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Effect of precursor anion in alcohol/water solutions during hydro/solvothermal synthesis on cobalt oxide morphology and catalytic ability
Full text linkThesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2020The textile industry requires water for practically every step during its manufacturing process, and would benefit from water reuse systems. This is challenging, as the reactive dyes used in this industry often escape the conventional wastewater treatment methods used. The use of advanced oxidation processes combats these challenges, as it allows for the conversion of organic toxic waste to harmless H2O and CO2. Potassium peroxymonosulphate (Oxone®) has become popular in these treatment methods, as highly active sulphate radicals are activated once in contact with a transition metal. Such reactions are dependent on the catalyst used, and therefore require control of its morphology for enhanced capabilities. Cobalt oxide is deemed the best activator of peroxymonosulphate. The use of alcohols in its synthesis has been studied, but a systematic study increasing the alcohol chain lengths, in addition to the cobalt anion during hydro/solvothermal synthesis, has not been studied. Although the cobalt complex formed from cobalt chloride in water and alcohol has been studied, the use of these complexes as a precursor to cobalt oxide nanoparticles has not been studied.
Cobalt hydroxide precursors were therefore synthesised in pure alcohol, pure water and alcohol/water solutions in the ratios 1:1 and 1:0. Five alcohols were selected, namely methanol, ethanol, propanol, butanol and octanol. and cobalt chloride hexahydrate and cobalt nitrate hexahydrate were used to study the effect of the anion. The effect of calcination temperature was also studied by varying it between 300°C and 500°C. The resulting particles were characterised using TEM, SEM, XRD, BET, EDS, FT-IR and ELNEFS, and its catalytic ability was tested treating a methylene blue solution in an in-house developed continuous reactor.
Both α- and β-cobalt hydroxide polymorphs were encountered as precursors from cobalt chloride. The β-phase was evident when the water was exhausted from the system, whereas the α-phase was evident when water was present in the system. Only α-cobalt hydroxide was formed from cobalt nitrate. This provided a relationship between the cobalt complex formed to the phase of cobalt hydroxide polymorph. A blue, tetrahedral orientated precursor complex, produced pink β-cobalt hydroxide particles, while a red, octahedral orientated precursor complex, produced α-cobalt hydroxide. Cobalt oxide nanoparticles were formed from both α- and β-cobalt hydroxides.
Anion morphology-dependent changes were observed in the presence of alcohol only. Rods were formed in the presence of the nitrate anion, while rhombic shapes dominated in the presence of chloride anions. Only rods were produced in water.
An increase in the calcination temperature increased the crystallite size, which negatively affected the catalytic activity. It was also noted that a crystallite size between 8 and 11 nm resulted in highly active cobalt oxide particles for both anions explored. The catalytic ability of the cobalt oxide resulting from the β-phase was better than that of the α-phase. The best catalytic activity was produced by the cobalt oxide synthesised from cobalt chloride hexahydrate precursor salt in 100% methanol for which the ELNEFS analysis revealed a Co3+/Co2+ ratio of ten times that of its 50% counterpart
A performance and energy evaluation of a dye drawn forward osmosis (FO) system for the textile industry
Full text linkThesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2020Continuous growth in the world population has raised significant fears with regards to the sustainability of energy and water resources. Globally, water is an indispensable resource as it is essential for the sustenance of human, animal and plant life. Water is essential for all forms of life and plays a pivotal role in economic growth. The textile industry is one of the greatest consumers of water, it is, therefore, necessary to effectively treat the large amounts of wastewater before discharge to the environment. It is estimated that annually, more than 700,000-tonnes of textile wastewater is produced by the dyeing industry. Textile wastewater is generally characterised by electrolytes, suspended solids, mineral oils and multiple textile dyes, and has therefore been classified as one of the most polluting wastewaters. These dyes are toxic and, in most cases, are not biodegradable. The presence of very small amounts (i.e. < 1 ppm) of dyes in water has aesthetic impacts and is thus undesirable. It is, therefore, necessary to treat textile wastewater before discharging.
Currently, membrane technology is widely used for wastewater treatment, as well as water purification. Forward osmosis (FO) is a promising technology for both these applications. FO is characterised by the flow of water through a semipermeable membrane from a feed solution (FS) characterised by the low solute concentration or low osmotic pressure (OP) to a draw solution (DS) characterised by the high solute concentration or high OP, due to the OP gradient across the membrane. The FO process eliminates the need for high hydraulic pressure, as required in traditional membrane technologies, and also has low fouling tendencies. Furthermore, FO has the advantage of lower energy requirements and membrane replacement costs. However, there are still many disadvantages such as reverse solute flux (RSF), membrane fouling, and concentration polarisation (CP) amongst others that still need to be addressed. Therefore, more research needs to be done in light of these limitations to better understand and mitigate these limitations to increase the effectiveness and efficiency of the FO process.
This study aimed to evaluate a dye-driven FO system for the reclamation of water from textile wastewater and synthetic brackish water (BW5) by investigating the effects of membrane orientation, system flowrate, change in DS, and membrane fouling on the FO systems performance and energy consumption. The FS used was BW5 with sodium chloride (NaCl) content of 5 g/L whereas Reactive Black 5 (i.e. a reactive dye) and Maxilon Blue GRL (i.e. a basic dye) dyes were used as a DS, respectively. The membrane utilised was a cellulose triacetate (CTA) membrane and was tested in FO mode and pressure retarded osmosis (PRO) mode whilst the system flowrate was adjusted to 400, 500 and 600 mL/min, respectively. Experiments were performed using a bench-scale FO setup which comprised of an FO membrane cell, a double-head variable speed peristaltic pump, a digital scale, two reservoirs for the FS and DS, respectively, a digital multiparameter meter and a digital electrical multimeter to measure system energy consumption. Each experiment comprised of six steps: baseline 1 (membrane control), main experiment (dye-driven FO experiment), baseline 2 (membrane control repeat), membrane cleaning, membrane integrity (membrane damage dye identification) and membrane cleaning (preparation for next experiment). The baseline 1 and baseline 2 experiments operated for 3 h whilst each membrane cleaning procedure operated for 30 min. The main experiments operated for 5 h in the FO mode and 4 h in PRO mode whilst the membrane integrity experiments operated until a minimum of 10 mL water was recovered.
Results showed that the PRO mode achieved both higher forward flux () (i.e. 8.87, 8.71 and 9.13 L/m2.h for flowrates of 400, 500 and 600 ml/min) and water recovery () rates compared to FO mode (i.e. 6.60, 6.88 and 7.58 L/m2.h for flowrates of 400, 500 and 600 ml/min). The variation of flowrates had little to no influence on the , and of the system. The system consumed less energy in PRO mode (i.e. 381 kWh/m3 average consumption for all three flowrates) than FO mode (i.e. 417 kWh/m3 average consumption for all three flowrates). It was also observed that at a higher DS , the system consumed less energy. Therefore, selecting an optimum initial is essential for a FO process to minimise the pumping energy.
Furthermore, a change in DS from Reactive Black 5 dye to Maxilon Blue GRL dye had no significant impact on the system performance and energy consumption. In this study, no significant membrane fouling was observed, however, minute traces of fouling in the form of foreign functional groups could be observed in the attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) spectrums of the used membranes. Additionally, the observation of negligible changes in baseline 2 (membrane control) Re and Jw results suggested the possible occurrence of membrane fouling during the main experiment (dye-driven FO system)
A Phenomenological Investigation of Architecture in Dementia Facilities,
Full text linkThesis (MTech (Architectural Technology))--Cape Peninsula University of Technology, 2020No Abstract availabl
Application of bioprocess-supercritical fluid extraction techniques in the production and recovery of some selected bioproducts
Full text linkThesis (PhD (Chemical Engineering))--Cape Peninsula University of Technology, 2020The use of bioproducts in different commercial sectors such as medicine, agriculture, cosmetics, food, and chemical industries motivates the need for easy production and recovery techniques of bioproducts at laboratory and pilot scale. This study aims at the production and recovery of some selected bioproducts using supercritical fluid extraction techniques. Three products are chosen as case studies: these are ethanol, acetoin, and vanillin, since the ease of separation is influenced by the concentration of the product in the broth, these compounds were selected based on their concentration in the fermentation broth, according to literature sources. A standard method was developed in a spectrophotometer for quantifying the targeted product in the broth, while the product recovery studies was carried out using a supercritical fluid extraction pilot plant. Saccharomyces and Bacillus species were chosen for the bioproduction of the selected bioproducts. Experimental design and statistical analysis of results were carried out using response surface methodology (RSM) and artificial neural network (ANN). Studies on each of the selected bioproducts are as justified in the paragraphs below.
Bioethanol production has recently become an increasing trend in research, with a focus on increasing its economic viability. Hence, the need to develop a low-cost fermentation medium with minimum redundant nutritional supplements, thereby minimizing the costs associated with nutritional supplements whereby inoculum preparation becomes necessary for ethanol production. Corn steep liquor (CSL) in glucose fermentation by Saccharomyces Type 1 (ST1) strain and Anchor Instant Yeast (AIY), which are low-cost media, are used as replacements for yeast extract (YE). The fermentation process parameters were optimized using artificial neural networks (ANN) and the response surface methodology (RSM). The study shows that for CSL, a maximum average ethanol concentration of 41.92 and 45.16 g/L representing 82% and 88% of the theoretical yield were obtained after 36 h of fermentation in a shake flask for ST1 and AIY respectively. For YE, ethanol concentration equivalent to 86% and 88% of theoretical yield were obtained with ST1 and AIY respectively after 48 h. Although, ANN predicted the responses of ethanol yield better than RSM, optimum conditions for ethanol production were better predicted by RSM.
The consumers’ preference for ‘naturally’ produced aromas drives the development of bioproduction of acetoin from glucose with a view to optimize its production. The results revealed that by using a cheap nitrogen source, corn steep liquor, the yield of acetoin was similar to those of yeast and beef extracts. Furthermore, it was shown that by using Box-Behnken design, the optimum parameters such as glucose concentration, corn steep liquor, and inoculum size to maximize the concentration of acetoin produced were 78.40 g/L, 15.00% w/v and 2.70% v/v respectively. The validated concentration of acetoin produced in a triplicate analysis, 10.7 g/L, was 0.06% less than the predicted value.
Increasing awareness of consumers of healthy, eco-friendly flavors and fragrances motivates the bioproduction of vanillin. The interactive effects of three variables on vanillin yield were evaluated by response surface methodology (RSM) with Box-Behnken design (BBD) model. The results showed the optimum conditions for the biotransformation of ferulic acid into vanillin can be achieved with maximum overall desirability (D) of 1.0 and a significant (p<0.05) quadratic model with regression coefficient (R2) of 0.995. Corn steep liquor, initial ferulic acid concentration and pH significantly influence the concentration of vanillin in the broth. The results in triplicate experiments confirmed vanillin yield of 386 mg/L after validation, which was in agreement with the prediction of the model. The maximum vanillin yield of 384.40 mg/L was predicted when corn steep liquor, ferulic acid concentration and pH were 7.72 g/L, 2.33 g/L, and 9.34 respectively.
Fermentation system in a bioreactor has been proven to be an efficient system for the study of controlled fermentation variables when compared to a shake flask study. The influence of agitation, aeration, time and pH were analysed by Taguchi orthogonal array design for the upscale of acetoin in a bioreactor. The optimized parameters in 1.3L of fermentation vessel were as follows: 300 rpm agitation, 1.5 slpm aeration; 2 days’ fermentation time and 6.5 pH value. Agitation with above 70% was the most contributing factor and other variables were less than 30% in the percentage analysis of variance of each fermentation variables in the batch study of acetoin. A fourfold gain in acetoin titre (42.30 g/L) was obtained with the same substrate concentration in a lab-scale bioreactor on scaling up when compared with the shake flask batch study. The validated acetoin concentration of 41.72 g/L was obtained after a triplicate experiment to confirm the possibility of reproducing acetoin using the optimized conditions.
Many separation techniques have been proven to recover value-added products from fermentation broth with a preference for several methods above other and new techniques that are emerging. Supercritical fluids separation using CO2 is one such technique. The feasibility of acetoin concentration and recovery was studied in supercritical CO2 pilot plant with pressure ranges of 100 to 300 bar, CO2 feed rate of 5 to 15 kg/h, at a process temperature of 37 and 80 °C in simulated and fermentation broth, respectively. The validated conditions for the fractionation of acetoin by supercritical fluid extraction (SFE) were determined as follows: extraction pressure, 300 bar; CO2 feed rate, 15 kg/h; extraction temperature 37 °C; and fractionation time of 30 minutes. At these operating conditions, the percentage recovery of acetoin with respect to the feed solution at the raffinate for the simulated and actual ermentation broth was 77.8% (0.20 g/L) and 77% (0.15 g/L) respectively. A two-fold extract increase was obtained after 30 minutes of fractionation.
The study provides the technical feasibility and the base case data which are critical to the development and design of processes for production and recovery of acetoin. The lesson gleaned from this study may be extended to develop processes for the production and recovery of other bioproducts (ethanol and vanillin)
Effect of planting density and nitrogen application rate on grain quality and yield of three barley (Hordeum vulgare L.) cultivars planted in the Western Cape Province of South Africa
Full text linkThesis (Master of Agriculture)--Cape Peninsula University of Technology, 2020Grain yield and its components are very important and complicated in barley (Hordeum vulgare L.) and are highly influenced by environmental factors and agronomic management practices. For 2018 growing season, a study was designed under rainfed conditions to evaluate the effects of nitrogen (N) fertilizer rate (0, 10, 20, 30 and 40 kg ha-1 of N) and planting density (120, 140, 160, and 180 to 200 seeds m-2) on the agronomic performance of three barley cultivars (Elim, Hessekwa and S16). A randomized complete block design with 3 replications was used. Combined analysis of variance showed significant (p<0.1) differences among cultivars, N rates and planting densities. The main objective of this study was to determine the effects of planting density and different fertilizer application strategies on barley grain yield and quality. The results showed that biggest increases on yield and yield components were observed at 180 seeds m-2 and 80kg ha-1 N rate. Higher N rates generally reduced kernel size. Kernel size was both increased and decreased by increasing planting density as well as N rate. Increasing planting density from 180 to 200 seeds m–2 generally provided slight reductions in grain N concentration and reduced kernel size. The three cultivars expressed a significant effect on kernel plumpness and N content of grain. The most beneficial agronomic practices for malting barley production in Western Cape were application of N fertilizer at optimum rate depending on cultivar, locality and rainfall and planting seeds at a rate of 160-180 seeds m-2 depending on cultivar. A planting density of 160-180 seeds m-2 at a rate of 80 kg N ha-1 is recommended for planting barley under dry land in the Western Cape
Effect of round orifice aspect ratios on Non-Newtonian fluid discharge from tanks
Full text linkThesis (MEng (Civil Engineering))--Cape Peninsula University of Technology, 2020Flow rate measurement of Newtonian and non-Newtonian liquids out of tanks and reservoirs has been conducted broadly dating as far back as the 16th century. However, as far as can be ascertained, the outflow of non-Newtonian liquids from the bottom of a tank has only been reported in a few papers. Non-Newtonian liquids behave differently from water; they have complex rheological characteristics. It is therefore difficult to determine the flow rate of these liquids when they are discharged from the bottom of a tank. The aim of this work is to establish the impact of round orifice aspect ratios (L/d) on the gravitational discharge of non-Newtonian liquids from a tank, as a function of liquid properties.
Tests were carried out in the Flow Process and Rheology Centre laboratory of the Cape Peninsula University of Technology. A rectangular tank with clear Perspex walls (0.4, 0.4 and 0.6) m was used for conducting the tests. Four circular orifices – 20 mm in diameter with lengths of 1, 20, 60 and 100 mm and L/d ratios 0.05 (sharp-crested), 1, 3 and 5, respectively – were each fitted in the bottom centre of the tank, flush with the inside surface. The change in liquid weight was measured by a load cell. For calibration purposes, water was used. Various concentrations of glycerine solutions were used as Newtonian liquids, and aqueous solutions of carboxymethylcellulose (CMC) and water-based suspensions of kaolin and bentonite were used as non-Newtonian liquids. The rheology of the tested liquids was established using a Paar-Physica MCR 300 rotational rheometer. Flow rate measurements were conducted for each liquid and concentration. From these, the coefficient of discharge (Cd) values and appropriate Reynolds number was calculated.
Data analysis was presented in the form of Cd against the Reynolds number. The existing literature shows that in the turbulent region, Newtonian and non-Newtonian liquids have an average Cd value of 0.62 and 0.67, respectively, irrespective of the L/d ratio used. Calibration results of the current study showed that in the turbulent flow there was a non-consistent increase in Cd values as the L/d ratio increased. For Newtonian liquids the Cd was nearly constant with average Cd values of 0.60, 0.59, 0.80 and 0.78 for L/d ratios of 0.05, 1, 3 and 5, respectively. For Newtonian liquids, a single composite power-law function was used to relate the Cd versus Re relationship for each L/d ratio. The correlations estimated the Cd values to within ±3 % error margins.
This thesis adds new coefficient of discharge and Reynolds number data from laminar to turbulent region for an L/d ratio of 5 to the literature. It also adds other kinds of non-Newtonian liquids. Findings from this research will benefit the food processing and engineering industries where high concentrations of non-Newtonian liquids are stored and transported from one tank to the other
Copper and zinc in water, sediment and gastropods in the harbours of the Cape Town Metropole, South Africa
Full text linkThesis (Master of Environmental Health)--Cape Peninsula University of Technology, 2020The harbours in Cape Town are an important hub for development and socio-economic activities, some of which include shipping traffic, ship repair and maintenance, commercial and artisan fishing, construction (dredging and reclamation) and recreational vessel activities. These harbour related activities have contributed enormously to the influx of contaminants such as metals into the coastal environment. The semi-enclosed nature of the harbours associated with limited water exchange is conducive for water pollution. Thus, harbours are increasingly becoming a hotspot for metal loading into coastal ecosystems.
Copper and zinc are metal-based biocides in present-day antifouling (AF) paints. Concerns have been raised over the effect of these metal ions in the marine environment with high levels being detected in areas of intense vessel activities such as harbour. The aim of the study was to determine concentration levels of copper and zinc in seawater, sediment and gastropods (Burnupena spp. and Nucella spp.) from selected harbours and reference sites in the Cape Town metropole. Also, to determine the suitability of the two gastropods for use as biomonitors of metal contamination as well as whether there was a causal relationship between copper and zinc content in the gastropods and the concentrations in water and sediment from the harbours.
Samples were collected once-off seasonally in March (dry season) and September (wet season) 2016 from sampling point(s) in the harbours and reference sites at spring low tides. Samples of seawater, sediment and gastropods (soft tissue and shell) were acid digested and metal concentrations analysed in quintuplicate using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Statistical analyses were conducted using the SigmaPlot 13 software. Statistically significant differences in copper and zinc concentrations between sampling points in harbours and the reference sites were evaluated using a Kruskal–Wallis One-Way ANOVA on Ranks and Student Newman Kuels Method for post hoc tests as datasets were non-parametric. Dunn’s Method was used for Post hoc test after the ranked based ANOVA to evaluate significant differences in copper and zinc concentrations between harbours (unequal datasets). The Mann Whitney Rank Sum Test was used for comparisons in copper and zinc concentrations between the two seasons per sampling point, per sampling sites and between soft tissue and shell per sampling point. The Spearman’s Rank Order Correlation was used to determine if there was a relationship between the metal concentrations in the ambient samples (seawater and sediment) and soft tissue and shells of the gastropods.
The results showed that the mean copper and zinc concentrations (mg/L) in seawater ranged between not detected (ND) to 0.0818±0.0494 and ND to1.7679±0.639, respectively. The
corresponding mean concentrations (mg/kg dry weight) of copper and zinc in sediment were ND to 3432.16±2306.68 and 1.20±1.53 to 2380.43±1456.79, respectively. The highest mean copper and zinc concentrations (mg/kg dry weight) were found in Nucella soft tissue with a range of 19.84±6.43 to 2211.61±3168.07 and 77.20±15.14 to 5045.44±2447.15, respectively. The mean copper and zinc concentrations in seawater, sediment and gastropods (soft tissue and shell) were found to be generally higher in the dry season than the wet season. Generally, the mean copper and zinc concentrations in the soft tissue of the gastropods were higher than in the shells. The findings indicated that variations in copper and zinc concentrations in seawater, sediment and gastropods (soft tissue and shells) at sampling points in the harbours could be attributed to proximity to contamination sources, the rate of water exchange, metal handling strategies of gastropods as well as changes in environmental factors. The highest mean copper and zinc concentrations were found at sampling points close to areas of intense vessel-related activities in the harbours. Therefore, it could be suggested that AF paints are a predominant source of copper and zinc in seawater, sediment and the gastropods in the harbours. The correlation analyses revealed that there were generally no significant correlations between copper and zinc contents in the soft tissue or shell of the gastropods (Nucella spp.) and the ambient environmental concentrations in the harbours and reference sites although some distinct trends were observed. It was shown that copper and zinc concentrations in the soft tissue or shell of Nucella spp. may not be directly affected by those of the ambient seawater and sediment. It may, therefore, be presumed that the changes in copper and zinc loading in seawater and sediment were not the only factors that influenced the level of bioavailability of these metals to the Nucella spp. It is possible that the bioaccumulation of copper and zinc in the soft tissue or shell of Nucella spp. may have been influenced by many physicochemical and biological parameters. By comparing the data with water and sediment quality guidelines, it was observed that mean copper and zinc concentrations in seawater from some of the sampling points in the harbours exceeded the South African Water Quality Guidelines (SAWQGs). Likewise, the mean copper and zinc concentrations in sediment from some sampling points in the harbours were moderately or seriously polluted based on the Benguela Current Large Marine Ecosystem Sediment Quality Guidelines for southern Africa (BCLME-SQGs). It is, therefore, strongly suggested that source identification and continuous monitoring of copper and zinc in water, sediment and biota in the harbours is imperative
Heavy metals in soil and vegetables of allotment gardens in the Cape Town environment
Full text linkThesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2020This study investigated the concentration of selected heavy metals in soil, water and vegetable crops from selected allotment gardens in Cape Town. Heavy metals occur naturally in the earth’s crust, but due to human activities, their biochemical balance and geochemical cycles have been altered. Heavy metals are abundant in air, soil and water due to environmental pollution. It was therefore of interest to conduct this study to determine the levels of heavy metals (Pb, Cd, Mn, Zn, Cr, Cu, Ni, Fe and Co) in soil, water and vegetables such as spinach, cabbages, green peppers, brinjals and leek onions. Soil, water and vegetables were sampled during winter and summer from the allotment gardens of Cape Town environment and were analyzed using Inductively Coupled Plasma (ICP).
The physicochemical parameters of soil and water were determined during both seasons. The average pH of water in winter was 6.53 ± 0.6, while the summer pH was 6.71 ± 0.7. The average soil pH was 6.58 ± 0.2 in winter, while in summer the soil pH was 6.60 ± 0.2. The soil organic matter ranged from 1.7 % to 13.5 % in both seasons.
The heavy metals in water and soil showed seasonal fluctuation (p < 0.05). In summer the concentrations in water ranged from 0.062 mg/L to 0.947 mg/L, while in winter it ranged from 0.002 mg/L to 2.347 mg/L. The soil heavy metal concentrations in summer ranged from 0.52 mg/kg to 1127.41 mg/kg, while in winter it ranged from 0.59 mg/kg to 1209.95 mg/kg, Fe having the highest concentrations for both seasons.
The heavy metal concentration in vegetables was generally higher in summer than in winter, although Fe was still the highest in both winter and summer. Fe was particularly high in spinach with a concentration of 144.28 mg/kg in summer, while in winter the concentration was 116.56 mg/kg, followed by leek onion and cabbage.
The results for water and soil showed a decrease and weak correlation with a decreasing order Fe > Cu > Cr > Ni > Pb > Co > Zn > Mn > Cd > and Fe > Zn > Mn > Cu > Pb > Cr > Ni > Co > Cd, respectively. The distribution sequence of the heavy metals in vegetables during winter is in the order; spinach (Fe > Zn > Cr > Mn > Cu > Co> Cd ≥ Pb ≥ Ni); cabbage (Fe > Mn > Cr > Zn > Cu > Co > Cd ≥ Pb ≥ Ni) and leek onion (Fe > Zn > Mn > Cr ≥ Co > Cu > Cd ≥ Pb ≥ Ni). The corresponding sequence during summer was; spinach (Fe > Zn > Mn > Co > Cr > Cu > Cd ≥ Pb ≥ Ni); cabbage (Fe > Mn > Cr > Zn > Pb > Co > Cu > Cd ≥ Ni) and leek onion (Zn > Fe > Pb ≥ Mn > Cr > Co > Cu > Cd ≥ Ni); brinjal ( Fe > Mn > Zn > Cr > Cu > Co > Cd ≥ Pb ≥ Ni) and green peppers ( Fe > Zn > Mn > Co > Cu > Cr > Cd ≥ Pb ≥ Ni).
Results showed that concentration levels of all the selected heavy metals were below the permissible limits in soil, water and vegetables set by WHO
Process optimization and environmental assessment of municipal solid waste conversion to liquid fuels and/or chemicals
Full text linkThesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2020South Africa currently faces an energy security issue with regards to the country’s rather insignificant petroleum reserves. The Fischer-Tropsch Synthesis process has found great application in converting the reserves available to products of economic value in terms of fuels and chemicals finding the adequate application at Sasol and Petro SA alike. However, in the realisation of the fact that coal is a high pollutant and natural gas reserves at a critical low with Sasol and Petro SA respectively, new innovations have become of critical importance. Solid waste management has become an ever-growing problem world-wide due to rapid urbanization and population growth. South Africa was found to have generated 9 million tons of general waste in 2011 with the Western Cape generating 675 kg/capita/annum. The convention of management has been that of landfilling however, this method is fast becoming insignificant due to the lack of space and detrimental nature to the environment. Considering the energy security issue South Africa is facing, and the global drive of finding alternate sources of fuel with the depletion of fossil fuel, attention has turned to MSW as a sustainable source of energy while remediating its effect on the environment. Thermochemical conversions of Municipal Solid Waste (MSW), this presents an attractive means of harnessing the potential value in this waste stream thus thermochemical conversion poses an attractive means of converting this waste stream into valuable fuel products.
In the realisation of the 2 problems of energy security and solid waste disposal, Biomass to Liquid (BTL) technology was found to be the most suitable to tackle these issues. BTL is an established process that uses the thermal conversion of biomass into various liquid fuels products through a series of technologies. MSW is highly heterogeneous which poses a processing challenge, unlike virgin biomass which is normally used in BTL technologies. The study investigated the production of high-quality syngas through an Aspen simulation of thermal gasification which would be suitable for liquid fuels and chemicals via Fischer-Tropsch synthesis to bridge the energy security issue in South Africa. As the study also possesses an environmental facet, it was necessary to assess the pollution load caused by the process of landfilling in terms of Heavy Metals and Radionuclides which will be determined by means of radionuclide analysis and heavy metal analysis. The procedures were accomplished by use of the gamma-ray spectroscopy, High Purity Germanium detector, (HPGe) and Inductively Coupled Plasma Optical Emission Spectrometry, (ICP-OES) methods.
The study was conducted by making use of Refuse Derived Fuel (RDF) pellets produced from the MSW. 4 Different binders in form of corn starch, guar-gum starch, waste palm oil and waste engine oil were used in the production of the pellets, thus the effect of this on energy content and thermal degradation behaviour was studied. The energy content of MSW in Cape Town was investigated using a bomb calorimeter and the thermal degradation behaviour was studied using Thermogravimetric Analysis (TGA). The South African Government, through the National Development Plan of South Africa, aims to provide access to the grid and off-grid electrical power to a minimum of 95 % of the population by 2030, of which 20 GW of the required 29 GW required for this needs to come from alternative and renewable energy sources. This study using the MSW from the City of Cape Town Municipality in South Africa shows that the MSW has a calorific value of approximately 19 MJ/kg which is significantly high, meaning that the waste can be directly used as fuel in many applications but more importantly that of electricity generation. The calorific value for the pelletised waste was found to be higher at an average of 23.9 MJ/kg which can be compared with South African coal being 25.1 MJ/kg. Using TGA, 3 distinguishable major mass loss regions were found between temperatures 55 – 265 ℃, 270 – 410 ℃ and 410 – 502 ℃. The total sample reduction was found to be more than 90 % on average which is a reduction of the waste.
Heavy metals and Radionuclides (HM and R) are abundant in various types of municipal solid waste, including industrial waste, construction waste, medical waste, and household waste. Products containing HM and R are commonly disposed of in MSW or hazardous waste landfills and dumpsites. Approximately an average of 0.8 to 3 kg per capita per day of MSW is generated by suburban areas in South Africa. This method of managing or processing the waste has fast become inadequate and hence the need for new innovations. This has led to the focus on thermochemical conversion as an alternative. The soil is amongst the most considerable sources of radiation exposure to human beings and the migration for the transfer of radionuclides to the immediate environment. Exposure is a direct result of gamma-ray emissions that are produced by the most common terrestrial radionuclides, which are the member of the 238U and 232Th series and 40K of which concentrations differ with respect to the type of soil and the geology of the area. Environmental pollution by chemicals and heavy metals such as Cd, Ni, Zn, and Pb etc., showed a great increase in recent times due to various industrial operations including that of MSW disposal. All heavy metals at high concentrations have strong toxic effects and are regarded as environmental pollutants.
Naturally occurring radionuclides activity was investigated at landfill sites from the City of Cape Town using a Hyper-Pure Germanium (HPGe) detector with appropriate shielding coupled to a Palmtop Multichannel Analyzer. Activity concentrations of the radionuclides 238U, 232Th and 40K were obtained from the activity concentrations of their respective daughter radionuclides. To obtain the overall combined effect in terms of activity concentration from the 3 parent radionuclides, the radium equivalent was calculated and 38.273, 41.019 and 83.007 Bq/Kg were obtained from Bellville, Coastal Park, and Vissershok respectively. Other radiological hazards in terms of Internal and External hazard indices and Representative hazard index were determined and found to be within safe limits. The dose rate in the air at 1m above the ground was determined to obtain a characteristic of the external gamma-ray and was found to be 17.490, 18.609 and 38.667 nGy/y for Bellville, Coastal Park, and Vissershok respectively. The health effects of the radiation in terms of annual effective dose and excess lifetime cancer risk were determined to be 0.031 mSv/y and 0.0961×10-3 which are lower than limits set by the
United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and the Nuclear Industry Association of South Africa (NIASA).
The gasification part of the study was through process simulation models on ASPEN Plus Process simulation software. This investigation proposes a model of syngas creation from Refuse Derived Fuel (RDF) Pellet gasification with air in a fixed bed reactor. The model (utilizing Aspen Plus process simulation software) is utilized to model the anticipated results of RDF gasification and to give some processes fundamentals concerning syngas generation from RDF gasification. The fixed bed reactors are an updraft fixed bed reactor which can be divided into 3 sections which are drying, pyrolysis and gasification. The model is based on a combination of models that the Aspen Plus simulator provides, representing the three stages of gasification. Thermodynamics package used in the simulation comprised the Non-Random Two-Liquid (NRTL) model. The model works on the principle of Gibbs free energy minimization and was validated with experimental data of MSW gasification found in the literature. The RYield module was combined with the RGibbs module to describe pyrolysis section, while the RGibbs module was used for the gasification section individually. Proximate and ultimate analysis of RDF pellets and operating conditions used in the model are discussed. The sensitivity analysis module of Aspen Plus was used to research the effect of air equivalence ratio, ER and temperature value on the syngas composition, and carbon conversion. The results indicate that higher temperature improves gasification as the composition of H2 and CO increase, as well as carbon conversion until a temperature of 900 ℃ and higher air equivalence ratio increases the carbon conversion while decreasing syngas quality as there is an increase in CO2 and H2. The most suitable binder for the gasification of RDF derived from MSW is maize starch, with the optimal process parameters for the production of syngas being that of temperature at 780 0C and airflow rate of 6 kg/hr which translates into a fuel-to-air feed ratio of about 1:2. Results obtained are in good agreement with the experimentally measured data in the literature
Analysis and characterisation of a closed-loop control system for laser cooling and trapping experiment
Full text linkThesis (MEng (Electrical Engineering))--Cape Peninsula University of Technology, 2020This research is aimed at analysing the performance of a closed-loop feedback system of an external cavity diode laser (ECDL) for a laser (Doppler) cooling and atom trapping experiment.
External cavity diode lasers (ECDL) are commonly used in laser cooling exper-iments involving rubidium atoms. The laser frequency is controlled by adjusting the cavity length and the diode current. Using feedback control method, the laser is locked to an appropriate rubidium transition using a saturation absorption spectroscopy (SAS) setup together with a proportional-integral-derivative (PID) controller.
At the CPUT Quantum Physics research group, we have a laser cooling and atom trapping experimental setup. This setup is a combination of multiple optical, electrical and mechanical components. We first analyse this system experimentally using test signals. By passing in basic test input signals, we were able to measure the system by identifying and extracting certain properties such as the resonant frequency, the damping constant and transient response of the system. The re-sults generated from the experimental analysis further enabled us to estimate the transfer function of the external cavity diode laser (ECDL).
We then analyse the feedback setup numerically using known parameters from the experiment, and estimated parameters from the experimental analysis. We do this by first getting the mathematical model of the laser and then solving the differential equation using Euler methods in Matlab. By numerically analysing this feedback system, we are able to understand its transient behaviour. We were also able to test the system for different test scenarios e.g. tests for various controller constants, system response to different disturbance types and so on.
The similarities observed between the experimental and numerical analysis pro-vide a reliable framework for future improvements when developing the feedback system. Elements such as the integrator constants, disturbance magnitudes and so on can be evaluated using the developed numerical closed-loop system