October 2012
4-45
4.9
Food Disposals
Equation 4-20. Water Use of Garbage Disposal (gallons per year)
= Flow Rate Through Garbage Disposal x Daily Use Time x Days of
Facility Operation
Where:
••
Flow Rate Through Garbage Disposal (gallons per minute)
••
Daily Use Time (minutes per day)
••
Days of Facility Operation (days per year)
Water Use After Replacement
To estimate the water use of a replacement food pulper, use Equation 4-20, substi-
tuting the flow rate of fresh water through the food pulper. Freshwater flow rate
through a food pulper that recirculates water for pre-rinsing is typically 2.0 gpm.
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Water Savings
To calculate the water savings that can be achieved from replacing an existing con-
ventional garbage disposal with a food pulper, identify the following information and
use Equation 4-21:
••
Current water use as calculated using Equation 4-20.
••
Water use after replacement as calculated using Equation 4-20.
Equation 4-21. Water Savings FromGarbage Disposal Replacement (gallons per year)
= Current Water Use of Garbage Disposal –Water Use of Garbage
Disposal After Replacement
Where:
••
Current Water Use of Garbage Disposal (gallons per year)
••
Water Use of Garbage Disposal After Replacement (gallons per year)
Payback
To calculate the simple payback from the water savings associated with replacing a
garbage disposal with a food pulper, consider the equipment and installation cost
of the food pulper, the water savings as calculated in Equation 4-21, and the facility-
specific cost of water and wastewater.
Because garbage disposals can use hot water, a reduction in water use could also
result in energy savings, which can further reduce the payback period and increase
the cost-effectiveness.
57
Ibid.
