I used to work for a company that made these, back in the 80s and sold them all over the world. I have always been curious what happened to the pressed / dewatered end product. Obviously it is fairly inert, but would contain certain contaminants, bacteria and a percentage of fat, so would have to be disposed of in a manor that wouldn't cause pollution. I guess it could be incinerated, but it would have a very low calorific value, so would have to be burned alongside a more combustible fuel source.
