Xiwu Thermal Power Plant

THE SOLUTIONRESULTS

Toray's UF membrane modules were operating at Xiwu's sister plantin Liaoyang for an industrial wastewater reuse system. Due to Toray
UF modules' excellent performance at this site and other thermal
plants using reclaimed secondary effluent as the feed, Xiwu evaluated
Toray for retrofit alongside other leading UF manufacturers. The newUF system would require a minimum product water flow of 80 m³/
hr and accept pre-treated circulating cooling blowdown water fromthe power plant. Evaluations revealed that Toray UF modules could
exceed the minimum flux rate requirement with fewer modules thanthe previous installation with capillary UF modules. With Toray's UF
modules, the existing backwashing and CIP ancillary equipment
could be repurposed, further reducing capital costs. Xiwu selected
Toray based on these advantages.

The new UF modules started operating in November 2017. The UF
permeate flow was running between 90 to 110 m³/hr, at a stable
TMP of around 50 kPa after running for a year (Figure 2). During
upshots in the feedwater, regular backwashing and daily cleaningby Toray Maintenance Cleaning (TMC) helped maintain the flow.
Xiwu's power plant experienced the following benefits by using
Toray pressurized hollow-fiber UF modules:•At the beginning of 2019, the recirculating cooling water
blowdown replaced 20 to 35% of the feed water, which
was earlier than anticipated, demonstrating the Toray UF
modules' high productivity;•Toray membranes' low fouling properties successfullyreclaimed the industrial wastewater even as the feed water
quality decreased;•Xiwu considerably reduced costs associated with purchasing
secondary effluent from the sewage treatment plant anddisposal fees related to the recirculating cooling water.

Figure 2: TMP and permeate flow of Toray UF

Figure 3: Toray UF system at Xiwu's thermal power plant

TORAY INDUSTRIES, INC.
Head Office: Nihonbashi Mitsui Tower 24th Floor, 1-1, Nihonbashi-Muromachi 2 chome, Chuo-ku,
Tokyo, 103-8666, JAPANwww.water.toray+81 3 3245-4542

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All information presented herein is believed reliable and in accordance with accepted engineering practices. Toray makes nowarranties as to the completeness of this information. Users are responsible for evaluating individual product suitability forspecific applications. Toray assumes no liability whatsoever for any special, indirect or consequential damages arising from thesale, resale or misuse of its products. © 2021 Toray Industries, Inc. Subject to change without notice.
03-CN-MB2-Xiwu-202108

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