Waste processing system, for performing a waste processing process, the system including a shredder, a grinder and a steam explosion device such as a cooking extruder. The waste processing system is used to process raw waste, such as consumer waste, into an end product such as pellets. The waste processing includes an acid treatment step to sanitize, purify and/or increase a cellulose content of the waste. The acid is preferably a weak acid and/or an organic acid.