Page 49 - Industrial Wastewater Treatment, Recycling and Reuse

32 Industrial Wastewater Treatment, Recycling, and Reuse

exchange resins for effective salt removal, removal of ionics, and removal of
organics, which finally results in a large reduction in COD levels and also
removal of ammoniacal nitrogen.
In the cation exchange process, ammoniacal nitrogen typically gets
removed in the following way:
+ +
R H +NH 4 NO 3 ! R NH 4 + HNO 3
+ +
ð
R H +NH 4 Þ SO 4 ! R NH 4 +H 2 SO 4
2
The regeneration of the resin is carried out using acid to reverse the
above reaction:
+ +
R NH 4 + HNO 3 ! R H +NH 4 NO 3
Selection of suitable resins for obtaining high operating capacity with
ease of regeneration is very important in the design. High operating capacity
results in lowering the quantity of resin required for operating the treatment
process, and easy regeneration results in lowering regenerant consumption
and also minimizing the secondary waste stream.
The design of the ion exchange process involves selection of an appro-
priate resin as a first step. Not all resins are suitable for any specific applica-
tion. It is necessary to make proper selection of the resin once objectives of
wastewater treatment are clearly defined (e.g., salt removal, removal of ionic
species, or removal of organics in the present context). The second step
involves characterization of the resins through capacity determination, size
analysis (important from the pressure drop point of view in the final design),
and pore size/size distribution (important from the kinetics/rate point of
view). The important parameter is the maximum or theoretical capacity
of the resin and the operating capacity that is required for the design of
the column. The third step requires ion exchange breakthrough studies in
wastewater treatment, an important parameter in plant operation. The
nature of the breakthrough curve gives a lot of information required for
the design of ion exchange systems in terms of length of used/unused
bed. The sharpness of the breakthrough profile indicates near total capacity
utilization for the resin while a more dispersed/spread nature of the break-
through curve indicates poor capacity utilization (which in turn indicates
that the resin may not be suitable for actual application). Other aspects, such
as fouling of the resin and extent of color removal, also need careful evalu-
ation. The final step requires regeneration studies for the selected resin.
Typically, for adsorption/ion exchange, the useful number of experi-
ments can be seen as: