(A) Grease interceptor sizing.
(1) This section of Appendix A is intended to be example guidance for the designer. The tank size shall be based on design criteria set forth in Bulletin S.E. 13 from the Indiana State Board of Health, latest edition.
(2) The recommended grease interceptor size may be calculated as follows:
Tank Size (in gallons) = Meals Served During Peak Hour x Waste Flow Rate Factor x Retention Time Factor x Storage Factor
(3) Components of the equation are:
(a) The peak meals served per hour = the maximum number of meals served in any given hour of kitchen operation (maximum seating capacity may be substituted for peak meals served per hour).
(b) The waste flow factor may be determined as one of the following:
1. For a commercial kitchen with a dishwashing machine, the waste flow factor = 6;
2. For a commercial kitchen without a dishwashing machine, the waste flow factor = 5;
3. For a single service kitchen (food served on, in, or with disposable service ware), the waste flow factor = 2; or
4. For food waste disposal only, the waste flow factor = 1.
(c) The retention time factor may be determined as one of the following:
1. For a commercial kitchen, the retention time factor = 2.4; or
2. For a single service kitchen, the retention time factor = 1.5.
(d) The storage factor may be determined as one of the following:
1. For a commercial kitchen, the storage factor = 0.125 X the hours/day of kitchen operation; or
2. For a single service kitchen, the storage factor = 1.5.
(4) Sample calculation no. 1.
(a) Calculate the size of a grease interceptor for a fast food restaurant that is open 24 hours per day and has a seating capacity of 66. There is no dishwasher and food is served with disposable service ware.
Tank Size (in gallons) = 66 x 2 x 1.5 x 1.5 Tank Size = 297 gallons |
(b) Note: The minimum size of a grease interceptor as stipulated by the FOG policy is 1,000 gallons. Therefore, a 1,000 gallon grease interceptor must be installed in this case.
(5) Sample calculation no. 2.
(a) Calculate the size of a grease interceptor for a commercial kitchen of a nursing home serving a maximum of 76 meals/hour. The kitchen is equipped with a dishwasher and the kitchen operates 15.5 hrs/day.
Tank Size (in gallons) = 76 x 6 x 2.4 x (0.125 x 15.5) Tank Size = 2,120 gallons |
(b) Note: The maximum size of a grease interceptor as stipulated by the FOG policy is 1,500 gallons. Therefore, two grease interceptors must be installed in series in this case.
Newburgh Wastewater Treatment Facilities Grease Interceptor Size Calculation For Commercial Sanitary Sewer Connections |
Newburgh Wastewater Treatment Facilities Grease Interceptor Size Calculation For Commercial Sanitary Sewer Connections |
Date: |
Owner: |
Contractor: |
Name of the Facility: |
Facility Address: |
Contract Maintenance Provider: |
General |
Grease traps shall be installed at any commercial kitchen or food service business which produces waste that may contain large amounts of grease, fat or oil. These traps shall remove the grease before it enters the sanitary sewer system. Wastes from sinks, dishwashers and kitchen floor drains should be combined and routed through the grease trap prior to entering the sanitary sewer system. The tank size shall be based on design criteria set forth in Bulletin S.E. 13 from the Indiana State Board of Health, latest edition. |
A typical detail drawing is shown on Figure A2.4 in the Town of Newburgh Sanitary Sewer Design and Construction Standards. |
The recommended grease trap size may be calculated as follows: |
Tank Size (in gallons) = Meals Served During Peak Hour x Waste Flow Rate Factor x Retention Time Factor x Storage Factor |
Peak Meals Served/Hour or Seating Capacity: |
Waste Flow Rate Factor: |
[ ] a.
Commercial kitchen with dishwashing machine: 6
|
[ ]
b. Commercial kitchen without dishwashing machine: 5
|
[ ]
c. Single service kitchen: 2
|
[ ]
d. Food waste disposal only: 1
|
Retention Time: |
[ ] a. Commercial kitchen waste 2.4 |
[ ] b. Single service kitchen: 1.5 |
Storage Factor: |
[ ] a. Fully equipped commercial kitchen |
0.125 x hours of operation = |
[ ] b. Single service kitchen: 1.5 |
Using the above equation, calculate the grease trap size: |
Tank Size = x x x |
Tank Size = Gallons or CU ft. (as determined by the distance from the discharge pipe’s invert to the floor.) |
Calculated by: Date: |
Notes:
1. All buried exterior lank surfaces shall be coated with ten ml. thickness coal tar epoxy.
2. All lateral piping shall be gasketed, six in. SDR 26 PVC.
3. Internal piping may be glue joint.
4. All tank joints shall be provided with water tight seals.
5. The minimum setback from the bottom of the building foundation to the bottom of the interceptor excavation shall be one to one.
6. The length to width ratio for the tank shall be two to one.
7. A cleanout shall be required in the discharge pipe within three feet of the tank.
TYPICAL GREASE INTERCEPTOR: FIGURE A2.4
(B) Internal grease tap sizing. Grease traps may be substituted for grease interceptors as provided in § 52.01(E) and (F) of the FOG policy. When grease traps are required by the utility, each grease trap shall have an approved rate of flow, which is not less than that given in the following grease trap sizing table for the total number of connected fixtures or as calculated using the sum of all modified flow rates for each fixture (modified flow rates for each fixture = gpm/fixture x the fixture rating). No more than four fixtures may be connected to one grease trap and dishwashers should have dedicated grease traps.
(1) Grease trap sizing table.
Table A | ||||
Total Number of Fixtures Connected | Maximum Total Capacity (Volume) of Fixtures | Required Rate of Flow (gallons/ minute) | Grease Retention Capacity (pounds) | |
(gallons) | (cubic feet) | |||
1 | 50 | 6.7 | 20 | 40 |
2 | 62 | 8.3 | 25 | 50 |
3 | 87 | 11.6 | 35 | 70 |
4 | 125 | 16.7 | 50 | 100
|
(2) Calculating the modified flow rates of various kitchen fixtures.
Modified flow rate = gpm/fixture x the fixture rating
(a) GPM/fixture. This is derived from the Manning formula. It takes into account the slope; roughness of the pipe (plastic) used and pipe diameter size. The drainage rates of various pipe diameter sizes are:
1. 0.5 inch pipe diameter = 0.8 GPM/fixture;
2. 1.0 inch pipe diameter = 5.0 GPM/fixture;
3. 1.5 inch pipe diameter =15 GPM/fixture;
4. 2.0 inch pipe diameter = 33 GPM/fixture;
5. 2.5 inch pipe diameter = 59 GPM/fixture; and
6. 3.0 inch pipe diameter = 93 GPM/fixture.
(b) Fixture ratings of grease-laden waste streams. Fixtures that have more grease in their waste stream receive higher values while less grease corresponds to a lower value. Common commercial kitchen fixtures and their corresponding rating (for each) are as follows:
Kitchen Fixture | Rating |
Kitchen Fixture | Rating |
1 or 2 compartment meat prep sink | 0.75 |
1 or 2 compartment vegetable prep sink | 0.25 |
2, 3, or 4 compartment pot sink | 1.0 |
Can wash | 0.25 |
Floor drain | 0.00 |
Mop sink | 0.25 |
Pre-rinse sink | 0.5 |
(c) Example calculations of fixture modified flow rates. A restaurant’s kitchen is supplied with the following fixtures. What is the modified flow rate for each fixture?
1. A two compartment pot sink with a one and one-half inch drain.
Fixture modified flow rate = 15 x 1.0 fixture modified flow rate = 15 gpm |
2. A two compartment vegetable prep sink with a one and one-half inch drain.
Fixture modified flow rate = 15 x 0.25 fixture modified flow rate = 3.75 gpm |
3. A mop sink with a two inch drain.
Fixture modified flow rate = 33 x 0.25 fixture modified flow rate = 8.25 gpm |
4. A dishwasher with a manufacture’s rated maximum discharge capacity of 10.0 gpm.
Fixture modified flow rate = 10.0 gpm |
(3) Example grease trap size determination.
(a) Given the information in divisions (B)(2)(c)1., (B)(2)(c)2., (B)(2)(c)3. and (B)(2)(c)4., the grease trap size(s) may be determined as follows:
1. Using Table A and number of fixtures. Using Table A, three fixtures require a grease trap with a flow rating of 35 gpm and a grease retention capacity of 70 pounds. Per § 52.03(K) of the policy, the dishwasher will require an additional grease trap capable of receiving ten gpm. In this case, the dishwasher will require the installation of a second grease trap which meets the minimum requirements of § 52.03(D). A grease trap with a flow rating of 20 gpm and a grease retention capacity of 40 pounds (per Table A) is required for the dishwasher.
2. Using Table A and fixture modified flow rates.
a. When using fixture modified flow rates, the size is determined using Table A and the sum of all fixture modified flow rates flowing into the grease trap:
15 gpm + 3.75 gpm + 8.25 gpm = 27 gpm |
b. In this case, 27 gpm is the minimum flow rating required, and, when this is compared to Table A, a 35 gpm grease trap will be required with a grease retention capacity of 40 pounds. The dishwasher will require the installation of a second grease trap as determined in division (B)(3)(a) above.
(Ord. 2012-20, passed 8-22-2012)