AMIE INDIA Students Forum

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CHAPTER-8 ENVORONMENT DEGRADAITON

MODEL QUESTIONS
(Essay/Long type)

8: 1 Explain in brief the causes for environmental degradation in the Third World countries.
Ans : India today is one of the First ten industrialized countries of the world. What these industries have provided and what has come out is noteworthy. There is no sustainable development. We have both non-degradable and bio-degradable pollutants. Pollutant emission within the permissible limit is a fine approach of development but the moment permissible limit is crossed may be due to anyone's carelessnessit becomes hazardous to the health of both living and non-living organisms. Air, water, soil and noise pollution is being experienced by society. This is not sustainable development We all know that pollutants are present in water, air, soil and sound. Their dimension, source and reduction procedures upto tolerable limits is discussed below one by one.

8.2 What is "organic growth"? Give some examples of unplanned growths.
Ans: we had unbounded faith in science and technology and the miracles they would" work to eradicate poverty, disease and other ills of the society. Since independence, India has made tremendous progress on all fronts. India has also achieved near self-reliance in many core sectors such as iron and steel, crude oil refining and petrochemicals, drugs and pharmaceuticals, fertilizers, engineering goods, food and food processing, building materials and consumer goods. Unfortunately, this industrial transformation of the country was not well-planned from the point of view of environmental conservation and this improperly planned development has resulted in
pollution of our air, water and land. The main factor of environmental pollution in the Indian sub-continent (i.e., in India, Pakistan, Bangaladesh, Nepal, Bhutan, Myanmar and Sri Lanka) appears to be over-population that throws heavy demands on natural resources including air, water, soil, flora and fauna resulting in a serious imbalance in the ecosystem.
An extreme example of this was the Bhopal Gas Tragedy. In January, 1984, an insecticide plant of Union Carbide leaked a toxic gas, methyl isocyanate, 4 that killed more than 2,000 people within hours and blinded or otherwise sickened thousands. Most of the victims of this biggest industrial accident in the world were the poor people living in the slums adjacent to the plant.
According to many authorities, the main problem concerning environmental degradation is not "growth" but "unplanned growth". These authorities have formulated a new concept known as “organic growth". As an answer to the problem of environmental degradation. According to the principal of organic growth, the only answer to this universal problem is that governments should make universal decisions above their short-term and narrow national interests. Rich countries should transfer more of their resources to poor nations, and each country should specialize in what it is best equipped to produce.
Development in harmony with the environment should be the spirit of our Five-Year Plans. If we build a large dam, for example, hundreds of thousands of trees are felled, thousands of acres of fertile land is lost, and thousands of poor people are displaced. This is the dilemma of development No one can deny the need for development; but every effort should be made to minimize its environ-mental cost. While planning for any developmental project, there should be specific provisions for environmental protection. Attempts should also be made to remove some of the weaknesses existing in the planning system, which include the lack of co-ordinated institutional support, gaps in the necessary information and data required for the assessment of environmental impact of various developmental projects, inadequate availability of trained manpower and lack of strong public interest in environment issues.

8.3 Write a critical note on "Environmental Degradation by the Rich".
Ans: The food requirements and habit of the rich Western countries have been instrumental in destroying the forests and degrading the land of many poor Third World countries. Despite the worldwide process of decolonization after the Second World War, it is almost certain that much more land is being used today in the developing countries to meet the food requirements of the Western countries than in the years before the Second World War. More than one-fourth of all the Central American forests have been cleared since 1960 for the purpose of cattle ranching and about 90% of the beef produced in these ranches are being exported to the USA, while the domestic consumption of beef in Central America has fallen dramatically during this period. In the US, on the other hand, the beef imported from Central America is mostly used to make pet food and hamburgers. The price of the Central American beef in the US (which is roughly half the price of the beef produced in the US from grass-fed cattle) does not represent its real ecological cost. The reason is that cattle ranching has proved to be the worst form of land use for the fragile soil of Central America on which the tropical forests existed before 1960. It was found that within 5 to 7 years of clearing the forest, the productivity of the soil dropped dramatically and the cattle ranches had to move on to some other areas and clear more forests. In our own country, the first major attack on the forests of the North-Eastern India came when tea plantations were established. The current over fishing on India's coast is taking place mainly because of the heavy demand for prawns in the markets of rich Western countries and Japan. This over- fishing often leads to tension and violent encounter between traditional fishermen and the owners of the mechanized trawlers. As a result, India and several other countries in South-East Asia have established regulations to prevent trawler operators from fishing in the first few kilometers from the coast, a zone reserved for the traditional fishermen. Similarly, the export of frog-legs from India to France and other European countries to cater to the palates of rich Western consumers has led to tremendous increase in the population of agricultural pests in the affected areas. To control these pests, farmers have to use large amounts of costly pesticides which, in turn, leads to more environmental pollution.
The pattern of mindless exploitation of natural resources that we see on the global scale simply repeats itself on the national scale. Exactly what the industry of the rich Western countries does to the environment of poor Third World countries, the Indian industry does the same to the environment of the resource-rich and economically poor states of India like Orissa, Jharkhand and Chhattisgarh. Nearly half the industrial output in India comes from biomass-based industries like cotton, textiles, rayon, paper, plywood, rubber, soap, sugar, tobacco, jute, chocolate, tea, coffee, food processing, packaging and vegetable oils. Each of these industries exerts heavy pressure on the cultivated and forest lands of the country. These biomass-based industries need crop lands, forests, irrigation and energy. Thus, we see that one of the main sources of environmental degradation in the world is the heavy demand for natural resources by the high rate of consumption of the rich, whether they are rich nations or rich groups and individuals within the nation itself, and it is mainly their wastes that contribute to the global pollution.


8.4 Explain in brief the effects of environmental degradation in India.
Ans: One of the major effects of environmental degradation due to industrialization is the large-scale destruction of our forests, and this has a major impact on the productivity of our crop lands. The reduction of crop-land productivity due to the destruction of forests occurs in two ways. In the first place, when forests arc destroyed, there is a many-fold increases in the rate of soil erosion. The result is that the soil literally gets washed leading to an intensified cycle of floods and drought. Secondly, the destruction of forests leads to the shortage of firewood and this has an adverse impact on the productivity of crop lands. The reason is that when firewood becomes scarce, people begin to use cowdung and crop wastes as fuel for cooking and other purposes. As a result, every part of crop plants gets used (as fodder or fuel) and nothing goes back to the soil to enrich it. Over a period of time, this constant drain of nutrients from the soil adversely affects it productivity. The more intensive the agriculture (due to the use of high-yielding varities); without any manure and crop wastes going back into the soil, the faster is the nutrient drain. The district of Ludhiana in Punjab, for example, has the highest yield per hectare of many cereals today; but Ludhiana has also the highest deficiency of many micronutrients in its soil. In Punjab, many fanners have already started using zinc routinely as a fertilizer. If the dram of micronutrients from the soil continues, the farmers will soon be using sulphur, manganese and iron as fertilizers. The micronutrient fertilizer industry is likely to become a boom industry in the near future.

8.5 How is the ozone layer being destroyed? Explain in detail.
Ans: ln the stratosphere, the destruction (or depletion) of the ozone layer is mostly Caused by elemental chlorine a toms. The mechanism for this destruction of ozone involves the following two reactions:

O3 + Cl ClO+O2
ClO + O3 Cl 9+2O2


Of course, there are some other chemical reactions going on in the stratosphere that modify and compete with the above two reactions. But if we ignore the other reactions and add the above two reactions, then we find that the net result is the following reaction:

2O3 + Cl 3O2+Cl

Thus, in the presence of chlorine atoms (Cl), two ozone molecules are converted into three oxygen molecules, while there is no net consumption of Cl atoms, which merely act as a catalyst. As a result, one Cl atom can go on converting many ozone molecules (O3) to ordinary oxygen molecules (O2) before it is consumed by some other chemical reactions. It has been estimated that a single chlorine atom in the stratosphere can convert as many as 106 to 106 O3 molecules to 0, molecules before being consumed by some other reactions. This mechanism is often referred to as the catalytic destruction of ozone since the chlorine atoms act as a catalyst for the reaction.
Most of the chlorine in the world is in the form of chemically stable sodium chloride (NaCI), either dissolved in the oceans or in underground salt deposits formed by the evaporation of ancient oceans. Elemental chlorine (Cl), which is a very reactive chemical, has a very short life-time in the lower atmosphere and has few natural ways to get from the lower atmosphere up to the ozone layer in the stratosphere. The only naturally occurring chemical that can transport much chlorine high enough into' the stratosphere to damage the ozone layer is methyl chloride (CH3CI), which is produced in large quantities by biological processes in shallow oceans. Most of this methyl chloride is destroyed in the troposphere (the lower atmosphere), but approximately 3% of the world-wide methyl chloride emissions reach the stratospheric ozone layer. Chemically active solar ultraviolet light in the range of 200 to 280 nm, which enters the ozone layer but does not penetrate below it, is strong enough to split up the methyl chloride molecules, releasing Cl atoms, which initiate the reactions given earlier and destroy the ozone molecules. Before we had the synthetic halogen compounds known as chlorofluorocarbons (CFCs), methyl was probably the main natural destroyer of the ozone layer. However, this destruction of the ozone was in balance with its natural production mechanisms, leading to a steady-state ozone layer.
Starting about a hundred years ago (i.e., from the first decade of the twentieth century), humans began releasing into the atmosphere synthetic chlorine-containing compounds in significant amount. The compounds like methyl chloride (CH3CI) that also contain hydrogen atoms can be attacked in the atmosphere by the OH radical. As a result, most of such chlorine- containing compounds do not survive long enough in the atmosphere to reach the stratosphere. Carbon tetrachloride (CCI,), on the other hand, has no hydrogen atom; so most of it is believed to reach the stratosphere and participate in the destruction of the ozone layer. The world production of carbon tetrachloride, however, has remained more or less constant over the last 70-80 years.

8.6 How should we protect the ozone layer? Write in brief.
Ans: So far the only method we know to protect the stratospheric ozone layer is to limit the emission of those substances (mainly CFCs) that can destroy it. No one knows of another material we could send into the stratosphere to protect the ozone layer from CFCs. The threat to the ozone layer is so severe that international conferences have been held and declarations and treaties have been adopted that commit the nations to restrict and eventually eliminate the use of CFCs. For some applications of the CFCs, satisfactory replacements are alread available and for others, they are being sought on an emergency basis. Many of the proposed substitutes for CFCs are hydrochlorofluorocarbons (HCFCs), which contain atleast one hydrogen atom; so they are susceptible to attack by OH radicals in the stratosphere.
Huge amounts of money and effort are being spent now to develop suitable substitutes for the CFCs. The original CFCs were designed to be non- toxic, non-flammable and chemically inert. There replacements should have all these properties and, in addition, a low ozone depletion potential (ODP). The ODP is a relative measure of the ability of a gas or vapour to attack and destroy the stratospheric ozone layer. It is expressed as a function of the percentage weight of chlorine in the halogenated hydrocarbon (to be used a CFC substitute) and its lifetime in the stratosphere.
The chemical industry' is developing two major types of CFC substitutes. One of these, known as the hydrochlorofluorocarbon (HCFC) family, has a fairly low ODP. The other group, known as the hydrofluorocarbon (HFC) family, has zero ozone depletion potential since the members of this family have no chlorine atoms in their molecules. It may be noted, however, that the members of both families (HCFC and HFC) contribute to the greenhouse effect and global warming. Many chemical companies, including the industrial giants like Du Font (USA) and the Imperial Chemical Industries (UK), argue that the world should switch over to the HCFCs as an interim step because they are cheaper to produce and simpler to use.
Compared to the CFCs, the hydrofluorocarbon (HFCs) are less stable and readily hydrolysed in the troposphere by the OH attack; so they are believed to be more environment tally acceptable than the CFCs. The data on the new HFCs are, however, scarce and of Limited accuracy and this is a major deterrent to their adoption as CFC substitutes.
Another problem with the CFC substitutes is that they are not as good as the CFCs. For example, one HCFC (known as HCFC-2), which, is already being used in large-scale refrigerator installations in supermarkets, etc., cannot be used in domestic refrigerators. Another substitute, a hydrofluorocarbon known as HFC-134a, is under development for domestic refrigerators; but it is likely to cost at least five times more than the CFCs used currently for this purpose.
In addition to the problems mentioned above, the CFC substitutes will require a substantial amount of re-engineering in many applications. In case of domestic refrigerators, for example, larger compressors and pumps may be needed when CFC replacements are used. These substitutes may also require more energy, thus forcing us to burn larger amount of fossil fuel, leading to more global warming.

8.7 Describe some methods to treat and dispose the municipal sewage.
Ans: In developing countries, the organic pollutional load (contributed mainly by municipal sewage) is a major problem in connection with water pollution. In India, it has been estimated that municipal sewage contributes 90% organic pollutants to our river systems, 7% is contributed by large and medium industries, while the remaining 3% comes from small-scale industries. Thus treatment, utilization and proper disposal of municipal sewage are very important steps towards the control of water pollution. Some of the important methods used for the disposal of sewage are as follows :
(1) Land Disposal and Sewage Irrigation. In this method, the sewage is disposed off on land (often for the purpose of irrigation) instead of discharging it into a water body. In this case, the land area acts as a crude filter and stabilizes the sewage by aerobic filtration. The sewage is usually given primary treatment before its disposal on land. This method is very similar to intermittent sand filtration. In case of sewage irrigation, the water and the fertilizing elements in the sewage, viz., nitrogen, phosphorous and potassium, are utilized to raise crops. Hence, this method has the special advantage of fertilizing the land.
(2) Dilution. In this method, the sewage is discharged into a large body of water like river lake or sea. The sewage is usually treated before discharging it into a water body to ensure that the condition of the receiving water body does not deteriorate to the extent of impacting on its normal use. I he cities arid towns which are situated near a large river (Allahabad, Kanpur, Varanasi and Patna, all of which are situated near the river Ganga) mainly use the method of dilution to dispose off their sewage. This method is considered quite satisfactory during the rainy season when the dilutionfactor is extremely high, but not suitable for the period from November to June, when the volume of river flow or the volume of water in the river is low,
Treatment of Sewage
Primary Treatment: The primary treatment of sewage mainly consists of physical separation of floating and suspended solids (that are settleable) from the sewage. The main equipment used for the primary treatment are screens, grit chambers, detritus tanks, skimming tanks and settling tanks.
Secondary Treatment: The secondary treatment of sewage includes flocculation and precipitation of the remaining materials in the sewage with the help of biological agencies, and their physical separation in secondary settling tanks. The by-products of the secondary treatment process are screenings, grit and sludges of different kinds. Out of these, the first two can be easily disposed off by burial or burning. Sludge, on the other hand, contains unstable volatile organic substances; so it may be treated by the method of digestion. In the process of digestion of sludges, various gases are produced with high calorific value which can be successfully utilized for heating or power generation. The solid materials left behind (i.e., the digested sludge) contain many fertilizing materials and are useful as manure or soil builder.
Sludge Digestion: The process of sludge digestion consists of liquefaction of organic materials in the sludge by anaerobic bacteria, which produce an alkaline reaction. When the sludge is first placed in the digesting tank., acid digestion with the production of noxious gases results and eventually, alkaline digestion prevails. Once established, the alkaline condition remains in the digestor for an indefinite period. The gases given off by the sludge are mainly methane (CH~) with some carbon dioxide (CO;) and small quantities of other gases. Among the sludge gases, methane has a calorific value of 8,000 kcal/m3 Since methane forms about 67% of the sludge gases, the calorific value of the sludge gas can be taken to be approximately 5,334 kcal/m3 The sludge gas occupies about 0.95 m3/kg of volume at normal temperature and atmospheric pressure. The main use of the sludge gas, apart from heating the digestion tanks, is for generating power. The power thus generated is enough to pump the entire sewage. Dried digested sludge can be used as a fertilizer since it contains 0.8% to 3.5.% nitrogen, about 1.6% phosphorous and 0.35% potassium on the basis of the dry weight of solids. The digested sludge may also be used for land filling, incinerated to produce heat and power, or dumped into large bodies of water.

(Objective/Short Type)

8.8 What are SOx and NOx.?
Ans; The two oxides of sulpher are sulpher dioxide (SO2) and sulpher trioxide (SO3), which are collectively known as SOx , where x=2 or x=3.
There are several oxide of nitrogen (such as N2O, NO,NO2,N2O2 and N2O5), Which are collectively known as NOx.

8.9 List four hea vy me tals that pollute water.
Ans: heavy metals like Hg (murcury), Cd (cadmium), Pb (lead), As , Se and Sb.

8.10 What is a septic tank ?
Ans : An important method used to process the domestic sewage is the septic tank, which is an underground sewage container madeof concrete.



8.11 What are the c-wastes ?
Ans : It has been estimated that more than one billion PCs (personal computers) have already been sold globally and there has also been a spurt in the sales of other electronic items like refrigerators, air conditioners, cellular phones and personal stereos. As a result, the quantum of electronic As a result, the quantum of electronic waste (discarded electronic items or “e-waste”)

8.12 What is ozone?
Ans : The ozone (O3) is a variant of oxygen (O2), which contains three oxygen atoms instead of the usual two, as in the case of the oxygen molcule.

8.13 The common methods for the disposal of solid wastes are:

(A) Sanitary land-fill (b) Incineration
(c) Composting (d) None of these.

8.14 India is a:
(a) Developed country among developing nations
(b) Developing country among developed nations
(c) Both
(d) Only (a).

8.15 Thermal power plants use:

(a) Coal (b) Oil
(c) Uranium (d) Strontium

8.16 Purification of gaseous pollutants maybe achieved by;

(a) Catalyric conversion (b) Adsorption
(c) Absorption (d) All of these.

8.17 Complex soil pollutants include:

(a) Fly-ash (b) Plastics
(c) Both (d) Neither.

8.18 Write true or false:

Qua: Herbicides, fungicides and insecticides belong to the family of pesticides.
Ans : True

8.19 Write true or false—

Qua: Detergents are inorganic chemicals.
Ans : Detergents are organic chemicals.
8.20 Write true or false:

Qua: Radioactive isotopes have a Very long half-life.
Ans : Radioactive isotopes have a short half-life.

8.21 Write true or false:

Qua: Cadmium poisoning may lead to formation of kidney stones
Ans: Cadmium poisoning may lead to toxic effect

8.22 Write true or false:
Qua: Increase in dissolved oxygen adversely affects the aquatic plants and animals.
Ans : Reduce in dissolved oxygen adversely affects the aquatic plants and animals.
8.23 Write true or false:
Qua: Lime can not be used to precipitate phosphorous.
Ans : Lime can be used to precipitate phosphorous.
8.23 Write true or false:
Qua: The anaerobic treatment process is not effective for effluents containing high concentration of orgaiuc matters.
Ans: The anaerobic treatment process has been effective for effluents containing high concentration of orgaiuc matters.
8.24 Fill up the blank:
Prolonged exposure to noise may cause hearing loss.
8.25 Fill up the blank:
Gobar gas is a mixture of methane (60%) and carbon dioxide (35%)
8.27 Fill up the blank:
Heat is an example of Thermal pollutant
8.28 Match thefollowing:
(A) Noise pollution (a) Carcinogin
(B) Dioxin (b) Detritus tank
(C) Fly-ash (c) Auditory effect
(D) Sewage (d) Power plant
A-c,B-a,C-d,D-b
8.29 Match the following:
(A) Brain damage (a) DDT
(B) Deforestation (b) Population
(C) Third World countries (c) Soil erosion
(D) White lung lung (d) Textiles
A-c,B-a,C-d,D-b

Write the odd ones :
(a) Greenhouse effect (b) Global warming
(c) Suspended particulate matters (d) Acid rain.

CHAPTER –9 WASTE MANAGEMENT

Long Type Questions:

9.1 Describe in brief the sanitary land-filling method for solid wastes disposal.
Ans: The basic principle of a landfill operation is to deposit the refuse, compact it with the help of bulldozers and then cover the material with at least 15cm of dirt at the conclusion of each day's operation. When the area is full, a final cover of about 60cm of dirt is applied, which is necessary to prevent rodents from burrowing into the refuse. The selection of a proper land-fill site is a difficult problem.
The engineering aspects of land-fill site selection include:
(1) Drainage: Rapid runoff reduces the mosquito problems, but close proximity to streams or dug-wells may result in water pollution.
(2) Wind: It is preferable that the sanitary land-fill be situated in the down wind direction from the city or town.
(3) Size: A small land-fill site with limited capacity is generally not acceptable because finding a new site involves considerable amount of trouble.
(4) Ultimate Use: At the planning stage, one has to consider whether the area can be utilised for public or private use after the land-filling operation is completed.
The above engineering problems are quite important, but even more important are the social and psychological problems of sanitary land-fills. No one in his right mind will be happy about having a sanitary land-fill near his house. A community may be rewarded with playgrounds, tennis courts, golf courses, etc., for tolerating a land-fill operation for a few years. If this operation is conducted according to accepted practice, there will be very little adverse environmental impact; but it is very difficult to convince and explain this to the people living near a land-fill. The reason is that most of the sanitary land-fills in the past were nothing but glorified garbage dumps.
The sanitary land-fill operation is, in fact, a biological method of waste treatment. In the absence of oxygen, anaerobic decomposition steadily degrades the organic material to more stable form. This process, however, is very slow. The decomposition may still be going on after 25 years. The end products of anaerobic decomposition are mostly gases like carbon dioxide (CO2), methane (CH4), aminoma (NH3), and a small amount of hydrogen sulphide (H2S). Since these gases have to find an escape, it is a good practice to install vents in land-fills to prevent the build-up of the above gases. The decomposition reactions are self-sustaining and temperature inside the land-fill often reaches 55-60° C.
The biological aspects of the land-fill as well as the structural properties of the compacted solid waste dictate the ultimate use of sanitary land-fill sites. It is suggested that nothing should be constructed on a land-fill site for at least two years because uneven setting may often create problems. If initial compaction is poor, it may take as long as five years for just 50% settling to occur. If pilings are used as foundations on a land-fill, they should extend through the fill and onto rock or some other sufficiently strong material.

9.2 Describe a modem composting method.
Ans: composting of solid wastes is an aerobic method of decomposing the wastes. Many types of micro-organisms, which are already present in the wastes, stabilize the organic matters in it to produce a soil conditioner. The micro-organisms that decompose the wastes include bacteria (which predominate at all stages of the process), fungi (which often appear after the first week) and actinomycetes (which exist during the final stages).
Initially, the process starts with the mesophilic bacteria, which oxidize the organic matters in the wastes to carbon dioxide (CO2) and liberate heat. As a result, the temperature rises to about 45°C. At this point, the thermophilic bacteria take over and continue the decomposition. During this phase of decomposition, the temperature rises further to about 60°C. The refuse is periodically turned over to a How enough oxygen to penetrate all parts of the material to support the process. The compost is stabilized after about three week's. The end point of a composting operation can be determined by noting a drop in the temperature, earthy smell and a dark brown colour.
The moisture content of the wastes is a critical factor in the aerobic composting process. Excessive moisture makes it difficult to maintain aerobic conditions. Dearth of moisture, on the other hand, inhibits the growth of microorganisms. For an optimum rate of composting, a moisture content of about 55% is required, and it may be necessary to add water in order to maintain a satisfactory moisture content.
Modern methods of composting may be classified into two broad categories:
(1) Manual method.
(2) Mechanical method.
The manual method is more attractive for towns with a rural bias. Manual methods are widely practiced in India and many other developing countries. In India, two manual methods have been developed for composting the refuse/night-soil mixture. These are:
(1) The Indore process.
(2) The Bangalore process.
In the Indore process, layers of vegetable waste and night-soil are alternated, each about 8cm thick, to depth of about 1.5m in a trench, or form a mound above the ground. The mixture is kept aerobic by turning it at regular intervals for two or three months. The resulting compost is then left for another month or so without turning. The whole process takes about 3-4 months. The Bangalore process of composting is a modified form of the hid ore process. The Bangalore process has been widely adopted now by various municipalities all over India. In this process, the refuse/ night-soil mixture is placed in layers (as in the Indore process) in a trench of about one metre deep. In contrast to the Indore process, however, the material is not himed in the Bangalore process, but is digested under essentially anaerobic conditions, whereby the decomposition is complete in about 4-5 months. Though the Bangalore process avoids turning the material altogether, it lays great emphasis on the carbon to nitrogen (C/N) ratio of the compost heap and its initial moisture content.
The resulting compost is free from pathogenic (i.e., disease-causing) organisms. On dry basis, the compost contains approximately 1.5% nitrogen, 1.1% phosphorous (as P205;) and 1.5% potassium (as K20) and proves to be a valuable nutrient for the soil. Fully mechanized composting plants involve shred ding, grinding and mechanical separation of high density solids.
There are basically four processes of mechanical composting available in India;
(1) The Buhler process.
(2) The Dano process.
( 3 ) The Tollemache process.
(4) The Nusoil process.
In the Buhler process, the waste material is ground in two stages in hammer mills. The non-compos table inorganic materials (metals and glass) are separated from the waste by the strong sifting action on circular swinging sieves. The remaining corn postable materialis then decomposed aerobicatly in open trenches or mounds. Stabilisation by this process may take about 2-3 months.
The Dane process uses a long rotating drum, called a bio-stabiliser unit, for decomposing the waste. The rotating drum is inclined so that the waste flows from one end to the other. The refuse is partially decomposed in the drum and the outcoming refuse is generally free from odour and pathogenic micro-organisms. This partially decomposed refuse is then completely decomposed in open trenches or mounds. The entire operation may take about a month.
In the Tollemache process, the waste is pulverized in a vertical pulveriser and then passed through a screening plant to screen out plastics, etc. The pulverised and screened refuse is allowed to decompose in trenches mounds for about three weeks, with three or four turnings. The resulting compost is then cured for 4-5 weeks. The complete stabilization, therefore, takes about two months.
In the Nusoil process the non-compostable inorganic material is separated from the waste, the resultant waste is pulverised and the pulverized waste is led to a vertical digester where decomposition takes place. The vertical digester is a cylindrical unit having seven sections. The refuse moves downward through each section of the digester. The rates of air flow and water addition are regulated so that the decomposition of the waste takes place under optimum conditions. The refuse is kept for about a day in each section of the digester and thus, the digestion process is completed in about seven days. The resulting compost is quite satisfactory' for direct field application without addition of supplementary nutrients.

9.3 Write a critical note on biogas.
Ans: It has been estimated that approximately 1,100 million tonnes of wet animal dung per annum are available in our country from 2.50 million catties. Even at 66 % collection rate, this cattle dung can produce 22,500 million cubic litres of biogas through biogas plants and save 14,000 million liters of kerosene per year, which is mainly used in the villages for lighting and partly for cooking. In addition, the slurry from biogas plants can produce 210 million tonnes of organic manure, which can replace 1.4 million tonnes of nitrogen (N2), 1.3 million tonnes of phosphate (P203) and 0.9 million tonnes of potash (K2O) per year.
Unfortunately, this tremendous source of bioenergy has not yet been fully tapped. The variable factors range from cattle dung availability and its calorific value to biogas yield and appliance efficiency. Two major research needs in the area of biogas technology are restricted use of water in biogas plants and better strains of methane generating bacteria. In addition, temperature is a critical factor for the amount of methane generation in a biogas plant. The ideal temperature for maximum methane production is approximately 35° C since the bacteria are sensitive to lower temperatures, particularly in the northern regions of India. There is a fall in biogas production below 20° C and it stops altogether at 10°C. There is an urgent need, therefore, to develop new strains of methane generating bacteria which can produce methane at temperatures less than 20° C.

9.4 Describe a method to manufacture particle boards from wastes.
Ans: Scientists at the Indian Pl)"wood Research Institute, Bangalore have developed a technology for manufacturing particle board from rice husk. The particle board obtained by using this technology is a versatile substitute in a wide range of applications. The particle boards, moreover, can also be made decorative by incorporating suitable colours, so they can be made more elegant looking and attractive than any other wood or plywood substitute. The particle board has been found to be superior to wood or plywood boards because of the following advantages it offers:
(1) Particle board is resistant to termites (white ants)
(2) It has a high resistance against decay.
(3) The particle board has excellent mechanical properties such as elasticity, dimensional stability, screw and nail holding capacity, abrasion resistance and surface hardness.
(4) It has an improved water resistance.
(5} It has a high durability.
Depending on the market demand, a varied of product-mix can be produced by varying the density and resin content of the boards. The method of particle board manufacture involves the following basic steps:
(1) Cleaning of the raw material (the rice husk).
(2) Application of adhesive.
(3) Matformmg.
(4) Edge trimming.
(5) Sanding.
(6) Stacking.
The process has been licenced to several firms in India and Malaysia. The particle boards produced by these firms have shown excellent market acceptance and gained popularity because of their elegant look, better mechanical properties and lower prices.

Short Answer Questions:

9.5 What are social wastes?
Ans: Solid waste, the third pollution after air and water pollution, is that solid material which arises from various human activities and which is normally described as useless or unwanted.

9.6 What do you mean by "shredding the solid wastes"?
Ans: Shredding the solid wastes (also known as pulverizing) and then spreading the shredded material on fields has been found to be successful in a number of places. Since spreading it out dries the pulverized refuse, it avoids the problems of offensive rats and file.

9.7 What is a green fuel?
Ans: The fuel obtained from waste plastic contains no lead and had a high octain rating, it is known as GREEN FUEL.

9.8 Define biomethanation?
Ans: Instead of throughing the garbage , this garbage is mixed with water and bacterial species, specifically cultured for production of methane. These bacteria decomposes the waste by eating and as a result produces methane. This process is known as BIOMETHANATION.

9.9 What is fly-ash?
Ans: Fly-ash from coal-fired power plants is a major industrial waste product in India.
9.10 What is incineration?
Ans: It is the final solution for the solid waste problem (including volume reduction).
9.11 The highest calorific value can be obtained from:
(a) Garbage (b) Rubbish
(c) Fathological wastes (d) All have equal value.

9.12 The important vectors of human diseases in regard to solid wastes are:

(a) Rats (b) flies
(c) Both (d) non

9.13 Aquatic weeds cause:
(a) Water-born diseases
(b) Evapotranspiration
(c) Blockage of waterways
(d) none

9.14 Pyrolysis of plastics may yield:
(a) Wax (b) Grease
(c) Adhesive (d) All

9.15 Match the following:
(A) Anthracene (C)Coal tar
(B) Hydrometailurgy (D)Electroplating
(C) Polymerized wastes (B)Metal Extraction
(D) Silver (A)Nonbiodegradable

9.16 Match the following;
(A) Cement (C)Biomass
(B) Compost (A)Flyash
(C) Gasifier (B)Dano process
(D) Magnesium (D)Refractory

9.17 Write True or False:
Open Dumping of solid waste is exclusively practiced in India.(T)

9.18 Write True or False:
Sanitary land fill is an aerobic process.(F)

9.19 Write True or False:
Composting is an anaerobic process.(T)
9.20 Write True or False:
Generally the agricultural waste are non-hazardous.(T)

9.21 Fill in the blanks:
The compound furfural, obtained from corn cobs, is the basic chemical used for the synthesis of nitrofurans.

9.22 Fill in the blanks:
Land-fill operations are quite difficult to carry out during the raining season.

9.23 Fill in the blanks:
One can recover -------- and -------- from the pickle liquor.

9.24 fill in the blanks:
Pathological wastes have a moisture content of about 85%.

9.25 Write the odd one:
(a) Nitrogen (b) Oxygen
(c) Phosphate (d) Potash

9.26 Write the odd one:
(a) Slurries (b) Strong Acids
(c) Solids (d) Sludges