Why Compare Composting and Garbage Disposals?
Many households dispose of vegetable peels, coffee grounds, and plate scrapings using an in-sink garbage disposal. These devices grind food waste with an electric motor while cold water flushes the slurry into municipal sewer systems. The process is convenient but consumes electricity and water with every use. In regions facing drought or high electricity prices, the cumulative cost over years can be surprising. Moreover, sending organic matter into the waste stream eliminates a valuable resource: compost. A backyard or countertop compost bin can transform the same scraps into nutrient-rich soil amendment for gardens and houseplants. Yet composting requires small investments of money and time. This calculator weighs those competing factors so you can choose the most economical and sustainable method.
The choice between a garbage disposal and composting has broader environmental implications. Composting keeps organic material out of landfills, reducing methane emissions, while garbage disposals contribute to increased load at wastewater treatment plants. Utilities sometimes discourage disposal use during peak water stress because each operation requires a continuous stream of tap water. On the other hand, composting can attract pests if done improperly and demands periodic turning or collection. By quantifying both the monetary and ecological trade-offs, this tool helps you select a method aligned with your budget and values.
How the Calculation Works
The model assumes you run the disposal once per day to handle the weekly quantity of scraps. Each cycle consumes a fixed amount of electricity and water. The annual operating cost is the sum of the water bill and energy bill attributable to those cycles. For composting, the main cash expense is the initial bin or tumbler purchase, spread evenly across the number of years you plan to use it. Labor, worms, or optional carbon-rich bulking agents are not monetized but can be noted in the limitations. The output shows the annual cost for each approach and their difference.
The total disposal cost per year Cd is derived as:
Where is the number of uses per year, is water per use in cubic meters, is water cost per cubic meter, is energy per use in kWh, and is electricity cost per kWh. The annual composting cost equals the bin cost divided by years of use. The difference presented in the result is .
Worked Example
Consider a family that processes about 3 kilograms of scraps per week. Their garbage disposal draws 0.5 kWh and uses 10 liters of water each time it runs. If they run it daily, that is 365 cycles per year. At an electricity price of $0.20 per kWh and water cost of $2.50 per cubic meter, the annual disposal cost becomes 365 × (0.010 m³ × $2.50 + 0.5 kWh × $0.20) = $73.00. For composting, a durable outdoor bin costs $80 and is expected to last 5 years, giving an annualized cost of $16.00. The difference is $57.00 in favor of composting. The result also suggests that composting avoids roughly 3 × 52 = 156 kilograms of waste water processing annually.
Scenario Comparison
The following table shows how costs shift with different water and energy rates, assuming one disposal use per day consuming 0.5 kWh and 10 liters of water, and a $80 bin lasting five years.
| Water Cost ($/m³) | Energy Cost ($/kWh) | Annual Disposal Cost ($) |
|---|---|---|
| 1.00 | 0.10 | 36.50 |
| 2.50 | 0.20 | 73.00 |
| 4.00 | 0.30 | 109.50 |
A second table explores different bin prices and lifespans to show how frugal or upscale compost setups influence the break-even point.
| Bin Cost ($) | Years of Use | Annual Compost Cost ($) |
|---|---|---|
| 40 | 3 | 13.33 |
| 80 | 5 | 16.00 |
| 200 | 10 | 20.00 |
Limitations and Assumptions
The calculator treats compost bin cost as the only expense for composting. It does not assign monetary value to labor, browns like shredded paper, or potential savings from reduced fertilizer purchases. Likewise, garbage disposal costs exclude device depreciation or plumbing repairs. Water usage per disposal cycle varies by model and user habits; some people run the water longer for safety or cleaning, raising costs. Energy consumption also depends on motor power. Real-world savings may be higher if disposal use is more frequent than once per day or if compost prevents trash bag purchases.
Environmental benefits are generalized. Not all municipalities handle sewer sludge in the same way, and some may capture biogas for energy. Composting could emit methane if piles are not aerated. Users should research local regulations, as some areas restrict backyard composting or mandate food scrap separation. This tool focuses on household-level economics and simplifies complex ecological impacts into a cost difference.
Further Reading
For more insight into the value of composting, explore the compost ROI calculator which quantifies fertilizer savings, or compare municipal collection options using the home composting vs municipal food waste service calculator.