Hazardous waste may be defined as wastes or a combination of the wastes that pose a substantial present or potential threat to human health or living organisms because:
1. Such wastes are non-degradable or persistent in nature;
2. They can be biologically magnified;
3. They may otherwise cause or tend to cause cumulative detrimental effects.
From practical standpoint, wastes are categorized into five groups. These are:
a. Radioactive substance;
b. Toxic chemicals(acids)
c. Hazardous biological wastes (hospital wastes);
d. Flammable wastes (oil);
e. Explosives (ordinance materials).
Collection, processing, treatment and disposal of hazardous wastes:
The hazardous waste is collected in sealed container to deliver it to a treatment or disposal facility. The processing of hazardous waste in undertaken for recovering useful materials and for preparing the waste for disposal. The treatment of such waste can be accomplished by physical, chemical, thermal or biological means depending upon the nature of wastes. Most hazardous waste and disposed of either near the surface or by deep burial. In some cases, they are disposed into controlled sanitary landfill sites.