A hazardous waste is a waste with properties that make it dangerous or capable of having a harmful effect on human health or the environment. The hazardous wastes are generated from many sources, ranging from household to industrial manufacturing processes and may come in many forms, including liquids, solids gases, and sludges. The harmful properties of the hazardous wastes are mainly three types:

• Physical hazards – potentially triggering explosion, fire, corrosion
• Health hazards – being irritative, toxic, cancerogenic, mutagenic to the human health
• Environmental hazards – damaging the soil, air, water, vegetation and the living organisms by their toxicity

Once generated, the hazardous wastes needs to be treated with care during collection, transportation, storage, pre-treatment and final recovery.

In most of the cases, the hazardous wastes cannot be recycled and in order all the dangerous (unknown for the nature and living organisms) chemical compound to be neutralized, they need to be decomposed – this can be done in very high temperatures (energy recovery or incineration).