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Reuse of a treated textile effluent from cobalt oxide and sulphate radical-based advanced oxidation process
Author(s)
Depgni, Flash Colombe Tchono
Date Issued
2020
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
Reactive dye waste effluents are the most difficult to treat, as they are highly polluted due to the
structure of the dyestuffs and chemicals used during the dyeing process. Due to the water shortage and
environmental pollution, textile industries are encouraged to treat the waste effluent produced during
dyeing processes so as to facilitate its reuse, as this will contribute to mitigating environmental pollution
and minimise water consumption. However, relatively few of the treatment technologies employed for
the treatment of textile wastewater are applicable for water that is intended for reuse. Many treatment
technologies exist for the treatment of textile waste effluents, but are either limited in efficiency or high
in operating and energy cost. Chemical treatment methods such as the cobalt oxide mediated sulphate
radical-based advanced oxidation process (CO-SR-AOP) shows promise but have not yet been evaluated
for the reuse of textile wastewater in the dyeing process.
The purpose of this work is to study the reusability of a treated reactive dye effluent obtained from
dyeing cotton fabrics using peroxymonosulfate (PMS) activated by a cobalt oxide (Co3O4) catalyst and
using a laboratory-scale continuous wastewater treatment reactor. In order to achieve this, a cobalt oxide
catalyst was hydrothermally synthesised, cotton fabrics were bleached as pre-treatment prior to being
dyed using blue reactive dye and tap water to produce the necessary textile waste effluent. The produced
waste effluent was treated with Oxone (PMS) and a cobalt oxide catalyst; then reused in the next dyeing
process, using an identical dyeing recipe. The pH of the treated effluent was corrected to neutral before
its reuse. The waste effluent from the first cycle of dyeing was treated before its next reuse. This process
was carried out for a maximum of three cycles. The dyed fabrics obtained using the treated effluent were
compared with the ones dyed with tap water in terms of colour fastness. The optimisation of the
reusability of a treated effluent from cobalt oxide and sulphate radical-based advanced oxidation process
was carried out using Design-Expert software version 11.1.2.0 using a Box-Behnken design taken from
response surface methodology. The effects of three factors were studied: Oxone level, dye concentration
and reuse cycles at low, high and medium levels in fifteen experimental runs. Colour fastness of the dyed
fabrics was studied as the response of the trials.
Based on the preliminary results, the treated effluent can be reused in two successive reuse cycles
without altering the fabric’s quality. To obtain more or less 80% colour removal, waste effluent with 3%
dye concentration must be obtained and treated with a high dosage of Oxone (3.5 g/l). Salt can be
recovered by using this process, but with a darker shade of dyed fabric as a result, when compared with the reference. Varying dilution factors and standing times of the treated effluent were investigated but
did not have significant influence on the colour quality of the dyed fabrics.
A useful model was found to predict the colour fastness of dyed fabrics with an effluent treated with the
continuous wastewater treatment reactor system using PMS activated by Co
3
O
4
. The study of the
interaction effects of all three parameters led to the finding that to obtain good colour fastness grading of
the dyed fabrics, the treated effluent can be reused a maximum of two iterations, with a dye
concentration of 5% and an Oxone concentration of 1 g/L. The predicted optimum process conditions for
this process were 1.3 g/l of Oxone used to treat a waste effluent with 4.4% dye concentration and reuse
in a maximum of three reuse cycles.
structure of the dyestuffs and chemicals used during the dyeing process. Due to the water shortage and
environmental pollution, textile industries are encouraged to treat the waste effluent produced during
dyeing processes so as to facilitate its reuse, as this will contribute to mitigating environmental pollution
and minimise water consumption. However, relatively few of the treatment technologies employed for
the treatment of textile wastewater are applicable for water that is intended for reuse. Many treatment
technologies exist for the treatment of textile waste effluents, but are either limited in efficiency or high
in operating and energy cost. Chemical treatment methods such as the cobalt oxide mediated sulphate
radical-based advanced oxidation process (CO-SR-AOP) shows promise but have not yet been evaluated
for the reuse of textile wastewater in the dyeing process.
The purpose of this work is to study the reusability of a treated reactive dye effluent obtained from
dyeing cotton fabrics using peroxymonosulfate (PMS) activated by a cobalt oxide (Co3O4) catalyst and
using a laboratory-scale continuous wastewater treatment reactor. In order to achieve this, a cobalt oxide
catalyst was hydrothermally synthesised, cotton fabrics were bleached as pre-treatment prior to being
dyed using blue reactive dye and tap water to produce the necessary textile waste effluent. The produced
waste effluent was treated with Oxone (PMS) and a cobalt oxide catalyst; then reused in the next dyeing
process, using an identical dyeing recipe. The pH of the treated effluent was corrected to neutral before
its reuse. The waste effluent from the first cycle of dyeing was treated before its next reuse. This process
was carried out for a maximum of three cycles. The dyed fabrics obtained using the treated effluent were
compared with the ones dyed with tap water in terms of colour fastness. The optimisation of the
reusability of a treated effluent from cobalt oxide and sulphate radical-based advanced oxidation process
was carried out using Design-Expert software version 11.1.2.0 using a Box-Behnken design taken from
response surface methodology. The effects of three factors were studied: Oxone level, dye concentration
and reuse cycles at low, high and medium levels in fifteen experimental runs. Colour fastness of the dyed
fabrics was studied as the response of the trials.
Based on the preliminary results, the treated effluent can be reused in two successive reuse cycles
without altering the fabric’s quality. To obtain more or less 80% colour removal, waste effluent with 3%
dye concentration must be obtained and treated with a high dosage of Oxone (3.5 g/l). Salt can be
recovered by using this process, but with a darker shade of dyed fabric as a result, when compared with the reference. Varying dilution factors and standing times of the treated effluent were investigated but
did not have significant influence on the colour quality of the dyed fabrics.
A useful model was found to predict the colour fastness of dyed fabrics with an effluent treated with the
continuous wastewater treatment reactor system using PMS activated by Co
3
O
4
. The study of the
interaction effects of all three parameters led to the finding that to obtain good colour fastness grading of
the dyed fabrics, the treated effluent can be reused a maximum of two iterations, with a dye
concentration of 5% and an Oxone concentration of 1 g/L. The predicted optimum process conditions for
this process were 1.3 g/l of Oxone used to treat a waste effluent with 4.4% dye concentration and reuse
in a maximum of three reuse cycles.
Additional information
Thesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2020
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