I have some compost material from a group of homes, if I wanted to sell them to organic farmers, will steam treating them kill all the weed seeds inside it?
The composting process should result in high temperatures (over 130 Fahrenheit) for at least 3 days in a row. If you achieve that, and maybe more days, then weed seeds should be killed by that process already. Commercial composters will lay out their compost in a small area like 10 square yrds and add water for a few days to cause germination of any seeds in the mix. If seeds start germinating then that has to be disclosed to the purchaser and some other method, like steaming it, I guess, should be used to fix the problem.