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CHAPTER 2

Advanced Physico-chemical

Methods of Treatment for

Industrial Wastewaters

Vinay M. Bhandari, Vivek V. Ranade
Chemical Engineering and Process Development Division, CSIR-National Chemical Laboratory, Pune, India

2.1 INTRODUCTION

Industrial wastewater treatment is a vast area encompassing a number of
physical, physico-chemical, and biological methods of treatment. The selec-
tion and practice of any particular method depends largely on a variety of
factors, the most important being quality of wastewater in terms of number
and nature of pollutants and desired level of reduction of these pollutants. In
this context, it is usually presumed that the only goal of industrial wastewater
treatment is removal of pollutants from the effluent to such levels that it
meets the prescribed norms of discharge into surface waters. However,
where the nature of the pollutant is such that the recovery becomes attractive
and contributes to value addition to the existing process, the objectives need
to be modified to removal and recovery of the pollutants to the desired
levels. Another goal that is becoming increasingly important and relevant
is not just removal/recovery of pollutants but that of water as well. Water
recycling and reuse should also be considered in addition to elimination
of pollution. Some of these aspects have already been discussed in Chapter 1.
Wastewater processing often requires a combination of different methods
because a single method is seldom satisfactory. The overall treatment meth-
odology generally consists of primary methods, secondary methods, and
tertiary methods, each having a specific task to perform on the effluent.
Primarymethodsusually modifyeffluent qualityto suitaspecificrequirement
of further processing and include pH modification, clarification, removal of
suspended particles, and to a certain extent, removal of part of the Chemical
Oxygen Demand (COD) from the effluent. The secondary treatment
includes both physico-chemical and biological methods, either alone or in
combination. For example, coagulation, oxidation, membrane separations,
cavitation, and/or biological methods mainly perform the major task of

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