Maximizing Pathogen Removal

Credits for NF and RO in Direct

Potable Reuse Schemes Through

Continuous Monitoring of a

Fluorescent Microbial Surrogate

Jim Lozier, CH2M

Michael Hwang, CH2M

Seong-Hoon Yoon, Nalco

6th Annual Texas Water Reuse Conference

Presentation Overview

• NF/RO Pathogen Removal Capabilities• Drivers for NF/RO Pathogen Removal Credit• Integrity monitoring methods – available and employed• Fluorescent dye use for integrity testing• Pilot and bench testing of NF and RO elements

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Microfiltration

Contaminant removal is function of membrane

pore size

0.001µ 0.01µ 0.1µ 1.0µ 10µ 100µ 1000µ

Bacteria

Giardia (7-12 μ)

Viruses (0.01-0.05 μ)

Na/Cl Colloids

Ultrafiltration

Nanofiltration

Reverse Osmosis

Ca/Mg

Cryptosporidium (4-6 μ)

TurbidityDissolved Organics

• NF and RO membranes contain pores much smaller than all known pathogens

• Pathogen removal capability is very high

Reported removal requirements

Viruses Bacteria Protozoa Reference

NF RO RO RO

6.7 4.2 Madireddi et al. 1997

2 - >5.9 6.5 4.5 - >5.7 Adham et al. 1998a

2.7 - >6.5 Adham et al. 1998b

3 – 4.8 Kruithof et al. 2001

4 6 Lozier et al. 2004

5.4 Mi et al. 2004

7 Casani et al.

1.4 - >7.4 2.9 - >5.3 >4.7 -

Why log removal credits for RO?

• With push towards direct potable reuse, the need to achieve very high levels of pathogen removal via multiple barriers is essential

• RO is an essential DPR treatment process and maximizing its removal capability makes economic sense and may avoid the need

for an additional treatment barrier

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Why log removal credits for NF?

• NF will become more important for DPR in inland areas where RO concentrate disposal is problematic

• NF is being planned or considered for two potable reuse projects in U.S.

– El Paso Water Utilities direct potable reuse facility

– Tucson Water indirect potable reuse facility

• Limited integrity testing has been performed with NF membranes, whose characteristics (MWCO, surface

morphology, charge) vary considerably

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UV-AOPMF NF GAC Cl2 ESBSE DS

O3SAT NF BACSE Cl2 DS

Viral surrogates for NF/RO integrity testing

Surrogate Advantage Disadvantage

MS-2 phage Proven surrogate for enteric

viruses

Expensive; requires skilled

facilities for production and

analyses

Fluorescent microspheres Good correlation with MS-2 phage Expensive

FD&C Red Dye #40 Inexpensive to use and measure High detection limit (5 ug/L)

Rhodamine WT Inexpensive to use and measure;

Low detection limit (10 ng/L); low

dose required (

Current full-scale (RO) integrity methods

• Online (U.S. and Australia)– Conductivity and TOC are both used to confirm integrity of RO

systems

• Conductivity: on a train by train basis. Reflects the historic

use of this parameter to measure and track salt rejection/salt

passage by the train

• TOC: across the RO system (system feed and system

permeate). Reflects the high cost and high maintenance

requirements of on-line TOC analyzers with sufficiently low

detection limits

• Periodic (Australia)– Rhodamine WT used to demonstrate required (awarded) log

removals at plant start-up and once per year

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Current RO log removal credits

• RO pathogen log removal credits and bases for credit awarded within potable reuse framework vary by State and by Country

• A similar approach is anticipated for NF• Lack of consistency reflects agency’s comfort with technology or

ability to demonstrate higher log removals at full-scale

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Challenge On-line

CA DDW 2 NR Cond, TOC

TCEQ 0 NR ???

Vic DoH 2 R-WT Cond, TOC

WA DoH 3 R-WT Cond, TOC

TCEQ = Texas Commission on Environmental Quality

Vic DoH - Victoria Department of Health

WA DoH - Western Australia Department of Health

RO Log

Removal

CreditRegulatory Agency

Validation Method

ND: not determined; NR: not required; R-WT: rhodamine WT

DDW = California Division of Drinking Water

Benefits of Fluorescent Dyes• Rhodamine WT removal by RO correlates well with MS-2 phage

removal (WRF 435)

• R-WT is a conservative surrogate for virus removal by RO

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0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5 15 30 45Time (min)

Lo

g R

-WT

Re

mo

va

l

o-ring cut (2-mm) o-ring cut (4-mm)

Practicality of Fluorescent Dye Use

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• Rhodamine WT (R-WT)– Cannot be fed to RO train during normal operation

– Used on a periodic basis only for ‘challenge testing’ to demonstrate required log

removal at a single point in time

– Because of cost & potential impact of concentrate discharge, typically used

following RO system commissioning and then every 6-12 months thereafter

• Fluorescent-based scale inhibitor– Nalco PC-191T product

– Contains fluorescent tracer scale

inhibitor (TRASAR™ technology)

– 610 MW versus 566 MW for R-WT

– Can be dosed continuously to NF/RO

feedwater during operation at

concentrations up to 15 mg/L

– Recent research shows TRASAR™

removal by RO correlates well that of

R-WT Modified from Jacangelo et al., 2015

TRASAR Testing of NF and RO membranes

• Pilot testing conducted using both NF and RO elements with PC-191T dosing

• Nalco1 3D TRASAR™ technology using proprietary fluorimeters allow for online measurement of antiscalant fluorescence in both feed and permeate

streams

• Technology was tested using continuous dosing of antiscalant at pilot scale with different NF and RO elements

121An Ecolab company

NF-Based Potable Reuse Treatment Process

• Pilot testing conducted in Tucson, AZ; related to, but not part of, WRRF-13-09

NF System

NF and RO Membrane

Characteristics

Characteristic NF-270 NF-90 ESPA

Active Layer PZ-PA PA PA

NaCl rejection 40% 85% 99.4%

Zeta P, mV (pH 6) -40 -18 -30

MWCO, daltons 300-350 200-250 100-150

PZ-PA – polypiperazine-polyamide; PA - polyamide

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NF-270 testing (stage 1)

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#1

#2

#3

#4

#5 #6Feed Concentrate

PC-191T(5 ppm)

To Feed

TRASARTo

Permeate

TRASAR

To Feed

TRASARTo

Permeate

TRASAR

Vessels ApproximateRecovery

TRASAR Salt Rejection

Removal LRV Removal LRV

#1, #2, #3, #4 65% 0.9882 1.93 36.6% 0.20

#1, #2 45% 0.9898 1.99 40.6% 0.23

#3, #4 45% 0.9846 1.81 31.7% 0.17

Lower LRV in #3 and #4 than in #1 and #2 suggests imperfection in

trailing vessels (o-ring or glue line)

NF-90 Testing (stage 2)

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#1

#2

#3

#4

#5 #6Feed Concentrate

PC-191T(5 ppm)

To

Permeate

TRASAR

To Feed

TRASAR

To

Permeate

TRASAR

Vessels ApproximateRecovery

TRASAR Salt Rejection

Removal LRV Removal LRV

#5, #6 45% 0.9936 2.19 0.906 1.03

#5, #6 45% 0.9937 2.20 0.909 1.04

#6 25% 0.9956 2.36 0.929 1.15

#6 25% 0.9966 2.47 0.926 1.13

* With 1 mm cutout in the endcap in the reject side of vessel #6After 14 hours run time

ESPA Testing (modified stage 1)

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#1

#2

#3

#4

#5 #6Feed Concentrate

PC-191T(5 ppm)

To

Permeate

TRASAR

To Feed

TRASAR

To

Permeate

TRASAR

Vessels ApproximateRecovery

TRASAR Salt Rejection

Removal LRV Removal LRV

#5, #6 45% 0.9972 2.55 96.7% 1.48

#5 25% 0.9983 2.78 97.6% 1.62

#5 25% 0.9989 2.96 97.6% 1.62

#6 25% 0.9980 2.69 97.5% 1.60* O-rings were replaced with other recycled ones before the test

After 2-3 hours run time

After 14 hours run time

Lower LRV in vessel #6 than in vessel #5 suggests a leak in vessel #6

Log Removal Value (LRV)

ESPA2 (RO)

NF90

NF270

O-rings Replaced

NF270 NF90 ESPA (RO)

O-ring with

1mm cutout

Summary of Results

1.931.99

1.81

2.19 2.20

2.362.47

2.55

2.78

2.96

2.69

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

#1, #2, #3,#4

#1, #2 #3, #4 #5, #6 #5, #6 #6 #6 #5, #6 #5 #5 #6

Lo

g R

em

ova

l V

alu

e (

LR

V)

TRASAR

Conductivity

Follow-up Laboratory (Bench) Testing

• Following completion of pilot testing, one of each pilot-tested element was shipped to Nalco’s laboratory for follow-up bench

testing.

• This was done to assess whether log removals obtained with pilot system could be replicated with single elements used in

pilot

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F2

F1

NF/RO elementP

S S

Test Conditions• 1,500 mg/L NaCl feed solution

• 12 gfd flux

• 10% recovery

• 15 mg/L PC-191T

Log Removal Comparisons

Element Type Conductivity LRV TRASAR LRV

Pilot Lab Pilot Lab

NF270-2540 (fouled) 0.23 0.24 1.99 2.95

NF270-2450 (cleaned) -- 0.24 -- 2.85

NF90-2540 (fouled) 1.13 1.30 2.47 2.55

NF90-2540 (cleaned) -- 1.30 -- 2.70

ESPA-2540 1.60 1.95 2.96 3.00

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• TRASAR LRVs correlate well between pilot and bench for NF90 and ESPA given differences in recovery and feed composition

• Lower TRASAR LRV for NF270 at pilot suggests mechanical defects present (e.g., o-ring leak)

• Higher ESPA conductivity LRV at bench scale reflect lower recovery

Putting the Results in Context

• Pathogen removal by membranes, be it MF, UF, NF or RO, is a function of membrane pore size versus pathogen size

• Commercial NF and RO membranes are composites: a thin salt-rejecting layer* polymerized to a based polysulfone (PS) UF layer

• Reduced TRASAR (or dye) removal by NF reflects higher permeability rejecting layer versus RO

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• PS layer has very little if any TRASAR/dye rejection properties

• However PS is a ‘tight’ UF membrane (100,000 MWCO) and capable of high log

virus removal

• Fluorescent markers are conservative indicators of pathogen removal given the

double-barrier nature of composite

membranes

*Polyamide or polypiperazine/polyamide

Conclusions

• Fluorescent markers, including dyes and tagged compounds like TRASAR, are practical for demonstrating pathogen log

removals greater than conventional integrity methods

(conductivity and TOC)

• TRASAR allows continuous integrity monitoring; a max log removal of 4.5 is achievable based on max feed dose of 15

ppm and fluorimeter detection limit of 0.5 ppb. This exceeds

the maximum log removal anticipated for RO and NF

membranes for potable reuse applications.

• For NF and RO membranes, where salt rejection is limited, TRASAR can demonstrate 1-2 log higher removal compared

to conductivity, a significant benefit where these processes

are used as part of a DPR scheme.

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Questions?

• jlozier@ch2m.com

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