Use of Microporous Membranes Use of Microporous Membranes

for Compliance with the New for Compliance with the New

Drinking Water RegulationsDrinking Water Regulations

Peter Hillis, Research Associate, Peter Hillis, Research Associate,

North West Water LtdNorth West Water Ltd

IntroductionIntroduction

�� BackgroundBackground

�� THMTHM

�� ArsenicArsenic

�� CryptosporidiumCryptosporidium

�� ConclusionsConclusions

BackgroundBackground

�� New Drinking Water Directive 98/83/EC New Drinking Water Directive 98/83/EC

November 1998 November 1998

�� THM, As andTHM, As and CryptosporidiumCryptosporidium

�� Question over conventional technologies Question over conventional technologies

�� Ultrafiltration (UF) and Microfiltration (MF) Ultrafiltration (UF) and Microfiltration (MF)

membrane technologiesmembrane technologies

BackgroundBackground

�� decrease in membrane costsdecrease in membrane costs

�� development of higher flux membranesdevelopment of higher flux membranes

�� better understanding of process parametersbetter understanding of process parameters

�� automation potentialautomation potential

�� simplicity of operationsimplicity of operation

�� more stringent water quality requirements, e.g. more stringent water quality requirements, e.g.

CryptosporidiumCryptosporidium

THMTHM

�� Nanofiltration (NF) Nanofiltration (NF)

�� Combined Coagulation and MF or UFCombined Coagulation and MF or UF

�� Operational benefitsOperational benefits

–– increased permeate flux, reduced backflushing, increased permeate flux, reduced backflushing,

reduced chemical cleaningreduced chemical cleaning

�� eliminating the penetration of colloidal material eliminating the penetration of colloidal material

into the poresinto the pores

�� modification of the deposit characteristicsmodification of the deposit characteristics

Reduced pore

penetration

More porous

cake

Without Coagulation With Coagulation

Effect of Coagulation on TMP Development

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7 8

Days Run

TMP (kPa)

No Coagulation

With Coagulation

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

90.0%

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

Coagulant dose (mM Fe)

% Removal

%Removal THMFP

%Removal TOC

THMTHM

�� >80% removal of THM>80% removal of THM

�� No floc breakthroughNo floc breakthrough

�� Enhanced membrane operationEnhanced membrane operation

�� Enhanced membrane performanceEnhanced membrane performance

ArsenicArsenic

�� Reverse OsmosisReverse Osmosis

�� Ion ExchangeIon Exchange

�� Lime SofteningLime Softening

�� Adsorption on Granular Ferric HydroxideAdsorption on Granular Ferric Hydroxide

�� Adsorption on Activated Adsorption on Activated AluminaAlumina

�� CoagulationCoagulation

Effect of pH on As (V) Removal

0

20

40

60

80

100

120

4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9

pH

% Removal

Alum (0.06mM)

Fe (0.03mM)

ArsenicArsenic

�� ferric and aluminium coagulation can remove ferric and aluminium coagulation can remove

As (V)As (V)

�� The removal by aluminium sulphate is clearly The removal by aluminium sulphate is clearly

related to the pHrelated to the pH

�� iron (III) hydroxide is able to operate over a iron (III) hydroxide is able to operate over a

much wider pH rangemuch wider pH range

% Removal of As (V) at Different Ferric Chloride Doses at pH 7

0

20

40

60

80

100

120

0.000 0.020 0.040 0.060 0.080 0.100 0.120 0.140

Metal Concentration (mM as Fe)

% Removal

% As (III) Removal for Alum and Ferric Chloride

0

10

20

30

40

50

60

70

80

90

100

0 0.05 0.1 0.15 0.2

Metal Concentration (mM)

% Removal

% Rem Fe (pH 7)

% Rem Al (pH 7)

Pre-oxidation

Coagulant pH 7

Flocculation

MF or UF

Waste

Treated Water

Process schematic for combined coagulation and MF or UF

for arsenic removal

ArsenicArsenic

�� As (V) more readily removed than As (III)As (V) more readily removed than As (III)

�� As (III) not removed by Aluminium SulphateAs (III) not removed by Aluminium Sulphate

�� PrePre--oxidation will enhance removaloxidation will enhance removal

�� Chlorine, ozone or permanganateChlorine, ozone or permanganate

�� A significant concern for any arsenic removal A significant concern for any arsenic removal

process is waste disposal for arsenicprocess is waste disposal for arsenic--laden laden

sludgessludges

CryptosporidiumCryptosporidium

�� Conventional treatment processes are Conventional treatment processes are

susceptible to the passage of susceptible to the passage of CryptosporidiumCryptosporidium

into the drinking water supplyinto the drinking water supply

�� MF and UF offer significant advantages due to MF and UF offer significant advantages due to

barrier nature of the processesbarrier nature of the processes

Principles of Operation of Immersed Membranes

Feed

Permeate

Airinjection

Immersedmembranes

Purge

QF

QP

Qf

Membrane tank

Qbp

YQ Q

Q

F P

F

=−

Recovery

The ZeeWeed® Hollow Fibre

The ZW-4000

ZeeWeed® Cassette

Surface area: 370 m2

Dimension:Height: 180 cmWidth: 60 cmDepth: 160 cm

Packing density: 210 m2/m3

USF Memcor CMFUSF Memcor CMF--SS

Filtrate manifold

Clover

Modules

USF Memcor CMFUSF Memcor CMF--SS

Liquid backwash Liquid backwash

plus air scour within plus air scour within

membrane modulemembrane module

Key Benefits Drinking WaterKey Benefits Drinking Water

�� Retrofitting / upgrading existing plants byRetrofitting / upgrading existing plants by

�� immersion of the membranes in clarifiersimmersion of the membranes in clarifiers

�� or sand filtersor sand filters

�� or contact tanksor contact tanks

�� or backwash holding tanksor backwash holding tanks

ConclusionsConclusions

�� Microporous membranes can be used to ensure Microporous membranes can be used to ensure

that companies comply with the changes under that companies comply with the changes under

the new drinking water regulationsthe new drinking water regulations

�� Combining coagulation with either a MF or UF Combining coagulation with either a MF or UF

system can enhance their performance in terms system can enhance their performance in terms

of their removal capabilitiesof their removal capabilities

ConclusionsConclusions

�� Performance associated with much higher Performance associated with much higher

pressure driven processes can be achieved using pressure driven processes can be achieved using

lowlow--pressure membrane processes by pressure membrane processes by

combining coagulation with MF or UFcombining coagulation with MF or UF

�� The barrier nature of MF and UF membranes The barrier nature of MF and UF membranes

combined with removal of contaminants with combined with removal of contaminants with

coagulation means that multiple drivers can be coagulation means that multiple drivers can be

met in on stagemet in on stage

SummarySummary

�� Question over RGF efficacy Question over RGF efficacy -- ripening, ripening,

breakthrough and transience (flow changes)breakthrough and transience (flow changes)

�� MF/UF offer a more secure barrierMF/UF offer a more secure barrier

�� Technology is maturingTechnology is maturing

�� Recent innovations make further adoption more Recent innovations make further adoption more

likelylikely