“Carpet”, or rather flooring, waste can be broken into a few sub categories. As a general rule this covers exactly what it sounds like, materials which “carpet” a floor. So underlay, carpet, laminate flooring, carpet tiles. Some carpet tiles are actually collected for separate recycling by some businesses, and carpet itself can be split into wool and nylon. These can both be used as Solid Refuse Fuel, but in other recycling operations are treated differently. Nylon is not biodegradable, so can be shredded for use as animal bedding, whereas wool will degrade over time, so is not a practical solution. If separated nylon can be recycled into new nylon for manufacturing, but at the current time the amount needed to make the process financially viable makes it uneconomical in the UK.
Most carpet waste goes for use as SRF to cement kilns and Waste-to-Energy plants, or land fill.