Page 378 - Industrial Wastewater Treatment, Recycling and Reuse

350 Industrial Wastewater Treatment, Recycling, and Reuse

8.4.2 Adsorbent Modification Using Phosphoric Acid
Treatment
8.4.2.1 Activated Tea Waste
TW can serve as a potential low-cost adsorbent for the removal of phenolic
compounds, especially in a country like India, which is the second largest
producer of tea (Camellia sinensis) in the world, with the state of Assam alone
having a major share. A huge amount of TW is generated by a number of tea
industries during the processing of tea leaves, resulting in a solid waste dis-
posal problem. Keeping in mind this large-scale availability of TW from
Camellia assamica and C. sinensis in this Indian region, research on utilization
of TW for phenolic compound removal will certainly be one step toward
utilizing waste in the form of a cost-effective adsorbent requiring no
regeneration.
The experimental equilibrium data for 4-CP adsorption by ATW indi-
1
cated that the theoretical maximum adsorption capacity was 43.10 mg g .
The adsorption efficiency of 4-CP by ATW is found to be relatively lower
than that of 4-NP, having a capacity of 142.85 mg g 1 (Ahmaruzzaman and
Laxmi Gayatri, 2010b). In both cases, the Langmuir adsorption was found to
be the best fitting isotherm in describing the adsorption process with a coef-
2
ficient of determination, R , value greater than 0.9. On the other hand, the
adsorption of phenol by the same adsorbent was found to be best explained
by the Freundlich model. This shows that every adsorption system is unique,
and the adsorption phenomenon is not only influenced by adsorbent prop-
erties but by certain adsorbate properties such as degree of solubility/hydro-
phobicity, molecular size, and adsorption energy. These adsorption capacity
values using ATW give evidence of increased performance of the same bio-
mass with specific modifications.

8.4.2.2 Activated Egg Shell
Chicken egg shells were activated for use as a low-cost adsorbent for the
removal of phenolic compounds. Calcite and calcareous soil are known
to be good adsorbent sources, and since egg shells are mainly composed
of calcium carbonate, they are also expected to show good adsorption prop-
erties. Figure 8.16 illustrates the single-solute equilibrium adsorption for the
three-phenol system at 298 K using AES. It also indicates an adsorption
order (decreasing) of 4-NP, 4-CP, and phenol, respectively. Analysis of
the data for both 4-CP and phenol adsorption by AES indicates a physical
adsorption process. When isotherm modeling with the five different linear-
ized isotherms was conducted, the Temkin model was found to describe the