1 Waste – types and classification

Dr. Yogalakshmi K. N

epgp books

 

Objectives:

 

1.      To familiarize the definition of waste

 

2.      To gain knowledge on classification of waste based on physical state

 

3.      To understand to differentiate and categorize waste into different groups

 

 

Waste is defined as any unwanted or unusable substance that is discarded after primary use. Wastes are normally generated as a result of human and animal activities. Urbanization and rapid advancements in industrialization has led to an increase in the production and consumption processes resulting in the generation of wastes from various sectors that include agricultural, commercial, domestic, industrial, institutional, social and from community activities. Over time, these waste accumulate and can have real impacts on the health and the environment. Waste management is intended to reduce adverse effects of waste on health, the environment or aesthetics. So to carry out efficient management of wastes, knowledge about the source of wastes, its types and classification must be known. Hence, this module gives us an overview about wastes and its classification.

 

Classification of wastes

 

Wastes are commonly classified based on the physical state as solid wastes, liquid wastes and gaseous wastes.

 

Solid wastes are any discarded or abandoned materials that can be solid, liquid, semi-solid or containerized gaseous material discarded by the human society. These include urban wastes, agricultural wastes, biomedical wastes and radioactive wastes. The term refuse is also used for solid wastes.

 

Examples of solid wastes include waste tires, septage, scrap metal, latex paints, furniture and toys, garbage, appliances and vehicles, oil and anti-freeze, empty aerosol cans, paint cans and compressed gas cylinders, construction and demolition debris, asbestos, plastics, styrofoam containers, bottles etc.

 

Liquid wastes : Liquid wastes can be defined as liquids/fluids that are generated from washing, flushing or manufacturing processes of the industries. They are also called as sewage. The most common practice of disposing liquid waste is to discharge it in ground or rivers and other water bodies without treatment.

 

Examples: domestic washings, chemicals, oils, waste water from ponds, Wastewater from manufacturing industries, manure, waste oil, fats, oils or grease (FOG), used oil, and hazardous household liquids.

 

Figure 1 Classification of waste based on their physical state

 

Gaseous wastes

 

It is a waste product released in the form of gases from automobiles, factories, industries, burning of fossil fuels etc and get mixed in the atmosphere. These gases include carbon monoxide, carbon dioxide, sulphur dioxide, nitrogen dioxide, ozone and methane etc.

 

Classification of solid wastes

 

It is mandatory to classify solid wastes into groups that pose similar risks to the environment and human health for safe disposal. According to the modern systems of waste management, solid wastes are classified based on their source, type, properties and its effect on human health and environment.

 

Source based classification

 

Wastes are produced from different sources and are categorized as follows

 

Municipal solid waste (MSW)

 

Municipal solid waste commonly referred to as trash, garbage or refuse comprises of street wastes, dead animals, market wastes, abandoned vehicles, household garbage, rubbish, construction and demolition debris, sanitation residue, packaging materials, trade refuges etc. They are collected from residential houses, markets, streets and other places mostly from urban areas and disposed of by municipal bodies. The proportion of different constituents of municipal wastes vary from place to place and season to season depending on the food habits, life style, standard of living and extent of commercial and industrial activities in the area. Municipal wastes their contents and source are illustrated in table given below. Municipal solid wastes are further categorized based on their physical, chemical and biological properties

 

Industrial wastes

 

Wastes generated during industrial activities such as manufacturing and processing involved in chemical plants, paint industry, cement factories, metallurgical plants, thermal power plants, petroleum, coal, gas, sanitary, textile, food processing and paper industry are referred to as industrial wastes. Some examples of industrial wastes are chemical solvents, paints, sandpaper, paper products, industrial by-products, metals, and radioactive wastes. Industrial solid wastes are further classified as hazardous and non-hazardous wastes.

 

Institutional/ Commercial wastes

 

Solid wastes originating from administrative, educational and public buildings such as offices, schools, colleges, hospitals, government centres, prisons and other commercial establishments like wholesale and retail stores, restaurants, hotels, markets, warehouses. Paper, cardboard, plastics, wood, food wastes, glass, metals, special wastes, hazardous wastes are the examples of industrial and commercial wastes

 

Agricultural wastes

 

Agriculture wastes includes both natural (organic) and non-natural wastes generated through farming activities. These activities include but are not limited to dairy farming, horticulture, seed growing, livestock breeding, grazing land, market gardens, nursery plots, and even woodlands. Some of agricultural wastes include spoiled food grains, vegetables, animal and plant wastes, litter, pesticides, fertilizers etc. Other agricultural wastes are produced from agricultural products processing industries like sugarcane factories, tobacco processing units, slaughter houses, livestock, poultry etc. Agricultural wastes are mostly biodegradable but few wastes like pesticide and fertilizers are toxic. When discharged to the environment, agricultural wastes can be both beneficial and detrimental to living matter.

 

Table 1 Types of wastes with examples

 

Biomedical wastes

 

Wastes produced from hospitals, medical centres and nursing homes are called biomedical wastes. Hospital wastes are generated during diagnosis, treatment or immunisation of human beings/animals or in research activities in these fields or in the production/testing of biologicals. These wastes are highly infectious and may pose severe threat if not managed properly. Biomedical wastes may be solid or liquid wastes that includes discarded blood, sharps, soiled wastes, disposables, anatomical wastes, cultures, discarded medicines, chemical wastes etc.

 

Type based classification

 

Garbage

 

Garbage wastes mean and include animal and vegetable wastes generated from kitchen, cooking, serving of foods, slaughter houses, market refuse. These wastes contain putrescible organic matter which produces strong odour. They attract rats, vermins, flies and other insects and so they requires immediate attention in handling and disposal.

 

Rubbish

 

Solid wastes arising as a result of households, commercial and institutional activities excluding garbage and ashes is termed as rubbish. They are categorized into combustible and non-combustible wastes. Combustible wastes consists of all rubbish and refuse that can be incinerated to flames at 1400-1500◦F which includes leaves, plants, clothes, paper, leather, rubber, grasses. Non-combustible wastes are characterized as wastes that cannot be incinerated to flames at 1400-1500◦F and that includes glass, metals, plastic materials, stones, auto parts etc.

 

Bulk waste

 

Bulky household wastes consists of household furniture; appliances such as stoves, washing machines and refrigerators; mattresses and springs, rugs, TV sets, water heaters, tires, lawn mowers, auto parts, tree and brush debris etc.

 

Commercial bulky wastes include packaging and containers such as cardboard, wood boxes, fiber, plastic and steel drums, loose and bundled paper, bundles of textiles and plastics, wires, furniture and equipment etc.

 

Industrial bulky waste includes crates, cartons; steel, fiber and plastic drums; bales and rolls of paper, plastics, and textiles; miscellaneous metal items etc.

 

Ashes

 

Ashes are defined as fine powdery residues, cinders and clinkers arising from the burning of wood, coal, charcoal, coke and other combustible materials during cooking and heating in houses, institutions and outer industrial establishments.

 

Figure 2 Classification solid waste based on source of generation, type and physio-chemical property

 

Street wastes

 

Wastes comprising of leaves, dirt, dust litter, paper, plastics and other vegetable matter collected from streets, walkways, alleys, parks, beaches and vacant lots are termed as street wastes.

 

Dead animals

 

Animals that die naturally or accidentally comprises of dead animal wastes. They are categorized as small animals such as cats, dogs, rats, rabbits, poultry and large animals like horses, cows, goats, Sheep etc. However, animal carcasses and animal parts from slaughterhouses are excluded from dead animal wastes and considered as industrial wastes. These dead animal wastes are putrescible and attract flies and other vermin posing severe health risk to the environment. Hence they must be collected and disposed off promptly.

 

Construction and demolition wastes

 

Construction and demolition wastes are the waste materials generated in large amounts during the construction, refurbishment, repair and demolition of houses, commercial buildings, roads and other structures. They consists of earth, stones, concrete, bricks, lumber, steel, roofing materials, plumbing materials, heating systems and electrical wires.

 

Sewage wastes/sludge

 

Settled solid components, residual or semi-solid materials that are discharged from sewage treatment plants and septic tanks are classified as sewage waste. The raw and the treated sewage consist of organic and inorganic fraction. The sewage wastes contains putrescible organic matter which may contain pathogens and so must be disposed off without delay.

 

Plastics

 

Plastic due to their versatile property of being light, durable, easy to mould and economical has invaded almost all sectors of the economy. Likewise, they are generated as wastes from almost all sectors that includes agriculture, construction, consumer goods, household, health care, hotel and catering, packaging, telecommunications, air and travel industries. Some of the plastic wastes include carry bags, bottles, plates, spoons, glasses, gloves, boxes, syringes, catheter tubes, surgical items etc. Plastics due to its non-biodegradable nature are now considered a serious threat to the environmental and health.

 

Mining wastes

 

Mining wastes are generated from extractive operations of mineral resources. They include materials such as topsoil, overburden and waste rock that must be removed to gain access to the mineral resource. Also, other waste material like slags, mine water, mine tailings, water treatment sludge and gaseous wastes etc are released during or after processing of mineral ores. Some of these wastes are inert and are not considered as threat to the environment. However, other fractions, generated by the non-ferrous metal mining industry contains large quantities of dangerous substances such as heavy metals. These metals and metal compounds after extraction and subsequent mineral processing, tend to become chemically more available resulting in the generation of acid or alkaline drainage. Therefore, mine wastes requires to be carefully characterized to prevent and minimize air, water, and soil contamination.

 

Radioactive wastes

 

Radioactive wastes are hazardous, by-products of nuclear reactions. They pose severe threat to human life and environment. Radioactive wastes decays over time ranging from a few days for highly radioactive isotopes to millions of years for slightly radioactive ones. Hence, these wastes have to be isolated and confined at appropriate disposal facilities for it to completely decay. The sources of radioactive wastes are from mining of radioactive substances, atomic explosion, nuclear fuel cycle, nuclear weapons reprocessing, medical and industrial wastes etc.

 

Property based classification

 

Solid wastes are also classified based on their biological and chemical property.

 

Biodegradable / Organic wastes

 

Biodegradable wastes are those that can be decomposed by the natural processes such as composting, aerobic/ anaerobic digestion and converted into the elemental form like carbon dioxide, methane, water or simple organic molecules. Some of the biodegradable wastes include municipal solid wastes (green waste, food waste, paper waste, biodegradable plastics, human and animal wastes, sewage, sludge, slaughter house wastes etc).

 

Non-biodegradable /inorganic wastes

 

Non-biodegradable wastes are those that cannot be decomposed and remain as such in the environment indefinitely. They are persistent and threaten to overwhelm landfills and create disposal problems creating environmental concern. As non-biodegradable wastes cannot be decomposed, recycling is the ideal option for managing it. Example of non-biodegradable wastes includes plastics, nuclear wastes, glass, rubber tyres, styrofoam, fiberglass and metals.

 

Hazardous wastes

 

Hazardous waste is defined as chemical material that can no longer be used for its intended purpose and is known to be harmful or potentially harmful to plants, animals and human health or to the environment. Hazardous wastes may be in the form of solids, liquids, sludge’s or gases. In some cases, although the active agents may be liquid or gaseous, they are classified as solid waste because they are confined in solid containers. They are generated primarily by chemical production, manufacturing and other industrial activities. The hazardous waste materials may be toxic, reactive, ignitable, explosive, corrosive, infectious or radioactive. If improperly handled, they can cause substantial harm to human health and to the environment. So good management practice should ensure that hazardous wastes are collected, stored, transported and disposed off separately, to render them innocuous. Some of the important hazardous wastes are lead, mercury, cadmium, chromium, many drugs, leather, pesticides, dye, rubber, solvents, paints and effluents from different industries.

 

Non-hazardous wastes

 

Non-hazardous wastes are defined as substances safe to use commercially, industrially, agriculturally or economically. Some of the non-hazardous wastes produced are from the food processing plants, cotton mills, paper mills, textile mills and sugarcane industries. Other non-hazardous wastes includes paint, oil, antifreeze, buffers, salts etc.

 

Summary

  • To summarize, at the end of this module we have studied about
  • definition of waste
  • classification of waste based on the nature as solid, liquid and gaseous waste definition of municipal solid waste
  • source and type based classification of solid waste
you can view video on Waste –types and classification

Reference