Many different environmental researches were done on the treatment of water, wastewater
and air pollutants by different biological, physical and chemical processes. Pollution of water
sources by dye pollutants from various industries such as textile, paper, rubber and plastic
industries is a major environmental problem. Organic dyes cause irreparable damage to
the environment due to the avoiding the light entry to water, disruption of photosynthesis,
reduction of oxygen transfer to water, occurrence of eutrophication, interference with
the ecology of the receiving waters, toxic effects as well as unpleasant appearance [1-18].
Different methods are used for the treatment of dye wastewater [19-25].
One of the new methods in dye wastewater treatment is oxidation using cavitation and
ultrasound as well as sono-electrochemical methods. In fact, the photocatalytic oxidation
process by visible or UV light in the presence of catalysts such as titanium dioxide or zinc
oxides one of the advanced oxidation processes in the removal of organic pollutants, that is
more efficient than other processes . Also, using the ultrasonic and acoustic wave motion
in the aquatic environment oscillates the molecules, which creates contractile and expansion
cycles [27,28], breaking the bonds and thus accelerating the purification process.
In this study, the combination of photocatalytic and ultrasonic methods in the treatment
of dye wastewater was investigated. The studied catalyst is zinc oxide which is highly resistant
to light and chemical corrosion. Also, it was applied for oxidizing the wide range of organic
compounds due to its non-toxicity, insolubility, ability to decompose toxic organic compounds,
ability to absorb a wide range of electromagnetic waves and the photocatalytic capability for
We used the response surface methodology, the best multivariate techniques . For
this purpose, Visible Light Source (W), Ultrasonic Power (W), Dye Concentration (mg/L), pH,
Synthesis Temperature (C), nano-particle concentration (gr/L) as variable and percentage of
dye removal as the answer were considered.
In this study, a cubic reactor with dimensions of 30 * 30 * 20cm Figure 1, incandescent
lamps and ultrasonic device with the power 0 to 400w and 20KHz driving frequency were
used. Zn(CH3COO) 2.2H2O and Poly Vinyl Pyrrolidone (PVP) manufactured by Merck were
used for this synthesis. The catalyst synthesis was performed at various temperatures (300,
325, 284.33, 350 and 365.66 °C). The synthesized nanoparticles had almost similar colors and
were close to dark gray. Finally, the optimum temperature was determined after photocatalytic
tests were performed on each of these nanoparticles in the presence of ultrasound and visible
light. In this study, the model was presented based on response surface methodology tests
using Design Expert 10 software and Quadratic model to evaluate the nonlinear behavior
of the results. The target contaminant is methylene blue dye with the chemical formula of
C16H18N3SCl and molecular weight of 319.85gr/mol made by Merck, Germany. It is a cationic
dye that has a pH=3 at 20 °C and is one of the aromatic chemical
dyes. For this reason, it is carcinogenic, mutagenic, often toxic
and resistant to biodegradation. According to the results, the
simultaneous effect of the variables on the dye removal percentage
was investigated presented in Figure 2.
As can be seen, the higher synthesis temperature caused the
lower removal rate; The better synthesis temperature for the ZnO
nanoparticles is 300 °C. The above nanoparticles also perform
better at the alkaline pH (about 10) and the removal rate increases
Figure 2(a). According to Figure 2(b), as the dye concentration
decreases, the removal percentage also increases. By increasing the
synthesis temperature, the removing ability of the nanoparticles
and consequently the dye removal percentage decreased. So, the
optimum synthesis temperature and contaminant concentration
is 300 °C and 25ppm. On the other hand, it observed a better
removal percentage in 30 minutes because the nano-particle bonds
broke under irradiation and ultrasound waves and produced more
negative hydroxyl. So, higher removal rates could be observed
at higher times. As shown in Figure 2(c), the optimum time and
dye concentrations 30 minutes 25ppm. Also, the interaction
graphs showed the antagonistic effect of pH on temperature and
temperature on dye concentration. But time has a synergistic effect
on the color concentration pollutant removal percentage.
Figure 1:The schematic of used reactor.
Figure 2:Simultaneous effect of variables on removal percentage.
AzizpourF, Qaderi F (2019) Optimization modeling and uncertainty investigation of phenolic wastewater treatment by photocatalytic process in cascade reactor. Environment Development and Sustainability, Netherlands.
Dejohn PB, Hutchins RA (1976) Tex Chem Color 8: 69.
Professor, Chief Doctor, Director of Department of Pediatric Surgery, Associate Director of Department of Surgery, Doctoral Supervisor Tongji hospital, Tongji medical college, Huazhong University of Science and Technology