Waste Material An Asset

The world was full of resources at the start of human civilisation. In the process of being civilised, creating luxury to his life consuming almost all type of natural resources man has never thought of his future and the future of his home planet. The very fact that all the conventional energy resources in the universe are limited has been never taken into consideration by the humans. However we do not forget to generate the report like the given below in table-1:

Table-1

Thus 93% of the total energy consumed in the world is taken from fossil fuels & nuclear energy elements. These are highly polluting the surroundings & also producing lots of solid wastes, which have lost their carbon content & generally possess pozzolanic property. The above report says that we must have another energy options in this new millennium. The non-conventional energy sources such as solar energy, hydrostatic energy etc. will be very good energy sources for this era. But in our country the technology for production of energy from these means is not much sufficient so in our country from total energy 97% is consumed from these conventional fuels. In this situation an environmental friendly solution for our country is efficient utilisation of waste, in which carbonic wastes fulfil the little requirements of energy and other wastes used to produce different materials which preserve the natural materials.

DEFINITION: It is defined as the conventionally non-usable by product or end product of any industry or agriculture.

Organic wastes: These are combustible wastes that may be utilised for energy production.

Inorganic wastes: These are not combustible and generally posses pozzolanic properties so it may be used for manufacturing of many different materials.

Here in table given below major wastes produced in our country in different industries & agriculture are shown with the application for which they may be utilised. From figures shown in table-2 of production we can see that if proper utilisation of these millions of tonnes of wastes is not done properly than it may cause major environmental problem. From these 9 major wastes first five are pozzolanic & other are organic wastes.

Table-2

9.      Bio mass                                Decomposition of               large      energy for heating, lighting
                                                Organic wastes                quant.      & running engines
                                                as biogas

There are hundreds of waste materials other than these that are produced in little quantities, each of these wastes has different characteristics & as per studies conducted each of these may have different applications. From the wastes, listed above, we first see the detailed description about flyash and its uses.

INORGANIC WASTES

Considering the size of its economy, India is poorly endowed with energy resources. Its major source of energy is coal. Coal currently meets about two-third of India’s total energy. At present the major coal based thermal power stations in India are being planned with an installed capacity of about 1000 MW during the starting phase with provision for adding another 1000 MW to 2000 MW during the expansion phases. In these plants, the use of Indian coal having relatively low calorific values and with higher ash content of about 40 to 45% only are being planned. On an average, the rate of ash production in 1000 MW power plant will be in the order of about 5000 tonnes per day. Hence with the expansion of units, at the ultimate stage of power plants, about 10,000 to 15,000 tonnes of ash will be produced every day. 75% of it is finer flyash & rest is coarser bottom ash. Management of such large quantities of ash is a real challenge to the Engineers.

It is projected that by this year 2000, the annual ash generation in India will be of the order of

about 110 million tonnes. The common environmental pollution problems created by disposal of flyash, besides air and water pollution, are wastage of large tracts of land which otherwise could be utilised for useful purposes. It has been estimated 1000 MW power station for an operational period of 30 years requires about 500 acres of land for disposal of flyash.

a) Flyash after getting dry, gets airborne in the nearby areas and causes ailments like allergic bronchitis, silicosis, asthma etc.

b) Flyash contaminates surface water and may have leaching effects on underground water.

c) Aquatic life cycle gets seriously affected if the flyash gets into nearby river/sea or any public utility water body.

d) Supernatant water from ash bund if used for agriculture purpose, may have harmful effects on the plants.

e) Corrosive and abrasive nature of ash affects the structures and exposed metals in the vicinity.

f) Environment degradation is caused as flyash disposal requires huge land and enormous amount of water.

Due to increasing concern for environmental preservation and material conservation, utilisation of fly ash as construction material has therefore become an urgent and challenging task for scientists and engineers all over the world.

A point of special importance for the use of fly ash as a building material is the fact that most of the particles were found to be of spherical nature. Since it is well known that admixture of spherical particles with cement imparts better workability to the mix by reducing friction at the aggregate interface the use of fly ash a complete or partial replacement of sand in reinforced structures, high rise building and bridges and of mass concrete in dams.

The utilisation of fly ash as a important building material has been accepted as an engineering reality in the technologically advanced countries for the past more then quarter of the centuries. Its entry for corresponding applications in India has however, been unduly slow despite the Bureau of Indian Standards had prepared different standards pertaining to its uses, not with standing the crusade of several research and development organisations in favour of its use.

PCC is made by blending 15 to 20 percent of fly ash with Portland cement or grinding the ash with cement clinker. The PPC shows good resistance to sulphate attack. Leads to energy savings reduces permeability of concrete and having ultimate strength approximately the same as that of PCC.

The use of flyash concrete in production of various types of precast building units such as concrete building blocks. RCC transmission poles, columns, beams, hollow core slabs, doors and window frames, etc. has been made in a limited way by different organisations in India. It is found that flyash concrete with 20% less cement by weight can produce the same 1 day compressive strength as produced by plan concrete.

Portland cement concrete in which a part of the cement has been replaced with flyash is termed as flyash concrete. When it is prepared and supplied to consumers in a plastic unhardened, ready for use state, it is called ready mixed flyash concrete. The ready-mixed concrete has the advantages of better quality control reduction in wastage and pilferage of materials, labour and supervision, which one normally associated with concrete prepared at site.

1 cubic meter of flyash concrete of grade M150 to M250 is 12.7% to 15.7% cheaper than the grade of plain cement concrete, it would be profitable to produce ready mixed flyash concrete but in terms of cement, which is in short supply and of over all cost.

The lime flyash cellular concrete consists of fine grained silicate structure having small non-communicating air cells. It can be produced to confirm to different dry bulk density requirements in the range of 400 to 1442 kg/m³ and a good fire resistance. Like wood it can be sawn, chiselled, planed, screwed and nailed. Its low density permits use of larger building units with saving in the cost of handling and construction.

Good quality high strength building bricks can be produced from fly ash using sodium silicate, cement or lime as binder. The mixture of fly ash, binder & coarse filler such as bottom ash, cinder , sands, etc. in suitable proportion is moulded in to bricks under pressure. While the sodium silicate bonded flyash bricks are autoclaved under saturated steam at a pressure of about 14 kg/cm², the cement bonded flyash bricks are water cured at ambient temperature to obtain the desired strength and dried before use.

In places where suitable clays are not available for making quality bricks an flyash is available nearly, good quality bricks can be made by mixing flyash with inferior clays. Mixing 20% to 30% reduces drying and firing shrinkage and improves compressive strength of the bricks (70 to 100 kg/cm²) and moisture absorption 15% to 20% can be made.

Lime flyash bricks can be made near the thermal power plants sites to reduce the transportation cost of flyash. The hot water available from power plants can be utilised for autoclaving the bricks. In this method 8% to 15% of lime is mixed with flyash long with chemical additives and bricks are cast in brick moulding machine and steam cured. The flyash bricks are slightly lighter, gives better insulation and does and require plaster. Quality building bricks of 75-200 kg/cm² and low moisture absorption can be made.

In this method the clay and flyash are mixed together and the bricks are moulded and fired in the usual way the bricks thus produced are lighter as the bulk density of flyash is about one half of clay. Butter Worth suggested that at least 25% addition of flyash can be made to plastic clays for the manufacture of bricks to give improved physical properties.

The clay bonded flyash bricks are lighter than the normal bricks and results in lower thermal conductivity values. These type of bricks are found suitable for the construction of kilns, cold storage and air conditioned buildings for better insulation.

Bricks can be safely used upto 800^oC hotface temperature can be manufactured by using flyash, lime and aluminium powder. These bricks can be used in boilers as they have very good thermal properties.

The portland-pozzolana cement confirming to IS: 1489-1976 can be manufactured using flyash by inter grinding Portland cement clinker, flyash and gypsum. The Portland pozzolana flyash cement is suitable for marine, hydraulic structures and other mass concrete constructions, because it produces less heat of hydration and offers greater resistance to attack of aggressive waters than ordinary Portland cement.

( II ) Sintering the flyash pellets at 1100^oC – 1200^oC in a vertical shaft kiln. The production of SFALA from the Indian flyash had been successfully carried out on a pilot plant moving grate sintering strand at CBRI. The aggregate is suitable for use in the production of structural light weight concrete and precast high weight concrete building units for use as load bearing and non load bearing elements.

Oil well cement is used for cementing the steel casting of oil wells to the rock formation. Work carried out at CBRI has shown that flyash can be interground with Portland cement clinker, gypsum and some additives in certain proportions to produce cement confirming to the requirements of and oil well cement.

Flyash is a waste material having pozzolanic property which can be converted into cementing material in civil Engineering works. A few flyash based road construction techniques for adoption in construction of road, run ways as developed at the central Road Research Institute, New Delhi, have been recommended by central Assessment committee of the ministry of shipping and transport, Govt. of India for wide adoption.

The roller compacted is a new concrete paving technology in which 30% to 50% of flyash can be used as a partial replacement of cement and sand. Flyash increases the fines in the zero slump concrete and hence increases its workability and strength due to its pozzolanic action.

The use of flyash as a part replacement of cement in the precast concrete industry is well established abroad. The quantity of cement replaced with flyash by different organisations ranged from 15% to 20% by weight. The use of flyash in production of precast concrete units has economic advantage and yields a quality product.

Flyash consist of silica and alumina and is alkaline in nature. It is largely used as a pozzolanic material in building construction and get huge quantity remains unused, therefore it is also used as an extender pigment in emulsion paint formations. The natural colour of flyash gives and excellent silver grey shade if no pigment other titanium dioxide is added.

The strength and workability of lean cement mortars increased of cement, 20% of sand in the mortar mixes replaced by weight with flyash. The strength of flyash mortars is equal or higher than the strength of corresponding plain cement mortars.

Wherever soil stabilisation is required flyash can be very effectively used in place of cement. It in fact imparts strength to soil. Side slopes can be very well produced if soil is mixed with flyash.

Fine textured alluvial soil mixed with about 15% flyash can be used to manufacture thin structural clay products including wall and floor tiles. This technology is available with CBRI Roorkee.

The abrasive nature of flyash makes it suitable as domestic cleaning powder. Metal ware, floor and wall tiles and porcelains can be cleaned with this powder.

Very alkaline nature of the flyash makes it useful treatment of particularly acidic nature soil. Free reactive silica, sulphur and micronutrients present in ash are favourable factors for its useful application in agriculture.

Quite a good amount of work has been done in this direction by many institution for extracting aluminium and magnetite from flyash. In fact flyash magnetite is of better quality than commercially available magnetite.

Hollow microscopic particles formed from flyash are called cenosphere. These are used as fillers in composites, paints and insulation cable tape, fabrics, noise attenuation and fabrication of light refractories. Ministry of environment is understood to have suggested setting up such plant at Korba.

Geo-textiles & jute are the cheapest reinforcing materials, their combination with flyash will provide a most economical construction of embankments.

Flyash may be used economically when treated and reinforced with optimised percentage of lime, surfactant and geofiber for the construction of embankments and low cost buildings. The improvement in the load bearing characteristics of flyash treated with lime, surfactant and reinforced with non woven geofibres is based on shear transfer related to shear intensity.

We have seen so many application of flyash in different industries but then also only about 30% of flyash is being utilised mostly in the manufacture of clay flyash bricks. Very negligible amount of ash is being used in manufacturing of pozzolanic cement, ready made hollow blocks, asbestos sheets and in road embankment and agriculture purpose.

In some countries where utilisation levels are high(table-3) it is because of consistent efforts over a time period of 3-5 decades.(table-3)

Country Utilisation of flyash (%)

Belgium 95%

Germany 98%

Netherlands >100%

b) Higher cost of production of building material by using flyash as thermal stations are faraway from the flyash utilisation centres requiring prohibitive transportation cost.

c) Non availability of dry flyash collection facilities at many stations which is required by many manufactures.

d) Psychology of prospective users to keep away from flyash utilisation specially in agriculture sector since the flyash is made available free of cost to them which creates a question mark in their minds regarding the wisdom in using flyash.

e) Lack of proper co-ordination and dialogue between thermal plant and ash users.

f) Wide variations in quality & fineness of ash not desired by many manufactures of speciality items like sheets, tiles, cenospheres etc.

Considering very low percentage of ash utilisation in out country Govt. of India through Dept. of power had constituted a task force to study the problem in details and to evolve a strategy to boost up the flyash utilisation on large-scale basis by resolving the hurdles and constrains presently being observed in a large scale utilisation of flyash. The recommendations are as below:

a) To provide dry flyash free of cost to entrepreneurs for at least first 10 years.

b) Exempt building material manufactured by using flyash from excise duty to the extent of 25%.

c) Relief may be given in custom duty in import of suitable and efficient plants and machinery for manufactures of flyash products.

d) It should be made mandatory for coal companies to utilise at least 30% flyash from the power stations to which coal is supplied by them. Flyash can be utilised for abandoned mines filling.

These much material regarding the usefulness & applications of flyash is more than sufficient for the reader to believe that flyash can be very important row material for various types of products. In the present scenario common man of India should support any kind of initiative in the direction of more & more utilisation of flyash.

This was about just one of the major wastes, and many other pozzolanic wastes are produced in India. However there applications & other details are not required to discuss here. Better option is to discuss organic wastes that are quite different from the pozzolanic wastes represented by the flyash.

It is organic matter, in which solar energy is stored in the form of chemical energy by the process of photosynthesis, in the plants & from plants in the animals. In practical purpose the residues of plants & animals is known as bio mass.

This category is to burn the biomass directly and get the energy. However we all know convention uses of wood & other biomass so they are not discussed.

By modifying the conventional method of utilising biomass we can produce more amount of energy which is referred to garbage energy.

· Rotter dam, the world’s largest single waste burning facility burns more than a millions tons of waste annually to fuel a 55- MW electrical generating plant.

In the second category, biomass is converted into ethanol & methanol to be used as liquid fuels in engines.

Solid biomass generally possesses high water content so it requires considerable energy to drive of the water. So it is usually more appropriate to convert wet organic matter directly into premium fuels by a wet process like digestion or fermentation.

Fuels derived from biomass are easily handled and burnt. Most importantly, refined biofuels can be used in existing fuel systems, often with little or no modification, and are compatible with current patterns of energy use. This improves their economic potential and the speed with which they can be introduced. Refined biofuels have high calorific values, and can be stored for long periods without deterioration.

They are now replacing petrol & diesel as transport fuels in several countries and this process is likely to accccelerate as oil prices rise. They have a high ocatne rating, but a low calorific value than petrol. Methanol contain 25% less energy per gallon than ethanol, and 50% less than petrol. However, alcohols can improve engine performance and are for cleaner than petrol or diesel; they burn with higher efficiency and at lower temperatures and are free from lead and sulphur.

Methanol & Ethanol : They can be blended with unleaded petrol and burnt in present day internal combustion engines. Minor engine modifications are necessary for blends containing more than about 20% alcohol, or for almost pure alcohol, these include the increased compression and altered timing and carburation. Pipes, pumps and fuel tanks must also be protected because alcohols, particularly methanol containing traces of water and corrosive organic impurities. With 98% alcohol the fuel must be pre-heated by circulating hot air or water from the engine exhaust. A small electric heater is necessary for starting in cold climates. Diesel engines have been modified for dual fuel use.

From crushed seeds & nuts (e.g. sunflower and rapeseed, peanuts, palm, soya and corn) can be burnt in unmodified diesel engines. They can be blended with diesel fuel or used directly. Research on improving engine performance is underway in several countries. Vegetable oils offer an attractive fuel for tractors and other agricultural machinery and are already in use by farmers in, for example South Africa, Brazil.

iii. To ferment the biomass anaerobically to obtain a gaseous fuel called bio-gas.

Bio gas or methane is produced by the anaerobic decomposition of organic materials. This gas is produced from cow dung and other wastes such as cornhusks, leaves, straw, garbage, flesh, flesh of carcusses, poultry droppings, pig dung, human excreta and sewage.

Production : It is estimated that about 100 crore tonnes of fresh dung is available in the country, and 67.1 cubic meter of gas per tonne of wet dung can be produced.

The rate of gas production will be highest if the mixture in the digester contains solids between 7-9%. Cow dung originally contain about 18% of solids.

· It has an energy content equivalent to about two-thirds that of natural gas and can be used in stationary engines or turbines to generate heat and mechanical or electrical energy

· The use of dung as row material for bio gas, is a much better use of dung and profitable, than using it as fertiliser or fuel, because main product of bio gas is very good fuel & side product is good fertiliser.

· It is environmental friendly because it creates nil pollution and also remove wastes from that place.

There are lots more application of bio gas, so in our country the use of bio gas increases from day to day.

It may be defined as the branch of science that employs the resources of Biology, inorganic and organic materials of nature and living organisms to produce something beneficial for mankind.

With the rapid growth of biotechnology there are so many experiments are conducted for proper utilisation of organic harmful wastes. We see one example of this as given below:

This is specialised field in biology. With the help of biotechnician enzymes of higher organisms and conjugated proteins can be produced on industrial hydrocarbon wastes. From, which a computerised protein model can be formulated and after which synthetic gene can be produced. From these two a desired protein can be made. Several other components can also be made eg. Glucose isomerease enzyme is used in the synthesis of syrups as well as in soft drinks.

Having gone through the above report the reader must have been aware of the impact of proper utilisation of various types of wastes. In a highly populated country like India this has dual advantage of saving conventional energy resources & row materials and allowing efficient disposal of wastes. The author would like to point out the need of intensive scientific research & studies in this field. The best way to improve the present situation & implement this idea, according to the author, is to develop a new branch of engineering, where young & enthusiastic students can put their efforts to utilise the wastes in the most effective way towards the development of our nation.