engineers scientists architects constructors case study uv disinfection interference at big rapids...
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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