GasIDs from Composting
Diverting food waste and green waste from landfills to composting facilities is a critical strategic initiative for reducing GHG emissions globally. For a comprehensive overview of the importance of composting to climate change, closing the loop on the carbon cycle, and its contribution to the quest for reaching global Zero Waste, see Carbon Credits section.
Calculating the avoided emissions (AE) from composting requires that we add an additional layer of understanding to the basic formula described in the GasID creation section. Because the work of composting involves mixing together different biowaste mass types (e.g. food waste and green waste) it is necessary to combine TRCs for each mass type in order to calculate the actual greenhouse gas emissions that were avoided. A composting mix ratio is determined for each mass type utilized at each composting facility in accordance with actual verified application on site. Because greenhouse gas emissions are not a linear relationship for composting mixes it is important to ensure this is properly measured.
As an example, a composting facility in San Francisco might use a 60% food-waste and 40% green-waste ratio, or (6/4), while another in Munich might use a 55% food-waste and 45% green-waste ratio, or (11/9) for its average composting mix. In order to calculate the GasIDs generated, TRCs are combined in accordance with the composting ratio of each facility. So for the examples above, the composting facility in San Francisco will combine 6 TRCs of food-waste and 4 TRCs of green-waste to calculate a GasID. And, for the facility in Munich the Carrot Fndn will wait until 11 food-waste TRCs and 9 green-waste TRCs are available before a GasID can be created. Establishing the right ratio of food-waste to green-waste is necessary to calculate the GHG emissions for the baseline (BE) and the real emissions (RE) of the facility.
And, like the example in the previous section, the first step to find the avoided emissions (AE) is to find the baseline emissions (BE). The equation mentioned is from the methodologies from the United Nations Framework Convention on Climate Change (UNFCCC), specifically the Clean Development Mechanism, TOOL04 for Emissions from Solid Waste Disposal Sites (SWDS).
For a breakdown of the coefficients and constants of this variable see Appendix.
In addition to requiring a ratio of Food Waste to Green Waste, this equation specifies constants for three distinct baseline scenarios depending on where the waste would have been disposed:
Landfill without methane burning,
Landfill with methane burning (flaring,) or,
Dump site.
For better understanding of the equations below, let’s use an example where a Brazilian composting facility in Rio de Janeiro’s municipality #1 utilizes the ideal ratio of 50/50 food-waste to green-waste in its composting mix. In this case, 1 TRC of food representing 1 ton of Food Waste and 1 TRC of green waste representing 1 ton of Green Waste is packaged to calculate the GHGs emissions avoided of 2 tons of composted biowaste with a 50/50 ratio.
Next, let’s define the baseline emissions (BE) for food and green waste composted at this facility. Let’s assume that in this region if the composted waste mass in the TRCs wasn’t composted it would have been disposed of through Scenario 1 (“Landfill without methane burning”). With this knowledge, the UNFCCC’s Baseline Emissions (BE) equation informs us that 2.451 tons of CO2 would have been emitted. In this case,
However, because the composting facility performed the important work of composting, these GHGs were not emitted. To determine the real emissions (RE) generated at the facility, the Carrot Fndn utilizes the UNFCCC’s CDM AMS-III.F, Tool 13, version 02.0, called “Project and leakage emissions from composting”. The equation is as follows:
For a breakdown of the coefficients and constants of this variable see Appendix
Project and leakage emissions from composting (PE) shown in the equation above is utilized by the Carrot Fndn to determine the Real Emissions (RE) from composting at Rio’s facility. Continuing with the example, the equation reveals that after composting the food waste and green waste from the TRCs and , the CO2 emissions would be 0.218 tons.
Now, the actual emissions (AE) can be calculated as follows:
This process is performed every time a food-waste and green-waste TRC combo can be established in accordance with the facility’s composting ratio.
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