Use your own production records, or
Estimate using industry average loss rates (see example below)
Experts typically recommend at least 20 cubic feet of primary bin volume for every pound of daily average loss
The number and volume of secondary composting bins should equal that of the primary bins
Add at least 2 additional bins for dry storage of cover material
Maximum recommended loaded bin depth = 5 ft. (bin wall height 6 ft)
Select bin width at least 2X width of bucket on equipment that will be used to load and unload bins
This example is for the Iowa State Univeristy Bilsland Farm composter which is featured on this web site (see Tour Composting Facilities section for photos and operating data). The Bilsland Farm is a farrow to finish operation with 300 sows producing approximately 625 litters per year.
To size the composter the following assumptions were made:
- 12 pigs/litter born alive
- 9.5 pigs/litter weaned
- pre-weaning mortality averaged 3 lbs/pig
- nursery death loss is 2 percent averaging 25 lbs/pig
- finishing death loss is 2 percent averaging 150 lbs/pig
- breeding herd death loss is 3 percent averaging 350 lbs/animal
625 litters/yr * (12 pigs born alive 9.5 pigs weaned) * 3 lbs/pig = 4688 lbs/yr
625 litters/yr * 9.5 pigs weaned = 5938 nursery pigs/yr
5938 pigs * 2 % death loss * 25 lbs/pig = 2969 lbs/yr
5938 pigs * (1 2% nursery death loss) = 5819 pigs
5819 pigs * 2 % death loss * 150 lbs/pig = 17457 lbs/yr
Breeding herd mortality:
300 sows * 3 % * 350 lbs. = 3150 lbs/yr
Total annual herd mortality:
4688 lbs preweaning + 2969 lbs nursery + 17,457 lbs finishing + 3150 lbs breeding herd = 28,264 lbs/yr
Daily Mortalities = 28,264 lbs/ yr divided by 365 days/yr = 77.4 lbs/day
Size the primary bins by allowing 20 cubic feet per pound of daily mortality.
77.4 lbs/day * 20 cubic ft/lb = 1549 cubic ft of PRIMARY composting space and an equal amount of SECONDARY bin space.
Bucket width on skid loader that will be used to load/unload bins = 4 ft.
So bin width should be at least 2 X bucket width…… select 10 ft width
Try bin lengths of 10 and 12 ft, assuming 10 ft width and average loaded bin depth of 5 ft:
IF: 5 ft deep x 10 ft wide x 10 ft long = 500 cubic ft per bin …… so would need 3 to 4 primary bins to meet required primary capacity.
IF: 5 ft deep x 10 ft wide x 12 ft long = 600 cubic ft per bin …… so 3 primary bins meets 1550 cubic ft capacity required.
Use 3 primary bins 5 x 10 x 12
Use 3 secondary bins the same size
Provide 2 additional bins for dry cover material storage
Bin Layout Considerations:
IF space and traffic patterns allow, a bin layout that shares common walls (as shown below) reduces building material requirements, AND helps retain bin heat during cold weather.
To view the facility which resulted from the design calculations shown above, visit the composting demonstration site located at the Bilsland Swine Research Center.
Department of Agricultural & Biosystems Engineering, Iowa State University