Cash for ash pellets were simple wood pellets.
Creating pellets from waste is far from simple. There was a government research laboratory working on for decades before giving it up as a bad job.
First you have to sort the waste - ideally to remove recyclables, but as a minimum to remove anything that will produce unacceptable levels of toxins, or that will explode during processing or burning (such as batteries).
After sorting you're left with a mix of materials and particle sizes that varies unpredictably from batch to batch. Extruding machines for pellet manufacture do not like variability - you need consistent moisture levels, hardness, size of pieces, fibrousness etc. Just getting pellets that will consistently hold together is difficult enough. Getting ones that will burn consistently, with a predictable heat output, without creating too much residue, soot or other pollution, and that can be produced at an economically viable cost is nigh on impossible.