New technique for validation of UF membrane processes. Alice Antony and Greg Leslie

Transcription

1 New technique for validation of UF membrane processes Alice Antony and Greg Leslie

2 Overview Background Project outline Results Nanoparticles development UF challenge tests Conclusions & Future Work

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

4 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, Phase 2 Development and testing of novel integrity test (Completed in 2013) Journal of Membrane Science 454, 2014,

5 Phase 1 outcomes / Phase 2 Objectives 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 basis 1 (for revalidation) Developing a non-microbial indicator for challenge testing and challenge testing on ultrafiltration membranes o Existing integrity test methods are for breaches 1µm; Identifying direct or indirect integrity testing for detecting breaches less than virus-sized particles ( µm)is a necessary Testing size exclusion chromatography and fluorescent spectroscopy for their sensitivity to detect membrane breaches in UF and RO membranes 1 Water Research, 2002, 36(17):

6 MS2 challenge testing 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 surrogate 1,2,3 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 inactivation Particle aggregation may enhance the filtration capacity PFU does not provide tools to control denaturation and aggregation 1 Journal of Applied Microbiology, 2007, 103(5): , 2 Journal of Membrane Science, 2009, 326(1): Critical Reviews in Environmental Science and Technology, 2012, 42, Rotavirus Norwalk Hep A Poliovirus

7 Non-microbial alternative MS2 Phage Non-microbial substitute Citrate stabilized silver (zerovalent) nanoparticle Diameter 24 nm Icosahedral Isoelectricpoint (pi) , net negative change above ph 3.9 Virus sized Spherically shaped Negatively charged at ph 7 Stable during filtration

8 Synthesis of nanoparticles Silver nitrate solution 1% sodium citrate solution Boil 423 nm Constant stirring for 1 hr) Centrifuge, redisperse in water spherical or roughly spherical silver nanoparticles 1,2 1 The Journal of Physical Chemistry B, 107 (2003) The Journal of Chemical Physics, 116 (2002)

9 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

10 Characterisation of Nanoparticles Transmission electron microscopy Near spherical shape, size ranging from nm Crystal lattice pattern, d-spacing of 0.24 nm, characteristic of zerovalent silver

11 Challenge testing Membrane - PVDF, UF membranes, average pore size µm Effective membrane area m 2 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

12 Challenging compromised membranes with nanoparticles Physical compromise through punctures and cuts SEM images of the punctures made with a 100 µm diameter needle 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

13 Challenge testing contd., LRV and TMP change during the testing of intact UF membrane Flux, (L m 2 h -1 ) Nanoparticle concentration, (mg L -1 of Ag) LRV ± ± ± ± ± ± 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

14 Challenge testing contd., One puncture, compromise ratio was % 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

15 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

16 Summary MS2 vs silver nanoparticles Criterion Analysis, lead time Microbial indicators, bacteriophages Long, 24 h to measure the integrity breach Citrate stabilised silver nanoparticles Small, using onsite measurement techniques Generation labour intensive, needs PC2 Relatively low labour requirements Plant Preparation Safety/hazards Background interference Measurement limitations Indicator rigidity High levels of disinfection of sample points and preventative measures to avoid contamination Host bacteria require microbial safety procedures Potential chances of interference from background virus and bacteria PFU method may suffer from limitations due to viral aggregation Potential to deform under high pressure and pass through the membrane Non-microbial, very little risk of contamination by outside sources Minimal PPE Low Ag conc. In background No known limitations Unlikely to deform under high pressure

17 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 4 Key Conclusions

18 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

19 Acknowledgements