10/20/2017 1

Pathogen Removal Mechanisms and Pathogen Credits in MBR-Based Potable Reuse Trains

Ufuk G. Erdal, PhD, PE

2017 NWRI Clarke Conference

Outline

• Background

• Objectives

• Comparison of Pathogen Credits

• MBR Pathogen Removal Mechanisms

• Approaches to Improve Pathogen Removals in an MBR Based AWTF

• Discussion

• Questions and Comments

2

Background

• Currently full advanced treatment (FAT) consisting of RO and AOP is required to meet GWRR via subsurface injection

• MF for pretreatment of RO

• Very effective; meets all primary and secondary MCLs, notification level chemicals, and other requirements

3

SODIUM HYPOCHLORITE

SULFURIC ACIDH2O2

MICROFILTRATIONREVERSE OSMOSIS

UVAOP

RO CONC.

OCSD

PLANT #1

SEC. EFF

LIME

BW Waste to

WWTP Influent OCSD OCEAN

OUTFALL

ANTISCALANT

DECARBONATOR

TO BARRIER INJECTION WELLS AND

SPREADING BASINS

Comparison of Pathogen Credits

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Primary and SecondaryTreatment1

MF/UF RO UVAOP6-Month

Retention in Ground

TotalMinimum

LRV for GWR via Injection

Crypto 1.2 4 1-2 6 0 12.2-13.2 10

Giardia 0.8 4 1-2 6 0 11.8-12.8 10

Virus 1.9 0 1-2 6 6 14.9-15.9 12

1Based on lower 10th percentile values, Rose (2004)

MBR RO UVAOP6-Month

Retention in Ground

TotalMinimum

LRV for GWR via Injection

Crypto 0 1-2 6 0 7-8 10

Giardia 0 1-2 6 0 7-8 10

Virus 0 1-2 6 6 13-14 12

FAT

MB

R A

T

Background and Objective

• Due to lack of DIT or other approved methods to assess membrane integrity, no pathogen credits have been given to MBR in many states.

• Several questions arise.• Can we apply DIT to MBR systems for pathogen credits?• Can MBR, in reality, achieve better pathogen removal?

• What surrogate we can use to assess membrane integrity?

• Can MBR deserve pathogen credit?

• How can we improve pathogen credits in an MBR based AWTF?

• Objective is to provide answers to above questions.

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MBR Pathogen Removal Mechanisms

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1. Direct Removal via Size Exclusion - Molecules larger than membrane pore sizes will be rejected regardless of their surface properties (i.e., charge, polarity)

4 µ0.1 µ

2. Absorption into Biomass (MLSS) and Sequential Removal through Membrane Filtration

Floc

0.1 µ

3. Pore Blocking - Large molecules block the pores of the membranes and restrict passage of small viruses

CH0.1 µ

4. Reduction of Effective Pore Size due to Biofilm Growth, Gel and Cake Layer Formation on Membrane Surface and Pores

0.1 µ

5. Self Healing of Damaged Membranes

0.1 µ

Can We Apply DIT to MBR Systems?

• DIT begins by pressurizing membrane fibers from inside to approximately 12-20 psi about 30-45 seconds.

• Once the pressure is stabilized the pressure source was isolated and the decay test started. The pressure was recorded over a 5-minute, or till the pressure decreased to the minimum permissible pressure as required by the test resolution, whichever occurred first.

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Dailypressure

decay test

Calculate pathogen removal

Concerns with DIT in MBR Systems

• DIT test pressure is relatively high and cannot be applied to flat sheet MBR membranes

• DIT test pressure also exceeds most of the MBR hollow fiber membrane suppliers pressure requirements (3-5 psi)

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Concerns with DIT in MBR Systems

• Lack of correlation between PDT and LRV in MBR; due to the action of mechanisms other than pure size exclusion

– Pore blocking, cake and gel layer formation

– Presence of predator organisms that consume pathogenic organisms

– Absorption of pathogens to MLSS and their removal thru membrane filtration and periodic sludge wasting

– VCF?

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Continuous Monitoring of Turbidity

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Limited data collected from

NV tests indicate

good correlation between

MBR permeate turbidity and

MS-2 LRV

Australian Experience

• In Australia, Amos Branch and Pierre Le-Clech (2015) documented LRVs for MBR systems.

• Based on the data collected, they proposed the following LRV credits:

• For MBR systems, with 95th percentile permeate turbidity ≤ 0.4 NTU, and 95th percentile flux≤16.9 gfd

• Virus LRV: 1.5, Protozoa LRV: 2.0 and Bacteria LRV:4.0

• With membrane nominal pore size <0.1 µ, with 95th percentile turbidity ≤ 0.3 NTU and flux never exceeding 17.7 gfd.

• Virus LRV: 1.5, Protozoa LRV: 4.0 and Bacteria LRV:4.0

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Now DDW is Providing Conditional Approval for MBR Projects in CA

• If 95th percentile turbidity <0.2 NTU and some other conditions meet:

• Virus LRV: 1.5, Crypto LRV:2.0 and Giardia LRV: 2.0

• Is it enough to meet pathogen LRVs?

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MBR RO UVAOP6-Month

Retention in Ground

Total

MinimumLRV for

GWR via Injection

Crypto 2 1-2 6 0 9-10 10

Giardia 2 1-2 6 0 9-10 10

Virus 1.5 1-2 6 6 14.5-15.5 12

Approaches to Improve Pathogen Credits in an MBR Based AWTF

1. Get better pathogen credits for RO systems

2. Explore options to get better credit for UVAOP

3. Incorporate additional treatment processes into AWTF

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1. Get Better Pathogen Credits for RO

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Why Are We Getting ~2-log LRV for RO?

• Conductivity monitoring is widely used method to assess RO performance (i.e. salt passage)

• Easy to implement with a relatively low cost

• However, resolution of this method is low (up to 2-log)

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CF CP

LRV RO=log(CF/CP)

TRASAR

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TRASAR dye dosage in RO feed=40 –100 ppb

TRASAR dye in permeate=0.001 –0.05 ppb

3-3.5 LRV can be reliably demonstrated with TRASAR

DLR

V=2

.3

DLR

V=2

.4

(Fues, 2017)

MS

-2

Ob

se

rve

d

TR

AS

AR

Co

nd

.

2. Explore Better Pathogen Credits for UVAOP

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Can We Get Better Pathogen Credits for UVAOP?

• Given that UVAOP gets 6-log credit for V/G/C

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UVAOP Design

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• UVAOP is designed to meet <10 ng/L NDMA

• Minimum 0.5-log 1,4-dioxane removal

• UV doses >850 mJ/cm2 are needed for 0.5-log 1,4-diaxone removal

• Multiple reactors/banks are operated in series to deliver the target UV dose

• Each reactor/bank is operated and monitored independently

UVAOP Validation at Oxnard

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UVAOP was designed to meet

Minimum 1.2-log NDMA removal

Minimum 4-log MS-2 Inactivation

Three chambers in series each has two reactors, (total of 6 reactors), each reactor has 72 lamps

At MS-2 RED Dose of 115 mJ/cm2, each reactor can achieve >>4-log Crypto and Giardia inactivation

At an assumed validation factor of 3 for Crypto, five reactors in series could achieve

>20-log Crypto and Giardia Inactivation

• UVAOP + Free Chlorine

• Ozone + UV• Ozone + UVAOP• UVAOP+ Low

Dose UV• Chlorine +

UVAOP

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Disinfection Processes in Series vs. UVAOP

Disinfection processes in series each may get up to 6 log pathogen credit (up to 12-log total)

For systems with multiple UVAOP reactors in series, may deserve credit for each reactor if all the monitoring requirements are met?

Are these disinfection processes in series different than UVAOP reactors in series?

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3. Add a UV Disinfection System to MBR Based Train

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UV Dose Requirements

A validation factor must be applied to these UV doses for full-scale operation

Where Can We Put UV Disinfection?

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After MF/UF (Before RO) Lower UVT (typically 70-78%) Without residual chlorine does

not provide effective biological fouling control for RO

After RO Higher UVT (typically 95-98%)

Reduces both CAPEX and O&M Costs

MBR UV RO AOP

MBR UVRO AOP

MBR AOPRO UV

Discussion and Conclusions

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• MBR is a robust secondary treatment technology that produces solids free effluent and effectively removes all particulate material and most of the pathogens

• Using TRASAR, Rhodamine Dye, TOC, Sulfate may provide 2-log additional LRV for RO over conductivity monitoring

• UVAOP may deserve a better pathogen credits than currently given • UV disinfection with <50 mJ/cm2 dose can provide 4-log Crypto and

Giardia inactivation

Questions and Comments