Page 163 - CW E-Magazine (24-6-2025)

Free to Die

How do increasing CO and methane sugar and fats (A 10-15 year plan for recycle and reuse. The entire coastline
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levels increase the temperature of the India’s energy security and carbon of Mumbai looks dark due to discharge
globe? neutrality, Chemical Weekly, March 19, of untreated sewage. (I feel bad for the
The heat liberated by burning oil, 2019, pp 206-208). millions of tourists who visit Mumbai in
coal or natural gas is a reason, but CO sequestration the fond hope of taking a dip in the sea;
more important is the refl ection of heat Another approach that was consi- in my 56 years of stay in the city, I have
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radiation of the earth back from the dered about 20 years ago was to capture not dared to do this).
stratosphere.
CO , fi ll it in cylinders and dump the Mumbai gets its water from a dis-
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Emissions of methane are also cylinders in the sea. The idea was a tance of 50-60 km. It may as well trans-
contributing to global warming. In fact, nonstarter on day one given the energy port the untreated sewage 50-60 km
methane is 21 times more refl ective of needs to: produce the required amount away, along the sea to reduce pumping
heat than CO at the same concentration. of steel; capture and compress the CO ; costs, treat it there and use it locally for
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the life of cylinders under the sea in a
Lowering CO levels through highly corrosive environment; and the farming. Chennai collects all raw sew-
age in a nearly 50-m wide stream, treats
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conversion risk of sudden release of CO in the it close to the seashore and discharges it
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Many groups are researching reco- event of leakage. No one takes this to the sea. There is scope to consider use
very of CO from the atmosphere and approach seriously. of this water as fertigated water in sur-
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other sources and converting it to useful rounding areas. The high temperatures
products. However, carbon capture and of Chennai can be tackled by spreading
sequestration (CCS) in underground
Efforts are also being made to natural reservoirs, as well as in depleted the treated water on streets, trees,
recover CO directly from the oil & gas fi elds, is a reality. gardens and playgrounds.
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atmosphere (Direct Air Capture, DAC), Raising forest cover The entire used water of cities should
but the low concentration of CO The total forest cover of India is be divided in three parts: Sewage water,
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makes this process diffi cult.
7,15,343-sq.km., of which 14% is dense sullage water and storm water. Separate
Recovery of CO from industries forest. The easiest way to cool any treatment should be provided to each of
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that produce it in large concentration object is to spread water on its surface. these streams.
(up to 20%) such as cement, steel, This cannot be seawater; it has to be Sewage water is the most valuable
alcohol industry – is more feasible. reasonably clean and low-TDS (Total of all three. All sewage should be fi rst
Dissolved Solids) water. Most wastewater
The captured CO can be converted available in cities can be purifi ed and anaerobically digested to recover methane
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to useful industrial chemicals such as used for this purpose. If the wastewater for town gas as well as transportation.
methanol (which can be used as a fuel), from these cities are spread on forests, This sewage can be enriched with cow
and polyols (for polyurethane coatings). those which are lean can be converted dung and other green wastes (e.g., from
But the economics of these processes can to medium forests, and medium forests vegetable markets). The resultant water
only sustain on external fi scal support, as can be converted into dense ones. Such a should be disinfected with ozone and
the cost of hydrogen required to convert conversion of CO to biomass will bring sent to farms for watering crops.
CO to methanol, the energy required down CO levels. 2
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for conversion, and the cost of reco- 2 Phosphorous and potash, present in
very of CO from atmosphere, all add up, This can be tried in some of our sewage, are indestructible elements, and
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and cannot be supported by the value of deserts, as well as those in other essential parts of food. Their accumula-
methanol so produced. In other words, countries (USA, Australia, China and tion in adults is very little (only growing
such a project cannot sustain without parts of Africa) with the greening young people accumulate it). Thus, most
subsidies. Furthermore, after all the starting from the edges. fertilizer that India imports can be in-
effort, the chemical conversion may prove defi nitely recycled. Similarly, signifi cant
net carbon negative. Hence it is important Treating and spraying water quantities of urea can also be recycled
to look at the overall energy balance. Large scale investment in water from the treated sewage.
recycle and reuse is required in all
I have been advocating use of major cities of India. It is a matter of con- The sullage water is much larger in
solar energy to convert CO to a range cern that even a large city like Mumbai volume. It comprises water used in bath-
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of chemicals besides cellulose, lignin, has not invested adequately in water ing, kitchens and washings. It also may

Chemical Weekly June 24, 2025 163

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