Page 38 - Industrial Wastewater Treatment, Recycling and Reuse

Industrial Wastewater Treatment, Recycling, and Reuse: An Overview 21

waste is largely a myth; hence the maximum one can achieve is to approach
zero discharge. This base fundamental recommendation involves, primarily,
modification in the process part such that waste generation is avoided at all
the processing stages. This could imply changes in raw materials, changes in
solvents used in the process, changes in processing conditions/catalysts such
that no impurities are formed, and near total conversion to the desired prod-
uct. Process examination may reveal changes or alternatives that can elim-
inate or reduce pollutants, or at least decrease the volumes to be treated or
concentrations of the pollutants. To a great extent, substantial efforts have
been continuously directed in this direction for several decades, and many
times multiple options are available for the selection of any process for
manufacturing. Thus, a careful selection of the process based on technical
and societal issues along with economics can provide the most suitable
option in many cases. Further, there should be enough scope to include
further improvements as and when solutions to problems are available.
Next in the hierarchical approach comes wastewater treatment. As
discussed earlier, it is imperative that some waste gets generated in the pro-
cess. It is then essential to treat the wastewater and to determine whether this
water can be recycled and reused. This would imply reuse in the same indus-
trial setup—preferred—or it could also be reuse in other forms. Many times,
this theme is applicable to waste that does not contain any harmful sub-
stances. For example, if the wastewater has useful amounts of only ammo-
niacal nitrogen and phosphates that can serve as nutrients, it can be directly
used for gardening or agricultural purposes.
Third in the hierarchical pyramid comes recycling and reuse of treated
(waste) waters. This is quite challenging at times and requires careful eval-
uation of all the possible options before implementation. The second and
third levels in the pyramid are interlinked or should be interlinked, but this
may not be possible.
The fourth and last option in the hierarchical triangle is disposal. Waste
material that is absolutely untreatable and cannot be recycled in any way has
to be disposed of in a safe manner. Incineration and landfill are the common
examples of end disposals.
A wastewater flowchart is recommended that provides data for a
complete wastewater management plan. It involves the following steps:
1. Chemical reaction/reactant/catalyst modification for eliminating/reducing pollut-
ants. Effluent treatment is the last step in plant operations and therefore
has a lower degree of freedom as far as pollutant quality and quantities
are concerned, especially for hazardous effluents or for effluents