Over the transom just now came a press release about

The recycling company RGS90 in Copenhagen has developed a method for recycling waste water sludge: The sludge turns into an environmentally friendly blasting agent which saves a fortune. After that it can be used as insulation material. …

It sounds pretty good, but it should be noted that this device is basically an incinerator. As the press release continues:

Production takes place in a blast furnace where different adjustment products are added to the sludge after composting. It is then heated to around 2000° C. The high temperature makes the material liquid like lava. With shock cooling the material practically explodes into something resembling black gravel.

So, the blast material is basically the slag left after everything is burned up. It appears they are adding quite a bit of other material to the mix to come up with a useful product.