Design of Precast Concrete Grease Interceptors

Transcription

1 Design of Precast Concrete Grease Interceptors Claude Goguen, PE National Precast Concrete Association 2015 Onsite Wastewater Mega Conference

2 Terminology

3 Terminology

4 Terminology

5 Grease is the Word If you have been in a commercial kitchen, it is obvious why grease interceptors are needed.

6 Why are Grease Interceptors Necessary? Problems Downstream Grease blockages in pipes Issues in treatment field Issues in septic tanks (if they re in series)

7 Configuration Options

8 Configuration Options

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

10 Factors that influence sizing and design Concentration: strength of the influent waste

11 Wastewater Constituents Chemistry: Vegetable oils require longer retention times than animal fats. Emulsified oils require the longest retention times. (Soaps)

12 Globule Size

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

14 Temperature

15 Coagulation

16 Flow Rates

17 Different Types of flow 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.

18 Different Types of flow

19 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

20 Key Factors Affecting Grease Removal Retention Time 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

21 Baffle or no Baffle?

22 WERF Report

23 WERF Report

24 WERF Report

25 WERF Report

26 WERF Report

27 Proper design goes beyond sizing

28 Proper design goes beyond sizing

29 Proper design goes beyond sizing

30 Factors that influence sizing and design Pumping Frequency: Size shall be sufficient to optimize cleaning and pump-outs. - FOG is 25% of liquid level

31 Interceptor Sizing Sizing Codes EPA GPM WTF? What s the Formula? DFU UPC

32 Interceptor Sizing UPC Appendix H (pre-2006) # Meals * peak. hour flow. rate * retention. time * storage. factor

33 Interceptor Sizing UPC Appendix H (pre-2006) # Meals * peak. hour flow. rate * retention. time * storage. factor 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

34 Interceptor Sizing UPC - ( )

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

36 Interceptor Sizing UPC - ( ) Example: A restaurant with the following fixtures and equipment: 3 floor drains Mop sink Food prep sink 1 commercial dishwasher

37 Interceptor Sizing UPC - ( ) Example: A restaurant with the following fixtures and equipment: 3 floor drains Mop sink Food prep sink 1 commercial dishwasher

38 Interceptor Sizing UPC - ( ) Example: A restaurant with the following fixtures and equipment: 3 floor drains Mop sink Food prep sink 1 commercial dishwasher

39 Interceptor Sizing UPC - ( ) Example: A restaurant with the following fixtures and equipment: 3 floor drains Mop sink Food prep sink 1 commercial dishwasher

40 Interceptor Sizing UPC - ( ) Example: A restaurant with the following fixtures and equipment: 3 floor drains Mop sink Food prep sink 1 commercial dishwasher

41 Interceptor Sizing UPC - ( ) 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

42 Interceptor Sizing UPC - ( ) 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

43 Interceptor Sizing U.S. E.P.A. gal hours. open # seats * storage factor loading factor meal *. * *. 2 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

44 Interceptor Sizing

45 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.

46 Proper design goes beyond sizing 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 only 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 m/s. Only include baffle walls with specific inlet/outlet configurations. Design baffle wall to distribute the flow and minimize the occurrence of high local fluid velocities.

47 All Specifications should include.. ASTM C Standard Specification for Precast Concrete Grease Interceptor Tanks o Materials and Manufacture o Structural Design Requirements o Physical Design Requirements o Quality Control o Watertightness Requirements

48 Difference? Septic Tank ASTM C1227 Grease Interceptor ASTM C1613

49 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

50 Additional Information Sources Claude Goguen : cgoguen@precast.org

51 QUESTIONS?

52 Design of Precast Concrete Grease Interceptors Claude Goguen, PE National Precast Concrete Association