They give a good explanation here: http://www.saaea.org/waste-to-energy.html
But basically it’s this:
a) organic waste in a landfill releases CO2 and other gases in an uncontrolled way.
b) take that same organic waste and burn it, you can control the emitted gases and recycle what you can.
c) Since they are burning the organic waste they created and are planting for next season, the gas CO2 emissions are recycled and the net CO2 is much lower than the CO2 transmitted by trucks hauling the waste combined with natural uncontrolled CO2 emissions from the landfill.
Releasing CO2 that was trapped underground in oil/coal for millions of years burned to create energy added to natural uncontrolled CO2 from the landfill…