Majid Kermani, Mitra Gholami, Abdolmajid Gholizade, Mahdi Farzadkia, Ali Esrafili,
Volume 5, Issue 1 (4-2012)
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Background and Objectives: Phenols in trace quantities are usually present in the treated
effluent of many wastewater-treatment plants. Phenol compounds even at low
concentration can cause toxicity, health and significant taste and odor problem
in drinking waters. This research focuses on understanding the sorption process
and developing a cost-effective technology for the treatment of water
contaminated with phenolic compounds, which are discharged into the aquatic
environment from a variety of sources. In order to remove phenolic compounds
from water, a new natural sorbent, rice husk ash, was developed.
Materials and Methods: Removal of phenol, 2-chlorophenol and 4-chlorophenol were characterized by
spectrophotometric technique at wavelengths of 269.5, 274 and 280 nm,
respectively, under batch equilibrium conditions and via changing the
parameters of contact time, initial pH, and initial concentration of adsorbates
and dosages of sorbent. Finally, the results were analyzed by the kinetic and
isotherm models.
Results: in this
study, the equilibrium time was found to be 240 min for full equilibration of
adsorbates. Removal percent of 2-chlorophenol was lower than two others. The
maximum removal of phenol, 2-CP and 4-CP was observed at an initial pH of 5.
The percentage removal of these phenolic compounds increased with increasing
adsorbent dose and decreasing initial concentration. In kinetics studies,
correlation coefficient and ARE factor showed that the sorption of phenol
(R2=0.9999), 2-chlorophenol (R
2=0.9992) and 4-chlorophenol (R
2=1)
fitted by pseudo second order model. Isotherm studies also revealed that,
Langmuirmodel for phenol (R
2=0.9499), Freundlich model for
2-chlorophenol (R
2=0.9659) and 4-chlorophenol (R
2=0.9542)
were the best choices to describe the sorption behaviors.
Conclusion: Sorption
process is highly dependent on the pH and it affects adsorbent surface
characteristics, the degree of ionization and removal efficiency. At high pH
hydroxide ions (OH-)
compete for adsorption sites with phenol molecules. The sorption was done
rapidly and a plateau was reached
indicating the sorption sites occuupied till
they were saturated. Since the increasing sorbent dose would improve
sorption site, its increasing enhances phenolic compounds removal.
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