Theses and Dissertations (Civil and Chemical Engineering)https://hdl.handle.net/10500/29242024-03-28T12:18:03Z2024-03-28T12:18:03ZApplication of chlorine dioxide as an alternative pre-oxidant in the treatment of eutrophic raw waterStrydom, Willem Frederickhttps://hdl.handle.net/10500/309562024-03-18T11:38:15Z2017-10-01T00:00:00ZApplication of chlorine dioxide as an alternative pre-oxidant in the treatment of eutrophic raw water
Strydom, Willem Frederick
The Vaalkop water treatment works (WTW) abstracts water from the Vaalkop Dam, which is situated in the Crocodile West/Marico Water Management Area of South Africa. The bulk of the inflow into the dam is through a canal fed from the Hartebeespoort Dam. The water quality of the Vaalkop Dam was of pristine quality during the time the dam was constructed but has since deteriorated gradually to highly eutrophic. The high nutrient levels have caused high concentrations of NOM, taste and odour problems, leaching of high concentrations of metals and operational problems such as reduced filter run times and high plant water losses. The currently available pre-treatment options have become inadequate to deal with the deteriorating raw water quality and this has prompted an investigation to explore the use of an alternative pre-oxidant in order to address these challenges in the raw water. An assessment of chlorine dioxide (ClO2) as an alternative pre-oxidant was undertaken. The aim was to investigate the effectiveness and economic viability of using ClO2 as a pre-oxidant as well as conditions under which ClO2 should be applied to obtain high quality water.
The ClO2 was generated on site using the two chemical generation method whereby sodium chlorite is reacted with chlorine gas and the resulting ClO2 is directly injected into the raw water pipeline. A full scale plant trial was conducted in parallel with lab scale jar test experiments. The trial was conducted over a twelve month period. The operation of the generator was monitored by determining the generation efficiency and dosing adjustments were carried out based on the ClO2 demand. The water of the various treatment steps and the final water were sampled. Various parameters including NOM indicators, physicochemical and plant operating parameters as well as metal content, disinfection by-product (DBP), bacterial and algal concentrations were monitored.
The two chemical generation method produced an excellent ClO2 yield of ≥96%, and the produced ClO2 was generally found to be a very effective pre-oxidant. This technology was used with very little operational interruptions and no safety related incidents were reported during the trial period. When compared with chlorine, the ClO2 pre-oxidant proved to be much more effective in the prevention of the formation of DBPs in the final water. Whereas a good algal removal rate of ≥97% was achieved during severe cyanobacterial blooms when ClO2 was used as a pre-oxidant, the algal removal rate dropped to 93% when the pre-oxidant was changed to chlorine. Compared to Cl2, a superior taste and odour removal efficiency was achieved when the ClO2 was used as a pre-oxidant. However, similar removal efficiency towards geosmin and 2-methyl-isoborneol (2-MIB) was recorded for the two pre-oxidants. Therefore, it was concluded that: (i) in addition to geosmin and 2-MIB, other unidentified taste- and odour-causing compounds were present in the raw water; and (ii) the ClO2 appears to selectively target these unidentified compounds much more effectively than chlorine. In addition, ClO2 was able to effectively remove the iron and manganese present in the raw water to below the South African National Standard (SANS) 241 limits in the presence of high levels of NOM and the unidentified taste- and odour-causing compounds. Other than leading to the formation of trihalomethanes (THMs), the application of Cl2 under such conditions has previously proven to be ineffective in the removal of iron and manganese as well as taste- and odour-causing compounds.
Since ClO2 is much more expensive than Cl2, the chemical treatment cost increased by 6.8 c/kl at an average dosage of 0.8 ppm when ClO2 was used as a pre-oxidant. However, this increase seems to be offset by additional benefits such as reduction in coagulant demand and increase in treatment rates during times of severe algal blooms. To this end, an initial economic assessment points to ClO2 as a viable option for the treatment of raw water of poor quality for potable use.
As evidenced by results obtained from the assessment of water quality and water treatment plant operational parameters, the application of ClO2 as an alternative pre-oxidant at the Vaalkop WTW was a success. However, Cl2 still remains the cheaper of the two pre-oxidant (Cl2 vs ClO2) and should be applied during periods of reduced organic loading when high rainfall and dam levels are experienced. Chlorine gas is also an efficient and cost effective treatment option to utilise when no taste and odour problems are experienced and low levels of iron and manganese are present in the raw water. Chlorine dioxide is definitely a pre-treatment step of choice during periods of high organic loading when reduced filter run times and high plant losses are experienced. It should also be applied during drought periods and/or low dam levels. During such periods, high algal concentrations coincide with anaerobic conditions, which is normally associated with high levels of iron and manganese contaminants in the raw water.
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2017-10-01T00:00:00ZSynthesis and characterization of hybrid iod exchange resins embedded with hydrous ferric oxide nanoparticles for the removal of metal ions from acid mine drainageSodzidzi, Zizikazihttps://hdl.handle.net/10500/309522024-03-18T13:19:43Z2020-10-01T00:00:00ZSynthesis and characterization of hybrid iod exchange resins embedded with hydrous ferric oxide nanoparticles for the removal of metal ions from acid mine drainage
Sodzidzi, Zizikazi
Acid mine drainage (AMD) is a serious water pollutant that contaminates freshwater sources such as rivers, lakes, ground water and even sediments with heavy metals which include Cr(VI), Cd(II) and Pb(II). In this study a novel remediation strategy for the remediation of Cr(VI), Cd(II) and Pb(II) was developed.
Hybrid anionic and cationic exchange resins embedded with hydrous ferric oxide nanoparticles were synthesized and then subjected to batch adsorption tests to determine the factors influencing the adsorption of Cr(VI), Pb(II) and Cd(II). Lastly, the hybrid cationic resin, HCIX-HFO was used to determine the adsorption of metal ions from a real AMD water sample.
The hybrid anion exchanger (HAIX-HFO) was used for the remediation of Cr(VI). The optimum pH for the removal of Cr(VI) was found to be pH 4. The adsorption of Cr(VI) with and without sulphate was a better fit to the pseudo-second order kinetic model, with an equilibration time of 360 minutes. In the absence of co-competing sulphate the experimentally determined adsorption capacity for Cr(VI) was 4.9 mg.g-1. In the presence of 3000 mg/L sulphate the adsorption capacity for Cr(VI) decreased to 2.2 mg.g-1 while percentage of Cr (VI) adsorbed was 50.8 % in the presence of sulphate. The isotherm studies for Cr(VI) in the absence of sulphate was found to be a better fit to the Langmuir isotherm model, and with the Temkin isotherm model in the presence of sulphate.
The hybrid cationic ion exchange resin (HCIX-HFO) was used to adsorb both Cd(II) and Pb(II). The pH for the optimum adsorption both the two metallic species (Cd(II) and Pb(II)) was found to be pH 4. Like in the case for Cr (VI), the kinetic studies for Cd(II) and Pb(II) in the presence of sulphate followed the pseudo-second order kinetic model and equilibrium was achieved in 360 minutes. The experimentally determined adsorption capacities for Cd(II) and Pb(II) were 1.45 mg.g-1 and 2.27` mg.g-1 respectively. The isotherm adsorption data for both Cd(II) and Pb(II) were a good fit to the Freundlich model. In a competitive study with both Cd(II) and Pb(II) the adsorption of Pb(II) was favoured. HCIX-HFO was effectively regenerated by NaCl with 99.9% of Cd(II) and 98.8% of Pb(II) recovered. On contacting HCIX-HFO with real AMD containing ten different metal ions, high percentage removals were found for Ni(II) (92.6%), Cu(II) (92.5%) and Pb(II) (46.8%). HCIX-HFO has been shown to adsorb cationic metal species in the presence of sulphate and HAIX-HFO has been shown to effectively adsorb Cr(IV) in the presence of sulphate.
2020-10-01T00:00:00ZMetal supported on carbon based materials for adsorptive desulphurisation of fuelsMguni, Liberty Lungisanihttps://hdl.handle.net/10500/305662023-10-12T07:06:54Z2021-09-19T00:00:00ZMetal supported on carbon based materials for adsorptive desulphurisation of fuels
Mguni, Liberty Lungisani
The transport industry is one of the biggest contributors to air pollution, with the major air pollutants being COx, NOx, and SOx. SOx is produced by the combustion of the organic sulphur compound found in fuels, e.g. thiophene, mercaptan and sulfides. Adsorptive desulphurization with novel adsorbents was investigated at ambient conditions in this study, to find an economically viable and effective alternative method of removing sulphur from diesel fuel.
First, a review of adsorbent improvement strategies was done, including their effects on thermodynamics, kinetics and equilibrium adsorption isotherms, as well as the screening of the most promising adsorbent. Activated carbon (AC) was the most promising adsorbent, based on the figure of merit (FoM), while metal-organic frameworks (MOFs) were the most active. There is no consensus on the parameters that have the most influence on adsorption activity, and machine learning presents an opportunity to investigate this phenomenon. In this work, three regression techniques were used in research: linear regression; multiple regression; random forest. The findings suggest that adsorbent properties (metal ion, metal properties, surface area and pore volume) need the most attention in order to improve adsorbent activity.
The first experimental work done was to screen a number of commercial adsorbents using both model and conventional diesel. AC showed good activity with both model diesel and conventional diesel. For the first time, the sulphur adsorption order for conventional diesel produced in South Africa was reported on, with decreasing order of: 4-MDBT>> 4,6-DMDBT̴̴̴̴̴̴̴̴̴ 4 E,6-MDBT̴̴̴̴̴̴ 2,4,6-TMDBT̴̴̴̴̴̴1,4,6-TMDBT. The study also investigated the effect of different supports and Lewis acid metals, and the analysis indicated that AC and NiO were the most promising. The high activity level of NiO was attributed to it having the lowest acidity level, based on the ionic-covalent parameter.
MOFs are an emerging class of porous materials that are constructed from metal-containing nodes and organic linkers. They have the potential to be easily manipulated to synthesize an adsorbent with unique properties. In this study, Ni-doped MOFs (Ni-BDC) and the composites of AC@Ni-BDC were synthesized in the presence of formic acid, which has evidenced three effects, namely: i) accelerating MOF synthesis; ii) modulating crystallite size; iii) controlling crystallinity. The experimental results showed that modulated synthesis of Ni-based MOFs using formic acid improved the overall adsorptive activity of MOF almost twofold. The adsorption activity of the composite towards thiophene (TH) was the average of the two materials (i.e. AC and Ni-BDC), while the activity doubled for dibenzothiophene (DBT) and 4, 6-dimethyldibenzothiophene (4, 6 DMDBT) with respect to the expected average. The improved activity was attributed to enhanced pore structure, crystallinity and synergistic effects that produce stronger acidic sites. Finally, the synthesized composite has the potential to remove the sulphur compounds in a broad spectrum.
2021-09-19T00:00:00ZCharacterization and properties of sulfonated chitosan membrane for direct methanol fuel cellModau, Livhuwani Elsiehttps://hdl.handle.net/10500/305642023-10-12T06:15:28Z2023-04-11T00:00:00ZCharacterization and properties of sulfonated chitosan membrane for direct methanol fuel cell
Modau, Livhuwani Elsie
This dissertation examines the structure and properties of chitosan membranes regarding their applicability in fuel cells. The objective of this work is to synthesize a polymer membrane with improved properties such as high proton conductivity, low water uptake, low methanol permeability, and high efficiency. Membranes made of synthetic polymeric materials with enhanced functionality have been developed to compensate for Nafion® deficiency. Polymeric membranes have numerous benefits, including an excellent mechanism for pore-forming control, high mechanical strength, low cost, and greater flexibility.
The membrane properties such as identification of functional groups using Fourier Transform Infrared (FTIR), physical properties using Scanning Electron Microscope (SEM), water uptake, Ion Exchange Capacity (IEC), proton conductivity, methanol permeability, and tensile strength were evaluated. Silica is used as a filler, and it was synthesized through Sol-gel and Stober methods and was calcinated for 2h and 24h. Synthesized silica particles were categorized as pure and sulfonated.
The membranes showed successful modification with silica. It was found that the water uptake and proton conductivity of the unmodified and modified silica/chitosan membrane increase with an increase in filler content. The s-SiO2/Cs membranes show improvement in membrane properties, particularly, the 4% s-SiO2/Cs (Sol-gel 24h) which has superior proton conductivity of 0.238 Scm−1 which is higher than that of Nafion® of 1.43 x 10-2 Scm−1. However, this membrane has a methanol permeability of 0.97 × 10−7 cm2s−1 which is higher than 2.83 x10-6 cm2s−1 of Nafion®. The selectivity of the fabricated membrane is 1.269 x 105 S.s/cm-3 which is higher compared to that of Nafion® of 3.71 x 104 S.s/cm-3.
It was found that the incorporation of silica particles successfully improves the chitosan membrane’s proton conductivity while suppressing its methanol permeability. The recommended synthesis method of silica is by Sol-gel, and it is significant to introduce sulfonic groups in the silica as to improve its suitability as a membrane filler.
2023-04-11T00:00:00Z