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Selected operating process variables for a bioflocculant supported column flotation system
Author(s)
Mukandi, Melody
Date Issued
2023
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
The poultry industry generates significant volumes of slaughterhouse wastewater, which is laden with
numerous pollutants, thus requiring treatment prior to discharge. However, the current typical water and
wastewater treatment technologies have reached their limits due to the concentration of the pollutants
therein and the large volumes of the wastewater to be treated, which influence the resultant water quality.
Hence, there is a need for new technologies, re-engineering of the existing wastewater treatment equipment,
and incorporating new unit designs to improve the treatment processes or system performance. Flotation is
a well-known separation technology with the potential to be applied in wastewater pretreatment. Flotation
is highly dependent on bubble size generated by air diffusers. However, inherent drawbacks underscore the
significance of air diffusers design, making their design and study important. Currently, chemical
flocculants, although widely used, are discouraged in flotation systems as some are considered harmful to
humans and the environment. Meanwhile, the use of bioflocculants is considered eco-friendly, albeit their
application requires further studies at an industrial scale. For the current study, the main aim was to evaluate
the effect of selected operating process variables, i.e., diffuser type, bioflocculant form, and feed flow rate,
on the performance of a bioflocculant-supported column flotation system for poultry slaughterhouse
wastewater (PSW) pretreatment.
Firstly, the design and production of laboratory-scale 3D-printed spargers using the Laser-Powder Bed
Fusion, a part of additive manufacturing, was explored to determine their applicability in a flotation system
for wastewater pretreatment. Furthermore, they were compared to conventionally sintered/molded diffusers
through microstructural analysis employing optical microscopy, tested for Vickers hardness, and analyzed
for surface topography, including composition, using a scanning electron microscope and energy-dispersive
spectroscopy. The application of 3D-printed spargers was proven feasible, revealing their porous nature,
albeit with fewer pores than molded diffusers. Notably, the latter’s, dense pores and better microstructure
was thought to significantly enhance their suitability for optimizing the column flotation process. To
overcome limitations related to pore properties, there is a need to explore new-generation alloys and
optimize the 3D-printing process to make the final product more competitive and efficient than molded
diffusers.
Secondly, the study went on to focus on the isolation of bioflocculant-producing microorganisms from
PSW. Characteristics of the produced bioflocculant were determined, including the optimum storage
conditions and the flocculation mechanism. Twenty microorganisms were isolated, and the D2 isolate had
maximum flocculation activity. It was identified using 16S rDNA to be a Bacillus species and using RpoD to be a Bacillus megaterium. The bioflocculant was composed of mainly polysaccharides and proteins and
was better stored in a crude form under frozen conditions.
Thirdly, the flocculation mechanism was assessed by Response Surface Methodology (RSM) at pH 4 (min)
to 9 (max); bioflocculant dosage of 1% (min) to 3% (max) v/v with an assessment of changes in zeta
potential as a measure of the changes in the electrostatic potential of the bulk solution. Zeta potential results
confirmed that the bioflocculant was ionic, albeit charge neutralization was not the primary mechanism.
These results were inconclusive in determining optimum conditions for flocculation activity; hence, flocs
were viewed under a microscope, showing the optimum conditions for flocculation activity at pH 6.5 with
a bioflocculant dosage of 2% (v/v). A bonding type test was carried out, and hydrogen bonding was
identified as predominant, suggesting a bridging mechanism. This assertion was supported by the type of
functional groups present in the structure of the bioflocculant produced by the D2 isolate.
Fourthly, three variables, i.e., diffuser design/type, bioflocculant form, and influent flow rate, were
evaluated to determine their effect on the performance of a bioflocculant-supported column flotation
system. It was found that diffuser type and feed flow rate were influenced by bioflocculant efficacy,
thus affecting the overall column flotation system performance. In addition, it was determined that
3D-printed air diffusers and cell-free bioflocculants were a superior type and form, respectively, compared
to their counterparts, i.e., molded diffusers and cell-bound bioflocculants. Combining 3D-printed air
diffusers and cell-free bioflocculants at a feed flow rate of 1 ml/min resulted in relatively high pollutant
removal (COD, TSS, protein, and turbidity reduction).
The study laid a foundation for exploring 3D-printed air diffusers, a relatively new technology in
conjunction with bioflocculants usage that are regarded as eco-friendly, for application in wastewater
pretreatment to enhance the performance of column flotation systems.
numerous pollutants, thus requiring treatment prior to discharge. However, the current typical water and
wastewater treatment technologies have reached their limits due to the concentration of the pollutants
therein and the large volumes of the wastewater to be treated, which influence the resultant water quality.
Hence, there is a need for new technologies, re-engineering of the existing wastewater treatment equipment,
and incorporating new unit designs to improve the treatment processes or system performance. Flotation is
a well-known separation technology with the potential to be applied in wastewater pretreatment. Flotation
is highly dependent on bubble size generated by air diffusers. However, inherent drawbacks underscore the
significance of air diffusers design, making their design and study important. Currently, chemical
flocculants, although widely used, are discouraged in flotation systems as some are considered harmful to
humans and the environment. Meanwhile, the use of bioflocculants is considered eco-friendly, albeit their
application requires further studies at an industrial scale. For the current study, the main aim was to evaluate
the effect of selected operating process variables, i.e., diffuser type, bioflocculant form, and feed flow rate,
on the performance of a bioflocculant-supported column flotation system for poultry slaughterhouse
wastewater (PSW) pretreatment.
Firstly, the design and production of laboratory-scale 3D-printed spargers using the Laser-Powder Bed
Fusion, a part of additive manufacturing, was explored to determine their applicability in a flotation system
for wastewater pretreatment. Furthermore, they were compared to conventionally sintered/molded diffusers
through microstructural analysis employing optical microscopy, tested for Vickers hardness, and analyzed
for surface topography, including composition, using a scanning electron microscope and energy-dispersive
spectroscopy. The application of 3D-printed spargers was proven feasible, revealing their porous nature,
albeit with fewer pores than molded diffusers. Notably, the latter’s, dense pores and better microstructure
was thought to significantly enhance their suitability for optimizing the column flotation process. To
overcome limitations related to pore properties, there is a need to explore new-generation alloys and
optimize the 3D-printing process to make the final product more competitive and efficient than molded
diffusers.
Secondly, the study went on to focus on the isolation of bioflocculant-producing microorganisms from
PSW. Characteristics of the produced bioflocculant were determined, including the optimum storage
conditions and the flocculation mechanism. Twenty microorganisms were isolated, and the D2 isolate had
maximum flocculation activity. It was identified using 16S rDNA to be a Bacillus species and using RpoD to be a Bacillus megaterium. The bioflocculant was composed of mainly polysaccharides and proteins and
was better stored in a crude form under frozen conditions.
Thirdly, the flocculation mechanism was assessed by Response Surface Methodology (RSM) at pH 4 (min)
to 9 (max); bioflocculant dosage of 1% (min) to 3% (max) v/v with an assessment of changes in zeta
potential as a measure of the changes in the electrostatic potential of the bulk solution. Zeta potential results
confirmed that the bioflocculant was ionic, albeit charge neutralization was not the primary mechanism.
These results were inconclusive in determining optimum conditions for flocculation activity; hence, flocs
were viewed under a microscope, showing the optimum conditions for flocculation activity at pH 6.5 with
a bioflocculant dosage of 2% (v/v). A bonding type test was carried out, and hydrogen bonding was
identified as predominant, suggesting a bridging mechanism. This assertion was supported by the type of
functional groups present in the structure of the bioflocculant produced by the D2 isolate.
Fourthly, three variables, i.e., diffuser design/type, bioflocculant form, and influent flow rate, were
evaluated to determine their effect on the performance of a bioflocculant-supported column flotation
system. It was found that diffuser type and feed flow rate were influenced by bioflocculant efficacy,
thus affecting the overall column flotation system performance. In addition, it was determined that
3D-printed air diffusers and cell-free bioflocculants were a superior type and form, respectively, compared
to their counterparts, i.e., molded diffusers and cell-bound bioflocculants. Combining 3D-printed air
diffusers and cell-free bioflocculants at a feed flow rate of 1 ml/min resulted in relatively high pollutant
removal (COD, TSS, protein, and turbidity reduction).
The study laid a foundation for exploring 3D-printed air diffusers, a relatively new technology in
conjunction with bioflocculants usage that are regarded as eco-friendly, for application in wastewater
pretreatment to enhance the performance of column flotation systems.
Additional information
Thesis (DEng (Chemical Engineering))--Cape Peninsula University of Technology, 2023
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