• 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 (N 2 ), 1.3 million tonnes of phosphate (P 2 0 3 ) and 0.9 million tonnes of potash (K 2 O) 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.
• 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.
• 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:
• 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.
• 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.
• 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.
• 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.
• What is fly-ash?
Ans: Fly-ash from coal-fired power plants is a major industrial waste product in India.
• 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
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