Q.21 What is recycling? Discuss its
importance, by giving suitable examples, in solid waste management. Also give
the advantage of recycling and waste utilization. (AKTU. - 2007-08)
Ans. Recycling: -
The recovery of solid waste components for
possible use as raw materials is called recycling or salvaging. It involves
separating materials (such as scrap metal, glass, paper, plastic, etc.) from
refuse and reprocessing them for reuse.
Examples
of Recycling in Solid Waste Management: -
(i)
Construction Materials from Wastes: -
Construction materials can be
produced/harnessed from wastes such as slit from water works, red mud from
aluminium industry; agricultural wastes, fly-ash from thermal power plants, etc.
(ii)
Utilizing Agricultural Wastes: -
Agricultural wastes can be used
for the manufacture of paper and card-boards. Sugarcane bagasse, an
agricultural waste, is a chief source of cellulose; but it is burnt away as a
cheap fuel.
(iii)
Medicines from Agricultural Wastes: -
Filyal is readily available from
agricultural wastes such as corn cobs and oak hulls. Furfual (which is produced
commercially by the reaction of corn cobs with sulphuric acid) is the basic
material used for the synthesis of nirrofurans. These are important germicides
used for treating cattle disease.
(iv)
Utilizing Slaughter-Houses Wastes: -
Waste products of slaughter
houses can also be utilized. Blood is used in pharmaceutical industry; and
hides and skins are use for leather production.
(v)
Recovery of Heavy Metal Ions: -
The presence of toxic heavy
metal ions in industrial wastes is of major concern. These metals can be
recovered by chemical treatment and/or by bioextractive technology (i.e.,
bioleaching).
(vi)
Liquid Fuels from Agricultural wastes: -
The rising cost of petroleum has
renewed the need for the production of ethanol by fermentation of agricultural
wastes for use as a liquid fuel.
(vii)
Energy from Industrial and Urban Wastes: -
Huge quantities of urban,
municipal and industrial wastes produces are released into the environment with
little or no treatment in developing nations, resulting in environmental
pollution. These wastes can be utilized as an enormous source of potential
energy and thus help in reducing emissions.
(viii)
Conversion of Agricultural Wastes into Cheap and Efficient Fuel: -
Indian scientists, in
collaboration with Dutch researches, have developed a technology of converting
agricultural wastes like rice husk and groundnut shells into briquettes to be
used as an efficient, economical and non-polluting fuel.
(ix)
Rubber from Old Tyres: -
Sulphur-mounting bacteria
‘Seuephotobees’ consume the sulphate from tyre wastes and leave the polymer
backbone of carbons intact during recycling.
(x)
Proteins from Cellulose Waste: -
The tough protective coating of
lignin over cellulose fibers is destroyed. The cellulose matter is then
neutralized with an acid and led to fermentation chamber to be attacked by
cellulomonas bacteria. The bacterial enzymes disintegrate the cellulosic chains
to form disaccharides and render them digestible by micro-organism.
(xi)
Utilizing Aquatic Weeds: -
Aquatic weeds such as water
Hyacinth (Eichhornia) can be utilized by conversion into fertilizers, biogas,
animal feed, paper, etc.
(xii)
Oil from Plastic Waste: -
The synthetic waste-plastic
bags; cartons and computer casings are mixed with heavier oil residues and then
water is added. As a result, chemical compounds break-up to produce synthetic
oil, which is piped to a refinery to yield high quality oil based products.
(xiii) Plastic for Heat an Electricity Generation: -
The association incinerated
municipal waste containing 3 different proportions of plastic, viz., the waste
without added plastic, with 7.5% extra plastic, and with 15% extra plastic.
They found that greater the proportion of plastics in the waste, the greater
heat produced; this heat can be used for generating electricity and lesser
amount of air-borne pollutants produced.
(xiv)
Silk Industry Waste as Poultry Feed: -
The silk industry wastes
containing large quantities of waste-pupae can be used as poultry feed. Because
waste mugg (a wild silk obtained from the cocoon of an Arsanese moth) prepared
in dry form is very rich in animal protein. A mixture prepared from raw
mugg-pupae and its deoiled form compares well with conventional fish meal as a
rich source of protein.
(xv)
Utilized Fly Ash as Bricks: -
Fly ash a, waste material of
pulverised coal fired thermal power stations, has been utilized as building
bricks.
About 80% of the ash from the
coal fed to the boiler is collected in the form of fly ash about 20% is
collected as bottom ash. Fly ash is by nature very fine; whereas bottom ash is
a coarse, spongy material.
Advantages
of Recycling and Waste Utilization: -
By proper utilization of solid
waste, particularly in developing countries, many advantages can be availed.
These include:
(a) Directly or indirectly, waste utilization
contributes to economic development.
(b) Waste utilization is helpful in conservation
of natural resources.
(c) Recycling and waste utilization helps in
generating many useful products which are the basic necessities of life.
(d) Environmental pollution can be
controlled/reduced substantially.
(e) Employment opportunities are generated.
Q.22. Differentiate between BOD and COD. (AKTU. - 2012 - 13)
Ans. Biochemical Oxygen Demand (BOD): -
The amount of Oxygen (mg/1) is taken
up by microorganism that decomposes organic waste matter in water. It is
therefore used as the measure of the amount of certain types of organic
pollutants in water. BOD is calculated by peeping a sample of water containing
a known amount of oxygen for 5'days at 20°C in BOD incubator.
Chemical Oxygen Demand
(COD): -
A parameter of water quality which measures the
amount of oxygen in parts per million required to oxidize organic and
oxidizable inorganic compounds in the water sample. COD is preferable to the
BOD because it is rapidly measurable parameter for river, streams and
industrial waste studies and control of water treatment plants.
