Environmental Engg.

Lesson-23 Introduction to solid wastes

Solid waste

Any solid material in the material flow pattern that is rejected by society is called solid waste.  All human activities viz., domestic, commercial, industrial, healthcare and agriculture generate solid waste.  The quantity and nature of the waste vary with the activity and with the level of technological development in a country.  Solid wastes are all the wastes arising from human and animal activities that are normally solid and are discarded as useless or unwanted. 

Solid waste is the term used to describe non-liquid waste materials arising from domestic, trade, commercial, agricultural, industrial activities and from public services. Wastes that arise from a typical urban society comprise of garbage, rubbish (package materials), construction and demolition wastes, leaf litter, hazardous wastes, etc.  If not managed properly, these wastes can have an adverse impact on the environment and public health arising from contamination of soil, water and pollution of air and through spread of diseases via vectors living on waste. The relationship between public health and the improper storage, collection and disposal of solid wastes is quite clear.  Because of their intrinsic properties, discarded waste materials are often reusable and may be considered a resource in another setting. Ecological phenomena such as water and air pollution have also been attributed to improper management of solid wastes

From the days of primitive society, humans and animals have used the resources of the earth to support life and to dispose wastes. In those days, the disposal of human and other wastes did not pose significant problems as the population was very small and the area of land available for the assimilation of such wastes was large. However, today, serious consideration is being given everywhere to this burgeoning problem of solid wastes. Rapid population growth and uncontrolled industrial development are seriously degrading the urban and semi-urban environment in many of the world's developing countries, placing enormous strain on natural resources and undermining efficient and sustainable development.

Solid waste management

Management of solid waste may be defined as that discipline associated with the control of generation, storage, collection, transfer and transport, processing, and disposal of solid wastes in a manner that is in accord withthe best principles of public health, economics, engineering, conservation, aesthetics, and other environmental considerations. In its scope, solid waste management includes all administrative, financial, legal, planning, and engineering functions involved in the whole spectrum of solutions to problems of solid wastes thrust upon the community by its inhabitants

Solid waste management in India

India, as any other developing country, is currently facing an acute problem in the management of Municipal Solid Wastes. Open dumping of waste is wide spread throughout the country. This is because of the mistaken belief that it is the easiest and cheapest disposal method. Also there is insufficient will and allocation of resources to improve the prevailing disposal practices. The deposition of wastes along roadsides and on riverbanks and on marginal lands and then 'hoping' it will go away is both naive and dangerous. It is inevitable that chemical and biological contaminants in waste will pollute the surrounding natural environment and find their way back to humans to affect health, quality of life and working activities. Thus, in the ultimate run the society has to pay dearly for open dumping.

Solid waste management has become a major environmental issue in India. The per capita of MSW generated daily, in India ranges from about 100 g in small towns to 500 g in large towns. The population of Mumbai grew from around 8.2 million in 1981 to 12.3 million in 1991, registering a growth of around 49%. On the other hand, Municipal Solid Wastes generated in the city increased from 3 200 tonnes per day to 5 355 tonnes per day in the same period registering a growth of around 67% (CPCB 2000). This clearly indicates that the growth in Municipal Solid Wastes in our urban centres has outpaced the population growth in recent years. This trend can be ascribed to our changing lifestyles, food habits, and change in living standards. Municipal Solid Wastes in cities is collected by respective municipalities and transported to designated disposal sites, which are normally low lying areas on the outskirts of the city.

Now-a-days the concern for solid waste management has increased and government has created lot of awareness among the public for proper separation of solid wastes at the source level itself, so that it will become easier for treatment / disposal.

Hazards of mismanagement of solid wastes

There are innumerable potential hazards due to the mismanagement of solid wastes.  It has the potential to pollute all the vital natural resources viz., land, water and air.  Some of the hazards caused by solid wastes are listed below:

• Environmental pollution from waste leachates and gas evolving from dumped solid waste

• Air pollution from smoke by burning of waste and health hazards to the people through inhalation of dust and smoke

• Health hazards to waste workers and pickers through direct contact with waste.

• Generation of noxious odours

• Promotion of micro organisms that cause diseases

• Attraction and support of disease vectors (rodents and insects that carry and transmit disease carrying micro-organisms)

• Unaesthetic appearance

• Poor living ambience

Functional elements of a solid waste management system

The following are the key functional elements for implementing a solid waste management system:

• source reduction

• onsite storage

• collection and transfer

• processing techniques

• disposal

The following flow chart describes the relationship between the key functional elements of a solid waste management system

Waste generation

Waste generation encompasses activities in which materials are identified as no longer being of value (in their present form) and are either thrown away or gathered together for disposal.

Waste handling, sorting and storage

Waste handling and sorting involves the activities associated with management of wastes until they are placed in storage containers for collection. Handling also encompasses the movement of loaded containers to the point of collection. Sorting of waste components is an important step in the handling and storage of solid waste at the source. For example, the best place to separate waste materials for reuse and recycling is at the source of generation. Households are becoming more aware of the importance of separating newspaper and cardboard, bottles/glass, kitchen wastes and ferrous and non-ferrous materials. On-site storage is of primary importance because of public health concerns and aesthetic consideration. Unsightly makeshift containers and even open ground storage, both of which are undesirable, are often seen at many residential and commercial sites.

Collection

It includes not only the gathering of solid wastes and recyclable materials, but also the transport of these materials, after collection, to the location where the collection vehicle is emptied. This location may be a material processing facility, a transfer station, or a landfill disposal site.

Processing and Recovery

The recovery of sorted materials, processing of solid waste and transformation of solid waste that occurs primarily in locations away from the source of waste generation are encompassed by this functional element.  Waste processing is undertaken to recover conversion products and energy. The organic fraction of Municipal Solid Waste can be transformed by a variety of biological and thermal processes. The most commonly used biological transformation process is aerobic composting. The most commonly used thermal transformation process is incineration.

Waste transformation is undertaken to reduce the volume, weight, size or toxicity of waste without resource recovery. Transformation may be done by a variety of mechanical (eg shredding), thermal (e.g. incineration without energy recovery) or chemical (e.g. encapsulation) techniques.

Transfer and Transport

It involves two steps: (i) the transfer of wastes from the smaller collection vehicle to the larger transport equipment and (ii) the subsequent transport of the wastes, usually over long distances, to a processing or disposal site. The transfer usually takes place at a transfer station.

Disposal

The final functional element in the solid waste management system is disposal. Today the disposal of wastes by landfilling or uncontrolled dumping is the ultimate fate of all solid wastes.  A municipal solid waste landfill plant is an engineered facility used for disposing of solid wastes on land or within the earth’s mantle without creating nuisance or hazard to public health or safety, such as breeding of rodents and insects and contamination of groundwater.

Municipal solid waste is a potential source of the following useful materials

• Raw material to produce manufactured goods

• Feed stock for composting and mulching  processes

• Can be used as a fuel