- 1 Solid wastes
The waste materials which get accumulated in the environment for shorter or longer duration are termed solid wastes. These are the main source of soil pollution.
(1) Solid waste generally comes from residences, cattle sheds, industries, agricultural fields, and many other places.
(2) It includes peelings of fruits and vegetables, other kitchen waste, ash, paper, cow dung, human excreta, glass, plastics, leather and rubber articles, brick, sand, worn out clothes, and metal objects etc.
When accumulated, these heaps of solid waste make the surroundings dirty, and pollute the soil.
In the recent times, however, human population has increased tremendously and the technology has become greatly advanced. These two factors have contributed significantly in the deterioration of our environment. Advancement in the technology has resulted in improvements in our life styles and also has changed our attitudes. As a result, we have started using more and more of disposable articles thereby generating huge amounts of waste material.
Use of disposable plastic/paper cups in trains and Use of disposable materials in marriage and other parties are few examples.
Types of solid wastes
1. Biodegradable wastes
2. Non-biodegradable wastes
(1) Biodegradable wastes
These include substances such as household garbage, human urine and faecal matter (sewage), agricultural residues, cattle dung, wood, paper, cloth, hay, cotton, jute, tea leaves, cake, flowers, leaves, wool and several industrial wastes.
All these substances can easily be degraded by natural means (i.e., by the action of microorganisms such as bacteria and fungi of decay) into simpler, harmless substances in due course of time. Microorganisms such as bacteria and fungi of decay are present in abundance in our environment (air, water and soil). These secrete specific enzymes. The enzymes break down complex organic substances (present in biodegradable substances) into simpler, easily dissolvable substances. The latter reach the reservoir pool (air, water or soil) and are again available to autotrophs for photosynthesis.
Harmful effects of biodegradable wastes
These affect the human life in various ways :
(1) Decomposition of biodegradable wastes results in the production of foul smell which spreads to surrounding areas and makes the life miserable.
(2) Flies breed at huge heaps of solid wastes containing biodegradable substances, carry the germs and spread diseases such as diarrhoea, typhoid, tuberculosis, cholera, conjunctivitis etc.
(3) These biodegradable wastes may also block the drains, creating pools of water which become the breeding sites of mosquitoes. The latter are the carriers of diseases like malaria and dengue.
(4) Dumping of industrial wastes reduces the fertility of the soil leading to reduction in crop yields.
(2) Non-biodegradable wastes
In our daily life, we also generate lot of waste that can not be degraded by natural means, i.e., by the actions of microorganisms, into simpler, harmless substances in due course of time. Only physical processes such as heat and pressure can affect such type of waste substances.
Changes in the packaging technology in recent times have resulted in the generation of lot of non-biodegradable wastes.
Harmful effects of non-biodegradable wastes
(1) Some of the non-biodegradable substances such as pesticides (e.g., D.D.T.), industrial chemicals, heavy metals, and radioactive substances are very harmful. This is so because these enter the food chains and their concentration goes on increasing from one trophic level to the next As human beings occupy the top level in any food chain, the maximum concentration of these chemicals get accumulated in our bodies. As a result of biomagnification, these result in many harmful effects in human beings and other animals.
(2) Excessive use of fertilizers and pesticides, and dumping of industrial chemical wastes affects the soil fertility and subsequently reduces the crop yield. The soil, thus, may become acidic or alkaline.
Modes of Waste Disposal
Some prominent methods of waste disposal are :
5. Production of biogas and manure.
(1) Land fills
In urban areas, majority of the solid wastes are buried in low lying areas to level the uneven surface of land. This method of waste disposal is commonly called land fills.
(2) Recycling of wastes
(a) Paper is sent for recycling into special paper mills.(b) Broken plastic (e.g., plastic bags, buckets, bowls, dishes, mugs, disks, etc.) are sent to plastic processing factories where these are melted and then remoulded waste metals are sent to specific metal industries for recycling.
(c) Industrial wastes are treated in special plants where valuable wastes are recycled.
(d) Certain wastes are mixed to generate useful materials. For instance, molten plastic is mixed with asphalt and the material is used for making roads.
(3) Preparation of compost
Household waste such as peeling of fruits and vegetables, left-over food, fallen dead leaves of kitchen garden plants and potted plants etc. can be converted into compost and used as manure.
(4) Incineration or burning at high temperature
Incineration is the process of burning of substances at high temperature (usually more than 1000°C) and ultimately converting them into ashes. It is carried out in an incinerator. Household waste, chemical waste and hospital waste are generally disposed of by incineration process.
Bulk of waste is removed by this technique. Burning of waste at a very high temperature generates carbon dioxide and water vapours, which escape into the environment and only the ash is left behind.
This ash can be disposed of by land fills. In cities, municipal committees/corporations generally do large scale disposal of waste by incineration.