During cremation, some bones don’t burn and must be pulverized in some sort of a pulverizer/grinder. Perhaps the body is processed in some kind of water processer, like one for food, where the processing occurs with water and the bones can be ground. However, a wood chipper would work quite nicely.
It could be that he will simply be buried unembalmed, in a simple wooden casket that has been filled with water. Or buried in a place that is below the water table. Or buried at sea.