Can we re-use the ash from burning waste?

Yes.  There are two types of ash that come from thermal treatment – one is known as incinerated bottom ash and that's the majority of it which is the clinker that drops out of the bottom of the furnace if you like.  That can be safely recycled and used as good quality aggregate and that happens already.  They take the metals out, any metals that are left in it, and again those various metals are recycled.  The bottom ash itself is used as aggregate for road building, for block making, et cetera.

The interesting bit and where the science bit comes in, I guess, is the other type of ash - known as air pollution control residue - which is where you've injected lime and carbon, and things, to remove any pollutants.

Increasingly, we’re looking to re-use that particular type of ash in the manufacture of gypsum or the replacement of gypsum for gypsum board and such like.  So, science is being applied to look at new ways of recycling that because everything about both thermal treatment and energy recovery as well as the rest of the waste and recycling industry these days is all about getting the most resource efficiency that we can out of all the materials we use as a society.