Management of Soil Pollution: Methods of Disposal of Wastes!
Land/soil pollution can be controlled by adopting measures for the disposal of solid wastes, which unfortunately involves large finances and technology. Prior to disposal, the wastes have to be collected from the places by trucks to the disposal area.
It is estimated that about 80 per cent of the total cost of solid waste management is spent on collection only. The methods used for the disposal of waste are open dumps, ocean dumping and sanitary landfills.
Dumping is a popular and an inexpensive means of solid wastes disposal. Open dump is the least acceptable method but prevalent in most of the developing countries, including India, and is a cause of soil as well as general environmental pollution. In this method, waste is collected and hauled to a site where it is dumped on the ground.
Organic matter rots or is consumed by insects, rats or hogs. In some communities, the pile is set a-fire in the evening to reduce the total volume and the odour. All this creates serious ecological problems. The dump itself is a potential source of disease. Rain erodes the dump, and the polluted water flows into nearby rivers and groundwater reserves.
Sanitary landfill is commonly used for final disposal of solid wastes. This is cheaper than other disposal methods and has the advantage of avoiding acute pollution problems associated with discharging wastes into waterways or polluting air from incineration.
But, the main disadvantage over open dumps is in the aspect of public health. Leaching by surface water or groundwater may contaminate streams and other water supplies. The availability of land for the dumping of the growing volume of wastes is also a problem.
Ocean dumping of wastes is practiced by many coastal cities. It was considered to be the favourite disposal method under the prevalent notion that the ocean is an inexhaustible sink.
We are now learning that the ocean does not have an infinite capacity for covering, holding, absorbing or decomposing materials, nor the capacity for anywhere near the load of pollution that would result if the rate of ocean disposal continues, as in the past.
There were seven major categories of waste harbour dredging, industrial wastes, municipal sewage sludge, refuse and garbage, construction and demolition debris, military explosives and chemicals and miscellaneous wastes like agricultural land run-off, pesticides, fertilisers, sewage and garbage from vessels, oil spills, etc.
Now, the environmentalists have warned that ocean dumping is neither a safe nor a desirable method of the disposal of wastes. In 1970, the Council on Environmental Quality recommended a series of drastic actions to control ocean dumping because it upsets the ecological balance of regions of the sea.
Incineration is a method through which the volume of wastes can be reduced by 60 per cent and it also reduces the public health problems. This method is adaptable over a wide range of capacities from small domestic incinerators to large centralised municipal plants. It can handle a mixture of garbage and rubbish, and the physical nature of the residue called clinker aids in the disposal of the waste, although it aggravates the problem of air pollution.
Chemical processing of solid wastes is also applied but it is costly and technically not feasible for poor countries. But, due to prospect of energy production and recovery of certain usable materials, the salvage of some wastes by chemical methods is now considered economically feasible. The reclamation of non-ferrous scrap metals has long been an established industry.
Composting municipal refuse to convert it into a fertiliser and soil conditioner is appealing not only because it appears to be a good way to recycle the resources in solid wastes, but also because of the beneficial nature of the compost. This may be considered as useful method for the disposal of municipal refuse, especially in developing countries.
New methods of waste disposal that are under trial in various parts of the world are:
1. The transformation of the organic content into sugar or proteins.
2. The heating of organic refuse under anaerobic conditions to convert it into useful gases such as methane, which is usable as fuel, or into a liquid product.
3. The compression of refuse into building blocks that can be sheathed with more durable materials. One such plant is in operation in Japan.
4. The compression of refuse into briquettes that can be used as fill. A mixture of fly ash, dried sewage sludge, incinerator residue and river and Lake Dredging’s is under study.
5. The use of degradable plastic bags instead to trash cans in the collection and transport of municipal refuse.
6. The transport of refuse as liquid slurry in pipelines, a method now under study.
Energy from Refuse:
In many metropolitan areas of developed countries the garbage is burnt in a well-engineered furnace. The heat from the fire is used to boil water and produce steam. Then, the steam is sold for industrial use.
But, there are problems in this type of burning also as wet garbage and food scraps are difficult to burn and burying PVC products produces hydrogen chloride gas, which reacts with water to produce a strongly corrosive liquid hydrochloric acid.
In spite of these difficulties, incineration may become profitable in the future because:
1. Increasingly large quantities of dry paper and cardboard have appeared in refuse, thereby increasing the fuel content of the trash.
2. The price of fuel has skyrocketed and therefore the value of steam has also gone up, thus it will be more economical.
3. The rising cost of land has made it harder to find adequate sites for landfills, thus demanding alternative solutions and burying of refuse is the most suitable alternative.
Recycling of Waste Material:
Most refuse contains a wealth of raw materials that can be easily reused or recycled. A large quantity of metals can be obtained from waste dumps, as also paper, glass, tyres, manure, etc. Table 9.5 indicates the possibilities of recycling the various waste materials.
It becomes clear from the table that if the recycling process is adopted properly, not only the problem of waste disposal can be minimised but it will save financial resources also. An estimate indicates that about 21 per cent of the paper in United States was recycled, compared with about 50 per cent in Japan.
If the rate of recycling were increased to 50 per cent in United States, approximately 100 million trees would be saved annually, and the energy thus saved would be enough to supply 7,50,000 homes with electricity. If people would separate their household trash into piles of aluminium, steel, paper, plastic and food scraps, then, perhaps, all these materials could be recycled.