The term ‘solid waste’ refers to any unwanted solid material that can no longer be used. Solid waste is generated due to human, commercial, agricultural, and industrial activities. Almost every activity associated with us humans leaves behind some waste. Solid waste is not only limited to solid materials. Some solid wastes also contain some gaseous matter in them and also include semi-solid matter. They can be categorized according to their:
Origin: whether the waste has been discarded from home, from a factory, from a construction site, etc.
Content: whether the waste contains glass, metals, plastic, etc.
Hazard: whether the waste is inflammable, toxic, radioactive, poisonous, etc.
In a metro city such as Mumbai, a person on average generates 0.8 kg of waste every day. In India, the generation of municipal waste has been estimated at 68.8 million tons annually. Generally, waste generated in cities contains 50% of organic material, 21% of inert material, 17% of recyclable material, and 11% of hazardous material. However, a recent study found that 40% of all waste is not collected by municipal bodies at all. This waste can be found littering water bodies and in drains. They interfere with the functioning of sewage drains and cause choking and congestion of pipes. Not only that, but they also pollute and release toxins into the water.
Types of Solid Waste
Based on its source, waste can be classified into three types:
1. Municipal Solid Waste:
This includes waste from residential and commercial units and non-hazardous waste from construction sites. It also includes sanitary wastes. Generally, Municipal Solid Waste is a term used to describe all waste from cities, towns, and villages. These wastes require to be routinely collected and transported to a disposing facility or landfill. Municipal Solid Waste is not hazardous. The contents of the waste usually include wet garbage (food waste), newspapers, plastic packaging, tetra packs, pieces of metal, cardboard, etc.
2. Industrial Waste:
Industrial waste is generated from industries that process and package food, chemical and pharmaceutical industries, fertilizer industries, paper industries, plastic industries, etc. These wastes contain toxins and need to be treated before being disposed of. If not treated appropriately, it affects the health of people living around industries. They are at the risk of developing diseases of the nervous system, skin diseases, and sometimes even cancer. The entry of toxins from wastes into water bodies can cause damage to fish communities and fluvial ecosystems. They also contaminate groundwater.
3. Hazardous Waste:
Hazardous wastes are described as those wastes that are hazardous to humans and the environment. Waste is classified as hazardous if it contains:
Highly reactive material
Infectious material (such as waste from hospitals).
Hazardous waste is generated from companies that manufacture chemicals, petroleum, plastics, etc. Hazardous waste is also generated in hospitals. They most often contain heavy metals like mercury, lead, and arsenic. The most serious problem regarding the disposal of hazardous waste is the contamination of groundwater. The contamination of groundwater caused by hazardous waste is irreversible. When humans consume this water, they are at risk of developing kidney and liver disease. The contaminated water can also cause reproductive failure in mammals and birds.
Sources of Solid Waste
There are 6 main sources of solid waste. Let’s go through them one by one and also look at the content of the wastes each source generates.
The waste generated from this source consists of food, old electronics, cardboard, clothes, paper, plastics, metals, glass, batteries, and other household waste.
This source generated waste such as packaging, food, hazardous waste, ash, and construction and demolition material.
Commercial waste is waste from office buildings, shops, markets, restaurants, hotels, etc. Commercial waste consists of paper, plastics, cardboard, food waste, metals, glass, and some hazardous waste.
4. Construction sites
Here the waste is composed of wood, concrete, steel, dirt, ash, and other construction or building material.
5. Manufacturing processes
The sources of waste here include refineries, mineral extraction plants, power plants, chemical plants, etc. They generate scrap material, packaging, unfit products, hazardous waste, etc.
All waste associated with agricultural activities comes under agricultural waste. Agricultural waste is generated from vineyards, orchards, dairies, and farms. It includes spoilt food, hazardous waste like fertilizers and pesticides, irrigation equipment, etc.
Composition of Solid Waste
The composition of solid waste in different parts of a country is a reflection of that region’s income, cultural practices, social developments, climate, geographical location, standard of living, and socio-economic conditions. Therefore, there will be a variation in the composition and characteristics of waste throughout the world. However, some general observations can be made:
A major part of the waste is composed of paper and organic matter.
Ceramics, plastic, dirt, wood, metal, glass, and textiles are also usually present.
Even within a particular community, waste generated can vary depending on a person’s socio-economic status. This is so because waste produced by an individual or a family is highly dependent on income, which in turn influences lifestyle and consumption patterns.
A study on the waste generated by countries of different income levels made the following observations:
With an increasing national income, the amount of paper waste also increases.
The amount of organic (food) waste is lower in countries with higher incomes. At the same time, countries with lower incomes generate a higher amount of food waste.
The geographical location of a country plays a significant role in the type of waste the country generates.
Countries of low income generally produce a larger amount of waste as compared to countries of high income.
Properties of Solid Wastes
The knowledge of the physical properties of solid wastes helps disposing centres select appropriate equipment for the disposal of wastes. The following are some of the physical properties of solid waste:
It is the mass per unit volume of waste, and its unit is kg/m3. Density plays an important role in procuring the right type of systems and equipment for the storage and transport of waste.
The moisture content of waste is the ratio of the weight of water to the weight of waste. Higher the moisture content, the higher the weight of solid waste. Moisture content plays an important role in the incineration of waste. A higher amount of energy will be needed to incinerate waste with high moisture content. This happens because more energy is needed to evaporate water from the wastes.
Permeability is an important factor in determining the movement of gas and liquid through wastes in a landfill. It depends on the surface area and porosity of waste. The porosity of municipal waste typically ranges from 0.40 to 0.67. The porosity of waste depends on its composition.
Lipids include fats, oil, and grease. The main source of lipids is cooking oil. Lipids are biodegradable. They have a high heating value which makes them suitable for use in energy recovery processes.
These are generated from food that is rich in cellulose and starch. They are easily biodegradable and break down into carbon dioxide, water, and methane. However, its decomposition attracts flies and rats.
Proteins are found in gardens and in food waste. They contain oxygen, nitrogen, carbon, and hydrogen. When decomposed, they produce amines which give out a foul odour.
The chemical properties of wastes are important to understand the behaviour of wastes through a management system. Some examples of chemical properties are:
pH determines the acidity of wastes. The pH of fresh, solid waste is usually 7. As solid wastes decompose, they become more acidic in nature.
Toxicity is defined as the presence of pesticides, heavy metals, insecticides, etc. Toxins can be present in wastes generated from industries. It is important to regularly check waste for toxins as they can reach out and contaminate nearby water bodies.
Integrated Solid Waste Management
Integrated Solid Waste Management (ISWM) is a program that focuses on the prevention of waste, it’s recycling, composting, and disposal. ISWM works on the recycling and management of solid waste so that its disposal does not affect public health and the health of the environment. It involves the assessment of local and community needs. It selects and creates appropriate waste management systems based on those needs. Key ISWM includes waste prevention, composting, recycling, and disposal. The disposal of waste must take place at a properly designed and managed facility.
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