Page 390 - Industrial Wastewater Treatment, Recycling and Reuse

362 Industrial Wastewater Treatment, Recycling, and Reuse

obtained for 4-NP, 4-CP, and phenol, respectively. The maximum desorp-
tion was higher for AES-loaded adsorbents among the activated groups,
reaching 32.53%, 39.55%, and 58.01% for 4-NP, 4-CP, and phenol. For
4-NP, HNO 3 is a better desorbing agent, while for 4-CP and phenol,
NaOH was found to be a good desorbing agent. The study indicates that
4-NP desorption is the most difficult among 4-NP, 4-CP, and phenol.

8.9 DISPOSAL AND COST ANALYSIS

The safe disposal of phenol-loaded adsorbents is an environmental problem
because leaching of the loaded adsorbents due to rain or percolated water
may occur. Some of the methods, with their own inherent advantages
and limitations, include elution, incineration, and pyrolysis. In the elution
method, there is both recovery of the adsorbate molecules and regeneration
of the adsorbent for subsequent use in a number of cycles. Although simple
and inexpensive, there is some loss in efficiency after three or four cycles of
desorption that may be due to blocking of the pores present on the adsorbent
surface. The phenol-loaded adsorbent can be incinerated at high tempera-
tures to yield ash, which can be recycled and reused appropriately. The
release of toxic gases is one of the major disadvantages associated with
the incineration process, especially in the case of chlorinated phenols. This
method of regeneration involves a high cost of energy. However, a lot of
research is required to make the adsorption method technoeconomically
feasible.
Cost is an important parameter for comparing adsorbent materials. It is
usually the cost of the adsorbent that determines the cost of the adsorption
process. The capacity/dose of the adsorbent and kinetics control the cost
of treatment. The total cost for the preparation of the adsorbent can be cal-
culated in a stepwise manner where the breakup costs of heating, drying,
chemicals, and other overhead expenses are taken into consideration. The
typical cost of special-grade AC materials is generally above Rs. 1000 per kg
and many times runs into several thousand rupees per kg. The costs of the
adsorbents used in the present study are less than Rs. 700 per kg.

8.10 Summary
The adsorption technique, especially using new adsorbent materials, in
wastewater treatment provides a promising alternative to treat industrial
wastewaters, in general, and phenolic industrial effluents, in particular.
The study on several activated/nonactivated biomass-derived adsorbents