Determining Your Composting Pad Size
The following worksheet has been created to help you work through the necessary calculations for determining the size of your composting site. In each step a description of the step is provided, along with an example. After the example provided in each step you will find a calculation provided with blank spaces in which you can insert your specific information. Cumulatively, these steps will help you determine the area you require for your composting activities. Below you will find a list of questions that you need to answer in order to create the composting site you need to manage your program. This worksheet will help you address these questions step by step. In addition, you may find it helpful to develop a diagram as you go along in order to help you think through some of your space needs and how they might fit into a potential site.
- How much material per day or week?
- How long is the composting period?
- What will your windrow dimensions be?
- What will the volume of material in each windrow be?
- How many windrows will you need to fit on the site at once?
- What space needs do you have for working space – alleys, perimeter travel lanes, etc.
- What additional space needs, such as for curing , mortalities, feedstock storage, and access roads, might you require.
Step 1. - Volume of Primary Feedstock
Volume of Primary Material per day or week
Note: choose the timeframe by which you will base your projections, based on how often new feedstock will enter the site. Stick with this time period throughout the calculations – i.e. composting period
- Ex. – 1 1400# cow generates 115 pounds manure per day
50 cow herd generates 5,750 pounds manure per day
Manure bulk density – 1700 pounds per cubic yard
60 #s dairy manure = 1 cubic foot
50 cows = 96 cubic feet of manure per day
- Ex. – 2 tons of food scraps per week
4,000 pounds of food scraps per week
1700 pounds food scraps per cubic yard
60 #s food scraps = 1 cubic foot
2 tons food scraps = 67 cubic feet per week
YOUR ENTRY
(primary ingredient from Recipe Development Worksheet):
Livestock Manure
- Manure generation per day per animal: ________ pounds
- Number of animals: _______
- Total generation per day
- pounds per animal per day ____ x number of animals ____ = ______ pounds/day
- Manure bulk density: _____ Pounds/ YRD3
- Convert to cubic feet
- Bulk density _____ / 27 = Pounds per cubic foot______pounds
- Total cubic feet per day
- Pounds per day _____ / Pounds per cubic foot _____ = Cubic feet per day____ft3/day
Food scraps
- Food scraps per day per week: ________ lbs
- Food scrap bulk density: _____ lbs per cubic yard
- Convert to cubic feet
- Bulk density _____ / 27 = ______ lbs per cubic foot
- Total cubic feet per wk
- lbs per day _____ / lbs per cubic foot _____ = Cubic feet per wk ______ft3/wk
- Volume of Second Ingredient (second ingredient from Recipe Development Worksheet)
- Ex. – recipe - 3 yrds. wood shavings to one yard manure
(3 ft3 sawdust/ 1ft3 manure) x (96 ft3 manure/ day) = 288 ft3 sawdust/ day
YOUR ENTRY:
- Ratio (Step 8 of Recipe Development Worksheet) of second ingredient per cubic yard of primary feedstock: ____
- Cubic feet of primary feedstock per day ____ x ratio of second ingredient to primary feedstock ____ = Cubic feet of bulking material per day_______ft3/ day
• Ex. – 96 ft3 manure per day + 288 ft3 shavings = 384 ft3/ day
YOUR ENTRY:
- Cubic feet primary feedstock per day ____ + Cubic feet of bulking material per day _____ = Total cubic feet per day________ft3/ day
- Adjusted Volume (Reduction from feedstock combining 15-20%) –
Total Volume per day (or wk) x (100 – percent reduction/ 100) = Adjusted Volume
• Ex. - 384 ft3 x (100 – 20)/100) = 307 ft3/ day
YOUR ENTRY:
- Total cubic feet per day ____ x (100 - percent volume reduction ___ / 100) = Adjusted volume per day_____ft3/day
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Step 2. – Volume of Material on Pad
- Determine length of composting period (commonly 120 – 360 days). Correspond the unit of time (day or week) with the period of time incoming feedstocks are measured in.
YOUR ENTRY:
- Length of composting period (can be in days or weeks): ________
- Total Volume on pad
- 120 days x (307 ft3./ day) = 36,840 ft3
YOUR ENTRY:
- Length of composting period ____ x Adjusted volume per day ____ft3 =
Total Volume on pad at one time _________ft3
- Account for Shrinkage during composting (25-50 %)
- Shrinkage factor – 25%
- 36,840 ft3 x .75 = 27,360 ft3
YOUR ENTRY:
- Shrinkage factor: _____%
- Total volume on pad ______ft3 x (Shrinkage factor ___% / 100) =
Adjusted Total Pad Volume _________ft3
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Step 3. – Windrow Dimensions
- Windrow Dimensions -
- Ex. - 6’ tall x 12’ wide x 100’ long
YOUR ENTRY:
- Windrow Dimensions: _____ft tall x _____ft wide x _____ft long
Step 4. - Windrow Volumes
- Windrow Volume –
- Cross-sectional Area
- parabolic windrows – 2/3 x base width x height
- triangular windrows – ½ x base width x height
- Ex. – 2/3 x 12 x 6 = 47.5 ft2
C-S Area x Windrow Length = ft3 per windrow
- Ex. - 47.5 x 100 = 4,750 ft3
YOUR ENTRY:
- Determine windrow shape (parabolic or triangular): _________
- Cross- Sectional Area Factor: ____ (2/3 or ½)
- Cross-Sectional Area Factor _____ x base width ____ft x height ___ft =
Cross Sectional Area ______ft2
- Cross-Sectional Area ______ft2 x Windrow Length _____ft =
Total Volume Per Windrow ______ft3
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Step 5. – Number of Windrows Required
- # Windrows = Total Volume of Material
Single Windrow Volume
• Ex. - 27,360 ft3 / 4,750 ft3 = 5.76 windrows
YOUR ENTRY:
- Total Volume of Material (2C) _____ft3 / Single Windrow Volume ______ = Number of Windrows on Site _____
Step 6. – Work Space Needs
- Windrow Spacing (10’ for tractor-drawn windrow turners, 15’ for skid steers, 20-25’ for tractors, 25-35’ for pay loaders)
- Ex. – 20’ between windrows
5 alleys x 20’ ea. = 100’
YOUR ENTRY:
- Width of alleys: ____ft.
- Number of Windrows _____ - 1 = Number of Alleys ____
- Width of alleys ____ft. x Number of Alleys _____ = Total Alley Space ____ft.
B. Perimeter Travel Lane
Perimeter – pad width (perimeter travel lane x 2) = 30’
Perimeter – pad length (perimeter travel lane x 2) = 30’
YOUR ENTRY:
- Perimeter travel lane (pad width) ____ft. x 2 = ____ft.
- Perimeter travel lane (pad length) _____ft. x 2 = _____ft.
C. Total Work Space Needs
- Ex – Work Space Pad Width = 130’
100’ (Total alley space) x 30’ (Perimeter travel lane) = 130’ Total Width of Work Space
- Ex – Work Space Pad Length = 30’
30’ (Perimeter travel lane) = 30’ Total Length of Work Space
YOUR ENTRY:
- Total Alley Space (width) ____ft. x Width of Perimeter ____ft. = Width of Work Space _____ft.
- Perimeter (Length) ____ft. = Length of Work Space ____ft.
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Step 7. – Total Pad Area
*These calculations are based on a square pad
- Width –
- Ex -Windrow width – 12’ ea. x 6 windrows = 72’
- Ex - Work space width – 130’
- Ex - Pad width = 202’
YOUR ENTRY:
- (Windrow Width (3A) ___ft. x Number of Windrows (5A) ___ ) + Total Width of Work Area _____ft. = Total Width of Pad _______ft.
- Length –
- Ex - Windrow length – 100’
- Ex - Work space length – 30’
- Ex - Pad length = 130’
YOUR ENTRY:
- Windrow Length (3A) ___ft. + Perimeter Length_____ft. = Total Length of Pad _______ft.
- Total Area for Windrows–
- 130’ (length) x 202’ (width) = 26,260 ft2
YOUR ENTRY:
- Pad Length ____ft. x Pad Width ____ft. = Total Pad Area ________ ft.2
Step 8. – Total Site Area
In addition to the actual composting area, referred to here as the Pad Area, you may have additional space needs for activities that will support your composting, such as access roads and turnarounds, sheds, storage, curing, and feedstock receiving.
- Ex. - Identifying additional space needs:
- Storage & Receiving – 1500 square feet
- Curing – 500 square feet
- Shed – 500 square feet
- Turnaround – 1600 square feet
- Ex. – Total additional space needs – 4,100 square feet
- Ex – Total entire site square footage
Total pad area + Additional space needs = Total Site Area
26,260 sq. ft. + 4,100 sq. ft. = 30,360 sq. ft.
YOUR ENTRY:
- Additional space needs (list item and necessary square footage):
- ____________________
- ____________________
- ____________________
- ____________________
- ____________________
- Total additional space needs –
______ + ______ + ______ + ______ + ______ = _______square feet
Total pad area ________ + Total additional space needs ________ =
____________ TOTAL SITE AREA back to top |
