Page 47 - Industrial Wastewater Treatment, Recycling and Reuse

30 Industrial Wastewater Treatment, Recycling, and Reuse

specific molecules on the surface of the adsorbent. The attraction of a spe-
cific molecule is believed to be due to action of surface forces that are
responsible for the interaction with it. Apart from purely physical forces
such as van der Waals forces, both physisorption and chemisorption along
with electrostatic attraction can play an important role in the overall
adsorption process. The contribution of physisorption, chemisorption,
and electrostatic attraction can vary depending on the nature of the adsor-
bent (synthetic/biomass derived); the nature of the substrate molecules and
surface molecules; surface modification; presence of acidic or basic groups
on surfaces; and doping of the metal ions of specific functionality on
the surfaces (see, for example, Ahmaruzzaman and Laxmi Gayatri, 2011;
Bhandari et al., 2006; Mane et al., 2003, 2006). The most important cur-
rent applications of adsorption are odor and color removal, removal of
acids, removal of metals, and removal of refractory pollutants in the
chemical industry.
Itisveryimportantthatspecificinteractionsofpollutantswiththesitesavail-
ableonthesurfaceoftheadsorbentbeunderstoodinordertoachievemaximum
removal and therefore the most efficient process performance for COD/
ammoniacalnitrogenremoval.Toaccomplishthis,itisnecessarytocharacterize
process effluents in terms of the nature of contaminants along with their con-
centrationsandadsorbentmaterial.Apartfromtheseaspects,theprocessparam-
eterssuch aspH ofthesolution and temperature also affect the performance and
thereforeneedtobeproperlyaddressedwhiledesigningawastewatertreatment
strategy. Adsorbents can be classified in two major sections:
Inorganic Adsorbents
Zeolites
(A, X, Y, ZSM-5, silicalite, ALPO)
Oxides
(Silica, alumina)
Organic Adsorbents
Activated carbon
(powder, granules, molecular sieves, carbon fiber)
Polymeric adsorbents
Ion exchange resins
Biomass-derived adsorbents
Selection of the most suitable adsorbent is very important from the point of
view of techno-economic feasibility. A huge number of commercial adsor-
bents are available in the market, and proper selection is usually made based
on laboratory studies and prior experience. Although the type of adsorbents