Hazardous Waste: Meaning, Sources and Management

Read this article to learn about Hazardous Waste:- 1. Meaning of Hazardous Waste 2. Sources of Hazardous Waste 3. Classification 4. Management.

Meaning of Hazardous Waste:

According to USEPA, hazardous waste is defined as any solid, liquid or gaseous substance which, by reasons of any physical, chemical, reactive, toxic or infectious characteristics, causes danger to health or environment when improperly treated, stored, transported or disposed off.

Sources of Hazardous Waste:

Sources of hazardous wastes include industries, petroleum refineries, transportation, coke-ovens, blast furnace sludges, scrubbing sludges and biological waste generating laboratories, thermal and nuclear power plants and nuclear reactors etc.

Classification of Hazardous Wastes:

1. A simple approach to classify hazardous wastes is to consider these wastes into general categories such as toxic, inflammable and radioactive etc. Such a classification system helps the fire service to properly deal with the hazardous wastes under emergencies.

2. Many countries (e.g., UK, France, Germany and Netherlands) follow a Supplementary classification system for hazardous substances along with the general classification system. However, in Japan, the four types of wastes viz. sludges, slags, acidic waste and alkaline wastes, which contain any of the 9 materials (e.g., Cd, As, Hg, Pb, Cr (VI), CN, Se, PCBs and organic phosphates) beyond permissible limits, are considered to be hazardous.

3. The best way to classify the hazardous wastes is on the basis of algorithms that consider toxicity corrosivity, persistence, inflammability, quantity of waste involved, the extent of hazard to the environment and ultimate effects on living organisms.

4. In the US, the hazardous wastes are classified as per the Federal Register of May 19, 1980. The USEPA considers the following five basic criteria for classifying hazardous wastes:

(i) Whether the material falls under the category of solid wastes as defined by the Resource Conservation and Recovery Act of 1976? The term solid waste includes semi-liquids, liquids and contained gaseous materials as well.

(ii) Whether the waste has been legally discarded? This stipulation is applicable to the wastes that are stored or treated prior to disposal but not to those to be recycled.

(iii) Whether the waste is specifically excluded by the regulations? For instance, municipal solid wastes, agricultural wastes and animal manures are excluded.

(iv) Whether the waste has toxic or hazardous characteristics. That is, whether it has the potential to increase the mortality or illness or whether it poses a substantial threat to human health or environment on the basis of hazardous characteristics such as corrosivity, inflammability, toxicity or explosiveness.

As regards human toxicity, a waste is considered to be hazardous if:

(a) It has an oral LD 50 toxicity equal to or greater than 50 mg/kg (i.e., LD 50 is the lethal dose of the toxic waste at which 50% of the experimental animals die as a result of oral ingestion).

(b) It has an inhalation LC 50 toxicity of 2 mg/kg (LC 50 is the lethal ambient concentration of the toxic material in mg/L of air causing 50% mortality to test rats during 4 hour inhalation).

As regards the hazard to health or the environment, the following standard tests quantified by EPA are considered:

i. Ignitability that is, whether the waste causes or enhances fire.

ii. Corrosivity that is, whether the waste destroys the tissues or metal.

iii. Toxicity that is, whether the substance pollutes water supplies and threatens the health.

iv. Reactivity that is, whether the substance reacts violently or causes explosion.

As far as toxicity to the ground water is concerned, the 14 contaminants viz., 8 metals (Pb, Cd, Hg, As, Cr, Ba, Se, Ag), 4 pesticides (Lindane, endrin, toxaphene, methoxychlor) and 2 herbicides (2, 4-D and 2, 4, 5-T) are considered to be hazardous.

(v) Whether the waste is listed as hazardous?

Wastes which are known to be hazardous (carcinogenic and mutagenic etc.) but not amenable to Extraction Procedure Toxicity Test are listed in three categories.

(i) Spent solvents used for degreasing.

(ii) Process wastes from wood preservation or manufacture of halogenated hydrocarbons.

(iii) Discarded products like mercury compounds, toluene, xylene etc. and their containers.

Management of Hazardous Wastes:

The main objective of hazardous waste management plan is to eliminate or reduce the hazardous waste through process changes or resource recovery. The waste must be accounted for from its origin to ultimate disposal. This cradle to grave concept is followed by USA and Canada.

The major components of a hazardous waste management plan are as follows:

1. Inventory:

All the industries producing more than 100 kg of hazardous wastes per month should be registered. An inventory of such waste generating agencies and the quantity of waste produced per month should be prepared.

2. Storage:

The hazardous waste generating plants should equip themselves with special on-site tanks, chemically resistant containers or basins for storage of waste.

3. Transport:

The wastes must be transported by suitable tanker trucks, flat-bed trucks or rail cars of the approved disposal sites.

4. Spillage:

A well publicized emergency plan should be prepared to deal with unexpected spillage or accidental release of contaminants during transport to prevent environmental damage and public health hazard.

5. Disposal:

The wastes should be transported to a physical and chemical treatment plants for processing or concentration or hauled directly to an approved hazardous waste treatment facility for final disposal.

6. Waste Exchange:

When on-site recycling or recovery of waste is not feasible, the possibility of waste exchange should be explored. Transferring wastes from large industries to smaller ones which are able to reuse low purity oils, acids, alkalies, solvents or recover valuable metals and other materials from concentrated wastes, can also be considered.