Compliance Strategies for Stage I & II DBPR

4 Case Studies

William Bellamy

CH2M HILL

DBP Compliance Case Studies

• Aurora Colorado - Chlorine dioxide

• Casper Wyoming - Enhanced coagulation and inline ozone

• Henderson Nevada - UV• Denver Colorado - Optimized

chlorination / chloramination

Case StudyAurora Colorado

• Direct filtration plant• Chlorine primary disinfection• Chloramine residual disinfectant

Drivers• THMs can be as high as 90 ug/L• Disinfection with chlorine and

chloramines is minimal

Disinfectant Evaluation - Chlorine

Advantages

• Current practice – no change in technology required

• Does not form chlorite

• Does not form bromate

Disadvantages• Relatively weak disinfectant- not

capable of providing Crypto inactivation

• Forms TTHMs and HAAs – Aurora may not be able to meet Stage 2 of D/DBPR

• Requires construction of post-filter disinfection contact basin

• Relatively no benefit for T&O control

• Pre-chlorination can not be practiced. Loss of pre-oxidant will degrade performance of filtration process.

Disinfectant Evaluation - Chlorine Dioxide

Advantages

• Lowest capital cost (0 to $250,000) Minimal investment; nothing lost if ozone is implemented later.

• No construction of new contact basin (capital cost savings of $3,000,000)

• Does not form bromate

• Chlorite can be controlled to < 1 mg/L (for 1-log Giardia disinfection goal).

• Does not form TTHMs and HAAs. would meet anticipated Stage 2 D/DBPR regs

Disadvantages

• Requires change in technology/operations

• Will probably require that the existing contact basin be covered to mitigate UV degradation. ($400,000)

• Requires handling of sodium chlorite, and higher attention to safety.

• Chlorite control might be required. Higher dosages (for possible future Cryptosporidium inactivation requirement) would produce chlorite concentrations above 1 mg/L.

Disinfectant Evaluation - Chlorine Dioxide (cont’d)

Advantages• Can provide 0.5-log

inactivation of Cryptosporidium

• Strong oxidant – will help control Quincy T&O problems, and could eliminate KMNO4 and PAC system.

• Will reduce manganese concentrations though oxidation/filtration

• Application to raw water will provide

benefit to filtration performance (pre-oxidation)

Disadvantages• Could be more costly

(operations) than ozone for Cryptosproidium inactivation.

• Some negative experience with taste and odor. Mainly with inefficient systems, that used free chlorine for residual disinfectant. Chlorine oxidized chlorite and formed ClO2 in the distribution system. (Not a problem if chloramine is used).

Master Plan Evaluation of Disinfectant Costs

Initial Demand and Decay Rate Determines ClO2

Dosage & CT

00.10.20.30.40.50.60.70.80.9

1

0 5 10 15

Time (min)

ClO

2 (

mg

/L) Initial Demand

ClO 2 Concentration Decay

Area Under Curve Represents CT Achieved

Existing Contact Flocculation Basin Can Be Optimized for t10

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Hyd

raul

ic E

ffici

ency

(T10

/T) Hydraulic

EfficiencyRequired ofContact Basinw/o Filters(T10/T)

HydraulicEfficiencyRequired ofContact Basinwith Filters(T10/T)

Chlorine dioxide contactor modifications

Why Isn’t ClO2 More Common?

• Until recently, minimal regulatory incentive to increase disinfection

• Poor efficiency and performance of older style generators

• Toxicology gaps for ClO2- and ClO3-

– mclg for CLO2- was increased from 0.08 to

0.8 mg/L

– No mclg for CLO3-

Aurora Conclusions

• ClO2 can meet current disinfection requirements without construction of chlorine contact basin (saves $2.8 million)

• ClO2 provides some taste and odor control

Conclusions (cont’d)

• ClO2 can meet current disinfection requirements without chlorite control

• Implementation of ClO2 preserves capital and provides time to:– Evaluate alternatives

– Allow regulations to solidify

Casper Wyoming

• 52 mgd plant with conventional treatment for 27 mgd and 25 mgd wells

• Inadequate disinfection and DBPs approaching Stage I

Driving Factors for Casper’s Disinfection Evaluation

• GWDUI• Apply Disinfectant to Ground

Water & Surface Water• Discontinue Chlorination• Cost Estimates

Existing SurfaceWater Treatment System

FromNorthPlatteRiver

Screens

Floc/Sed

Alum

Filters TransferPumping

ChlorineStorage

HighService

Pumping

To DistributionSystem

WashwaterLagoons

SludgeLagoons

Raw WaterPumping

Upgraded Surface Water Treatment Process

FromNorthPlatteRiver

Screens

ActifloClarification

SO4FeCl3

Filters

NaOClNH4

Ortho-PO4High

ServicePumping

To DistributionSystem

WashwaterLagoons

SludgeLagoons

Raw WaterPumping

SettledWater

Pumping

OzoneOzone

Contactor

Level of Disinfection

Surface Water Ozone Demand

y = 0.137x - 0.068

R2 = 0.987

y = 0.3124x - 0.0383

R2 = 0.9898

y = 0.1514x - 0.1937

y = 0.3092x - 0.2016

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.0 1.0 2.0 3.0 4.0 5.0

Transferred Ozone Dose [mg/L]

Res

idua

l Ozo

ne, m

g/L

SW4 (No pH adjustment)

SW5 (pH adjustment)

SW4 + one std dev

SW5+ one std dev

Surface Water Ozone Decay

y = 1.000e-0.333x

R2 = 0.992

y = 0.9884e-0.0936x

R2 = 0.991

0.01

0.1

1

0 1 2 3 4 5 6 7 8 9 10

Time, minutes

Res

idua

l Ozo

ne, C

/Co

SW4 (no pH adjustment)

SW5 (ph adjustment)

Ozone Contactor Alternatives

• High-Pressure In-Line Contacting

• Low-Pressure In-Line Contacting

• Conventional Over-Under Baffled Contactor

Recommended Low-Pressure In-Line Ozone Contactor

Casper Conclusions

• Ozone will provide up to 2 log Cryptosporidium inactivation

• THMs and HAAs will be reduced to below 10 ug/L

• Bromate is not an issue• Inline ozone was the least cost

alternative

Henderson NevadaUV Disinfection

• Direct filtration plant• Chlorine disinfection for 1 log Giardia

and 2 log virus inactivation

• Need to achieve 2 log Crypto inactivation

• Future need for chloramines for THM and HAA control

DBP and Disinfection Drivers

Disinfection Objectives

• Provide Cost-Effective Disinfection• No Less Than 2-Log Cryptosporidium

Inactivation• No Less Than 2-Log Giardia

Inactivation• Provide Capability to Eliminate Use of

Free Chlorine for Primary Disinfection

Disinfection Alternatives Evaluated

• Ozone

• Ultraviolet Disinfection

• Chlorine Dioxide

• Membranes

Disinfectant Comparison

Ozone• Strong oxidant (+)• Powerful disinfectant (+)• Microflocculation (+)• Controls taste and odor (+)• Increases concentration of

D.O. (-)• High cost (-)• Disinfection mechanism not

completely defined (-)• Bromate formation (-) • Increases concentration of

AOC (-)• Operationally complex (-)

UV• No byproduct formation (+)• Effective protozoan and

viral disinfectant (+)• Generated onsite (does not

require LOX delivery) (+)• Lower cost (+)• Disinfection mechanism not

completely defined (-)• Lamp cleaning/replacement

(-)• No measure of disinfectant

“residual” (-)

Calculation of UV & Ozone Disinfection Performance

Ozone• Relies on

measurement of residual and hydraulic modeling to calculate CT

• Contactor design validated with tracer testing (t10)

• Monitoring disinfectant provides continuous measure of disinfection efficiency

UV• UV intensity sensors,

flow signal, lamp age, UV transmittance and power measurement to calculate dose (I x t), and assess possible problems

• EPA expected to publish IT values in near future (2-3 years)

Why Hasn’t UV Been More Prevalent for Potable Water

Treatment?

Previous Studies Used In Vitro Assays for Protozoan

Inactivation • Cell Excystation (Viability Assay Using In Vitro

Measure of Ability of Oocyst to Excystate [Open Up] Under Simulated Gut Environment)

• Vital Dyes (in Vitro Assay Using Fluorogenic Vital Dyes That Adhere to Viable Oocysts or Non-viable Depending on Dye)

• Study Showed UV Dose of 120 mJ/cm2 for 2-log Cryptosporidium Inactivation (Ransome et al, 1993)

Infectivity Tests Provide New Understanding of Protozoa Inactivation

By UV• Infectivity Assays

Using Neonatal Mice (In Vivo)

• In Vitro Assays Unable to Correctly Predict Infectivity

• Infectivity Accurately Tests the Ability to Cause Disease Not Just Viability

-5

-4

-3

-2

-1

0

0 50 100 150 200

UV Dose, mW-sec/cm2

Lo

g (

N/N

o)

Excystation

Infectivity

After Clancy et al., 1998After Clancy et al., 1998[Demonstration Scale Testing][Demonstration Scale Testing]

Medium-Pressure UV LampMedium-Pressure UV Lamp

Recent Research Indicates Capability of UV for Cryptosporidium Inactivation

Recent UV Inactivation Data for Cryptosporidium

• Clancy; 2.8 to 4.8 Log Crypto Inactivation Using 25 mJ/cm2

• Bolton; 3-Log Crypto Inactivation at 20 mJ/cm2

• Finch; 2.5 to 4.6 Log Crypto Inactivation Using 28 mJ/cm2

• Sobsey & Linden; 4-Log Crypto Inactivation Using 15 mJ/cm2

Giardia Inactivation Capability of UV

• Previous Studies (Hoff, Karanis) Showed Doses of 100 to 180 mJ/cm2 Required for 2.0-Log Giardia Inactivation

• Sobsey & Linden; 4-log Giardia Inactivation Using 15mJ/cm2

• Bolton; 3-log Giardia Inactivation at 20 mJ/cm2

UV Regulatory Status in the U.S.

• Widely Used Since 1980’s in WW Treatment and Reclamation (CA Title 22 Approval)

• SWTR Included UV Doses for 2 and 3 Log Virus Inactivation in 1989/1990

• EPA Proposes Groundwater Rule With UV As a Likely BAT in 1991

• 1998 - New Cryptosporidium Research Released

• 1999 - EPA Sponsors UV Workshop for FACA

Henderson’s UV Implementation Strategy

• Bench-Scale Testing– Conduct bench-scale collimated beam testing to

establish dose-response relationship for MS-2 and/or Bacillus subtilis for Henderson’s water

• Design and Construction– Evaluate/select the UV system vendor based on

an evaluated bid– Detailed design of UV system including controls

and monitoring– Installation– Full-scale performance validation

Henderson’s UV Implementation Strategy (cont’d)

• Validation– Full-scale demonstration using MS2

phage/Bacillus spores– Back-calculate full-scale system dosage

• Maintenance– Routine cleaning/replacement of UV lamps– Routine cleaning/calibration/replacement of UV

sensors

Henderson NV Conclusion

• UV achieved disinfection and DBP goals

• Lowest cost option• Regulatory approval can

coincide with design and construction

Denver WaterChlorine Disinfection

• Conventional water treatment at 3 water treatment plants

• Disinfection with chlorine followed by chloramines

• Need to reduce THMs and HAAs• Planning for future disinfection and

DBP regulations

DBP and Disinfection Drivers

Current Disinfection Practice

Chlo

rine

Headworks

Raw Water

Rapid Mix

Flocculation/ Sedimentation

Filter Clear Water Reservoirs

Chlo

rine

Am

monia

Project Goals

Continue to meet current EPA disinfection requirements

Improve safety / reliability

Identify strategies for future compliance

Develop implementation plan and costs

Disinfection Regulations

Current: 30 minutes contact

SWTR: 0.5-log Giardia inactivation

ESWTR: 0 to 3-log (0 to 99.9%) Cryptosporidium

inactivation

Short Term- 0.5-log Giardia Inactivation

- TTHMs < 80 ppb, HAAs < 60 ppb- Eliminate prechlorination

Long Term- Cryptosporidium inactivation

- Lower levels of DBPs

Disinfection Objectives

Short Term Planning

Will chlorine meet short-term

goals?

On-site NaOCl generation

$24.9M

Purchase NaOCl $21.8M

Evaluate other disinfectants

Can risks be mitigated?

BulkChlorine

Gas

Yes

No

No

YesBulk chlorine $10.2M

Purchase NaOCI

MeetsCriteria

Long-Term Planning

Evaluate Performance

of ChlorineChloramine

Chlorine

Ozoneor UV

ConductOzone / UV

Studies

CryptoInactivation

> 1.0 Log Crypto?

MeetsDBPR

Yes

Yes

NoYes

No

No

Yes

No

ImplementChlorination

Strategy

Chlorine

Chlorine Chloramine

Chlorine Chloramine

Long Term Disinfectants Costs

(0.5-Log Cryptosporidium)

Short-Term Implementation Elements

Construct well-baffled chlorine contact basins

Install emergency gas scrubbers

Update chlorination equipment and controls

Provide process monitoring and control for disinfection

Computational Fluid Dynamic Model T = 25 min.

Implementation Schedule

Design/Construct Chlorination System Improvements

Pilot Testing - Ozone

Pilot Testing - Chlorine/Chloramine

ESWTR Requirements Identified

Design/Construct Long-Term Disinfection Improvements

1997 1998 1999 2000 2001 2002 2003

Denver Water Conclusions

• Post Filtration chlorine will meet disinfection and DBP requirements

• Study ozone and UV• Wait for regulatory development• Initiate revised disinfection based

on regulatory requirements and study results

DBP Compliance Now and Into the Future

• Each case is site specific when balancing disinfection needs and DBP

• Chlorine, ozone, chlorine dioxide, and UV are all possibilities

• A thorough analysis and cost estimate is essential to a good decision