Section 18. As used in sections nineteen to twenty-four, inclusive, the following words shall have the following meanings:—

''Commissioner'', the commissioner of the department of environmental protection.

''Department'', the department of environmental protection.

''Residual waste'', solid waste or combination of solid wastes, which because of its quantity, concentration, or physical, chemical, or infectious characteristics may cause or significantly contribute to an increase in mortality or an increase in serious irreversible or incapacitating reversible illness, or pose a substantial present or potential hazard to human health or the environment when improperly treated, stored, transported, or disposed of or otherwise managed.

''Resource recovery facility'', a solid waste disposal facility utilizing processes for reclaiming the materials or energy values from solid wastes.

''Secretary'', the secretary of the executive office of environmental affairs.

''Sludge'', any solid, semisolid or liquid waste generated from a municipal, commercial or industrial wastewater treatment plant, water supply treatment plant, or air pollution control facility or any other such waste having similar characteristics and effects.

''Solid waste'', garbage, refuse, sludge from a waste treatment plant, water supply treatment plant, or air pollution control facility and other discarded material, including solid, liquid, semisolid, or contaminated gaseous material resulting from industrial, commercial, mining, and agricultural operations, and from community activities, but does not include solid or dissolved materials in domestic sewage, or solid or dissolved materials in irrigation return flows or industrial discharges, special nuclear, or radioactive byproduct material.

''Solid waste disposal facility'', incinerator, landfill, resource recovery facility, transfer station, composting plant, sorting or processing machine or plant, recycling plant, or other sanitary means of recycling or composting solid waste approved by the department, or any combination of one or more of the above facilities and appurtenant facilities.

''Storage'', when used in connection with residual waste, the containment of residual waste, either on a temporary basis or for a period of years, in such a manner as not to constitute disposal of such residual waste.

''Treatment'', when used in connection with residual waste, any method, technique, or process, including neutralization, designed to change the physical, chemical, or biological character or composition of any residual waste so as to neutralize such waste or so as to render such waste nonhazardous, safer for transport, amenable for recovery, amenable for storage, or reduced in volume. Treatment includes any activity or processing designed to change the physical form or chemical composition of residual waste so as to render it nonhazardous.