Design of Precast Concrete Grease Interceptors Claude Goguen, PE - - PowerPoint PPT Presentation

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Design of Precast Concrete Grease Interceptors Claude Goguen, PE - - PowerPoint PPT Presentation

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Design of Precast Concrete Grease Interceptors Claude Goguen, PE National Precast Concrete Association 2015 Onsite Wastewater Mega Conference Terminology Terminology Terminology Grease is the Word If you have been in a commercial kitchen,

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Design of Precast Concrete Grease Interceptors

Claude Goguen, PE National Precast Concrete Association 2015 Onsite Wastewater Mega Conference

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Terminology

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Terminology

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Terminology

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Grease is the Word

If you have been in a commercial kitchen, it is

  • bvious why grease interceptors are needed.
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Why are Grease Interceptors Necessary?

  • Grease blockages in pipes
  • Issues in treatment field
  • Issues in septic tanks (if

they’re in series)

Problems Downstream

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Configuration Options

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Configuration Options

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Factors that influence sizing and design

  • Wastewater Strength
  • Wastewater Constituents
  • Globule Size
  • Temperature
  • Flow Rate
  • Retention Time
  • Pumping Frequency
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Factors that influence sizing and design

  • Concentration: strength of the influent

waste

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Wastewater Constituents Chemistry:

  • Vegetable oils require longer

retention times than animal fats.

  • Emulsified oils require the

longest retention times. (Soaps)

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Globule Size

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Factors that influence sizing and design Grease globule size has an effect

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Temperature

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Coagulation

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Flow Rates

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  • Difference exists when draining a filled sink versus some sinks that

are never filled and the flow is associated with the associated fixture.

  • The potential contribution of the filled sinks is determined through the

use of Manning’s Equation in conjunction with various plumbing characteristics.

  • Faucet flow contributions are calculated based on known peak

discharge limitations for the various fixtures in a kitchen.

Different Types of flow

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Different Types of flow

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Factors that influence sizing and design

  • Retention Time: Amount of time it takes one

particle to travel through the system and discharge out.

  • Metcaff & Eddy recommend 30 minutes
  • Stokes Law
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Key Factors Affecting Grease Removal

  • Depends on the size and the influent flow rate
  • Baffles “can” increase retention time and prevent

short-circuiting

  • Size can increase retention time and promote

cooling of liquids

Retention Time

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Baffle or no Baffle?

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WERF Report

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WERF Report

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WERF Report

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WERF Report

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WERF Report

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Proper design goes beyond sizing…

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Proper design goes beyond sizing…

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Proper design goes beyond sizing…

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Factors that influence sizing and design

  • Pumping Frequency: Size shall be sufficient

to optimize cleaning and pump-outs.

  • FOG is 25% of

liquid level

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Interceptor Sizing

EPA

Sizing Codes

UPC DFU GPM

WTF?

What’s the Formula?

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Interceptor Sizing UPC – Appendix H (pre-2006)

     

factor storage time retention rate flow hour peak Meals . * . * . * . #      

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Interceptor Sizing

Example: Restaurant with 100 meals per peak hour. They have a dishwasher connected to the interceptor. They are open from 6:00am to 10:00pm # meals/peak hr. = 100 meals/hr Flow rate (with dishwasher) = 6 gallons / meal Retention time (with dishwasher) = 2.5 Storage factor (16 hours of operation) = 2 Tank Capacity = 100 x 6 x 2.5 x 2 = 3,000 gallons

UPC – Appendix H (pre-2006)

     

factor storage time retention rate flow hour peak Meals . * . * . * . #      

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Interceptor Sizing UPC - (2006-2009)

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Interceptor Sizing UPC - (2006-2009)

Example: A restaurant with the following fixtures and equipment: 3 floor drains Mop sink Food prep sink 1 commercial dishwasher (8GPM)

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Interceptor Sizing UPC - (2006-2009)

Example: A restaurant with the following fixtures and equipment: 3 floor drains Mop sink Food prep sink 1 commercial dishwasher

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Interceptor Sizing UPC - (2006-2009)

Example: A restaurant with the following fixtures and equipment: 3 floor drains Mop sink Food prep sink 1 commercial dishwasher

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Interceptor Sizing UPC - (2006-2009)

Example: A restaurant with the following fixtures and equipment: 3 floor drains Mop sink Food prep sink 1 commercial dishwasher

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Interceptor Sizing UPC - (2006-2009)

Example: A restaurant with the following fixtures and equipment: 3 floor drains Mop sink Food prep sink 1 commercial dishwasher

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Interceptor Sizing UPC - (2006-2009)

Example: A restaurant with the following fixtures and equipment: 3 floor drains Mop sink Food prep sink 1 commercial dishwasher

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Interceptor Sizing UPC - (2006-2009)

Example: A restaurant with the following fixtures and equipment: 3 floor drains 3 x 2 DFUs = 6 Mop sink 1 x 3 DFU = 3 Food prep sink 1 x 3 DFU = 3 1 commercial dishwasher = 2 Total DFU’s = 14 DFU’s

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Interceptor Sizing UPC - (2006-2009)

Example: A restaurant with the following fixtures and equipment: 3 floor drains 3 x 2 DFUs = 6 Mop sink 1 x 3 DFU = 3 Food prep sink 1 x 3 DFU = 3 1 commercial dishwasher = 2 Total DFU’s = 14 DFU’s 750 Gallon Tank

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Interceptor Sizing

where: # seats (assume = 100 seats) # gal / meal = 5 Storage Factor = 1.7 to 2.5 (2.5 for onsite disposal) Hours Open = 8 Loading factor = 0.8 Example Tank Capacity = 100 x 5 x 2.5 x 8/2 x 0.8 = 4,000 gallons

U.S. E.P .A.

     

factor loading

  • pen

hours factor storage meal gal seats . * 2 . * . * * #            

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Interceptor Sizing

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WERF Report

“The results of this study seem to suggest that the development of a universal GI design that can be sized solely on the hydraulic loading and the FOG storage capacity is too simplistic. It is possible that analysis of the FOG influent characteristics will have to be assessed prior to the selection of the most appropriate GI size and design.”

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As a result of the analysis of grease interceptor performance, the researchers concluded: ♦ Extending the residence time in a standard GI by a factor of 3

  • nly yielded a 10% improvement in performance, suggesting that

FOG loading is only one of the factors affecting performance. ♦ FOG droplet size significantly affected FOG removal performance. ♦ Decrease in GI separation efficiency will result with the use of detergents and mixing while cleaning in-kitchen FOG wastes. ♦ Inlet/out configurations must be designed to distribute the flow. ♦ More effective FOG separation was achieved when fluid velocities near the inlet and outlet were kept below 0.015 m/s. ♦ Only include baffle walls with specific inlet/outlet configurations. ♦ Design baffle wall to distribute the flow and minimize the

  • ccurrence of high local fluid velocities.

Proper design goes beyond sizing…

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All Specifications should include..

  • Materials and Manufacture
  • Structural Design Requirements
  • Physical Design Requirements
  • Quality Control
  • Watertightness Requirements

ASTM ASTM C1613 C1613 - “Standard Specification for Precast Concrete Grease Interceptor Tanks”

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Difference?

Septic Tank – ASTM C1227 Grease Interceptor – ASTM C1613

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Summary

  • Retention time important factor, but not only

factor

  • Smooth slow laminar flow
  • Many sizing formulas – in absence of one,

use UPC 2003 Appendix H

  • Specify ASTM C1613
  • Septic Tank is not a Grease Interceptor
  • Work with your precaster to find solutions
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Additional Information Sources

www.precast.org Claude Goguen : cgoguen@precast.org

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QUE QUESTIONS? STIONS?

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Design of Precast Concrete Grease Interceptors

Claude Goguen, PE National Precast Concrete Association