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Case Study UV Disinfection Interference at Big Rapids WWTP. 83 rd Annual Conference Michigan Water Environment Association June 23, 2008. Jack D. Fraser City of Big Rapids. Jerald O. Thaler, P.E. Fishbeck, Thompson, Carr & Huber, Inc. AGENDA. Historical Background Source of Problem

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case study uv disinfection interference at big rapids wwtp

Case StudyUV Disinfection Interferenceat Big Rapids WWTP

83rd Annual Conference

Michigan Water Environment Association

June 23, 2008

Jack D. Fraser City of Big Rapids

Jerald O. Thaler, P.E.

Fishbeck, Thompson, Carr & Huber, Inc.



  • Historical Background
  • Source of Problem
  • Control Mechanism
  • Summary and Questions
  • 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.
  • 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.
  • 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.
Suspected Culprit
  • 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.
potassium sorbate
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:

Local Limit Options
  • 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
general methodology for developing local limits
General Methodologyfor Developing Local Limits
  • Maximum allowable headworks loading (MAHL).
  • Domestic/background loading (LBKGD).
  • Maximum allowable industrial loading (MAIL):

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

  • Allocation of MAIL among industrial users.
transmittance t
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
absorbance a
Absorbance (A)
  • Related to T via Beer-Lambert Law:


  • Characteristics:
    • Proportional to concentration
    • Additive
    • Highly adaptable to mathematical manipulation
calculation procedure
Calculation Procedure
  • Assume effluent absorbance (AEFF) consists of three additive components:
    • Correction for total suspended solids present
    • Domestic/background residual
    • Industrial user pass-through
calculation procedure continued
Calculation Procedure (continued)
  • Assume remain below maximum allowable effluent absorbance:
  • Use site-specific data to calibrate parameters.
  • Solve for AIU, then transpose to TIU:
  • Solving for ASIU and transposing to TSIU:
permit conditions
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%...
  • 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.