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UV Disinfection for Drinking Water

David S. Briley, PE

Virginia AWWA 2015 Operators Conference

Virginia Beach, VA

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Principles of UV Disinfection

Applications of UV Disinfection for Drinking Water

Design Considerations

Validation Testing

Case Study – City of Raleigh, NC

Obtaining Giardia/Crypto Credit for UV

Agenda

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Principles of UV Disinfection

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Physical process using electromagnetic energy to

prevent DNA and RNA from further replication

Germicidal UV irradiation range - 200 to 300

UV produces no residual

Principle of Ultraviolet (UV) Disinfection

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Dimerization of DNA (thymine bases)

Inability to Reproduce Bug is Non-infective

Dark repair has been observed in some bacteria

5

Dimer

Dimer

Disinfection Mechanism

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Disinfection Effectiveness vs. Wavelength

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Adapted from Linden and Mofidi, 1999; Wright and Cairns, 1998; and Kolch, 1999

Characteristic

Low-Pressure,

High OutputMediumPressure Pulsed-UV

Spectral Emission Polychromatic

(185 – 1,387 nm)

Polychromatic

(185 – 800 nm)

Operating Temperature (°C) 100-200 500 – 850 7,000 – 15,000

Lamp life (hr) 8,000 – 12,000 2,000 – 8,000 925 @ 30 Hz

Efficiency (200-300 nm) 35 – 40% 15 – 25% <20%

Relative Light Intensity Low Medium High

Relative Footprint Required Medium Small Small

Nearly

monochromatic

Comparison of UV Lamps

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UV Equipment

Germicidal Output by UV Lamps

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Typical Municipal UV Disinfection Systems

Most prevalent UV technologies

Low-Pressure, High Output (LPHO)

Medium-Pressure, High Output (MPHO)

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Ratio of light at a specific wavelength (typically 254 nm)

exiting the water to that entering the water

Related to UV absorbance:

%UVT = 100 x 10-A

As UV absorbance increases,

UV transmittance decreases

Typical UVT Values:

DI / RO Water = 99%

Municipal Tap Water = 85-95%

Secondary Effluent = 60-70%

UV Transmittance (UVT)

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UV Transmittance in Water

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High UVT = High Dose

Low UVT = Lower Dose for same energy

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UV Dose = Intensity x Time

[mW-sec/cm²] = [mW/cm²] x [sec]

UV Dose

Dose – the energy per unit area incident on a surface (mJ/cm2)

No residual that can be measured, so must measure impacts Bioassay

Chemical Actinometry

Dyed Microspheres

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UV Intensity Sensor

UV Intensity is a function of:

Lamp output

Lamp age

Quartz sleeve transmissivity

Water quality (UV

transmittance)

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UV Disinfection Guidance Manual

US EPA published UVDGM in 2006

http://water.epa.gov/lawsregs/sdwa/lt2/compliance.cfm

UVDGM provides guidance for:

Design of UV facilities

Validation testing of UV equipment

Monitoring and operation of UV facility

Includes UV dose requirements for

Giardia, Crypto, and viruses to meet

LT2ESWTR

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Log Inactivation

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Cryptosporidium 1.6 2.5 3.9 5.8 8.5 12 -- --

Giardia 1.5 2.1 3.0 5.2 7.7 11 -- --

Virus 39 58 79 100 121 143 163 186

UV Dose Requirements

LT2ESWTR and UVDGM 2006

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UV dose in mJ/cm2

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Applications of UV Disinfection

for Drinking Water

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UV Disinfection Applications

Multiple barrier disinfection

Urbanized watershed

Source water quality variability

LT2ESWTR Compliance

Water system is classified as Bin 2 or higher

Receive inactivation credit for Crypto

DBP Compliance Strategy

Receive inactivation credit for Giardia and Crypto.

Reduce free chlorine contact in WTP

Can be effective if in combination with chloramines

UV produces no regulated DBPs

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UV Disinfection Treatment Objectives

Source: UV Disinfection Knowledge Base, WaterRF Report No. 3117 (2012)

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Example States Granting Credit for UV

Arizona

California

North Carolina

New York

Tennessee

Utah

Washington

Wisconsin

Virginia – coming soon

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Design Considerations

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Water Quality Factors

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Parameter Influence/Effect LimitsUV Transmittance Absorption of UV light > 85% UVT

Turbidity Shields pathogens < 1 NTU

Hardness Cause scaling on quartz sleeves reducing UV intensity

< 200 mg/L CaCO3

pH Affect solubility of metals, potentially affecting UVT and

fouling

6.0 - 9.0

Iron Fouling of lamp sleeves Perform pilot test for lamp sleeve fouling

Suspended Solids Absorption of UV light and shielding of pathogens

< 10 ppm

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UV Transmittance (UVT)

Most critical design parameter

Need large dataset to properly select design value

(95th percentile)

Typical UVT Values for municipal WTPs: 85-95%

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Site and Layout Considerations

Recommended location for UV system is post-filter

Reduces solids which can shield pathogens

Maximize WQ to achieve best UV performance and minimize fouling

Optimal location is between filters and clearwell

Layout considerations

Sufficient straight pipe

upstream of UV reactors

Flowmeter for each UV train

Ensure UV unit remains full

under all conditions

Motorized isolation valves

May require relocation of

post-filter chemical feeds

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Hydraulic Head Requirements

Existing WTPs have limited head b/w filters and clearwell

Need to identify available head in your WTP

Critical to understand headloss through UV to avoid

impacting filter operations or clearwell volume

Headloss not directly related to UV technology

Ways to reduce headloss

Locate UV Facility close to filters and clearwell

Install larger reactors or more reactors ($$)

Typical Headloss

UV Reactors 2 to 24 inches

UV Facility 36 to 48 inches

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Hydraulic Considerations

Hydraulic design to allow for even distribution b/w units

Ensure UV unit does not exceed validated flowrate

Ensure steady flow through UV units

Avoid rapid fluctuations in flow or pressure

Some UV units equipped with baffles to

distribute flow through reactor

More complex for pumped systems

Ensure UV units flooded at all times

Lamps can result in rapid heat buildup and

damage components

In large LPHO units, provided air release/vacuum valves

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UV System Section

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Electrical Design Considerations

Power Supply

Varies significantly by UV technology

Recommend pre-selecting UV equip. or

design bid alternates

LPHO Systems: 0.5 to 1.4 kW/mgd

MPHO systems: 2.0 to 2.4 kW/mgd

Uninterruptible Power Supply

Power conditioning (electronic

ballasts sensitive to power spikes)

Ensures UV operation (and continued

disinfection) until standby power

starts up

In event of generator failure, allows for

controlled UV shutdown to prevent flow

entering clearwell

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On-Site vs Offsite Validation

Significant challenges with on-site testing

Operational limitations with online WTP

Limited available water for test matrix

May require partial or full WTP shutdowns

Capacity of backwash handling facilities to handle test water

Consistency of water quality and UVT during testing

Issues with chlorine in UV influent

Offsite Validation Testing allows

for better control of test

parameters

UV manufacturers have validated

reactors for most applications

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Validation Testing

• Cannot directly measure UV

residual or inactivation

• Validation testing required to

confirm performance

• Validation testing should

cover design conditions

(max flow, min UVT, etc)

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UV Dose Response Curves

30

0

0.5

1

1.5

2

2.5

0 10 20 30 40 50 60

MS

-2 R

ed

ucti

on

[L

og

(N

o/N

)]

UV Dose (mJ/cm2)

MS-2 - low pressure

MS-2 - 255 nm UV-LEDS

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UV Definitions - UV Dose

Reduction Equivalent Dose (RED) – Inactivation

measured during full-scale reactor testing correlated to

UV dose-response curve from collimated beam testing.

Required Dose (Dreq) – UV dose specified in LT2ESWTR

to achieve target log inactivation for target pathogen.

Validated Dose (Dval) – UV dose delivered by UV reactor

as determined through validation testing. Compared to

the required dose to determine log inactivation credit.

Calculated Dose – The RED calculated using the dose-

monitoring equation that was developed through

validation testing.

31

reqval DVF

REDD

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UVDGM Requirements for UV Design

Relate UV facility design to

validation system setup

UVDGM Option 1

Straight pipe upstream of

UV unit during validation testing (X)

+5 pipe diameters

Requires coordination with UV

suppliers during concept design

X

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Relating Validation Setup to Installation

Option 2 – Site Specific Validation Test

Identical piping layout for 10D

upstream and 5 D downstream

Costly!!

Option 3 –Velocity Profiles

CFD modeling to demonstrate velocity

profile is similar or better than during

validation testing

Validated Reactor Installed Reactor

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Regulatory Approval for UV Disinfection

UV systems have been granted inactivation credit for

Crypto. and Giardia in:

Arizona

California

Tennessee

Utah

Washington

Wisconsin

NC: Granted credit to UV system at D.E. Benton WTP

(City of Raleigh) in Oct. 2013.

Other States are currently developing guidance or

protocols such as New York.

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Case Study: Raleigh, NC

Dempsey E. Benton WTP

Permitted Capacity: 16 mgd

Design Capacity: 20 mgd WTP

WTP online May 2010

Constructed to provide reliability in City’s water system

EM Johnson WTP

Capacity = 86 mgd

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Raleigh’s Goals for UV Disinfection

To provide multiple barrier disinfection

Urbanized watershed

Source water quality variability

Some Crypto. hits but still Bin 1

To lower DBPs – simultaneous compliance with

LT2ESWTR and Stage 2 DBPR

Receive inactivation credit for Crypto. and Giardia

DBP Compliance Strategy

Reduce free chlorine contact in WTP

Can be effective if in combination with chloramines

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UV Disinfection System Design

Three 10-mgd UV reactors

N+1 redundancy

Design Flowrate = 20 mgd

Design dose = 40 mJ/cm2

Design UV

Transmittance = 90%

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UV Disinfection System Design

LPHO Reactors (Wedeco K Series)

Space for 2 future reactors

UV Reactor

5 lamp rows

12 lamps per row

60 lamps total

Splitter weirs upstream

of each UV unit

36” mag flowmeter

upstream of each UV unit

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UV Disinfection System Design

UPS

Operate 2 UV reactors for 15 mins

Generator w/ ATS

Effluent valves on each UV reactor powered by UPS

Complete shutdown if standby generators do not

start to prevent plant flow without UV disinfection

Clean-in-place system for periodic cleaning of UV

lamp sleeves

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Key Issues for Approval for Inactivation Credit

Most States are following UVDGM

Off-Spec operations

UV Lamp Breakage Risks and Response Plan

Combined lamp aging/fouling factor (CAF)

Monitoring and controls to ensure disinfection

Backup plan in the event of UV system failure

Monitoring and reporting forms

Validation Testing

Low wavelength action spectra (applies to MPHO)

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Off-Spec Operations

EPA UVDGM: at least 95% of water delivered

through UV reactors operating within validated

conditions

UV System controls can limit off-spec operations

Some regulators don’t like 5% if UV is for primary

disinfection

Off-spec for no more than 15 mins at a time (NC, UT, WA)

Off-spec for no more than 0.1% (WI)

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UV Off-Spec Operations

• 58 off-spec events in 20 months

• Each event < 5 mins

• Most were due to faulty UVT analyzer at the time

• UVT analyzer issues have been since corrected

0.00%

0.02%

0.04%

0.06%

0.08%

0.10%

0.12%

0.14%

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

J F M A M J J A S O N D J F M A M J J A S

Pe

rce

nt

of

Tre

ate

d F

low

Off

-Sp

ec

Vo

lum

e (

MG

)

Total Off-Spec Flow (MG) Total Off-Spec Flow (%)

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UV Transmittance Analyzer

90

91

92

93

94

95

96

97

98

99

100

N F J S D A J O J

UV

Tra

nsm

itta

nce (

%)

UV Transmit (%) Minimun UV Transmit (%) Average

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Mercury Release Findings - LPHO

Following a lamp break, the concentrations of mercury

in the water passing through the reactor will be an order

of magnitude or more less than the regulatory MCL of 2

μg/L.

With amalgam lamps, the majority of the mercury will be

within the solid amalgam.

Liquid or amalgam mercury will settle to the bottom of

the reactor.

Mercury and quartz shards can be captured using

isolation valves and low velocity zones downstream of

reactor.

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Lamp Breakage Risks

Regulators concerned about lamp breakage and potential

mercury release

Identified lamp breakage risks and demonstrate how design and

operation will mitigate these risks

Debris:

Downstream of filters, and splitter weirs

Baffle at UV reactor inlet

Water Hammer:

Free water surface upstream and downstream

Partially full reactor:

Downstream weir set to keep reactor flooded

Level switch at top of reactor shuts down reactor when activated

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Lamp Breakage

Hg has high density and low solubility

LPHO lamps have order of

magnitude less Hg than MP lamps

WRF Research showed much of Hg

will be trapped in reactor and Hg

release << MCL

Only a release if quartz sleeve breaks as

well

Experience shows that most lamp break

events occur during lamp changeout –

outside of UV reactor

Developed a Lamp Breakage

Response Plan

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Lamp Fouling/Aging Factor

Lamp output measured by intensity sensors

Intensity affected by: Lamp aging

Quartz sleeve fouling

UVT

Lamp Aging Factor: 88-92%

Lamp Fouling Factor: 68-80%

Combined Aging Fouling Factor (CAF)

WRF Report (3117) found that CAF not monitored closely

NC PWS requires close monitoring of CAF to monitor when lamps require replacement or cleaning.

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UV Systems Control Sequences

Significant effort in reviewing control system logic with NC PWS

Developed UV Operations and Maintenance Manual

Fully automated controls for UV dose pacing

Unusual Conditions

If UVT > MAX VALIDATED UVT, UV dose calc will clamp at MAX VALIDATED UVT

If UVT < 90% [DESIGN UVT], all rows on at 100%, UV dose calc will clamp at 90%

If low intensity is detected, new lamp row will start

Flowmeter failure, design flow (10 MGD) used in UV dose calc.

If off-spec condition is detected

Auto start standby reactor

Approx 5 mins to start new reactor and achieve 100% power

Power Loss Standby generators called to start

UPS can power UV system for up to 15 mins

If generators fail to start, PLC will close effluent valves and shutdown UV system after set delay (~10 mins)

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Contingency Planning

NC PWS very focused on contingency planning

Recommend focus on redundancy and reliability during

design and development of control logic

Minimize under-disinfected water (off-spec) from entering

distribution system

City of Raleigh developed Plan for Total UV System Failure

Convert back to meeting Giardia CT via free chlorine disinfection

Requires moving point of ammonia feed and converting clearwell

from chloramines back to free chlorine

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Monitoring and Reporting

Date UVT

UV Reactor 1 UV Reactor 2 UV Reactor 3

Runtim

e (Hrs)

Flow

(MG)

Off-

Spec

Flow

(MG)

Min.

RED

(mJ/cm2

)

Runtim

e (Hrs)

Flow

(MG)

Off-

Spec

Flow

(MG)

Min. RED

(mJ/cm2)

Runtim

e (Hrs)

Flow

(MG)

Off-

Spec

Flow

(MG)

Min.

RED

(mJ/cm2

)

Runtim

e (Hrs)

1/1/11 24.11 4.38 0.00 82.04 24.04 4.34 0.00 82.00 0.00 0.00 0.00 0.00 N/A

1/2/11 24.04 4.41 0.00 82.06 24.04 4.34 0.00 82.00 0.00 0.00 0.00 0.00 N/A

1/3/11 24.12 4.41 0.00 82.04 24.10 4.34 0.00 82.00 0.00 0.00 0.00 0.00 N/A

1/4/11 24.06 4.44 0.00 82.05 24.06 4.38 0.00 82.00 0.00 0.00 0.00 0.00 N/A

1/5/11 24.05 3.84 0.00 82.06 24.04 3.80 0.00 82.00 0.00 0.00 0.00 0.00 N/A

1/6/11 24.02 3.94 0.00 82.06 24.05 3.87 0.00 82.00 0.00 0.00 0.00 0.00 N/A

1/7/11 24.00 4.44 0.00 82.26 24.05 4.34 0.00 82.00 0.00 0.00 0.00 0.00 N/A

1/8/11 23.90 4.34 0.00 82.04 23.90 4.28 0.00 82.00 0.00 0.00 0.00 0.00 N/A

1/9/11 24.02 4.28 0.00 82.06 24.02 4.28 0.00 82.00 0.00 0.00 0.00 0.00 N/A

1/10/11 24.03 4.69 0.00 82.05 17.03 2.91 0.00 82.00 0.00 0.00 0.00 0.00 N/A

1/11/11 24.08 4.28 0.00 82.05 24.03 4.19 0.00 82.00 0.00 0.00 0.00 0.00 N/A

1/12/11 21.89 3.19 0.00 82.07 24.01 3.72 0.01 82.00 0.00 0.00 0.00 0.00 N/A

1/13/11 24.09 3.05 0.00 82.06 24.01 2.89 0.00 82.00 0.00 0.00 0.00 0.00 N/A

1/14/11 24.03 3.41 0.00 82.07 24.01 3.28 0.00 82.00 0.00 0.00 0.00 0.00 N/A

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Summary

UV Disinfection can be effective for LT2 and Stage 2

DBP Rule Compliance

UV has been approved for log inactivation credit in

several states. With more installations, regulatory

agencies are developing a comfort level with

reliability of UV

Talk to regulatory agency early in the process and

about your unique design/circumstances

If you want to reduce chemical CT,

Don’t expect it to be a quick process

Prepare to dive into the details with regulatory agenday

Prepare to develop more in-depth SOPs and more elaborate

controls to ensure CONTINUED DISINFECTION

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David S. Briley, P.E.

(919) 833-7152

dbriley@hazenandsawyer.com

Questions