Page 19 - Industrial Wastewater Treatment, Recycling and Reuse

2 Industrial Wastewater Treatment, Recycling, and Reuse

Table 1.1 Typical water uses in chemical and allied industries
Usage Volume Extent of contamination

Reactant Low High
Solvent Low High
Cleaning/stripping agent Medium Medium
Cooling water Large Low
Boiler water Large Low

In the fertilizer industry water is used as a reactant. Production of nitric
acid (used for nitrogen fertilizers) using oxidation of ammonia gas requires a
reaction of NO 2 with water. Similarly, most commonly used wet process for
production of phosphoric acid (required for phosphate fertilizers) also
require water as a reactant. The quantity of wastewater generated in many
industries varies substantially from process to process and is substantially
higher in developing countries. This is also dependent on the nature of
the contaminants and the level of their concentration in the wastewaters.
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For example, the steel industry in India consumes 25–60 m water/ton of
steel, which is 8–10 times higher than that in developed countries. Cooling
waters from the steel and coke industry, therefore, constitute a high volume
and can have contaminants in the form of toxic components such as cyanide,
ammonia, phenols, and metals. In pharmaceutical industries, wastewater
is generated mainly from cleaning equipment. Although the volumes are
not very large, the generated wastewater is significantly polluted because
of the presence of high organic contaminants found in medicinal com-
pounds, solvents, and other materials.

1.1.1 Overall Water Availability
Of the total available water on earth, 97.5% is salty and is not usable as such;of
the remaining 2.5% of fresh water, only a marginal part, 1%, is available for
humanconsumption.Since1950,theworldpopulationhasdoubled,andwater
consumption has increased sixfold; industrial consumption has also grown rap-
idly. To a great extent, recently, parts of the world have already started feeling
the “water crunch.” It is believed that by 2025, India, China, and select coun-
tries ofEuropeand Africa will facewater scarcity.A recent UN reportindicates
that by 2025, two-thirds of the population of the world could face water stress
(UNEP, 2007; Water Scarcity, www.un.org/waterforlifedecade/scarcity.
shtml, Watkins, 2006). The scarcity of water could be in the form of physical
scarcity,wherewateravailabilityislimitedanddemandsarenotmet,oritcould