Let's say I have the option to send my food scraps to either a composting site, or a biogas digester. Both are industrial scale, following best practices.
The output from each is high quality and replaces conventional product in the market, to the extent possible (i.e., humus from the compost operation is sold in stores, and biogas from the digester is used for heating and/or electricity production). Let's assume in both cases the quantity is insufficient to significantly distort the market (i.e., the biogas digester will offset some level of natural gas combustion, but won't put the power plant out of business).
Which of these two options is better for the environment? I'm most interested in CO2 emissions (or global warming potential), but would also be interested in data on toxicity, water use, air pollution, etc.
A few related questions which prompted this one: