Commonly adapted different disposal methods by the municipal corporations are:
(a) Open dumping
(b) Land filling
(c) Sanitary land filling pyrolysis
(d) Incineration
(e) Composting
(f) Disposal into sea
(a) Open dumping:
In this method uncovered areas are used to dump solid waste of all kinds. The waste is untreated, uncovered and not segregated. These sites spread foul smell and become breeding grounds for pests, flies, thereby spreading disease in those areas.
(b) Land filling:
In this method, solid wastes are carried and dumped into the low lying areas. The refuse is filled up or dumped in layers of 1.5 m or so and each layer is covered by good earth of at least 20 cm thickness, so mat refuse is not directly exposed. Each layer is left out for at least seven days and compaction by trucks is carried out for its settlement, before starting filling the next layer. Insecticides like DDT should be prayed on top to prevent breeding of mosquitoes and flies.
With the passage of time, the filled up solid wastes get stabilized by the decomposition of the organic matter and subsequent conversion into stable compounds. Hydrolysis of complex organic matter takes place under anaerobic conditions and as a result gases like CH4, CO2, H2S etc are evolved and also ampler water soluble organic acids are formed which diffuse through the soil. For better biological degradation the moisture content should be less than 60%
The refuse gets stabilized, generally, within a period of 2 to 12 months, and settles down by 20 to 40% of its original height.
Advantages:
(i) Simple and economical
(ii) No costly plant and equipment is required
(iii) Skilled labour is not required.
(iv) Separation of different kinds of solid wastes is not required.
(v) No residue or by product; hence no further disposal.
(vi) Low lying areas can be reclaimed and put to better use.
Disadvantages
Large land area requirement
Continuous evolution of foul small near the site of disposal.
Use of insecticides is required.
Covering good earth required for top layer may sometimes be difficult to obtain.
The biggest disadvantage is formation of 'leachate'. It is a coloured liquid formed due to seepage of rainy water into the land fill. This water may dissolve the harmful and carcinogenic compounds present in the refuse. When such polluted water contaminates the ground water, it may lead to diseases like cholera, typhoid, polio, etc.
(c) Sanitary land filling:
Disposal of waste by sanitary land filling is environment friendly. They are more hygienic. These are lined with materials that are impermeable such as plastics and clay and are built over impermeable soil.
In sanitary Land fillings the solid waste is compacted and spread in thin layer, each layer being uniformly covered by a layer of soil. The final layer is covered by one meter of earth to prevent rodents from burrowing into the refuse and scattering.
This is a biological method of waste treatment and its decomposition products like CO2, NH3, H2S, CH4, H2O can be taken as renewable energy source, such as generation of biogas.
Advantages:
No danger of air and water pollution.
Disadvantages:
1. Very costly.
2. The rate of decomposition in sanitary is also extremely variable.
(d) Pyrolysis:
In this method, the chemical energy of some organic wastes is recovered by destructive distillation of solid waste. In pyrolysis, the combustible solid waste material is heated in a specially designed chamber, known as pyrolysis rector, at- 10000C temperature in oxygen less environment.
(e) Incineration:
The process of burning waste in a large furnace is known as incineration. In these plants, the recyclable material is segregated and the rest of the material is burnt. At the end of the process, ash is left. Some of the ash floats out with the hot air. This is called fly ash. Both the fly ash and ash have high concentrations of dangerous toxins such as dioxins and heavy metals. Disposing of this ash is a severe problem. The ash that is buried at the landfills leaches the area and cause severe contamination. Hence, incineration should be kept as the last resort and should be used mainly for the treatment of infectious waste.
(f) Vermin composting
The problem of waste disposal in now being tackled with a greater of efficiency by many eco friendly recycling technologies. Currently the most popular and widely employed technique for solid waste disposal relies on earthworms, generally referred to as "farmer's friend".
The earthworm is physically an aerator, crusher and mixer, chemically a degrader and biologically, a stimulator, in the decomposer subsystem.
For centuries, earthworms, as biological natural agents have been in the business of decomposing wastes and enriching the soil structure. Earthworms feed on any organic wastes. They consume organic matter, two to five times of their body weight and after using 5-10% of the feed stock for their growth, excrete the mucous coated undigested matter as worm casts.
Worm casts consist of organic matter that has undergone physical and chemical breakdown through the activity of muscular gizzard, which grinds the material to particle size of 1-2 micron.
The nutrients present in worm cast are readily soluble in water for the uptake of plants. Vermi casting is a rich source of macro and micro-nutrients, vitamins, enzymes and antibiotics.
Hence, this process of producing vermin compost is known as vermin-composting which is an appropriate technique for the disposal of non-toxic solid and liquid organic wastes. It helps in effective and economic recycling of agricultural residues, industrial wastes and animal wastes.
Organic matter (l) earthworms vermin compost
(ll) micro-organisms
(waste from kitchen, (black earthy smelling
hotels cattle dung etc) nutrient rich manure)
Benefits of composting:
(i) Recycling of organic material and nutrients back into the soil.
(ii) Reduction of the quantity of waste to be disposed bt the house hold and industries.
(iii) Conversion of organic wastes into valuable end products which are aused as manure in land farming.
(g) Disposal into sea:
This method can be used in coastal area having deep sea water (> 30 m depth) at a reasonable distance (< 16 to 20 km).
Advantage:
Simple and cheap method.
Disadvantage:
(i) This method is not successful during monsoons.
(ii) Light component of solid wastes may return to the shores and can spoil the beaches.