School of Engineeringhttps://hdl.handle.net/10500/29102024-03-28T21:03:01Z2024-03-28T21:03:01ZApplication 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.
2020-10-01T00:00:00ZDeveloping a framework for the classification of strategic and critical minerals in South AfricaPule, Dikgwatlhe Israelhttps://hdl.handle.net/10500/307012024-01-22T11:21:31Z2022-12-01T00:00:00ZDeveloping a framework for the classification of strategic and critical minerals in South Africa
Pule, Dikgwatlhe Israel
Minerals should be sufficient to sustain security of the nation as well as
growth of the economy and employment. Countries without minerals may
source minerals from mineral-rich countries. South Africa is endowed with
mineral resources and has a comparative advantage in minerals such as
manganese, chromium, vanadium and platinum amongst others. Mineral
wealth can contribute towards resolving the challenges of a high rate of
unemployment, poverty and inequality.
Most of the minerals in South Africa are exported as raw materials and
once produced, final products are sold back to the country and imported
as finished products. Trade-offs between exports as raw ore or
beneficiated minerals which have a higher value should be considered for
contribution in this country towards industrialisation and employment.
Identified and selected critical and strategic minerals can promote
economic growth and industrialisation. An assessment methodology
utilising three categories namely, economic importance, risk and impact
was used to develop a framework to classify minerals as strategic and
critical in South Africa. Thirty-eight minerals were identified, eighteen
potential strategic and critical minerals selected and most contributing
seven strategic are selected according to economic importance, risk and
impact factors. The framework contributes to policy-making, economic
growth, and security of supply. It also promotes development of minerals
and optimises value from the minerals and their economic use and
enhances industrialisation and employment.
In this research a survey was also conducted on the perceptions of local
people at or close to mines on the positive and negative socio-economic
impacts of mining in their communities. The first outcome indicated that
mining communities and employees are aware of the mineral wealth of the
country and have lamented on the level of poverty and inequality of
employment experienced in their areas where mining activities are taking
place.
The study further revealed misunderstandings and unfulfilled expectations
concerning the responsibilities of the mining companies and the
accountability of the government towards the community. Limited
resources and desperation for opportunities by employees and
communities could lead to a disaster in the mining industry if these
perceptions are not addressed.
2022-12-01T00:00:00ZDeveloping a framework for the classification of strategic and critical minerals in South AfricaDikgwatlhe, Israel Pulehttps://hdl.handle.net/10500/306892023-11-29T12:23:21Z2022-12-01T00:00:00ZDeveloping a framework for the classification of strategic and critical minerals in South Africa
Dikgwatlhe, Israel Pule
Minerals should be sufficient to sustain security of the nation as well as growth of the economy and employment. Countries without minerals may source minerals from mineral-rich countries. South Africa is endowed with mineral resources and has a comparative advantage in minerals such as manganese, chromium, vanadium and platinum amongst others. Mineral wealth can contribute towards resolving the challenges of a high rate of unemployment, poverty and inequality.
Most of the minerals in South Africa are exported as raw materials and once produced, final products are sold back to the country and imported as finished products. Trade-offs between exports as raw ore or beneficiated minerals which have a higher value should be considered for contribution in this country towards industrialisation and employment. Identified and selected critical and strategic minerals can promote economic growth and industrialisation. An assessment methodology utilising three categories namely, economic importance, risk and impact was used to develop a framework to classify minerals as strategic and critical in South Africa. Thirty-eight minerals were identified, eighteen potential strategic and critical minerals selected and most contributing seven strategic are selected according to economic importance, risk and impact factors. The framework contributes to policy-making, economic growth, and security of supply. It also promotes development of minerals and optimises value from the minerals and their economic use and enhances industrialisation and employment.
In this research a survey was also conducted on the perceptions of local people at or close to mines on the positive and negative socio-economic impacts of mining in their communities. The first outcome indicated that mining communities and employees are aware of the mineral wealth of the country and have lamented on the level of poverty and inequality of employment experienced in their areas where mining activities are taking place.
The study further revealed misunderstandings and unfulfilled expectations concerning the responsibilities of the mining companies and the accountability of the government towards the community. Limited resources and desperation for opportunities by employees and communities could lead to a disaster in the mining industry if these perceptions are not addressed.
2022-12-01T00:00:00Z