Removal of color, suspended solids and cod from textile wastewater using clinoptilolite and persulfate, in batch system
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Date
2015-09-01
Authors
Fagbenro Oluwakemi Kehinde
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Abstract
The supply of clean water is limited by various sources of pollution such as the dye and
textile industries. Previous studies have shown that textile wastewater is toxic,
carcinogenic and mutagenic. Its most obvious characteristics are the strong color, high
chemical oxygen demand (COD) and suspended solid (SS) caused by unfixed dyes and
stuff remaining in the wastewater after production. One of the textile industries in the
northern region, Malaysia, is experiencing difficulties in complying with the standard
discharge limit of effluent against these parameters. Hence they were selected as the
focus of this study. Because textile wastewater is recalcitrant to conventional treatment
techniques, chemical based pretreatment have been suggested to degrade and make
treatable by biological means, where necessary. In the light of this, the treatment potential
of each of clinoptilolite (CPL), persulfate (PS) and a combination of both were
investigated in this study by adsorption, oxidation, and adsorption-oxidation processes. A
series of batch preliminary experiments were conducted to determine the range of each
independent process variable that favours, the three processes (treatments via; CPL, PS,
and CPL/PS). Having predetermined the range of each working (operational) variable,
they were optimized in another series of main experiments using the classical method.
The response surface methodology (RSM) was applied to show the interrelationship
between the dependent and independent process variables. Also, the process variables,
especially dosage of media, initial pH of reaction and reaction time were optimized
alongside the response parameters (color, SS, and COD). The effect of thermal activation
of PS at temperatures of 40°C, 50°C and 60°C was investigated in the PS oxidation
process. In the final analysis, the performances of each optimized system were compared
to determine the most efficient system. Results indicated that, at the predetermined
optimum conditions (particle size: <75μm-250μm, agitation speed: 150rpm, pH: 2,
dosage: 8g and contact time: 100minutes) of treatment via CPL, the optimum removals
for color, SS and COD in terms of percentages (%) were; 90, 90 and 79 respectively.
While PS oxidation (at room temperature) had 90%, 78% and 50% removal of color, SS
and COD respectively at the optimum conditions (agitation speed: 150rpm, dosage: 1/4
(i.e. contaminant/oxidant ratio), pH: 3 and contact time in minutes: 360 (color), 420 (SS)
and 60 (COD). The combined CPL/PS treatment achieved 98%, 99% and 74% for
removal of color, SS and COD at t optimum conditions (CPL dosage: 8g, PS dosage: 1/4,
pH: 4 and contact time in minutes: 300 (color), 210 (SS) and 30 (COD). A comparison of
the three processes showed a better performance of the combined CPL/PS which
achieved an almost complete decolorization and SS removal. However, it achieved less
for COD removal while the sole CPL performed best in COD removal. The performance
of thermal activated PS was found better than the PS oxidation at room temperature. The
findings of this study have shown that the combination of clinoptilolite/persulfate is the
best of the three processes that were investigated and potential to be used to remove SS,
color and COD from raw textile wastewater. However, since all parameters except COD
met the discharge limit, a further treatment is suggested to completely remove the COD.