USCC Compost Operations Training Course Sizing a Compost Pad Objective: Students will apply compost site design principles to a hypothetical site and determine the size required to compost a certain amount of feedstocks using a straddle turner. Procedure: Work in groups of 2 with the information provided below. Then use the accompanying Compost Pad Area Worksheet to determine the size of the active compost pad you will need. Scenario: You will be opening a new compost facility and have contracts for the following feedstocks: • Ground greenwaste (GGW): 100 tons per day • Food processing residuals (FPR): 80 tons per day • Horse manure (HM): 200 tons per week Assumptions: C:N, moisture and porosity are acceptable Bulk density of ground geenwaste: 650 lbs/cy Bulk density of food processing residuals: 1500 lbs/cy Bulk density of horse manure: 500 lbs/cy More-­‐or-­‐less steady incoming flow, 6 days per week, 52 weeks/yr Required perimeter equipment lane: 25’ Maximum site length (with the slope): 400’ Width (across slope): to be determined Scenario Method Turned windrow Equipment Straddle turner Pile height x base width 7’x14’ Aisles 10’ Active pad time 4 months Cross sectional area of a windrow = 2/3 x height x width of base (see diagram on back) Cross sectional area of ASP cell = (width at top + width at base)/2 x height; top ≈ base – height 1 cubic yard = 27 cubic feet 1 acre = 43,560 square feet 1 ton = 2,000 lbs Sizing a Compost Pad Page 1 1
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USCC Compost Operations Training Course Cross Section of a Windrow (Use this for straddle turner) Height Area = 2/3 X Height X Base Base Cross Section of a Trapezoidal Pile Area = ((Top + Base) / 2) X Height Top ≈ Base – Height Sizing a Compost Pad Top Height Base Page 2 USCC Compost Operations Training Course Compost Pad Area Worksheet Part 1. Determine the planning figure for your site. 1a. Determine you total annual volume in cubic yards: Tonnage Annual Material received (per Tonnage day or week) 100 TPD
31,200
Ground greenwaste
Food processing residuals
Horse manure
Bulk density Annual volume (CY/yr) 650 lb/cy
96,000 cy/yr
80 TPD
24,960
1,500 lb/cy
33,280 cy/yr
200 TPW
10,400
500 lb/cy
41,600 cy/yr
Total Incoming Materials (TIM) 170,880 cy/yr 1b. As different composting materials are mixed together, smaller particles fill in the voids between larger particles. The volume of the resulting mixture is approximately 20% less than the combined volume of the original materials. Therefore, to estimate the volume of material to be composted, add together the volumes of the individual ingredients and multiply the sum by 0.80 (80%). TIM___170,880_ CY/YR x 0.8 = 136,704 CY/YR total combined material volume (TCMV) 1c. During composting, materials can lose one-­‐half or more of their initial volume. Part of this volume reduction represents the loss of CO2 and water to the atmosphere, and part of it occurs as loose, bulky raw materials are changed into crumbly, fine-­‐textured compost. Since the material on the pad is at all stages of decomposition, from fresh to ready-­‐for-­‐curing, the volume of material obtained from step 1b can be multiplied by an average shrinkage factor of 25% (multiply by 1-­‐.25). TCMV 136,704 CY/YR x .75 = 102,528 CY/YR total reduced volume (TRV) 1d. The faster you make compost the less space you need, since you can reuse that pad space. If the composting period is less than one year, multiply the total reduced material volume by the number of months in the composting period divided by 12. TRV 102,528 CY/YR x 4 months ÷ 12 months/year = 34,176 CY total adjusted volume (TAV) Sizing a Compost Pad Page 3 USCC Compost Operations Training Course Part 2. Calculate active pad size 2a. Calculate the cross sectional area of a single pile using the dimensions given for your scenario and the formulas provided for the cross sectional area on Page 2. 7 ft x 14 ft x 2/3 = 65 square feet 2b. Calculate the volume of a single pile. Volume equals the cross sectional area times the length. Length is limited by either site size or pipe length. Don’t forget to allow equipment lanes. Pile volume = cross-­‐section x pile length 66 ft2 x 350 ft = = 23,100 ft3 ÷ 27 cubic feet per cubic yard = 860 yard3 /pile 2c. Number of piles. The number of windrows or piles required equals the total adjusted volume (from step 1d) divided by the volume per windrow or pile (2b). Round up to a whole number. Number of windrows = total cubic yards ÷ cubic yards per windrow = 34,176 yd3 = 40 number of windrows (or piles) ÷ 860 yd3/windrow 2d. Pad length. For windrow systems, the length of the pad is the maximum site length. Pad length = 400 ft. (2d) Sizing a Compost Pad Page 4 USCC Compost Operations Training Course 2e. Pad width. Pad width equals the total width of piles across site plus the total width of aisles between piles, plus the equipment lanes. Number of aisles is one less than the number of piles. Total width of piles = width (base) of each pile x number of piles wide = 40 piles x 14 ft = 560 feet Total width of aisles = number of aisles x width of each aisle = (40 piles – 1) = 390 feet Total pad width = width of piles + width of aisles + perimeter space = 560 ft + 390 ft = 1,000 feet (2e) x 10 ft + (25 ft + 25 ft) 2f. Pad area = pad width (2e) x pad length (2d) = 1,000 ft = 400,000 square feet ÷ 43,560 ft2/acre = 9.2 acres x 400 ft OPTIONAL: Calculate the material processed per acre = TAV (1d) divided by 2f = 34,136 / 9.2 acres = ~3,700 cy /acre = amount at any one time = TIM (1a) divided by 2f = 170,880 / 9.2 acres = ~18,600 cy/acre/year = total amount processed per acre per year Sizing a Compost Pad Page 5