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Sembcorp Water Technology Prize (SWTP)

2013

COMPETITION MANUAL FOR ULTRAFILTRATION + BACKWASHING + REVERSE

OSMOSIS ULTRAFILTRATION

DURATION: 1 HOUR 100

The objective for using the UF-RO filtration system for this competition is to collect as

much drinking water using the Reverse Osmosis filter. The water quality (TDS)

should also be below 100.

Equipment List (for each group)

a. 2 x 120 L water tank shared by 4 groups

b. 2 Pedrollo liquid pumps

c. Valves , fittings, M8 and M12 tubings

d. 1 UF-RO Setup ( w pressure gauges, hollow fibre UF housing, and RO membrane housing)

e. 1 Submersible pump

f. 1 RO permeate tank

g. 1 UF permeate tank

h. 1 To-drain pail

i. UF and RO membranes

1.1. Methodology

A tank of dirty feed and a setup is supplied to each group of contestants. Contestants are

required to pump the dirty feed into the UF systems of the setup to obtain UF permeate,

before pumping it into the following RO systems to obtain clean RO permeates.

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UF membranes will be fouled by the particles during ultrafiltration process and thus UF

permeate produced will decrease over time. Backwashing the membranes with UF

permeate are able to recover the membrane performances. However, backwashing

process compromises the amount of UF permeates collected, which is used to produce

RO permeates later. Therefore, contestants have to decide their backwashing time in

order to maximize the recovery of the membrane performance with minimum amount

of UF permeate so to make sure that they can maximize the production of RO permeate

(Please refer to the attached Appendix A and Appendix B for detailed operating

procedures).

Appendix A

Objectives of running Ultrafiltration

1) To understand and operate the filtration process

2) To understand and operate the backwash process

3) To understand the effect of the timing of filtration and backwash process

Experimental Procedure for Filtration and Backwashing

[NOTE: Please use either your handphone or wrist watch for 2 stopwatches per group.]

PART I – Filtration and Backwashing

Filtration process

Refer to Appendix B Figure 3 for the schematic process.

1) Ensure the following are in “Off” position:

a. Feed Valve (connected to Feed Tank), Permeate Valve and RO Value (connected

to Permeate Tank).

b. UF Pump & RO Pump

c. V1 & V2, V3 & V4, V5 & V6 on the UR-RO System Module

2) Time for running UF process is 7 minutes.

3) Open Feed Valve and V-1 & V-2.

4) Switch on UF Pump to allow feed to be pumped through UF system.

5) Check to make sure UF Pressure Gauge is in the range of 1.8 bar to 2 bar by

tuning V-1.

6) Check constantly to ensure P1 is in the range of 1.8 bar to 2 bar by tuning V-1.

7) Switch off the UF Pump when the running time has ended.

8) Turn off the Feed Valve, V1 & V2.

Backwashing process (NOTE: Handle the UF module with care. Do not twist and

squeeze the fibers.) Refer to Appendix B Figure 2 for the schematic process.

9) Time for running backwashing process is 2 minutes.

10) Open Permeate Valve and V-3 & V-4.

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11) Switch on UF Pump to allow permeate to be forced through UF system in opposite

direction to backwash the hollow fibres.

12) Stop the pump when the backwashing time has ended.

13) Empty the To-Drain Pail.

NOTE: YOU NOW HAVE SUFFICIENT UF PERMEATE STOCK TO START PRODUCING RO

PERMEATE.

Objective of Running Reverse Osmosis

1) To maximize the amount of RO permeate collected within a certain period by varying the

filtration and backwashing time and

2) To determine the best filtration and backwashing timing for maximum permeate

collected

Ensure that the permeate collected is clear (Clarity of the permeate will be taken into

consideration)

REVERSE OSMOSIS (RO) EXPERIMENT

Objective of the Reverse Osmosis Experiment

1) To understand and operate the RO system to produce drinking water

2) To calculate the total dissolved solids (TDS) removal percentage after the RO system

Experimental Procedure for Reverse Osmosis

[NOTE: Place only the Tip of the TDS meter into the water

for accurate results]

PART 11 – REVERSED OSMOSIS

Reverse osmosis process

Refer to Appendix B Figure 4 for the schematic process.

1) Ensure the following are in “Off” position:

a. Feed Valve (connected to Feed Tank), Permeate Valve

and RO Value (connected to Permeate Tank).

b. UF Pump & RO Pump

c. V1 & V2, V3 & V4, V5 & V6 on the UR-RO System Module

2) You have to watch the UF permeate tank level to ensure there is sufficient volume to run

the ROS system.

3) Check and record the conductivity of UF permeate by using the TDS meter provided.

4) Open RO Valve and V5 & V6.

5) Disconnect the inlet of RO system and switch on RO Pump to allow UF permeate to purge

the tubing until clear flow is seen through the tubing. Switch off RO Pump and reconnect

the inlet of RO system.

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6) Switch on RO Pump to allow UF permeate to be pumped through RO system.

7) Constantly tune V-6 to make sure RO-P1 is at 3.8 bar.

8) Manually measure and record the RO permeate TDS with the tester.

[Note your water quality reading must be less than 100 to meet]

9) Switch off the RO Pump at your own time or when the UF Permeate Tank is depleted.

10) Repeat the ultrafiltration and backwashing processes described under PART I above

and reversed osmosis process here as many times as you wish until the 1 hours is up.

11) Our volunteer will come around and record the volume of RO permeate produced at the

end of 1 hour whose TDS reading MUST NOT EXCEED 100.

Appendix B

How ultrafiltration systems are maintained?

When hollow fibers are fouled, with foulant cake deposits on the surface, flux of permeate

drops as pressure of operation remained constant. The formula for the calculation of flux is as

followed:

����, ��/��/ℎ�� =�����������������/ℎ��

������������− − − �����������

Maintenance has to be done to recover the performance of the fibers, in order to maintained

the permeate flux and to extend the operation life. Backwashing is one of the easy and

efficient ways to restore the permeability of the fibers. It is done by pushing clean water,

usually the permeate produced, through the hollow fibers in an opposite direction of the

normal operation, forcing the particulates out of the membrane pores and away from the

surface of the membranes.

Figure 1 Flux recovery by backwashes

Operating a pilot UF system

For Sembcorp Water Technology Prize; a pilot UF-RO plant is built to treat model feed water.

The project is separated and carried out in two stages. The first stage comprises of a UF

system while the second stage consists of the UF-RO system.

Specifications:

Flu

x, J

Time, t

Backwash

starts

Backwash

ends

Normal operation

of ultrafiltration

Starting flux

Ending flux

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Ultrafiltration membrane : 9 ft2 (0.836 m2) hollow fibers cartridge

Configuration of UF system : “outside-in” filtration

Model feed water : 1g/L of Bentonite in UF water

Figure 2 and 3 shows the schematics of the filtration and backwash process. Figure 4 shows

the combined mode of operations.

Reverse Osmosis

Osmosis is the movement of solvent molecules through a selectively permeable membrane

into a region of higher solute ceoncentration, with the aim of equalizing the solute

concentrations on both sides (Refer to Figure 2(a). The solvent molecules passes through

the semi-permeable membrane from the filtered water to the unfiltered water due to the

difference in the osmostic pressure on both sides. The osmostic pressure is defined to be the

pressure required to maintain an equilibrium, with no net movement of solvent.

Reverse osmosis, on the other hand, force the solvent molecules from the unfiltered water to

move into the filtered water (Refer to Figure 2(b).

Figure 2(a) Osmosis Figure 2(b) Reverse Osmosis

Reverse Osmosis (RO) is a membrane-technology that removes large molecules and ions from

solution by applying pressure to the solution on the unfiltered water side of the selective

membrane. The solute will then be retained on the pressurized side of the membrane and the

pure solvent is allowed to pass through to the filtered water. The selective semipermeable

membrane allows only small molecules (such as solvent) to pass through while rejecting large

molecules and ions through the pores.

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Figure 3 Combined filtration and backwash model for UF system setup

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Figure 4 Combined filtration and backwash model for UF and RO system setup