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Case StudyUV Disinfection

Interferenceat Big Rapids WWTP

83rd Annual ConferenceMichigan Water Environment Association

June 23, 2008

Jack D. Fraser City of Big Rapids

Jerald O. Thaler, P.E.Fishbeck, Thompson, Carr & Huber, Inc.

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AGENDA

• Historical Background

• Source of Problem

• Control Mechanism

• Summary and Questions

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Historical Background

• Nestle Waters North America opened major pumping and bottling facility in Stanwood, MI.

• Produced Ice Mountain® and Pure Life® (“Splash”) fruit-flavored bottled waters.

• Process wastes trucked offsite for disposal.

2002

• Recurring fecal coliform violations led City to replace aging UV disinfection system.

• Nestle Stanwood approached City to accept trucked process wastes at WWTP.– Standard policy not to accept trucked wastes.– Significant revenue potential (up to $25,000/month).– Characterization study indicated “clean” wastes.

• City decided to accept wastes; construction of UV system began approximately the same time.

2003-2005

• Fecal coliform violations continued, even after start-up of new UV system.

• MDEQ initiated enforcement response action.

• Aggressive investigations into cause:– Revisited basis of design for new system.

– Collected daily transmittance data from WWTP effluent.

– Collected color/odor observations and transmittance data from each Nestle Stanwood truckload.

– Nestle Stanwood and Michael Goergen/Merit Laboratories evaluated chemicals potentially in waste.

2006

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Source of Problem

• Data suggested problem was potassium sorbate.

– Widely used preservative in the food industry.

– Additive in Splash fruit-flavored water.

– Salt of sorbic acid (C5H7COOH), a natural organic compound with anti-microbial properties.

Suspected Culprit

H H O

– – ═

C C C

H3C C C O- K+

– –

H H

Potassium Sorbate• Absorbs UV, unlike turbidity that blocks UV.

– Peak absorption at 255 nanometers (nm).

– Peak output of standard UV disinfection lamp is 254 nm.

Germicidal Curve:

0%

20%

40%

60%

80%

100%

205 225 245 265 285 305

Wavelength, nm

Rel

ativ

e E

ffect

UV Lamp Peak Output

Potassium Sorbate

Peak Absorbance

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Control Mechanism

• Maximum Concentration– No data to correlate discharge concentration to

interference

– Testing issues (costs and turnaround time)

• Minimum Transmittance+ Much data to correlate discharge transmittance to

interference

+ Straightforward testing

– No experience or USEPA/MDEQ guidance on developing limit

Local Limit Options

General Methodologyfor Developing Local Limits

1. Maximum allowable headworks loading (MAHL).

2. Domestic/background loading (LBKGD).

3. Maximum allowable industrial loading (MAIL):

4. Allocation of MAIL among industrial users.

MAIL = MAHL*(1-Safety Factor) - LBKGD

Transmittance (T)• Definition:

where: I = intensity of UV light leaving sample

Io = intensity of UV light entering sample

• Characteristics:– Not proportional to concentration– Not additive– Poorly adaptable to mathematical manipulation

100I

IT

o

Absorbance (A)

• Related to T via Beer-Lambert Law:

or

• Characteristics:+ Proportional to concentration+ Additive+ Highly adaptable to mathematical manipulation

A10100T

log(T/100)A

Calculation Procedure

1. Assume effluent absorbance (AEFF) consists of three additive components:

a. Correction for total suspended solids present

b. Domestic/background residual

c. Industrial user pass-through

BKGDA

)IU

R-1(*IU

A

TSSTSS

ΔA

Calculation Procedure (continued)

2. Assume remain below maximum allowable effluent absorbance:

3. Use site-specific data to calibrate parameters.

4. Solve for AIU, then transpose to TIU:

IUIU

A10100T

)1(*MAXEFF

A SFA

TSS CorrectionCoefficient (ΔATSS)

0.0

0.1

0.2

0.3

0.4

0.5

0 10 20 30 40 50 60

Effluent TSS, mg/L

Eff

lue

nt

Ab

sorb

an

ce

Slope = 0.000701

Domestic/BackgroundResidual (ABKGD)

0.0

0.1

0.2

0.3

6-Apr 7-Apr 8-Apr 9-Apr 10-Apr 11-Apr

Date

Ab

sorb

an

ce

Residual TSS = 0.144

Background = 0.096

Total = 0.240

No trucked waste during data collection.

Removal of Industrial User Absorbance (RIU)

AEFF = 0.065 + 2.30x10-8*QSIU

75%

80%

85%

90%

95%

100%

0 25,000 50,000 75,000 100,000 125,000 150,000

Trucked Waste Volume, gal/day

Abs

orb

ance

Re

mo

val

(Bac

kgou

nd-

and

TS

S-c

orre

cted

)

Maximum AllowableEffluent Absorbance (AMAX)

0

200

400

600

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Effluent Absorbance

Eff

lue

nt

Fe

cal C

olifo

rm,

cts/

10

0 m

L

Actual (T=56%) Design (T=50%)

Results• Solving for ASIU and transposing to TSIU:

0

20

40

60

80

100

0 25,000 50,000 75,000 100,000 125,000 150,000

Trucked Waste Volume, kgal/day

Min

imum

Tra

nsm

itta

nce,

Dai

ly A

vera

ge

%

>18.5 mg/L

17 mg/L

15 mg/L

10 mg/L

5 mg/L

Effluent TSS

Permit Conditions• Permit negotiations led to following:

– No acceptance if TSSEFF>15 mg/L

– Trucked waste volume up to 120,000 gal/day

• Minimum transmittance limit set at 70%...

0

20

40

60

80

100

0 25,000 50,000 75,000 100,000 125,000

Trucked Waste Volume, kgal/day

Min

imum

Tra

nsm

itta

nce,

Dai

ly A

vera

ge

%

>18.5 mg/L

17 mg/L

15 mg/L

10 mg/L

5 mg/L

Effluent TSS

Summary• Apparent “clean” waste caused interference.

• If using UV disinfection, be alert out for food processors using potassium sorbate.

• For local limit in T, best to work mathematics in A and then transpose.

• Other lessons learned:– Do not always know what you will get, particularly with

trucked waste.

– If get into problem, maximize expertise by using all available resources.

– Permit the discharger, not the transporter.

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Questions