UWCScholar :: Browsing by Author "Petrik, Leslie"

Browsing by Author "Petrik, Leslie"

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A comparison of Brine evaporation rates under controlled conditions in a laboratory
(University of the Western Cape, 2018) Bent, Denzil; Petrik, Leslie
There are growing concerns around the environmental issues related to processed water as the demand for potable water is on the increase in South Africa. Effluents discharged from various sectors such as water treatment facilities pose a constant threat to the environment and natural water resources, including rivers and groundwater due to their poor chemical and physical composition. As a result, the demand for predicting the elevated concentrations of salts in a spatial and temporal dimension is constantly growing. The effluent at the eMalahleni water reclamation plant in Mpumalanga, South Africa, is being processed through a triple reverse osmosis that improves the water quality of the mine water to potable standards. Two water quality streams emerge from this process, i.e. a potable standard and the other a brine concentrate which is stored in ponds. Brine ponds are used for inland brine disposal in the eMalahleni water reclamation plant. The large volumes and limited capacity to store brines has placed great emphasis on enhanced evaporation rates to increase the efficiency of the ponds. In order to improve the rate of brine evaporation in the pond, an understanding of the effect of brine salt content and other parameters affecting the rate of evaporation is required. This study aimed at establishing the physical and chemical behaviour of the brine from the eMalahleni plant in a controlled environment. The investigation incorporated actual brine from the eMalahleni plant as well as synthetic salts typical of the major components of the eMalahleni brine.
Active neutralisation and amelioration of acid mine drainage with fly ash
(University of the Western Cape, 2009) Surender, Damini; Petrik, Leslie; Faculty of Science
Fly ash and AMD samples were characterised by standard analytical methods for selection of the test materials. Active treatment by means of mixing fly ash with AMD in beakers and a large tank at pre-determined ratios have shown that fly ash is capable of neutralising AMD and increasing the pH beyond neutral values, which optimises the removal of heavy metals and ions. The trend was: the more fly ash added the quicker was the reaction time and higher the pH values achieved. Iron was reduced by as much 99 % in beaker scale experiments via Fe(OH)3 precipitation at pH values >4.0. A 99 % decrease in aluminium concentration was observed which was attributed to the precipitation of primarily gibbsite and various other mineral phases at pH values >5.5. As the pH increases, sulphate is adsorbed via Fe(OH)3 and gypsum precipitation at elevated pH. Sulphate attenuation with fly ash was excellent, achieving 98 % attenuation with beaker scale experiments and 1:1 fly ash:AMD ratio. Sulphate attenuation with fly ash was comparable to membrane and ion exchange systems and exceeded the performance of limestone treatment. Except for the larger volumes of fly ash needed to neutralise the AMD, fly ash proved to be a feasible and cost efficient alternative to limestone treatment. Fly ash produced competing results to limestone concerning acidity removal and sulphate attenuation. The comparison highlighted the advantages of utilising fly ash in comparison to limestone and demonstrated its cost effectiveness. The results of this study have shown that fly ash could be successfully applied for the neutralisation of acid mine drainage (AMD) and effectively attenuate the sulphate load in the treated water. The critical parameters to this technology are the variations of chemical composition and mineralogy of fly ash, which could influence the pH, contact time of the neutralisation reaction, and the same is true if the AMD quality varies.
Active neutralisation and amelioration of acid mine drainage with fly ash
(University of the Western Cape, 2009) Surender, Damini; Petrik, Leslie
Due to the constraints being placed on water resources and a drive for major industries to recycle waste water, improved and cheaper water treatment technologies are being investigated. During mining, pyrite (FeS2), a mineral naturally occurring in the earth’s structure, becomes oxidised when exposed to oxygen and water, resulting in the release of hydrogen ions, sulphate ions and metal cations. Coal mining operations, located in one of the largest coalfields in the country, in Mpumalanga province, is a major contributor to the generation of acid mine drainage (AMD) and is estimated to produce 360 Ml/d after closure of the entire Mpumalanga Coalfields. Commonly applied chemically treatment processes for AMD involve the use of limestone to neutralise the AMD, however elevated sulphate concentrations persist in the neutralised water. Membrane and ion exchange technology are more successful in attenuating sulphate in AMD; however, they are often complex and have exorbitant capital and operating costs. Universally, fly ash has been applied for the treatment of AMD primarily in passive treatment systems. Passive treatment technologies require little or no operation and maintenance e.g. constructed wetlands and anoxic limestone drains. However, with specific reference to AMD treatment, passive treatment systems require long retention times and greater space as well as provide uncertain treatment efficiencies. Recent research has demonstrated the potential to apply fly ash in active treatment systems for AMD treatment and amelioration. Active treatment technologies make use of some chemical addition or advanced technology e.g. membrane technologies and ion exchange resins. Whilst active treatment technologies are often more expensive than passive treatment systems, active treatment occurs at a faster rate and treatment efficiencies are more controllable and effective. This study investigated the potential of fly ash to actively neutralise and ameliorate or improve the quality of AMD at beaker and large scale with special attention given to sulphate attenuation. The results of the investigation were compared to data of state-of-the-art treatment technologies, obtained from literature. These included chemical treatment, membrane treatment, ion exchange and biological treatment systems. A comparative study was conducted to ascertain the feasibility of fly ash versus the commonly used limestone treatment technology. Fly ash and AMD samples were characterised by standard analytical methods for selection of the test materials. Active treatment by means of mixing fly ash with AMD in beakers and a large tank at pre-determined ratios have shown that fly ash is capable of neutralising AMD and increasing the pH beyond neutral values, which optimises the removal of heavy metals and ions. The trend was: the more fly ash added the quicker was the reaction time and higher the pH values achieved. Iron was reduced by as much 99 % in beaker scale experiments via Fe(OH)3 precipitation at pH values >4.0. A 99 % decrease in aluminium concentration was observed which was attributed to the precipitation of primarily gibbsite and various other mineral phases at pH values >5.5. As the pH increases, sulphate is adsorbed via Fe(OH)3 and gypsum precipitation at elevated pH. Sulphate attenuation with fly ash was excellent, achieving 98 % attenuation with beaker scale experiments and 1:1 fly ash:AMD ratio. Sulphate attenuation with fly ash was comparable to membrane and ion exchange systems and exceeded the performance of limestone treatment. Except for the larger volumes of fly ash needed to neutralise the AMD, fly ash proved to be a feasible and cost efficient alternative to limestone treatment. Fly ash produced competing results to limestone concerning acidity removal and sulphate attenuation. The comparison highlighted the advantages of utilising fly ash in comparison to limestone and demonstrated its cost effectiveness. The results of this study have shown that fly ash could be successfully applied for the neutralisation of acid mine drainage (AMD) and effectively attenuate the sulphate load in the treated water. The critical parameters to this technology are the variations of chemical composition and mineralogy of fly ash, which could influence the pH, contact time of the neutralisation reaction, and the same is true if the AMD quality varies.
Advanced oxidative water treatment process using an electrohydraulic discharge reactor and TiO2 immobilised on nanofibres
(University of Western Cape, 2013) Okolongo, Gauthier Nganda; Petrik, Leslie; Perold, Willem
The aim of this study was to design and build an electrohydraulic discharge reactor in such a way that the synthetic immobilized TiO2 nanophotocatalytic components could be integrated, for the production of active species such as OH radicals, ozone and hydrogen peroxide, as a cocktail to clean drinking water without the addition of chemicals. The research objectives include: • To design and construct the different AOP prototypes based on various electrode configurations and compare their operation. • To optimize the discharge parameters and conditions of the best AOP system. • To determine the effectiveness of the best prototype for the degradation of methylene blue as model pollutant. • To compare the designed AOP system with the Sodis method for the disinfection of contaminated river water. • To prepare supported TiO2 nanoparticles via electro spinning, followed by combustion and study the effect on the morphology of TiO2 nanoparticles. • To determine the stability and robustness of composite nano-crystalline TiO2 photocatalysts by sonication • To determine the enhanced effect of combining the composite TiO2 in the AOP system on degradation of methylene blue under the same conditions. • To detect the active species promoting disinfection.
Application of nano zinc oxide (nZnO) for the removal of triphenyltin chloride (TPT) from dockyard wastewater
(Water Research Commission, 2014) Ayanda, Olushola S.; Fatoki, Olalekan S.; Adekola, Folahan A.; Petrik, Leslie; Ximba, Bhekumusa J.
The use of triphenyltin chloride (TPT), a persistent organic pollutant, as a biocide has led to serious contamination of the marine environment. The potential of nano zinc oxide (nZnO) for the removal of TPT from contaminated dockyard wastewater was investigated. The adsorption of TPT onto nZnO has been found to depend on the adsorbent dose, contact time, pH, stirring speed, and temperature. Equilibrium data fitted well with the Freundlich model and the experiments showed that 97.0% TPT removal was achieved by treating 0.643 mg·l-1 TPT contaminated dockyard wastewater with 0.5 g nZnO at optimal conditions. The kinetic data for the adsorption process obeyed a pseudo second-order kinetic model, suggesting that the adsorption process is chemisorption. The nZnO investigated in this study showed good potential for the removal of TPT from contaminated dockyard wastewater systems.
Carbonation of brine impacted fractionated coal fly ash: Implications for CO2 sequestration
(Elsevier, 2011) Muriithi, Grace; Gitari, Wilson; Petrik, Leslie; Ndungu, Patrick
Coal combustion by-products such as fly ash (FA), brine and CO2 from coal fired power plants have the potential to impact negatively on the environment. FA and brine can contaminate the soil, surface and ground water through leaching of toxic elements present in their matrices while CO2 has been identified as a green house gas that contributes significantly towards the global warming effect. Reaction of CO2 with FA/brine slurry can potentially provide a viable route for CO2 sequestration via formation of mineral carbonates. Fractionated FA has varying amounts of CaO which not only increases the brine pH but can also be converted into an environmentally benign calcite. Carbonation efficiency of fractionated and brine impacted FA was investigated in this study. Controlled carbonation reactions were carried out in a reactor set-up to evaluate the effect of fractionation on the carbonation efficiency of FA. Chemical and mineralogical characteristics of fresh and carbonated ash were evaluated using XRF, SEM, and XRD. Brine effluents were characterized using ICP-MS and IC. A factorial experimental approach was employed in testing the variables. The 20–150 μm size fraction was observed to have the highest CO2 sequestration potential of 71.84 kg of CO2 per ton of FA while the >150 μm particles had the lowest potential of 36.47 kg of CO2 per ton of FA. Carbonation using brine resulted in higher degree of calcite formation compared to the ultra-pure water carbonated residues.
Chemical interactions and mobility of species infly ash-brine co-disposal systems
(University of the Western Cape, 2010) Fatoba, Ojo Olanrewaju; Petrik, Leslie; Dept. of Chemistry; Faculty of Science
The primary aim of these coal fired industries for co-disposing fly ash and brine was to use the fly ash as a sustainable salt sink. It is therefore important to study the interaction chemistry of the fly ash-brine systems to fully understand the leaching and mobility of the contaminant species, and to determine the possibility of capturing the salts from the brine solution when fly ash and brine are co-disposed. In order to achieve the aims and objectives of this study, several leaching procedures such as batch reaction tests, long-term fly ash-brine interaction tests, acid neutralization capacity (ANC) tests, up-flow percolation tests and sequential extraction tests were employed. The geochemical modeling software was applied to predict the formation of secondary mineral phases controlling the release of species in the fly ash-brine systems. Several analytical techniques such as x-ray diffraction (XRD), x-ray fluorescence (XRF), scanning electron microscopy-energy dispersion spectroscopy (SEM-EDS), inductively coupled plasma-mass spectroscopy (ICP-MS) and ion chromatography (IC) were applied to characterize the fresh fly ashes, solid residues recovered from the fly ash-brine interaction tests, the brine sample used in this study and the leachate samples in order to determine the chemical and mineralogical compositions and speciation of the waste materials.
Chemical, mineralogical and morphological changes in weathered coal fly ash: A case study of a brine impacted wet ash dump
(Elsevier, 2013) Eze, Chuks P.; Nyale, Sammy M.; Akinyeye, Richard O.; Gitari, Wilson; Akinyemi, Segun A.; Fatoba, Olanrewaju O.; Petrik, Leslie
The mobility of species in coal fly ash (FA), co-disposed with brine using a wet ash handling system, from a coal fired power generating utility has been investigated. The study was conducted in order to establish if the wet ash dump could act as a salt sink. The ash was dumped as a slurry with 5:1 brine/ash ratio and the dam was in operation for 20 years. Weathered FA samples were collected along three cores at a South African power station’s wet ash dump by drilling and sampling the ash at 1.5 m depth intervals. A fresh FA sample was collected from the hoppers in the ash collection system at the power station. Characterization of both fresh FA and weathered FA obtained from the drilled cores S1, S2 and S3 was done using X-ray diffraction (XRD) for mineralogy, X-ray fluorescence (XRF) for chemical composition and scanning electron microscopy (SEM) for morphology. Analysis of extracted pore water and moisture content determination of the fresh FA and the weathered FA obtained from the drilled cores S1, S2 and S3 was done in order to evaluate the physico-chemical properties of the FA. The XRD analysis revealed changes in mineralogy along cores S1, S2 and S3 in comparison with the fresh FA. The SEM analysis revealed spherical particles with smooth outer surfaces for the fresh FA while the weathered ash samples obtained from cores S1, S2 and S3 consisted of agglomerated, irregular particles appearing to be encrusted, etched and corroded showing that weathering and leaching had occurred in the ash dump. The moisture content (MC) analysis carried out on the fresh FA (1.8%) and the weathered FA obtained from the drilled cores S1 (41.4-73.2%), S2 (30.3-94%) and S3 (21.7-76.2%)indicated that the ash dump was water logged hence creating favourable conditions for leaching of species. The fresh fly ash (n = 3) had a pH of 12.38 ± 0.15, EC value of 4.98 ± 0.03 mS/cm and TDS value of 2.68 ± 0.03 g/L, the pH of the drilled core S1 (n = 45) was 10.04 ± 0.50, the EC value was 1.08 ± 0.14 mS/cm and the TDS value was 0.64 ± 0.08 g/L. Core S2 (n = 105) had pH of 10.04 ± 0.23; EC was 1.08 ± 0.06 mS/cm and TDS was 0.64 ± 0.04 g/L, while core S3 (n = 66) had pH of 11.04 ± 0.09; EC was 0.99 ± 0.03 mS/cm and TDS was 0.57 ± 0.01 g/L. The changes in pH values can be attributed to the dissolution and flushing out of alkaline oxides like CaO and MgO from the dumped ash. The variations in pH values shows that the fly ash is acidifying over time and metal mobility can be expected under these conditions. The large decrease of EC in the drilled ash cores S1, S2 and S3 compared to the fresh ash indicated a major loss of ionic species over time in the ash dump. The XRF analysis showed the progressive dissolution of the major alumi-nosilicate ash matrix which influenced the release of minor and trace elements into the pore water enhancing their mobility as the ash dam acidified over time. Brine co-disposal on the ash may have been responsible for the slight enrichment of some species such as Na (0.27-0.56%), SO4 (0.06-0.08%), Mg (0.57-0.96 %) and K (0.02-0.34%) in the disposed weathered FA. However, there was no significant accumulation of these species in the disposed FA despite continuous addition of large volumes of highly saline brine over the 20 year period that the dump existed, indicating that the ash dam was incapable of holding salts and continually released elements to the environment over the lifetime of the dam.
Chemical, physical and morphological changes in weathered coal fly ash : a case study of brine impacted wet ash dump
(University of the Western Cape, 2011) Eze, Chuks Paul; Petrik, Leslie; Akinyeye, R.O; Gitari, W.M
Fly ash is the major waste material produced by power plants in the combustion of coal to generate electricity. The main constituents of fly ash are Si, Al, Fe and Ca with smaller amount of S, Mn, Na, K, and traces of many other elements such as Co, Cd, As, Se, Zn, Mo, Pb, B, Cu and Ni. Fly ash is usually disposed either by dry or wet disposal methods. These disposal methods have raised major environmental concerns due to the potential leaching of chemical species from the ash heap by ingress of rainfall and brine used to transport the fly ash to the dam. This study focuses on the changes in chemical composition, morphology and mineral phases due to weathering, of coal fly ash co-disposed with brine over 20 years at Sasol Secunda ash dump in Mpumalanga Province, South Africa. The design and operation of the Secunda ash dump presupposes that the ash dump may act as a sink for the salts which originated from chemicals used for normal operation in the plants. The majority of these salts come from the brines generated during desalination and raw water regeneration. The aim of this study is to ascertain if the ash dump could serve as a sustainable salt sink.Samples were drawn along the depth of two drilled cores (S1 and S3) from the weathered Secunda ash dump and analysed in conjunction with the fresh (unweathered) Secunda fly ash taken from the fly ash hoppers for comparative analysis. Scanning electron microscopy (SEM), X-ray diffractive (XRD) and X-ray fluorescence (XRF) spectrometry were employed to obtain a detailed morphological, mineralogical and bulk chemical composition of all the samples. Pore water analysis was used to determine the pH, EC and moisture content of fly ash samples. A five step sequential chemical extraction procedure was used to establish the geochemical association of particular elements with various mineral phases. The total acid digestion test was also used to determine the total elemental compositions of the Secunda fly ash samples. The SEM results showed that the fly ashes consist of irregular and numerous spherically shaped particles. Changes (encrustations, etchings and corrosion) in the morphologies of the weathered ash particles were also observed. The XRD results revealed quartz, mullite, lime and calcite as the major mineral phases. Other minerals identified in very minor quantities in the drilled Secunda ash core that were dried prior to analysis were halite, kaolinite, nitratine, bassanite, microline. and hydrophitte. These phases may have formed during sample handling. XRF investigation revealed that the major oxides present in the dumped ash samples were SiO₂, A₂2O₃, CaO, Fe₂O₃, MgO, Na₂O, TiO₂ and the minor elements present were K₂O, P₂O₅, SO₃ and MnO. The sum of the mean values of the % composition of SiO₂, Al₂O₃, and Fe₂O₃ was 70.19 %, and 72.94 % for the two drilled ash core samples (S1 and S3) respectively, and 78.67 % for the fresh ash which shows the significant alteration of the Si, Al and Fe content in the ash matrix over time. The fly ash is classified as Class F using the ASTM C 618 standards. The loss on ignition (LOI) which is an indication of unburned carbon or organic content was 4.78 %, 13.45 % and 8.32 % for the fresh ash, drilled ash cores S1 and S3 respectively. The high LOI values for the drilled ash cores could indicate high hydrocarbon content in the ash dump because of co-disposal practises where hydrocarbon waste are included in the brine stream for disposal on the ash. While the ash samples from the surface appeared dry, moisture content (MC) analysis showed that there is considerable water entrained in the fly ash dump. The fresh ash MC was 1.8 % while core S1 ranged from 41.4 – 73.2 %; core S3 ranged from 21.7 – 76.4 %. The variations in the MC values can be attributed to uneven flow paths due to inconsistent placement conditions or variations in ambient weather conditions during placement. The fresh fly ash (n=3) had a pH of 12.38±0.15, EC value of 4.98±0.03 mS/cm and TDS value of 2.68±0.03 g/L, the pH of the drilled ash core S1 (n=35) was 10.04 ±0.50, the EC value was 1.08±0.14 mS/cm and the TDS value was 0.64 ±0.08 g/L. Core S3 (n=66) had pH of 11.04±0.09; EC was 0.99 ±0.03 and TDS was 0.57 ± 0.01. The changes in pH values can be attributed to the dissolution and flushing out from the dump basic alkaline oxides like CaO and MgO These variations in pH values shows that the fly ash is acidifying over time and metal mobility can be expected under these conditions. The large decrease of EC in the drilled ash cores S1 and S3 compared to the fresh ash indicated a major loss of ionic species over time in the ash dump. The sequential extraction scheme revealed that the elements Al, Si, Ca, Mg, Ba, Sr, Fe, Mn, Na, K, As, Pb, Cr, Mo, Cu, Ni and Zn are present in Secunda fresh and weathered fly ash and are partitioned between the water soluble, exchangeable, carbonate, iron and manganese, and residual fractions of the coal fly ash. It also showed that the trace elements As, Pb, Cr, Mo, Cu, Ni and Zn do not show permanent association with particular mineral phases as a continuous partitioning between different mineral phases was observed in the weathered drilled core. Generally, all the elements had the highest concentration in the residual fraction. But it was evident that the labile phase (water soluble, exchangeable and carbonate fractions) had fairly high concentrations of Si (± 6.5 %), Al (± 6.5 %), Ca (±10 %), Mg (± 5.5 %), Ba (± 7.5 %),Sr (± 7.5 %), Na (± 12 %) and K (± 12 %) for the Secunda drilled ash core (S1 and S3) and fresh fly ash samples. This indicates that these species can leach easily upon water ingress and could pose a danger to the environment. Na and K had the highest concentrations leached out in the labile phase in all the ash samples. The amount of Na leached out of the drilled Secunda ash core in the labile phase was 13.21 % of 18584.26 mg/kg in the five geochemical phases of core S1; and 9.59 % of 11600.17 mg/kg in the five geochemical phases of core S3 while the fresh Secunda fly ash leached out 11.28 % of 16306.30 mg/kg of Na in the five geochemical phases. This study provided significant insight into the pore water chemistry, morphology, mineralogy and chemical composition and the elemental distribution pattern of the major and trace elements in the Secunda fly ash and weathered drilled Secunda ashm core S1 and S3. Though results from XRF analysis and the sequential extraction scheme shows that Na, K, S, Ca and Mg were slightly captured from the co-disposed brine by the Secunda fly ash, these species were however released in the labile phase. Hence there was no significant retention of these species in the ash dump. The amount of these species retained in the weathered ash were (0.26 % and 0.55 %) for Na, (0.02 % and 0.34 %) for K, (0.08 % and 0.06 %) for S, (0.94 % and 0.01 %) for Ca and (0.37 % and 0.96 %) for Mg in drilled ash cores S1 and S3 respectively. This poor retention of Na K, S, Ca and Mg which are major components of Sasol Secunda brine in the drilled ash cores S1 and S3 clearly shows the unsustainability of the Secunda fly ash dump as a salt sink.
Chemistry and speciation of potentially toxic and radioactive elements during mine water treatment
(University of the Western Cape, 2012) Madzivire, Godfrey; Petrik, Leslie; Gitari, W. M.; Vadapalli, Viswanath R. K.
Mine water poses a serious environmental challenge and contains elements such as Fe, Al, and Mn in potentially toxic concentrations. The major anion in mine water is sulphate. The complexity and diversity of mine water composition makes its treatment very expensive, and there is no “one-fits-all” treatment option available for mine water. Active treatment of mine water produces water with good quality but the processes are not sustainable because of the costs. Previous studies have shown that acid mine drainage can be treated with coal FA to produce better quality water. The use of coal FA, a waste material from coal fired power station and mine water would go a long way in achievement of sustainable treatment of mine water as per previous studies. In this study mine water and coal FA were characterized to determine their physiochemical properties. This study linked the modelling results obtained by using the Geochemist’s workbench (GWB) software to the results obtained during the actual treatment of Matla mine water and Rand Uranium mine water using coal FA and lime. The chemistry involved when Matla mine water and Rand Uranium mine water were treated with flocculants was also investigated. Lastly the chemistry and kinetics involved was investigated when mine water was treated with various ameliorants such as Matla coal FA, lime and/or Al(OH)3 using jet loop mixing or overhead stirring. Mine water from Matla coal mine had a pH of 8 and therefore was classified as neutral mine drainage (NMD). Rand Uranium mine water had a pH of less than 3 and therefore was classified as acid mine drainage (AMD). The concentration of sulphate, Na, Ca, Mg, B, Hg, Se and Cd ions in Matla mine water was 1475, 956, 70, 40, 15, 2.43, 1.12 and 0.005 mg/L respectively. The concentration of sulphate, Fe, Ca, Mn, Mg, Al, B, Cr, Pb, U, Cd, Se and As ions in Rand Uranium mine water was 4126, 896, 376, 282, 155, 27, 5.43, 3.15, 0.51, 0.29, 0.007, 0.06 and 0.006 mg/L respectively . These concentrations were above the target water quality range (TWQR) for potable water set by the Department of Water Affairs (DWA) and World Health Organization (WHO). The gross alpha radioactivity was 6.01 Bq/L and gross beta radioactivity was 6.05 Bq/L in Rand Uranium mine water.
CO2 sequestration using brine impacted fly ash
(University of the Western Cape, 2009) Muriithi, Grace Nyambura; Petrik, Leslie
Coal combustion accounts for over 40 % of the world's energy production and this figure is projected to increase with increasing human population and industrialization. The combustion of coal leads to the generation of waste products such as fly ash (FA), brine from water treatment, bottom ash, slag, flue gas desulphurization products (FGD) and gas emissions such as N20, and C02. The emissions contribute to air pollution and global warming, while FA, brines, and FGD are possible soil and water pollutants. In order to minimize the environmental impact of coal combustion, mitigation of the effects of coal burning processes such as the waste products (FA, brine, bottom ash, slag and FGD) and gas emissions is required. This study investigated utilization of the Secunda FA (class F) and reverse osmosis (RO) Tutuka brine to sequester C02 in an attempt to make coal power production more environmentally sustainable. It was hypothesized that South African FA and brine could sequester C02 through mineral carbonation. A statistical approach was undertaken to optimize the % CaC03 formed from FAlbrine/C02 interaction with input parameters of temperature, pressure, particle size and solid/liquid ratio (S/L) being varied. The ranges adopted for the input parameters were: temperature of 30°C or 90 °C; pressure of 1 Mpa or 4 Mpa; four particle sizes namely bulk ash, > 150 11m, < 20 11m and 20 urn- 150 11m particle size range; S/L ratios ofO.1, 0.5 or 1. The FA! brine dispersions were carbonated in a high pressure reactor varying the above mentioned input parameters. The fresh Secunda FA of various size fractions was characterized morphologically using scanning electron microscopy, chemically using X-ray fluorescence and mineralogically using qualitative X-ray diffraction. The carbonated solid residues on the other hand were characterized using quantitative X-ray diffraction, scanning electron microscopy, thermal gravimetic analysis and Chittick tests. The raw brine from Tutuka together with the carbonation leachates were characterized using inductively coupled mass spectrometry and ion chromatography. Total acid digestion was carried out to evaluate the differences in the total elemental content in both the fresh ash and the carbonated solid residues. The results suggested that South African FA from Secunda belongs to class F based on the CaO content as well as the total alumina, silica and ferric oxide content, while the RO brine from Tutuka were classified as NaS04 waters. Mineral carbonation occurred and ranged between 2.75 % and 6.5 % of CaC03 depending on the input parameters. Two polymorphs of CaC03 were identified in the carbonated residues i.e. calcite and aragonite. The carbonated ash/brine leachates were cleaner with respect to major and trace element concentration compared to raw brine thus the carbonation process could be used to improve the quality of brines generated in the power industry. Removal of the major elements from brine was as follows Ca-74.8 %, Na- 28.7 %, Mg- 98 %, K- 82.9 %, S04- 20.8 %. Hundred percent removal was observed for traces of Fe, Al, Mn, Cu, Zn, Pb, Ni, As, Ti, Sr, Se, Si and N03. However Mo, V, B, and Cl concentrations increased by 72.5 %, 94 %,48.2 % and 7.2 % respectively after carbonation at 90°C, 4 Mpa, S/L ratio of 1 using the bulk ash. The parameters found to be of most significance in the carbonation process were the main effects of temperature, particle size and S/L ratio while the interactions of temperature and particle size as well as the interaction of temperature with S/L ratio were also found to be significant. The statistical approach led to a clear understanding of the effect of each input parameter as well as the ansmg interactions. The conditions of 90°C, 4 Mpa, using bulk ash at a S/L ratio of 1 resulted in the highest yield of % CaC03 with a value of 6.5 %. Theoretically one ton of Secunda FA containing 9.2 % of CaO could sequester 0.083 tons of C02. With the optimized protocol developed in this study bearing in mind that the carbonation efficiency is 75.54%, 1 ton of Secunda FA could sequester 0.062 tons of CO2. This translates to 0.65 % of CO2 produced annually at Secunda plant being sequestered in the FAlbrine dispersions. In other words, 16 tons of FA are required to sequester a ton of C02 annually. It was also observed that carbonation using brine resulted in higher carbonation efficiency than carbonation using water as the Ca2+ component in the brine contributed towards the Ca 2+concentration.
Coal fly ash and acid mine drainage based heterogeneous Fe catalysts Friedel-Crafts alkylation reaction
(University of Western Cape, 2020) Hlatywayo, Tapiwa; Petrik, Leslie
The catalytic support materials used in the present study are zeolite HBEA and MCM-41. These high silica zeolites were synthesised from coal fly ash (CFA) waste via a novel approach that involved a fusion step, acid assisted silica extraction and removal of Al, Ca and Na from the silica by treatment with oxalic acid. The generated silica was converted to HBEA and MCM-41 via conventional hydrothermal treatment. The metal incorporation onto HBEA was done via two approaches namely; liquid phase ion exchange (LIE) and wet impregnation (WI) while the loading on MCM-41 was only done via WI since the material does not possess exchange sites. The metal solution precursors were AMD and Fe extracted from CFA (FeAsh) via acid leaching followed by pH regulation by concentrated NaOH. This is the first time these solutions were tested as possible metal precursors in catalyst synthesis.
Comparison of CO2 capture by ex-situ accelerated carbonation and in in-situ naturally weathered coal fly ash
(Elsevier, 2013) Muriithi, Grace N.; Petrik, Leslie; Fatoba, Olanrewaju O.; M. Gitari, Wilson; Doucet, Frederic J.; Nel, Jaco; Nyale, Sammy M.; Chuks, Paul E.
Natural weathering at coal power plants ash dams occurs via processes such as carbonation, dissolution, co-precipitation and fluid transport mechanisms which are responsible for the long-term chemical, physical and geochemical changes in the ash. Very little information is available on the natural carbon capture potential of wet or dry ash dams. This study investigated the extent of carbon capture in a wet-dumped ash dam and the mineralogical changes promoting CO2 capture, comparing this natural phenomenon with accelerated ex-situ mineral carbonation of fresh fly ash (FA). Significant levels of trace elements of Sr, Ba and Zr were present in both fresh and weathered ash. However Nb, Y, Sr, Th and Ba were found to be enriched in weathered ash compared to fresh ash. Mineralogically, fresh ash is made up of quartz, mullite, hematite, magnetite and lime while weathered and carbonated ashes contained additional phases such as calcite and aragonite. Up to 6.5 wt % CO2 was captured by the fresh FA with a 60% conversion of calcium to CaCO3 via accelerated carbonation (carried out at 2 h, 4Mpa, 90 o C, bulk ash and a S/L ratio of 1). On the other hand 6.8 wt % CO2 was found to have been captured by natural carbonation over a period of 20 years of wet disposed ash. Thus natural carbonation in the ash dumps is significant and may be effective in capturing CO2.
The composition of photocatalytic nanofibres through electrospinning
(University of the Western Cape, 2014) Farao, Al Cerillio; Petrik, Leslie; Babajide, O.
The aim of this study was to enrich electrospun fibres with the active mineral phase TiO2 nanoparticles and then to evaluate how well the composite fibres performed in the photocatalytic degradation of methylene blue (MB). Electrospun hydrophobic PAN polymer fibres were used as support structures for the TiO2 nanoparticles. The photocatalytic activity of the TiO2 enriched fibres for dye degradation was evaluated and the effect of external stressors on the fibres was assessed. A comparison was also made to determine whether the TiO2 - photocatalyst catalyst should be coated on top of, or loaded inside the electrospun PAN fibres
Contaminants of emerging concern (cecs) and male reproductive health: Challenging the future with a double-edged sword
(MDPI, 2023) Marcu, Daniel; Keyser, Shannen; Petrik, Leslie
Approximately 9% of couples are infertile, with half of these cases relating to male factors. While many cases of male infertility are associated with genetic and lifestyle factors, approximately 30% of cases are still idiopathic. Contaminants of emerging concern (CECs) denote substances identified in the environment for the first time or detected at low concentrations during water quality analysis. Since CEC production and use have increased in recent decades, CECs are now ubiquitous in surface and groundwater. CECs are increasingly observed in human tissues, and parallel reports indicate that semen quality is continuously declining, supporting the notion that CECs may play a role in infertility. This narrative review focuses on several CECs (including pesticides and pharmaceuticals) detected in the nearshore marine environment of False Bay, Cape Town, South Africa, and deliberates their potential effects on male fertility and the offspring of exposed parents, as well as the use of spermatozoa in toxicological studies.
Degradation of persistent organic pollutants (pharmaceuticals & dyes) by combined dielectric barrier electrohydraulic discharge system and photo catalysts
(University of the Western Cape, 2019) Mouele, Emile Salomon Massima; Petrik, Leslie; Fatoba, Olanrewaju Ojo
Water pollution problems have continued to increase not only in South Africa but worldwide due to human activities. The presence of organic toxins and bacteria in water sources is mostly due to population growth, industrial development and agricultural run-off. The accumulation of persistent organic pollutants (POPs) in water and wastewater sources has raised various questions on the safety of potable water used for drinking, households and other activities. Traditional mechanical, biological, physical, and chemical methods such as flocculation, coagulation, reverse osmosis, filtration, ultrafiltration, adsorption and active sludge treatment methods have failed to remove these new xenobiotic from aquatic media. This is due to the fact that instead of degrading the toxins, the methods listed above often transform organic contaminants from one form another. Also, the post treatment of by-products resulting from these methods is costly. In addition, this new generation of contaminants, often referred to as compounds of emerging concern (CECs), exist in tiny concentrations (ng) and conventional techniques have not been designed for these low levels of pollutants which consequently pass through during treatment processes and end up in the treated effluents at minute concentrations (ug/L to ng/L). However, complete remediation of chemical toxins in wastewater treatment plants has not been achieved. A better option involves the direct oxidation of the pollutants in the effluent but so far their complete mineralisation has not been achieved. Advanced oxidation processes (AOPs) have emerged in recent years as adequate techniques for the complete removal of POPs. AOPs focus more on the production of non-selective hydroxyl radicals (OH.) which have been considered as the most powerful oxidants (2.8 V) that directly or indirectly mineralise the organic pollutant into dissolved CO2, H2O and harmless end-products. However, the use of excessive chemicals, corrosion of catalyst supports, wasted UV, ozone escapes and the cost associated with AOPs often limit their application for the removal of POPs from water and wastewater treatment facilities. The principal aim of this study was to optimise a double cylindrical barrier discharge (DBD) system for the removal of low concentration persistent organic pollutants (POPs). The efficiency of the DBD system was initially confirmed by quantification of three main reactive oxygen species including ozone (O3), hydrogen peroxide (H2O2) and hydroxyl radicals (.OH) among others. These three active species were successfully detected and quantified using indigo, per titanyl sulphate and terephthallic acid (TA) spectroscopy methods, respectively. Thereafter, the DBD reactor was optimised by assessing the effect of electrophysico-chemical parameters on the removal efficiencies of two selected pollutants including orange II sodium salt dye (O.II) and sulfamethoxazole (SMX), a pharmaceutical, as model persistent organic pollutants.
Desalination and seawater quality at Green Point, Cape Town: A study on the effects of marine sewage outfalls
(Academy of Science of South Africa (ASSAf), 2017) Petrik, Leslie; Green, Lesley; Abegunde, Adeola P.; Zackon, Melissa; Sanusi, Cecilia Y.; Barnes, Jo
This paper presents our collection methods, laboratory protocols and findings in respect of sewage pollution affecting seawater and marine organisms in Table Bay, Cape Town, South Africa, then moves to consider their implications for the governance of urban water as well as sewage treatment and desalination. A series of seawater samples, collected from approximately 500 m to 1500 m offshore, in rock pools at low tide near Granger Bay, and at a depth under beach sand of 300–400 mm, were investigated for the presence of bacteriological load indicator organisms including Escherichia coli and Enterococcus bacteria. A second series of samples comprised limpets (Patella vulgata), mussels (Mytilus galloprovincialis), sea urchins (Tripneustes ventricosus), starfish (Fromia monilis), sea snails (Tegula funebralis) and seaweed (Ulva lactuca), collected in rock pools at low tide near Granger Bay, and sediment from wet beach sand and where the organisms were found, close to the sites of a proposed desalination plant and a number of recreational beaches. Intermittently high levels of microbial pollution were noted, and 15 pharmaceutical and common household chemicals were identified and quantified in the background seawater and bioaccumulated in marine organisms. These indicator microbes and chemicals point to the probable presence of pathogens, and literally thousands of chemicals of emerging concern in the seawater. Their bioaccumulation potential is demonstrated.
Determination of toxic elements, rare earth elements and radionuclides in coal fly ash, products and waste
(University of the Western Cape, 2014) Eze, Chuks Paul; Petrik, Leslie; Fatoba, O.O.
Coal fly ash has been studied extensively to understand the environmental impacts associated with its disposal, management and reuse. Although several beneficiation processes have been proposed, there has been little or no emphasis on the environmental safety of such processes, products and wastes. Elemental analysis has revealed that toxic elements and radionuclides are present in coal fly ash. Rare earth elements (REE) such as La, Ce and Y are also present in significant amounts in coal fly ash. The aims of this study were to determine the total elemental composition of coal fly ash using different analytical techniques; to validate the application potentials of fly ash beneficiation processes in terms of their environmental safety; and to valorise coal fly ash with a view of recovering REE either by concentrating or leaching the REE in the coal fly ash, products or waste from the beneficiation processes. The beneficiation processes studied were treatment of acid mine drainage (AMD) with fly ash; and the synthesis of geopolymer from fly ash. The fresh fly ash sample used in this study was collected directly from the hoppers at Matla power station and the AMD sample was collected from Carletonville goldmine. A total of 54 major, trace and REE were accurately determined in the ash using different analytical techniques. It was shown that the elemental content of Matla fly ash was of the same order as the SRM NIST coal fly ash 1633b. The comparative study of the four analytical techniques established that ENAA can accurately determine the major, minor and trace elements; that XRF is best suited for the determination of the major and minor elements, whilst the LA ICP-MS is reliable for trace elements determination. The solid residue (AMD/FA) resulting from the AMD interaction with fly ash was characterized with fly ash and the results compared. The results revealed that the amounts of La (141.09 ± 3.85 mg/kg), Ce (27.45 ± 2.04 mg/kg), and Nd (63.73 ± 0.05 mg/kg) in AMD/FA residue was considerably higher than their average abundance in the earth crust that varies from 66 mg/kg in Ce and 40 mg/kg in Nd to 35 mg/kg in La. The results also showed that the AMD/FA residue contained As (11.39 ± 1.21 mg/kg), Cd (3.77 ± 0.02 mg/kg), Cr (72.43 ± 1.27 mg/kg), Hg (10.50 ± 0.85 mg/kg), Ni (124.15 ± 1.6 mg/kg) and Pb (22.46 ± 1.43 mg/kg) which are potentially harmful if leached in to the environment in excessive amounts.
Fabrication of nanomaterials from biomass for adsorption and antimicrobial applications
(University of the Western Cape, 2020) Uche, Cosmas Chinedu; Petrik, Leslie; Onwordi, Chionyedua Theresa
The Black soldier fly (BSF) is an environmentally friendly and sustainable insect utilised in the decomposition of organic waste. This is due to its voracious consumption capability, disruptive functions and economic importance. The sustained global increase in commercial BSF farming has resulted in an expanded waste generation from its carcases to which beneficial uses ought to be developed. This study focused on the beneficial use of the generated waste by extracting chitosan from waste pupae and commercially reared BSF adult carcases. The study also considered the conversion of the extracted chitosan to nanofibres and nanoparticles for application in adsorption of inorganic Pb2+ or Cd2+ and antimicrobial studies, respectively. To achieve the aim of this study, the optimal extraction conditions of chitin and chitosan from both pupal exuviae and adult BSF waste materials were attained after a series of experiments. The extraction process involved three stages which were demineralisation, deproteination and deacetylation. The extracted adult and pupal chitin and chitosan were characterised using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction studies (XRD), high resolution scanning electron microscopy (HRSEM) and solid-state carbon nuclear magnetic resonance spectroscopy (13C NMR). Additionally, the adult (ACH20_9) and pupal (PCH21_9) chitosan samples, due to their solubility, were further characterised to determine their molecular weight, fat and water binding capacities, solubility and ash contents.
The fate and transport of carbon-based nanomaterials in the environment
(University of Western Cape, 2020) MacDonald, Riccarda Thelma; Petrik, Leslie
The interest in carbon-based nanomaterials, such as carbon-nanodots and graphene, has grown exponentially because these materials have unique properties and applications in the medical, electronic, clean energy and several other fields for biochemical sensing, energy conversion, photocatalysis, optoelectronics, etc. Carbon dots were discovered in 2004, yet very little research has been done on the colloidal stability thereof. Nanomaterials such as carbon dots will inescapably make their way to natural waters with an unknown environmental fate. Therefore, it is of great importance to understand the behaviour of carbon dots under the influence of certain environmental conditions such as pH, ionic strength, and in the presence of natural organic matter.

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