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Design and application of a hydrodynamic cavitation system in textile wastewater treatment
Author(s)
Irakoze, Ninette
Date Issued
2020
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
The industrial sector has been growing in South Africa and in Africa in general. This has
caused an increase in generation of wastewater which needs to be treated to avoid polluting
the environment and those living in it. Textile industry is one of the major polluting industries
and textile dyes such as azo dyes are among dyes that are hard to degrade due to their low
biodegradability.
The azo dyes are among persistent organic pollutants (POPs) which are hard to treat using
conventional treatment methods namely biological methods, coagulation/flocculation,
chlorination, adsorption, reverse osmosis etc. This issue has created a need for the
development of advanced treatment methods. Advanced oxidation processes (AOPs) are
among advanced treatment methods that are effective in the removal of POPs from
wastewater. In recent years, one form of AOPs has emerged as a simple method, that is
energy-efficient and that has proved to be successful in the degradation of textile dyes. The
technology is cavitation, which is a technique that involves the generation, growth and collapse
of cavities/bubbles caused by rapid pressure changes. The collapse of the cavities/bubbles
produces high amount of energy releasing highly reactive free radicals (hydroxyl radicals) that
are generated through the dissociation of water molecules. Cavitation can be generated in
different ways and the names of the different types of cavitation are based on the way the
cavitation is generated. The common types of cavitation are hydrodynamic cavitation and
acoustic cavitation.
In this study, a hydrodynamic cavitation (HC) jet loop system with different cavitating devices
was designed and his performance in the treatment of simulated textile wastewater was
investigated. A 10 L of 20 ppm of Orange II sodium (OR2) dye solution was used as simulated
textile wastewater and its decolouration was monitored. The cavitating devices used were a
10 mm throat diameter venturi and 5 orifice plates with different hole diameters (2 mm, 3 mm,
4 mm, 5 mm, and 6 mm). The different cavitating devices were each used in the HC jet loop
system to determine their efficiency in decolourising OR2 dye. The combination of the venturi
and the best performing orifice plate in the HC jet loop system was also investigated. In the
study different inlet pressures (200 kPa, 300 kPa, and 400 kPa) were also investigated to
determine how they affect the performance of the HC jet loop system. Lastly, the energy
consumption and the cost of using the HC jet loop system as an extension on to an existing
plant was also determined. Results have shown that the HC jet loop system performs best at an inlet pressure of 400 kPa.
For the cavitating devices, the orifice plate having a 2 mm orifice plate was found to be the
best cavitating device among all the cavitating devices tested. It has allowed for a 91.11%
decolouration in 10 min when using 400 kPa inlet pressure. The combination of the 10 mm
throat diameter venturi and the 2 mm hole diameter orifice plate provided an intermediate
performance with a 74.08% decolouration while the 10 mm throat diameter venturi provided
the poorest performance with a 58.73% decolouration in 10 min at an inlet pressure of 400
kPa.
With regards to the consumption of energy, the HC jet loop system was found to use 0.548
kW/m3 for dye decolouration which is a relatively low energy consumption compared to the
energy consumption incurred by the UV for instance for dye decolouration. Regarding costs,
the investment costs was estimated to be R 104 843.00 for an HC jet loop system with a
capacity to decolourise 500 L of dye contaminated wastewater. The operating costs were
estimated at R 127.24 for the decolouration of 500 L of dye contaminated water when
considering that the system will be an extension to an existing plant.
Overall the designed HC jet loop system was found to be an effective technique to use for the
decolouration of textile dyes found in textile wastewater such as Orange II sodium salt.
caused an increase in generation of wastewater which needs to be treated to avoid polluting
the environment and those living in it. Textile industry is one of the major polluting industries
and textile dyes such as azo dyes are among dyes that are hard to degrade due to their low
biodegradability.
The azo dyes are among persistent organic pollutants (POPs) which are hard to treat using
conventional treatment methods namely biological methods, coagulation/flocculation,
chlorination, adsorption, reverse osmosis etc. This issue has created a need for the
development of advanced treatment methods. Advanced oxidation processes (AOPs) are
among advanced treatment methods that are effective in the removal of POPs from
wastewater. In recent years, one form of AOPs has emerged as a simple method, that is
energy-efficient and that has proved to be successful in the degradation of textile dyes. The
technology is cavitation, which is a technique that involves the generation, growth and collapse
of cavities/bubbles caused by rapid pressure changes. The collapse of the cavities/bubbles
produces high amount of energy releasing highly reactive free radicals (hydroxyl radicals) that
are generated through the dissociation of water molecules. Cavitation can be generated in
different ways and the names of the different types of cavitation are based on the way the
cavitation is generated. The common types of cavitation are hydrodynamic cavitation and
acoustic cavitation.
In this study, a hydrodynamic cavitation (HC) jet loop system with different cavitating devices
was designed and his performance in the treatment of simulated textile wastewater was
investigated. A 10 L of 20 ppm of Orange II sodium (OR2) dye solution was used as simulated
textile wastewater and its decolouration was monitored. The cavitating devices used were a
10 mm throat diameter venturi and 5 orifice plates with different hole diameters (2 mm, 3 mm,
4 mm, 5 mm, and 6 mm). The different cavitating devices were each used in the HC jet loop
system to determine their efficiency in decolourising OR2 dye. The combination of the venturi
and the best performing orifice plate in the HC jet loop system was also investigated. In the
study different inlet pressures (200 kPa, 300 kPa, and 400 kPa) were also investigated to
determine how they affect the performance of the HC jet loop system. Lastly, the energy
consumption and the cost of using the HC jet loop system as an extension on to an existing
plant was also determined. Results have shown that the HC jet loop system performs best at an inlet pressure of 400 kPa.
For the cavitating devices, the orifice plate having a 2 mm orifice plate was found to be the
best cavitating device among all the cavitating devices tested. It has allowed for a 91.11%
decolouration in 10 min when using 400 kPa inlet pressure. The combination of the 10 mm
throat diameter venturi and the 2 mm hole diameter orifice plate provided an intermediate
performance with a 74.08% decolouration while the 10 mm throat diameter venturi provided
the poorest performance with a 58.73% decolouration in 10 min at an inlet pressure of 400
kPa.
With regards to the consumption of energy, the HC jet loop system was found to use 0.548
kW/m3 for dye decolouration which is a relatively low energy consumption compared to the
energy consumption incurred by the UV for instance for dye decolouration. Regarding costs,
the investment costs was estimated to be R 104 843.00 for an HC jet loop system with a
capacity to decolourise 500 L of dye contaminated wastewater. The operating costs were
estimated at R 127.24 for the decolouration of 500 L of dye contaminated water when
considering that the system will be an extension to an existing plant.
Overall the designed HC jet loop system was found to be an effective technique to use for the
decolouration of textile dyes found in textile wastewater such as Orange II sodium salt.
Additional information
Thesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2020
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