Biological recycling: Composting and digestion

With biological recycling, greenhouse gas emissions can be reduced when using composting or digestion instead of landfilling. Composting organic waste saves 0.25 MTCE/ton (metric tons of carbon-equivalents). In 2021, 748 280 tons of organic waste were treated through biological recycling in Sweden.

1. Calculate how much carbon dioxide can be taken care of if all organic waste is composted (rather than landfilled). Compare the handled amount of carbon dioxide with carbon dioxide emissions from car traffic. Assume that an average car emits 140 g of carbon dioxide per km and that the annual distance per car is 15,000 km. Carbon dioxide savings from composting equals the carbon dioxide emissions of how many cars?

2. The advantage of digestion is that biogas (mixture of methane and carbon dioxide) is produced through the process. After upgrading (carbon dioxide is removed), biogas can be used as vehicle gas in traffic.

A. How many cars can we power if we treat all organic waste from 2021 through digestion?

We produce 0.126 m^3 of biogas per kilogram of organic waste. Biogas has a methane content of 67.6%. A gas car consumes 0.04 m^3 of natural gas (approx. 100% methane) per km. As in task A, we assume that the annual distance per car is 15,000 km.

B. How do you value the contribution of biogas from all organic waste in Sweden in relation to the Swedish energy supply? Why invest in digesting organic waste?