vu.edu.auCRICOS Provider No. 00124K (Melbourne)CRICOS Provider No. 02475D (Sydney)

Using nanotechnology to cost-effectively test wastewater treatment assets

Marlene Cran

Institute for Sustainable Industries and Liveable CitiesVictoria University

Background

• Wastewater treatment requires a multi-barrier approach to reclaim water from various sources

• Low pressure (micro- and ultra-filtration) and high pressure (nanofiltration and reverse osmosis) systems widely implemented

• Need the ability to verify removal of pathogens to ensure quality of produced water

Background

• RO/NF membranes capable of higher log removals than they are currently given by health regulators (≤ 2 log removal credits)

• Dye tests using Rhodamine WT can achieve >4 LRV

• Routine pressure-based UF direct integrity tests can only detect breaches ≥ 3 microns

• MS2 bacteriophage traditionally used, at high cost to industry, long lead times

Background

• Need an inexpensive, effective alternative that can replace current tests (RWT, MS2 challenge test) for pressure-based processes

• Ideally this should be in real-time and online

• Should not increase the costs of treating water

• Could potentially reduce the number of unit processes following membrane treatment

Projects

• Water Research Australia (WQRA) project 2018 Real time integrity monitoring for high pressure membranes

• WateReuse Research Foundation project WRRF-12-07 Assessment of selected methodologies for monitoring the integrity of reverse osmosis membranes for water recycling

• Water Research Australia project 2044 Alternative ultrafiltration integrity test using novel nanomaterials

Project: Real time integrity monitoring for high pressure membranes

• Review of established methods:

Type Examples Advantages and limitations

Direct integrity testing

• Pressure hold• Vacuum decay

Sensitive but frequency dependent; performed off-line; elements must be removed

Indirect integrity testing

• Particle counting• Turbidity monitoring

Insensitive depending on capabilities of instrumentation

Challenge testing • Microbial or non-microbial surrogate testing

Most appropriate for pathogen reduction; off-line analysis; can be costly

Objective & ScopeDevelop a challenge test to establish a representative LRV

• Should be easily rejected by the system: microbial surrogates (MS2), non-microbial surrogates (dyes, nanoparticles)

• Should be easily detected at low concentrations in permeate, i.e. by fluorescence

• Test should be performed at maximum operating flux and recovery and under typical operating conditions

Surrogate Criteria• Selection criteria for challenge species:

Parameter Criteria

Form

• for pathogens: insoluble, solid particles, size and shape similar to smallest pathogen of concern

• for chemicals: soluble in water, similar size and molecular weight to chemical of concern

Detection highly detectable at low concentration

Stability stable under environmental conditions

Reactivity inert, not reactive with pathogens or other chemicals

Toxicity should not adversely affect health or the environment

Adsorption minimum to no absorption on membrane

Cost readily available & inexpensive

Nanoparticle* Code Diameter / Coating Fluorescence Wavelengths

Carboxylic BB BB 50 nm / Coumarin λex 360 nm, λem 407 nm

Carboxylic YG YG 50 nm / Fluorescein λex 441 nm, λem 486 nm

Polychromatic Red PR 500 nm / Phycoerythrin 475-490 nm, 545-610 nm

Chemical Code Formula / MW (g/mol) Fluorescence Wavelengths

Fluorescein FL C20H10Na2O5 / 376.27 λex 490 nm, λem 514 nm

Quinine QN C20H24N202.0.5H204.H2O / 391.47 λex 331 nm, λem 383 nm

Rhodamine WT RWT C28H31NClN2O3 / 479.01 λex 566 nm, λem 582 nm

Riboflavin RB C17H20N4O6 / 376.36 λex 488 nm, λem 530 nm

Surrogate Selection• Several dyes and nanoparticles were selected:

* Polysciences Fluoresbrite® Microspheres

Surrogate Screening• Screening reagents and other conditions:

Reagent/Parameter Use/Properties Exposure/RangeSodium chloride (NaCl) monovalent salt 500-16000 ppmCalcium chloride (CaCl2) divalent salt 500-6000 ppmHypochlorite (NaOCl) disinfectant up to 1 ppmChloramine (NH2Cl) disinfectant up to 500 ppmUV light disinfectant 1-24 hpH HCl/NaOH 5 to 7Temperature thermal stability 10-35°CAcetic acid (CH3COOH) organic acid 10-50 ppmDextran (polysaccharide) neutral polymer 10 ppmBovine serum (protein) cationic polymer 10 ppmSodium alginate (polysaccharide) cationic polymer 10 ppmPolyethylenimine (polymer) anionic polymer 10 ppm

Surrogate ScreeningKey findings:

• Highest sensitivity for RWT > FL > RB/QN

• Reported detection limit for RWT 0.01-0.04 ppb

• For the same fluorescent compound, nanoparticles had considerably lower sensitivity and minimum detection limits

• RWT sensitive to hypochlorite, UV light but overall the most stable chemical surrogate

Membrane TestingPilot-scale• used intact BW30 2.5”

element• 15 bar• 2000 ppm NaCl• 5 ppm RWT• 15% recovery• 99.04 ± 0.42% salt rejection• average LRV 4.94 ± 0.89

• range of used RO and NF 2.5” elements

• generally lower salt rejection• average LRV 3.92 ± 0.81• LRV range 2.67-5.17

Bench-scale• flat sheet BW30 membrane• 15 bar• 2000 ppm NaCl• 1 ppm YG or BB nanoparticles• LRV (YG) 1.75, (BB) 2.23• limitation of feed concentration

Membrane TestingBench-scale pulse test• flat sheet BW30 membrane• 15 bar, 2000 ppm NaCl• 10 ppm RWT pulse• monitored for 150 s• 99.37 ± 0.33% salt rejection• average LRV 3.69• possibility to develop online pulse integrity test using RWT• calibrate various failure mechanisms with pulse data

Surrogate SummaryAdvantages Limitations

RWT Relatively inexpensive compared to nanoparticles

Easily detectable – commercially available sensors

Potential for real time/pulse monitoring

Can stain membrane surfaces

Affected by temperature, NaOCl

Not a true surrogate for virus, other pathogens

Nanoparticles More realistic pathogen surrogate

Range of sizes, fluorescent tags

Easily detectable

Lower stability

Very expensive

Lower detection limits

Further Developments• Trialled synthesising fluorescent nanoparticles, limited success

• However the nanoparticles showed unique optical properties

• New technique under development based on optical properties

• Has shown LRV up to 7 with relatively low feed concentration in bench/pilot trials

• Currently investigating commercialisation, full-scale trial, building prototype

Project: Assessment of Selected Methodologies for Monitoring the Integrity of Reverse Osmosis Membranes for Water Recycling

• Further review of established methods and new promising methods

• Fluorescent dyes (RWT, Uranine and Trasar), MS2 and nanoparticles

• Screening, pilot testing in the US, bench scale in our labs, pilot test in Tasmania

Quantum Dots (QDs)

• Nanocrystals of semiconducting material that have “tunable” properties, biocompatible, highly flurorescent, easy to synthesize and can be formed in a range of sizes (20 – 30 nm)

Fiber Optic Biosensors

• Laser derived evanescent wave is excited over sample and fluorescence measured

Electrochemical Biosensors

• Visible or near IR radiation via a hemispherical prism. Electromagnetic waves generated and detected

Whispering Gallery

Microlasers

• Label-free detection of single viral pathogens using evanescent wave (acoustic) sensor

• Immobilization of antibodies onto biofunctionalized electrodes (gold)

Resonance Biosensor

Emerging Pathogen Detection Techniques

NanoSight Particle Detection

Key specifications• Size: 10 – 2000 nm• Concentration: 106 – 109 particles/mL• Fluorescence detection

Parameter LRV

EC (µs) 1.39 - 1.98TDS (ppm) 1.22 - 1.45TOC (mg/L) 1.06 - 1.88TN (mg/L) 0.40 - 1.09Turbidity (NTU) 0.30 - 1.38UV254 (Abs) 1.26 - 2.33Fluorescent dissolved organics 0.35 - 2.08

LRV following UF and RO treatment (RO at lab scale for some plants)

LRVs Using Water Quality Parameters

No parameter able to achieve

LRV of 3 or greater

Surrogate Dye Screening

• TR and RWT the most stable under test conditions

• In some cases, application of specific calibrations can be used

Dye Continuous dose Pulse dose

RWT 4.19 ± 0.13 4.77UR 3.96 ± 0.10 4.04TR 4.59 ± 0.18 4.91

Continuous dosing at 1 mg/L and pulse dosing at 5 mg/L

Average LRV of Dyes

US Pilot Tests• 2:1 array• 4 inch pressure vessels• Dow Filmtec BWRO• 14 gfd• Recovery 20-30%• ZAPS system• MS2, conductivity, Trasar,

nanoparticles

Membrane Impairments

• Surface scratches created by rubbing pin across the membrane leaf

• Point source leak created near glue line with a pin

• Insertion point leak created with pin at the intersection of the scroll face and end cap

• Element exposed to chlorine (5,000 ppm, 24 hrs, pH 11)

• Cut O-ring

LRVs for Different Impairments

Australian Antarctic Division pilot plant

3 challenge tests performed:

• Nanoparticle test (~ 2 mg/L)

• Mixed dye test (1 mg/L each dye)

• MS2 test (~3 106 PFU/mL)

Australian Pilot Tests

• System operated at 70% recovery

• Feed/permeate sampling points and conductivity monitoring for each element

• Concentrate from element n = feed for element n+1

• Element 5 was compromised with an insertion scratch in the permeate channel

Pilot Plant Setup

• At ~1 mg/L, all intact elements achieved >4 LRV for each dye

• RWT most sensitive dye• All dyes passed through

defect with significant reduction in LRV

Removal of Mixed Dyes

• All intact elements achieved:• >6 LRV for MS2• >5 LRV for nanoparticles• >4 LRV for RWT

• Relatively high error for MS2• Lowest error for nano-

particle detection

Removal of MS2, Nanoparticles, RWT

• Online conductivities measured concurrently with each challenge test

• <1.8 LRV for all tests• Addition of challenge

species had minimal effect on conductivity

• Most conservative test, least sensitive

Removal of Conductivity

Summary

• Trasar and RWT gave high LRVs at bench/pilot scale

• Pulse dosing gave slightly higher LRVs than continuous dose

• Pilot scale tests resulted in high LRVs for MS2, nanoparticles and RWT, much lower for conductivity

• Evaluated new and emerging techniques for future development

Project: Alternative ultrafiltration integrity test using novel nanomaterials• Demonstrate and evaluate the cost and efficacy of new methods

including but not limited to silver, gold, polystyrene latex, fluorescent or other nanoparticles

• Engage with health regulators to facilitate acceptance of outcomes• Trial appropriately selected nanoparticles for use in the validation of

UF membrane rejection performance for viruses as a replacement for annual challenge testing

• Provide pilot plant-scale evidence of success and log removal evidence

To develop novel fluorescent biopolymer nanoparticles

Need to consider:• Cost and quantity of nanoparticles required for challenge test• Accessibility and availability of detection method• Appropriateness of the nanoparticle as a surrogate for viruses• Risks associated with the fate of the nanoparticles, in both the reject

water and the permeate

Objective

Requirements

• Relatively low cost• Easy to synthesise and characterise• Properties (size, charge etc.) similar to MS2• Minimal environmental impact, i.e. biodegradable nanoparticles

preferred• Easy to quantify to determine LRV, real time and online if possible

• To synthesise fluorescent nanoparticles directly from a range of starch sources

• Several different starch types: corn, potato, wheat, rice, tapioca• Various methods trialled: acid hydrolysis, hydrothermal

treatment etc.

amylose

amylopectin

First Approach

Corn starchWheat starch

• Need highly fluorescent starch nanoparticles• Fluorescence emission excitation matrix (EEM) data• Poor fluorescence, overlapping fDOM regions

Potato starch

Results

Rice starchTapioca starch

• Development of nanoparticles based on a biopolymer, poly(lactic acid) (PLA)

• PLA is an aliphatic polyester, similar structure to common PET, used in 3D printers

• Monomers derived from renewable starch resources including corn, beetroot, and sugarcane

• Traditionally an expensive biopolymer, costs have decreased rapidly over recent years

Revised Approach

• PLA nanoparticles relatively new, drug delivery, controlled release, tracing, good biocompatibility

• Easy to synthesize, excellent for encapsulation of bioactive compounds

• Selection of a natural fluorescent compound important, i.e. quinine, obtained from a plant source, common reference standard

• Quinine quenches in salt, fluorescence overlaps fDOM -interference

Biopolymer Nanoparticles

• Curcumin, strong antioxidant, highly fluorescent in some organic solvents, obtained from turmeric

• Fluorescence: Compound λem/λex pair

Quinine 350/450

Curcumin 420/500

Naturally Fluorescent Compound

• Synthesised curcumin encapsulated PLA nanoparticles via nanoprecipitation technique

• Characterization: particle size & charge, imaging, fluorescence, degradation

• Challenge test: bench-scale, pilot-scale hollow fibre membrane samples, ceramic membranes

Revised Method

• Curcumin solubility & fluorescence

Water Solvent A

Characterisation

Ethanol Solvent B

• Fluorescence of curcumin in PLA nanoparticles

Characterisation

PLA NPsSolvent B

• Imaging of nanoparticles

Characterisation

200 nm

Characterisation• Size and charge of PLA nanoparticles

• Reference MS2: 27 nm, -12 to -15 mV at pH 6-8

• Challenge test on new & compromised hollow fibre UF membrane samples (20 nm pore size)

• Qualitative test: different particle sizes

• Challenge test: nanoparticle ~35 nm, 5 mg/L feed

Peak size (nm) Size range (nm)

55 40-60

110 75-125

150 120-170

185 140-200

Challenge Tests

• Challenge test on used hollow fibre UF membrane element -SkyHydrant

• Challenge test: nanoparticle avg 37 nm, 10 mg/L feed

• LRVs Test time LRV

10 min 3.78 ± 0.18

20 min 3.94 ± 0.07

30 min 4.01 ± 0.12

Average 3.91 ± 0.16

Challenge Tests

• PLA inherently biodegradable, undergoes hydrolysis

Biodegradability

• Biodegradation of nanoparticles observed indirectly

• Fluorescence diminishes in 1 week, suggesting decomposition and release of curcumin

• Possible storage/stability issue• Costing of PLA nanoparticles: approx. $0.62 to

$2.57 per kg• Highly dependent on price of curcumin

Biodegradability & Costs

• Full-scale trials planned at 2 sites in Victoria• Difficulties producing enough nanoparticles for

the test (20+ g)• Developing technique to recover and recycle

solvent• Unstable for long-term storage in water, potential

for freeze/spray drying or prepare as needed• Can they be resuspended, maintain

fluorescence?

Final Stages

New Project• Following WateReuse Research Foundation project WRRF-12-07

Assessment of selected methodologies for monitoring the integrity of reverse osmosis membranes for water recycling

• New WRRF request for proposal New techniques, tools, and validation protocols for achieving log removal credit across NF and RO membranes (RFP 4958)

• Currently planning full-scale RO tests using PLA nanoparticles at several sites

Summary

RO/NF Integrity RO/NF Integrity UF Integrity RO/NF Integrity

Fluorescent dyesNanoparticles

Nanoparticle test commercialisation

Fluorescent dyesNanoparticlesMS2

Fluorescent dyesNanoparticlesMS2

Biodegradable nanoparticles

Potential for commercialisation

Water RA Water RAWRRF WRRF

Fluorescent dyesBiodegradable nanoparticlesMS2

Preparing RFP

Bench, pilot scaleBench, pilot scale

Bench, pilot, full scale

Pilot, full scale