New technique for validation of UF

membrane processes

Alice Antony and Greg Leslie

Overview

• Background

• Project outline

• Results

• Nanoparticles development

• UF challenge tests

• Conclusions & Future Work

Membrane validation

What is membrane validation?

Process of demonstrating that the system can produce water of the required microbial quality under defined operating conditions and the system can be monitored in real time assure the water quality objectives are continuously met.

How is this performed?

Through challenge test and operational integrity monitoring tests.

What guidance do we have?

1. Membrane filtration guidance manual (MFGM)1

2. Guidelines for validating treatment processes for pathogen reduction –Supporting Class A recycled water schemes in Victoria2

1MFGM, USEPA, 2005 2Department of Health, Victorian Government, February 2013

New techniques for real time monitoring of membrane

integrity for virus removal - Project outline

Phase 1 - Review of literature, identification of

knowledge gaps and recommendation of novel

integrity tests (completed in 2009)Critical Reviews in Environmental Science and Technology 42(9), 2012, 891-933.

Phase 2 – Development and testing of novel

integrity test (Completed in 2013)Journal of Membrane Science 454, 2014, 193-199

Phase – 1 outcomes

o Challenge test using MS2 bacteriophage, by plaque forming unit enumeration, PFU is presently considered the best process indicator for virus removal. However, the MS2 bacteriophage challenge test is difficult in on a full scale plant on a regular basis1 (for revalidation)

• Developing a non-microbial indicator for challenge testing and challenge

testing on ultrafiltration membranes

o Existing integrity test methods are for breaches ≤ 1 µm; Identifying direct or indirect integrity testing for detecting breaches less than virus-sized particles (0.01 – 0.04 µm)is a necessary

• Testing size exclusion chromatography and fluorescent spectroscopy for

their sensitivity to detect membrane breaches in UF and RO membranes

1Water Research, 2002, 36(17): 4227-4234

/ Phase – 2 Objectives

MS2 challenge testing

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Testing with native Viruses (NV)• Low conc. in real scenario• Assay of NV is complex, time consuming, definite analysis

methodology is not available in some cases• Issue of possible contamination

MS2 as a surrogate1,2,3 – Why and Why not?

• Ablity to cultivate in high concentration• sensitivity as high as 6LRV

• Impractical in full scale – high cost and effort

• Long turnover time, 24 h

• Physicochemical retention vs. inadvertent biological inactivationParticle aggregation may enhance the filtration capacity

• PFU does not provide tools to control denaturation and aggregation

1Journal of Applied Microbiology , 2007, 103(5): 1632-1638, 2Journal of Membrane Science, 2009, 326(1): 111-1163Critical Reviews in Environmental Science and Technology, 2012, 42,891-933.

Non-microbial alternative

MS2 Phage

Diameter – 24 nm

Icosahedral

Isoelectricpoint (pI) - 3.5-3.9, net negative change above pH 3.9

Non-microbial substitute

Citrate stabilized silver (zerovalent)

nanoparticle

Virus sizedSpherically shapedNegatively charged at pH 7Stable during filtration

Synthesis of nanoparticles

Centrifuge, redisperse in water

1% sodium

citrate solution

Boil

Silver nitrate solution

Constant stirring for 1 hr)

spherical or roughly spherical silver nanoparticles1,2

1The Journal of Physical Chemistry B, 107 (2003) 6269-6275.2The Journal of Chemical Physics, 116 (2002) 6755-6759.

423 nm

Characterisation of Nanoparticles concentration, size, charge & stability

Concentration of the finished nanoparticles – Inductively coupled plasma – Optical emission spectroscopy

Size - as average hydrodynamic size & charge by a dynamic light scattering, Brookhaven 90 Plus particle sizer

Eff. diameter (hydrated) : 50 nm Charge: -25 mV (negatively charged)

Particle properties stable over 3 days

• Near spherical shape, size ranging from 20 – 50 nm

• Crystal lattice pattern, d-spacing of 0.24 nm, characteristic of zerovalentsilver

Characterisation of Nanoparticles Transmission electron microscopy

Challenge testing

• Membrane - PVDF, UF membranes, average pore size - 0.04 µm

• Effective membrane area - 0.025 m2

• Flux - 30 or 50 L m-2 h-1

• Feed solution – Clean water with 5, 10 & 20 mg L-1 of silver

nanoparticles

• Parameters measured and/or compared – Clean water flux, TMP

• Change in TMP as a function of time, due t fouling of nanoparticles

Challenging compromised membranes with nanoparticles

• Physical compromise through punctures and cuts

• Chemical damage

o Exposure to hypochlorite solutions (Ct) of 2,500, 5,000, 10,000, 15,000 and 20,000 mg L-1.h

o Equivalent to a total exposure of 3.5, 6.9, 13.9, 20.8 and 27.8 months at 1mg/L concentration over multiple uses

SEM images of the punctures made with a 100 µm diameter needle

Challenge testing contd.,

LRV and TMP change during the testing of intact UF membrane

Flux,

(L m2 h

-1)

Nanoparticle

concentration,

(mg L-1

of Ag)

LRV

30 5 2.34±0.09 -0.3

30 10 2.61±0.10 0.5

30 20 2.94±0.09 0.5

50 5 2.31±0.10 0.0

50 10 2.61±0.10 0.5

50 20 2.83±0.10 0.3

• LRV ranging from 2.3 to 2.9 was demonstrated without any impact on the operating flux

• Slightly high LRV could be established with high nanoparticle concentration

Challenge testing contd.,

• One puncture, compromise ratio was 0.00003% and the LRV decreased from 2.8 to 1.5

• Four successive holes, the LRVs reduced to 1.1, 0.6, 0.5 and 0.3, respectively

• After three cuts, rejection was 7.1 % and LRV <0.1

Challenge testing contd.,

• Realistic representation of the impairment taking place in an operational plant with routine use of chemicals

• At 2500 and 5000 mg L-1.h, the membrane resistance (Rm)decreased to 19 and 38%, but the rejection capacity was almost unaffected

• Exposure to high concentrations seem to affect both the resistance and rejection

Summary MS2 vs silver nanoparticles

Criterion Microbial indicators, bacteriophagesCitrate stabilised silver

nanoparticles

Analysis, lead time

Long, 24 h to measure the integrity breach

Small, using onsite measurement techniques

Generation labour intensive, needs PC2 Relatively low labour requirements

Plant Preparation

High levels of disinfection of sample

points and preventative measures to avoid contamination

Non-microbial, very little risk of contamination by outside sources

Safety/hazardsHost bacteria require microbial safety

proceduresMinimal PPE

Background interference

Potential chances of interference from background virus and bacteria

Low Ag conc. In background

Measurement limitations

PFU method may suffer from limitations due to viral aggregation

No known limitations

Indicator rigidity

Potential to deform under high pressure and pass through the membrane

Unlikely to deform under high pressure

4 Key Conclusions

• Demonstrated the suitability of new

citrate stabilised silver nanoparticles as

virus surrogates in terms of shape, size,

rigidity, charge and ease of detection

• Demonstrated close to 3 LRV of virus

removal for intact UF membranes

• Demonstrated the sensitivity of the

system to differentiate intact membrane

fibres from those with a low number of

physical breaches or chemical

degradation

• Demonstrated the potential for the

validation of UF membranes in recycled

water applications

Project is complete…..however..

Would like to work

• with a water utility to use these particles in the field

• on the recovery of silver nanoparticles

Acknowledgements