Human activities related to livelihood and welfare generate waste. All wastes are pollutants and they create pollution in one way or other. Fundamentally air, land and water pollution results mostly due to improper disposal of wastes.
These are wastes capable of being removed or degraded by biological or microbial action. Waste from agricultural products, animal wastes and waste from food processing, leather, fibre, paper and wood etc. come under this group.
The substances which are normally not acted upon and decomposed by microbes are non-bio degradable wastes. It includes mineral waste, mining waste and industrial waste and non-degradable metallic and plastics substances.
It includes municipal waste and industrial waste. Municipal waste contains household garbage, piles of food scrapes, old newspaper, discarded and throw away materials, glass, cans, old appliances, broken materials, leather shoes, fibres, plastics and others. Construction waste materials, packaging materials, sewage, hospital waste, junk and vehicles are varied types of urban wastes. All these wastes are found in the form of semisolid, solid, semiliquid, sludge and in fly ash form.
Hazardous wastes may remain dangerous for thousands of years. The hazardous waste include radioactive refuse, metallic compounds, organic solvents, acid asbestos, organic cyanides, pathological hospital wastes, disposable medical equipments and tools.
The following methods are adopted for the disposal of hazardous wastes.
1. Land fills : There are permanent storage facilities for military related liquid and radioactive waste materials in secured lands. High level radio active wastes are stored in deep underground storage.
Wastes are carefully contained to prevent cross - mixing of reactive substances. The land fill is capped with impervious clay to prevent infiltration and percolation of water through the fill. Fill bottom is lined and provided with drainage system to contain and remove any leakage that occurs. Monitoring the wells provides a final check.
2. Deep - well injection : It involves drilling a well into dry, porous material below groundwater. Hazardous waste liquids are pumped into the well. They are soaked into the porous material and made to remain isolated indefinitely. However fractures in the impermeable layer may permit the injected wastes to escape and contaminate ground water.
3.Surface impoundments : This method is used to dispose large amounts of water carrying relatively small amounts of chemical wastes. Surface impoundments are simple excavated depressions (ponds) into which liquid wastes are drained. Solid wastes settle and accumulate while water evaporates. If the pond bottom is well sealed and if evaporation equals input, wastes may be stored in the impoundment indefinitely.
4. Incineration : The hazardous biomedical wastes are usually disposed off by means of incineration. Human anatomical wastes, discarded
medicines, toxic drugs, blood, pus, animal wastes, microbiological and biotechnological wastes etc are called Bio-medical wastes.
5. Bioremediation : This is another rapidly developing clean up technology. Cleaning the environment with biological options such as microbes and plants is called bioremediation. Some naturally occurring bacteria and other microorganisms have the capability to degrade or absorb or detoxify the wastes such as heavy metals. Many plant materials are successfully used as adsorbents for xenobiotics (phytoremediation). Genetically Engineered Microorganisms (GEMS) are currently produced in large scale to remove the hazardous radionuclides and heavy metals such as mercury, chromium, cadmium etc. Certain plants such as Gibberella fusarium were able to breakdown cyanide and reduce it to a non-toxic form. The bacteria Pseudomonas, nicknamed as 'super - bug' are capable of degrading variety of toxic compounds and also degrade oil.
Paper (54% recovery) can be repulped and reprocessed into recycled paper, cardboard, and other paper products; finally ground and sold as cellulose insulators or shredded and composted.
Glass (20% recovery) can be crushed, remelted and made into new containers or crushes used as a substitute for gravel or sand in construction materials such as concrete and asphalt.
Some forms of plastics (2.2 % recovery) can be remelted and fabricated into carpet fibre, fill for insulated apparel, irrigation drainage, tiles and sheet plastics.
Metals can be melted and refabricated (39% recovery).
Food wastes and yard wastes (leaves, grass etc.) can be composted to produce humus soil conditioner.
Textiles can be shredded and used to strengthen recycled paper products.
Old tyres can be remelted or shredded and incorporated into highway asphalt.
The main steps in typical water - treatment plants are coagulation, settling and filtration to remove suspended particles, aeration to remove the volatile substances most responsible for taste and odour, and chlorination to kill pathogenic organisms.
For the treatment of sewage, primary treatment consists of mechanical filtration, screening, and settling, followed by chlorination. It removes 50 to 65% of the suspended solids.
In secondary treatment the organic wastes are transformed by bacteria in the treatment plant, where oxygen is provided by aeration, instead of depleting dissolved oxygen in the receiving waters. The sludge from this process, consisting largely of bacterial masses, is concentrated and processed further in an anaerobic digester.