The most commonly used conversion methods – combustion of waste to produce heat or electricity; anaerobic digestion to produce methane for heat or power production etc. all are well-established and commercial technologies. A further set of conversion processes – for example, the production of liquid fuels from cellulosic materials by biological or thermochemical conversion processes, such as pyrolysis – are at earlier stages of commercialisation or still under development.

According to the EC (19 November, 2008) “waste means any substance or object which the holder discards or intends or is required to discard.” Recycling materials and products – that are considered waste - is an ancient practice which shows that in times of resource scarcity (i.e. shortage of virgin materials) societies attach more economic and societal value to their own waste. This implies that throughout time the definition of waste can change as well. Generally speaking longer use or re-use of materials and products this is often mainly to cover a society’s needs.