Chemical Engineering

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Electroflocculation of river water using iron and aluminium electrodes
(2008-09) Mashamaite, Aubrey Nare; Van der Merwe, H. C.
A novel technology in the treatment of river water, which involves an electrochemical treatment technique to produce domestic or drinking water is being investigated using aluminium and iron electrodes in an electrochemical circuit. Coagulation and flocculation are traditional methods for the treatment of polluted water. Electrocoagulation presents a robust novel and innovative alternative in which a sacrificial metal anode treats water electrochemically. This has the major advantage of providing mainly active cations required for coagulation and flocculation, without increasing the salinity of the water. Electrocoagulation is a complex process with a multitude of mechanisms operating synergistically to remove pollutants from the water. A wide variety of opinions exist in the literature for key mechanisms. A lack of a systematic approach has resulted in a myriad of designs for electrocoagulation reactors without due consideration of the complexity of the system. A systematic, holistic approach is required to understand electrocoagulation and its controlling parameters. An electrocoagulation-flotation process has been developed for water treatment. This involved an electrolytic reactor with aluminium and/or iron electrodes. The water to be treated (river water) was subjected to coagulation, by Al(III) and Fe(II) ions dissolved from the electrodes, resulting in floes floating after being captured by hydrogen gas bubbles generated at the cathode surfaces. Apparent current efficiencies for AI and Fe dissolution as aqueous Al(III) and Fe(II) species at pH 6.5 and 7.8 were greater than unity. This was due to additional chemical reactions occurring parallel with electrochemical AI and Fe dissolution: oxygen reduction at anodes and cathodes, and hydrogen evolution at cathodes, resulting in net (i.e. oxidation plus reduction) currents at both anodes and cathodes. Investigation results illustrate the feasibility of ferrous and aluminium ion electrochemical treatment as being a successful method of water treatment. Better results were achieved under conditions of relatively high raw water alkalinity, relatively low raw water turbidity, and when high mixing energy conditions were available.
An application of reverse osmosis process on effluent treatment for the rubber industry
(2009-05) Ralengole, Galebone; Van der Merwe, H.; Modise, S. J.
The methods used to remove potassium sulphate (K2S04) and other impurities contained within Karbochem finishing plant effluent were investigated. Reverse osmosis was explored for this application. The study was conducted in two steps. The first step focuses mainly on the effluent treatment using BW30 flatsheet as well as BW30-2540 spiral-wound reverse osmosis membranes for the rejection of potassium and sulphate ions. The membranes were supplied by Filmtec. The second step reveals the possible use of potassium sulphate obtained from the brine stream in the fertiliser and fertigation industry by a literature search. Reverse osmosis study was conducted on a laboratory scale unit using flat sheet membranes and also on a pilot plant scale using spiral wound membrane modules. The tests were conducted at a feed pressure of 20 bar(g) with the membrane rejections being 98% and 99.1% on flat sheet membrane, and 96.9% and 99.4% on spiral wound membrane for potassium and sulphates respectively. The results show that both membranes have completely desalinated. Significant reduction in the concentrations of all problematic quality parameters, especially of potassium and the sulphate ions was noted. Granular activated carbon (GAC) bed treatment was recommended for pretreatment of the effluent prior to exposure of the membrane to avoid organic fouling of the membrane. GAC treatment was tested to illustrate its effectiveness to adsorb the COD's.
The adsorption of Cu(II) ions by polyaniline grafted chitosan beads.
(Vaal University of Technology, 2013-11-06) Igberase, Ephraim; Ofomaja, A., Dr; Osifo, P.O., Dr
This work investigates the possible use of chitosan beads and polyaniline grafted chitosan beads (PGCB) for the adsorption of copper ions from copper contaminated water. For this purpose chitosan flakes were converted to chitosan beads. However, a variable from a number of reaction variables (aniline concentration, chitosan concentration, temperature, acid concentration, reaction time and initiator concentration) was varied while others was kept constant, in an attempt to determine the best conditions for grafting of polyaniline onto chitosan beads. Percentage (%) grafting and % efficiency were key parameters used to determine such conditions. The chitosan beads and PGCB were characterized using physical techniques such as Fourier transformed infra red (FTIR), X-ray diffraction (XRD), and scanning electron microscope (SEM). The beads were used as an adsorbent for copper ions removal. The effect of pH on the removal rate of copper (II) by PGCB was investigated on by varying the pH values from pH 3 to 8 at an initial concentration of 40 mg/l. The effect of contact time, initial concentration and temperature was also investigated. The Langmuir and Freundlich model were used to describe adsorption isotherms for chitosan beads and PGCB, with correlation coefficient (R2) as the determining factor of best fit model. The thermodynamics of adsorption of copper (II) onto PGCB was described by parameters such as standard Gibb’s free energy change (ΔGo), standard enthalpy change (ΔHo), and standard entropy change (ΔSo) while the pseudo first-order and pseudo second-order kinetic model was used to describe kinetic data for the PGCB, with R2 and chi- square test (  2) as the determinant factor of best fit model. From the desorption studies, the effect of eluants (HCl and HNO3) and contact time on percentage desorption of PGCB loaded copper (II) ion was investigated upon. In determining the reusability of the PGCB loaded copper (II) ion, three cycles of adsorption/desorption studies was carried out. The results obtained from determining the best conditions for grafting polyaniline onto chitosan beads revealed the following grafting conditions; [Aniline] 0.1 g/l, [temperature] 35oC, [chitosan] 0.45 g/l, [HCl] 0.4 g/l, [(NH4)2S2O8] 0.35 g/l, and [time] 1 h. These conditions were applied in the grafting of polyaniline onto chitosan beads. FTIR analysis showed increase intensity in the grafted beads which provided evidence of grafting, XRD measurement showed a decrease in crystallinity in the PGCB as against the partial crystalline nature of chitosan. In SEM analysis, evidence of grafting was revealed by the closed gap between the polysaccharide particles in the PGCB. From the investigation carried out on the effect of pH on the percentage removal of Cu(II) ions by PGCB, the optimal pH value was found to be pH 5 with a percentage removal of 100% and this value was used for all adsorption experiment. Also from the investigation performed on the effect of contact time and initial concentration, it was observed that there was a sharp increase in the amount of Cu(II) ions adsorbed by PGCB up until contact time of 30 min and thereafter, it increases gradually. From the experiment carried out on the effect of temperature on adsorption capacity, there was an increase in adsorption capacity with increase in temperature. Moreover, at temperatures of 25oC, 35 oC and 45oC the Langmuir model gave the best fit for the chitosan beads having R2 values that are equal and greater than 0.942 in contrast to Freundlich having R2 values that is equal and greater than 0.932. The maximum adsorption capacity (Qm) from Langmuir model at these temperatures were 30.3 mg/g, 47.6 mg/g and 52.6 mg/g respectively. Also, the Langmuir model gave the best fit for the PGCB having R2 values that are equal and greater than 0.956 in contrast to Freundlich model with R2 values that is equal and greater than 0.935. The Qm from Langmuir model at these temperatures were 80.3 mg/g, 90.9 mg/g and 100 mg/g respectively. The values of Qm for PGCB appears to be significantly higher when compared to that of chitosan beads and this makes PGCB a better adsorbent than chitosan beads. From the thermodynamic studies carried out on PGCB, the values of ΔGo were negative and this denotes that the adsorption of copper ions onto PGCB is favorable and spontaneous, the positive value of ΔHo shows the adsorption process is endothermic and the positive value of ΔSo illustrate increased randomness at the solid-liquid interface during the adsorption process. Also, from the kinetic studies carried out on the PGCB, the pseudo second-order kinetic model best described the kinetic data having R2 values that are equal and greater than 0.994 in contrast to the pseudo first-order kinetic model with R2 values that is equal and greater than 0.913. The  2 values for the pseudo first-order and pseudo second-order kinetic model were similar; however, there was a large difference for qe between the calculated (qeCal) values of the first-order kinetic model and experimental (qeExp) values. In the case of the pseudo second-order model, the calculated qe values agree very well with the experimental data. Desorption of the metal ions from PGCB was efficient. 0.5 M HCl was successfully used in desorbing the beads loaded with copper ions and a percentage desorption of 97.1% was achieved at contact time of 180 min. PGCB were successfully re-used for adsorption/desorption studies were a Qm of 83.3 mg/g, 83.3 mg/g and 76.9 mg/g was achieved in the first, second and third cycle respectively.
Biodiesel production and evaluation of heterogeneous catalyst using South African oil producing trees
(Vaal University of Technology, 2014-01) Modiba, Edward Magoma; Osifo, Peter, Prof.; Rutto, Hillary, Dr.
This study presents the use of sodium methoxide as a homogeneous catalyst and impregnated Perlite (potassium hydroxide/perlite) as heterogeneous catalyst for production of biodiesel using Baobab and Marula oil respectively. One factor at a time experimental design was used to study the effect of temperature, time, amount of catalyst and methanol to oil ratio on the transesterification of baobab oil using sodium methoxide as a catalyst. Response surface methodology was used to study the effect of temperature, time, amount of catalyst and methanol to oil ratio on the transesterification of marula oil using perlite as a catalyst. Biodiesel yield produced using sodium methoxide and baobab oil was 96% at 1 hr reaction time, 30 wt.% methanol to oil ratio, 1 gram of catalyst and 60°C reaction conditions. Biodiesel yield produced using perlite and marula oil was 91.38% at 3.55 hr reaction time, 29.86 wt.% methanol to oil ratio, 3.46 grams of catalyst and 70.41°C reaction conditions. Perlite catalyst was reusable for transesterification of marula oil while sodium methoxide was not reusable for transesterification of baobab oil. Baobab and Marula biodiesel fuel properties are comparable to American Society for Testing Materials standard (ASTM).
Treatment of acid mine drainage using constructed wetland and UV/TiO₂ photocatalysis
(2014-05) Seadira, Tumelo Wordsworth Poloko; Aoyi, Ochieng
Acid mine drainage (AMD) is a serious problem associated with mining activities, and it has the potential to contaminate surface and ground water. The aim of this study was to evaluate the performance of constructed wetland and photocatalysis in treating AMD. Three identical unvegetated upflow constructed wetlands packed with natural zeolite (clinoptilolite) and coarse silica sand were made of a cylindrical plastic pipe, and the slurry photocatalyst was prepared using quartz material. A hydro-alcohol thermal method was used to prepare an anatase core-void-shell TiO2 photocatalyst. The results showed that the three unvegetated upflow constructed wetlands (CW) had relatively similar percentage removal of heavy metals despite their varying concentrations within the AMD. The removals were: Fe (86.54 - 90.4%); Cr (56.2 - 64.5%); Mg (56.2 - 67.88%); Ca (77.1 - 100%); and 100% removal was achieved for Be, Zn, Co, Ni, and Mn. The removal of sulphate was also 30%. Heavy metals concentration in CW packing material was significantly higher in the outlet of the constructed wetlands than in the inlet. The adsorption isotherms revealed that the experimental data fitted the Langmuir Isotherms better, which suggested a monolayer coverage of heavy metals on the surface of the adsorbents; thermodynamic studies showed that the nature of adsorption taking place was physical; the kinetics models showed that the adsorption was first order reaction. A higher photocatalytic reduction (62%) of Cr(VI) was obtained at pH 2, 30 mg/l Cr(VI) initial concentration, and three hours of irradiation time. It was also found that the presence of Fe(III) enhanced the reduction of Cr(VI). The core-void-shell TiO2 photocatalyst showed a better activity than the commercial P25 Degussa for the reduction of Cr(VI) to Cr(III). The kinetic studies showed that the reduction of Cr(VI) was first order reaction. Photocatalytic reduction of Cr(VI) in real AMD sample was achieved only for the Douglas North Discharge (DND) sample (68%), and the Fe(III) reduction was found to be 83%. Therefore it was concluded that the combination of constructed wetland and UV/ TiO2 photocatalysis employing anatase core-void-shell TiO2 as a photocatalyst has a potential to reduce the toxicity of Cr(VI)-laden acid mine drainage.
Solar photocatalytic degradation and adsorption of emerging pharmaceutical contaminants in wastewater
(Vaal University of Technology, 2014-09-15) Akach, John Willis Juma Pesa; Onyango, Maurice S., Prof.; Aoyi, Ochieng, Prof.
Pharmaceutical pollutants in wastewater have become an increasing concern in recent years. Adsorption and photocatalytic degradation of pharmaceutical pollutants have proved to be very efficient in the removal of pharmaceutical contaminants. In this study, a composite catalyst of powdered activated carbon (PAC) and TiO2 bound by silica xerogel (CTS composite) was synthesized and characterised using SEM, XRD and XRF. The composite catalyst was then used to adsorb and photodegrade the pharmaceuticals sulfamethoxazole (SMX), diclofenac (DCF) and carbamazepine (CBZ) in a three phase fluidised bed photocatalytic reactor using sunlight to activate the TiO2. The solar radiation intensity at the Vaal University of Technology and the hydrodynamic behaviour of the reactor were also investigated. Additionally, the effect of catalyst composition and loading, hydrodynamics and solution characteristics on the adsorption and photodegradation of the substrates was investigated. It was found that the solar radiation intensity varied with the hour of day, weather and seasons of the year. SEM showed that the porosity of the composite catalyst increased with increase in the PAC loading and a decrease in the silica xerogel loading. The XRD results showed that the silica xerogel and the PAC did not alter the composition of the P25 TiO2. XRF showed that the method used in the preparation of the substrates resulted in the desired composition of the catalyst. The optimum CTS composition was 60% silica xerogel loading and 10% PAC/TiO2 ratio. The best mass of the composite catalyst was 1.5 g/l. Using the optimal composite composition resulted in over 90% removal of the substrates with low residual solution turbidity of less than 3.5 formazin attenuation units (FAU). The optimum hydrodynamic condition was obtained when the reactor inclination angle and superficial air velocity were 75° and 0.014 m/s, respectively. However, a reactor inclination angle of 75° and a superficial velocity of 0.007 m/s gave the best adsorption and photodegradation of the substrates. Reducing the initial concentration of the substrates resulted in an increase in the efficiency of removal of the substrates. The adsorption and photodegradation of SMX was observed to increase with a decrease in pH and was maximum at pH 4. The adsorption of SMX and DCF was found to follow the Langmuir isotherm model. These results show that the use of the synthesised composite catalyst in the fluidised bed reactor provided a stable and efficient system capable of long term use. The results from this work also show that this system can be used for the removal of pharmaceutical substrates at low concentrations.
Photocatalytic treatment of industrial wastewater containing citric acid and toxic heavy metals
(2014-12) Baloyi, Siwela Jeffrey; Aoyi, Ochieng
The co-existence of organic acids and toxic heavy metals in natural water creates harmful effects on human, plants and animals. Therefore, it is necessary to treat organic acids and toxic heavy metal contaminated wastewater prior to its discharge to the environment. The aim of this study was to apply co-treatment of industrial wastewater containing citric acid and toxic heavy metals in single and binary systems using photocatalysis process. The hydrothermal method was used to synthesise dandelion-like TiO2 structures. Modifications of the dandelion-like TiO2 by deposition of gold nanoparticles and immobilisation on calcium alginate were done using deposition precipitation and one-step encapsulation methods, respectively. Dandelion-like TiO2 and dandelion-like TiO2 immobilised on calcium alginate (Alg/TiO2) were used as photocatalysts for Cr(VI), Hg(II) and citric acid removal from water. The results showed that the production of dandelion-like TiO2 structures strongly depends on the reaction time and synthesis temperature as key process parameters. The characterisation of the dandelion-like TiO2 by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and Brunauer-Emmett-Teller (BET) revealed the crystal structure, morphology, chemical composition and surface area. It was found that the efficiency of photocatalytic process depends on the type of pollutants, initial pH of the solution, photocatalyst dosage, contact time, substrate initial concentration, UV wavelength and light intensity. The reduction efficiency of Cr(VI) ion and citric acid increased with decreasing the initial pH values and initial concentration. On the other hand, Hg(II) reduction efficiency increased with increasing the initial pH values and initial concentration. In a binary system, the reduction of Cr(VI) and Hg(II) was found to be faster than in the single and ternary systems. The relationship of the chemical reaction rate of Cr(VI), Hg(II) and citric acid were expressed by the pseudo-first-order kinetic equation. Addition of ferric ions to Cr(VI)-citric acid complex and Hg(II)-citric acid complex enhanced the reduction of Cr(VI) and Hg(II), a complete reduction was accomplished within 30 and 60 minutes (min) of irradiation time, respectively. The reduction efficiency of both Cr(VI) and Hg(II) in the presence of citric acid in a solution was still significant after four times of Alg/TiO2 reuse. These results indicated that the UV/TiO2 photocatalysis process can be considered as a suitable method to reach a complete reduction of Cr(VI) and Hg(II) in the presence of citric acid in a solution.
Integrated anaerobic digestion and UV photocatalytic treatment of industrial wastewater in fluidized bed reactors
(Vaal University of Technology, 2017-03-28) Apollo, Seth Otieno; Onyango, Maurice S., Prof.; Aoyi, Ochieng, Prof.
Anaerobic digestion (AD) is usually applied in the treatment of distillery effluent due to the fact that it is effective in chemical oxygen demand (COD) reduction and bioenergy recovery. However, due to the presence of biorecalcitrant melanoidins present in distillery effluent, AD is ineffective in colour reduction. For this reason, ultraviolet (UV) photodegradation, which is effective in melanoidins’ degradation, can be integrated with AD to achieve high efficiency in colour and COD reduction. However, the UV process is energy intensive, majorly due to the electricity requirement of the UV lamp. In contrast, the AD process has high potential of renewable energy production in the form of biomethane, which can be transformed into electrical energy and applied to supplement the energy requirement of the UV process. The aim of this study was to evaluate the efficiency of a combined AD-UV system in colour and COD reduction for the treatment of distillery effluent in fluidised bed reactors. The potential of the application of the bioenergy produced by the AD process to supplement the energy intensive UV process was evaluated and modelled using response surface methodology. In the first place, the optimal hydrodynamic conditions of the fluidised bed reactors were determined using optical attenuation technique. The best homogeneity in the bioreactor, in which zeolite was used as microbial support, was found to be at a superficial liquid velocity of 0.6 cm/s while the best catalyst and gas hold up in the photoreactor were found to be 0.077 and 0.003, respectively. At these conditions, it was found that the initial biological step removed about 90% of COD and only about 50% of the colour while photodegradation post-treatment removed 98% of the remaining colour. Kinetic analysis of the bioreactor showed that ~ 9% of the feed total organic carbon (TOC) was non-biodegradable and this was attributed to the biorecalcitrant melanoidins. Photodegradation post-treatment mineralized the biorecalcitrant melanoidins via a reductive pathway as was indicated by the formation of NH4+ in large quantity compared to NO3-. Kinetic analysis further showed that the rate of substrate utilization in the bioreactor increased with an increase in organic loading rate and it was inversely proportional to the rate of photodegradation post-treatment. Modeling using response surface methodology (RSM) was applied to predict the effects of the operating parameters of the initial AD step on the performance of the photodegradation post-treatment process and the energy efficiency. Energy analysis of the integrated system showed that the AD process could produce 59 kWh/m3 of electricity which could supplement the electricity demand of the UV lamp by 30% leading to operation cost reduction of about USD 4.8/m3. This led to a presumed carbon dioxide emission reduction (CER) of 28.8 kg CO2e/m3.
Activation of the carbonaceous material from the pyrolysis of waste tires for wastewater treatment.
(Vaal University of Technology, 2017-07) Malise, Lucky; Seodigeng, T., Dr.; Rutto, H. L., Dr.
The generation of waste tires is one of the most serious environmental problems in the modern world due to the increased use of auto mobiles all over the world. Currently there is a problem with the disposal of waste tires generated since there are strict regulations concerning their disposal through landfill sites. Therefore, there is a need to find ways of disposing these waste tires which pose serious health and environmental problem. The pyrolysis of the waste tires has been recognised as the most promising method to dispose the waste tires because it can reduce the weight of the waste tires to 10% of its original weight and produce products such as pyrolysis oil, pyrolysis char, and pyrolysis char. These products can be further processed to produce value added products. The char produced from the pyrolysis of waste tires can be further activated to produce activated carbon. This study is based on the chemical activation of waste tire pyrolysis char to produce activated carbon for the removal of lead ions from aqueous solution. This was done by impregnating the waste tire pyrolysis char with Potassium hydroxide and activating it inside a tube furnace under inert conditions to produce waste tire activated carbon. Adsorbent characterisation techniques (SEM, FTIR, TGA, XRF, XRD, BET, and Proximate analysis) were performed on the waste tire pyrolysis char and the activated carbon produced to make a comparison between the two samples. The results showed that the waste tire activated carbon produced has better physical and chemical properties compared to the raw waste tire pyrolysis char. Adsorption results revealed that waste tire activated carbon achieves higher removal percentages of lead ions from aqueous solution compared to waste tire pyrolysis char. The results also showed the effect of various process variables on the adsorption process. Adsorption isotherms, kinetics, and thermodynamics were also studied. The adsorption of lead ions agreed with the Freundlich isotherm model for both the waste tire pyrolysis char and waste tire activated carbon. In terms of adsorption kinetics, the experimental data provided best fits for the pseudo-first order kinetic model for both the waste tire pyrolysis char and the waste tire activated carbon. The adsorption thermodynamics study revealed that the process is an exothermic process and spontaneous in nature. Response surface methodology was used to determine the combined effect of process variables on the adsorption of lead ions onto waste tire activated carbon and to optimise the process using numerical optimisation. The optimum conditions were found to be adsorbent dosage = 1g/100ml, pH = 7, contact time = 115.2 min, initial meta concentration = 100 mg/l, and temperature = 25°C to achieve a maximum adsorption capacity of 93.176 mg/l.
Corrosion behaviour of ferrous and non-ferrous alloys exposed to sulphate - reducing bacteria in industrial heat exchangers
(Vaal University of Technology, 2018) Prithiraj, Alicia; Osifo, Prof. P. O.; Otunniyi, Prof. I. O.
Corrosion responses of some carbon steels, stainless steel and copper alloys in the presence of a culture of bacteria (referred to as SRB-Sulphate-reducing bacteria) found in industrial heat exchangers, was studied to recommend best alloys under this service condition, with techno-economic consideration. Water from cooling towers in three plants in a petrochemical processing complex were analysed for SRB presence. Two of the water samples showed positive indication of SRB presence. The mixed cultures obtained from plant one were grown in prepared media and incubated at 35 °C for 18 days. Potentiodynamic polarisation studies in anaerobic conditions were done on the selected alloys in aqueous media with and without the grown SRB. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were then used to study the corrosion morphology and corrosion products formation. The voltamograms show higher icorr for alloys under the SRB compared to the control media, indicating the SRB indeed increased the corrosion rates. The surface analysis showed pitting on steel alloy ASTM A106-B. Localised attack to the grain boundaries on a selective area, was seen on ASTM A516-70 dislodging the grains, and intergranular corrosion was seen throughout the exposed area of ASTM A179. Copper alloys showed pitting on ASTM B111 grade C71500 (70-30), and denickelification on ASTM B111 grade C70600 (90-10), and is a good alternative material for use apart from carbon steel alloys, recording a low corrosion rate of 0.05 mm/year. The EDS analysis supported the findings showing higher weight percent of iron and sulphur on surface of the alloys after exposure to the SRB media. This implies that the presence of the sulphur ion indeed increased the corrosion rate. ASTM A516-70 carbon steel was chosen as a suitable alternative material to the stainless steel in this environment. The Tafel plot recorded a corrosion rate of 1.08 mm/year for ASTM A516-70 when exposed to SRB media.
Desulfurization of waste tire pyrolytic oil (TPO) using adsorption and oxidation techniques
(2018-01) Mello, Moshe; Seodigeng, T; Rutto, H. L.
The presence of tires in open fields, households and landfills is a great threat to the wellbeing of the ecosystem around them. Tire creates an ideal breeding ground for disease carrying vermins and their possible ignition threatens the surrounding air quality due to the harmful gases produced during combustion. Pyrolysis of tires produces four valuable products namely; char, steel, tire pyrolytic oil (TPO) and noncondensable gases. TPO has been reported to have similar properties to commercial diesel fuel. The biggest challenge faced by TPO to be used directly in combustion engines is the available sulfur content of about 1.0% wt. Considering the stringent regulations globally for allowable sulfur content in liquid fuels, TPO therefore, requires deep desulfurization before commercialization. In this study, different desulfurization techniques were applied to reduce the sulfur content in TPO. A novel study on combination of adsorptive and air-assisted oxidative desulfurization (AAOD) was developed for desulfurization of TPO. Different carbon materials were employed as catalyst and/or adsorbent for the AAOD system. The effect of operating conditions; catalyst/adsorbent dosage, H2O2/HCOOH ratio, reaction time, temperature and air flowrate were studied. Oxidation equilibrium was reached at 80 °C for both commercial activated carbon (CAC) and activated tire char (ATC) at a reaction time of 50 min. With a total oil recovery of more than 90% and the initial sulfur content of 7767.7 ppmw, the presence of air at a flow rate of 60 l/hr increased oxidation from 59.2% to 64.2% and 47.4% to 53% for CAC and ATC, respectively. The use π-complexation sorbent was also applied to study the selectivity of such sorbents to organosulfur compounds (OSC) found in liquid fuels. The π-complexationbased adsorbent was obtained by ion exchanging Y-zeolite with Cu+ cation using liquid phase ion exchange (LPIE). Batch adsorption experiments were carried out in borosilicate beakers filled with modified Cu(I)-Y zeolite for both TPO and synthesized model fuels. For model fuels (MF), the selectivity for adsorption of sulfur compounds followed the order dibenzothiophene (DBT)> benzothiophene (BT)> Thiophene.
Modelling of Petroleum Wastewater Photodegradation in a Fluidized Bed Reactor
(Vaal University of Technology, 2018-04) Nyembe, N.; Lerotholi, M.; Aoyi, Ochieng, Prof.
Petroleum wastewater is highly contaminated with toxic organic pollutants that are harmful to the environment. The heterogeneous photocatalytic oxidation (HPO) process has shown the ability to remove these pollutants through the application of a fluidized bed reactor (FBR). The purpose of the study was to apply response surface modelling (RSM) and computational fluid dynamics (CFD) to optimize the operating conditions for the photodegradation process in an FBR. This was done by investigating the hydrodynamics, photodegradation efficiency and reaction kinetics; that gave a holistic view on the performance of the FBR. The hydrodynamic study focused on modelling the axial liquid velocity, gas hold-up and turbulence quantities due to their substantial impact on the design and performance of the FBR. This was done by implementing the Eulerian-Eulerian approach which solves the continuity and momentum equations for each phase. In addition, the standard k-ε turbulence model was used to capture the turbulent characteristics in the liquid phase. A numerical optimization technique (desirability) was used to determine the optimal simulation setting methods; that were found to be a fine grid size (500 000 cells), 2nd Order Upwind discretization scheme and a small time step size (0.001) and gave the best desirability (0.985). The axial liquid velocity was maximal towards the centre of the reactor and decreased towards the wall. The same trend was seen with the local gas hold-up, where it was high towards the centre and low near the wall region. This was an indication that the bubbles tended to gather towards the central region as they move up. Furthermore, the bubbles had a spherical–like shape due to the low superficial gas velocity and operating within the homogeneous regime. The turbulent kinetic energy increased at distances away from the distributor region, due to the bubbles accelerating, and it balanced well with the energy introduced by the bubbles. Central composite design (CCD), which is a type of response surface modelling technique, was used to investigate and optimize the photodegradation operating parameters. The maximal degradation efficiency in the current study was found to be 65.9%, which was relatively low when compared to literature (80.84%). This was attributed to the increase in the catalyst particle size from nanometer to micrometer. Furthermore, the second-order empirical model that was developed, using the analysis of variance (ANOVA), presented a sufficient correlation to the photodegradation experimental data. The optimal photodegradation operating conditions were found to be: superficial gas velocity of 17.32 mm/s, composite catalyst loading of 1.0 g/L, initial pH level of 3.5 and reaction time being 210 min. Using the Langmuir-Hinshelwood model, it was found that the photocatalytic degradation of petroleum wastewater follows pseudo first-order reaction kinetics. Since the photocatalytic degradation mechanism of phenol follows three stages whereby the second stage is the photocatalytic degradation on the surface of the catalyst to form by-products. This is the rate dominant stage and follows the pseudo firstorder reaction kinetics.
Thermomechanical and rheological properties of investment casting patterns
(Vaal University of Technology, 2019-10-02) Tewo, Robert Kimutai; Focke, W., Prof.; Seodigeng, T., Dr.; Rutto, H. L., Prof.
Investment casting process is the most suitable technique for producing high quality castings which are dimensionally accurate with excellent surface finish and complex in nature. Recently with the ever-changing manufacturing landscape, the process has been increasingly used to produce components for the medical, aerospace and sports industry. The present study looked at three investigative scenarios in the development of a pattern material for investment casting process: (i) the development of wax/ethyl vinyl acetate (EVA) and wax/linear low-density polyethylene (LLDPE) blends as the carrier vehicle materials for the development of pattern material for investment casting; (ii) the development of wax/EVA/polymethyl methacrylate (PMMA) based investment casting pattern and lastly (iii) the development of wax/LLDPE/PMMA based investment casting pattern material. The first part of the studies elucidates the effects in terms of the thermal, mechanical, surface and rheological properties when paraffin wax in blended with poly EVA and LLDPE. The developments involved the extrusion of seven formulations for EVA and also LLDPE using a twin-screw extrusion compounder. The paraffin wax weight percent investigated ranged from 33% to 87% thus encompassing both low and high wax loading ratios. The thermal properties of the developed binary blends were characterized via thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The mechanical properties were characterized using three-point bending test. The thermo-mechanical and rheological properties were determined using thermomechanical analysis (TMA) and a rheometer respectively. A scanning electron microscope (SEM) was used to study the surface texture of the extruded blends. The thermal properties indicated that the thermal stability of paraffin wax is improved when it is blended with both EVA and LLDPE. DSC curves showed two endothermic melting peaks and two exothermic crystallisation peaks. In the case of wax/EVA blends, there was no distinct peak showing the independent melting of neat wax and EVA. The peak at a temperature of 50 – 72 °C corresponds to the melting of the wax/EVA blend. In the case of wax/LLDPE blends, the peak at 50 -66 °C corresponds to the melting of wax whereas the large peak at 112 - 125°C corresponds to the melting of the LLDPE. Wax/EVA and wax/LLDPE had improved mechanical properties as compared to that of neat wax. The rheological properties of both the EVA based and LLDPE based blends indicated that the viscosity of the blends increased as compared to that of neat wax. SEM confirmed that EVA alters the wax crystal habit at higher concentrations. In the case of wax/LLDPE blends, at 20-30 % wax content, a heterogeneous surface was observed, indicating the immiscibility of the paraffin wax within the LLDPE matrix. At a high wax content, there was agglomeration of wax. LLDPE allows amorphous structure of wax to disperse easily between the chains. The second part of the studies focussed on the wax/EVA filled with poly (methyl methacrylate) (PMMA) microbeads. TGA behaviour on the pyrolysis of wax/EVA/PMMA showed that the compounds volatilise readily with virtually no residue remaining above 500 °C. The DSC curves indicated that, the incorporation of PMMA reduced the crystallinity of wax/EVA blend. A distinct endothermic peak and another small peak was observed in all the formulations. The mechanical properties of wax/EVA/PMMA improved significantly. The methylene group present in both wax and EVA combined to form a blend with enhanced mechanical properties whereas the PMMA microbeads improved the needle penetration hardness. The melt viscosity of wax/EVA/PMMA increased as the EVA and/or the PMMA content is increased. The rheological experimental data fitted with the data predicted using the modified Krieger and Dougherty expression. The maximum attainable volume fraction of suspended PMMA particles was at max = 0.81. The SEM micrograph of wax/EVA/PMMA revealed a near perfect spherical nature for the filler particles in the wax/EVA polymer matrix. It further shows that the PMMA microbeads were weakly bonded and well distributed in the wax/EVA matrix. The third part of the studies focussed on the wax/LLDPE filled with Poly (methyl methacrylate) (PMMA) microbeads. The incorporation of LLDPE and PMMA into paraffin wax had a strong influence on the thermal properties, tensile properties, flow properties and its morphology. The TGA analysis showed that there was a slight observable decrease in the melting onset temperatures when the wax content was increased. From the DSC curves, the corresponding values of onset temperatures observed are between melting and crystallization temperature of neat paraffin wax and neat LLDPE. The short chains of the paraffin wax and the fragments formed by scission of wax chain have sufficient energy to escape from the matrix at lower temperatures. The slight decrease in peak temperatures associated with melting and crystallization could be attributed to the decrease in the average lamellar thickness of the blends. The tensile properties by three-point bending tests indicated an increase in the stress with an increase in the LLDPE content. This can be attributed to the formation of paraffin wax crystals in the amorphous phase of the blend which may influence the chain mobility. Since the paraffin wax used for this study had a low viscosity as compared to LLDPE, both LLDPE or PMMA had an influence on the viscosities of the blends. The data obtained from the experiments fitted with the data predicted obtained from the modified Krieger and Dougherty expression. The maximum attainable volume fraction of suspended PMMA particles was at max = 0.74. Similar observation with that of wax/EVA/PMMA was made in terms of the morphology of the wax/LLDPE/PMMA blends. The excellent thermal stabilities, the superior mechanical strength of wax/EVA/PMMA and wax/LLDPE/PMMA and the flow properties with relatively high EVA and also with high PMMA loadings, open new opportunities for EVA and LLDPE based pattern material for in investment casting process. It is worth pursuing further comprehensive studies since it offers a strong potential for realizing further technological improvement in the field of investment casting and rapid prototyping technologies.
Optimization of ion exchange process on the removal of heavy metals from cooling tower water and regeneration of ion exchange resins.
(Vaal University of Technology, 2020-06) Mbedzi, Robert Mbavhalelo; Rutto, H. L., Prof.
In the present study, the removal of Ca2+ and Mg2+ from cooling tower water using Amberlite IR120 and Amberjet 1200 was studied by the application of one factor at a time method (OFAT) and response surface modelling (RSM). The effect of operational parameters such as contact time (min), pH, dosage (mL), concentration (mg/L) and temperature (K) were investigated using central composite design. The regeneration of the Amberlite IR120 and Amberjet were also studied. The purpose of the study was to apply OFAT and RSM to investigate and optimize the ion exchange operating parameters. Furthermore, the second-order empirical model that was developed, using the analysis of variance (ANOVA), presented a sufficient correlation to the ion exchange experimental data. The optimal ion exchange operating conditions for Amberlite IR120 and Amberjet 1200 were found to be: contact time was 120 min, dosage of 150mL, initial pH level of 2, concentration of 400mg/L and temperature of 343K. Regeneration of Amberlite IR120 and Amberjet 1200 using 0.5 M NaCl stripping solution initially showed an increase in % Ca2+ and Mg2+ removal, then a decrease in subsequent cycles. The correlation coefficients (R2) of Langmuir, Freudlich and Tempkin isotherms were found to range from 0.92 to 1 and this suggest that experimental data best described the models. However correlation coefficients (R2) for Dubinin–Radushkevich (D-R) model were found to range between 0.5 to 0.8 and this means that experimental data does not fit the model. Thermodynamic functions such as entropy (Δ𝑆𝑜), enthalpy (Δ𝐻𝑜) and change of free energy (Δ𝐺𝑜) were obtained from the gradient and intercepts of straight line graphs. The positive values of ΔG° were found meaning that the adsorption is not spontaneous and positive values of ΔH° were found meaning the endothermic type of adsorption which indicate the chances of physical adsorption.The correlation coefficient (R2) values of pseudo-first-order, pseudo-second-order and intraparticle models were found to range from 0.89 to 1 on both metals as shown in table 4.4. This observation clearly indicates that pseudo-first-order, pseudo-second-order and intraparticle diffusion models best describe the experimental data in the removal Ca2+ and Mg2+ from cooling tower water.
Modelling of in-situ real-time monitoring of catalysed biodiesel production from sunflower oil using fourier transform infrared
(Vaal University of Technology, 2020-10) Mwenge, Pascal Kilunji; Rutto, H. L., Prof.; Seodigeng, T. G., Dr.
The industrialisation of the twenty-first century and the worldwide population growth led to the high demand for energy. Fossil fuels are the leading contributor to the global energy, and subsequently, there is a high demand of fuels. The decrease of global fossil fuels and the environmental air pollution caused by these fuels are concerning. Therefore, eco-friendly and renewable fuel such as biodiesel is one the leading alternative. Chromatography and Spectroscopy are the most used analytical methods and proven reliable but are time-consuming, requires qualified personal, extensive samples preparation, costly and do not provide in-situ real-time monitoring. Fourier Transform Infrared (FTIR) has mainly been used for qualitative analysis of biodiesel, but not much work has been reported in real-time monitoring. This study focused on the modelling of in-situ real-time monitoring of the biodiesel production from sunflower oil using FTIR (Fourier Transform Infrared). The first part of the study investigated the effect of catalyst ratio and methanol to oil ratio on biodiesel production by using central composite design (CCD). Biodiesel was produced by transesterification using Sodium Hydroxide as a homogeneous catalyst. A laboratory-scale reactor consisting of; flat bottom flask mounted with a reflux condenser, a hot plate as heating element equipped with temperature, timer and stirring rate regulator was used. Key parameters including, time, temperature and mixing rate, were kept constant at 60 minutes, 60 oC and 600 RPM, respectively. From the results obtained, it was observed that the biodiesel yield depends on catalyst ratio and methanol to oil ratio. The highest yield of 50.65 % was obtained at a catalyst ratio of 0.5 wt% and methanol to oil mole ratio 10.5. The analysis of variances of biodiesel yield showed the R2 value of 0.8387. A quadratic mathematical model was developed to predict the biodiesel yield in the specified parameters range. The same set-up was used to produce waste margarine biodiesel using a homogeneous catalyst, potassium hydroxide (KOH). The effects of four reaction parameters were studied, these were: methanol to oil ratio (3:1 to 15:1), catalyst ratio (0.3 to 1.5 wt. %), temperature (30 to 70 oC), time (20 to 80 minutes). The highest yield of 91.13 % was obtained at 60°C reaction temperature, 9:1 methanol to oil molar ratio, 0.9 wt. % catalyst ratio and 60 minutes. The important biodiesel fuel properties were found to be within specifications of the American Standard Test Method specifications (ASTM). It was concluded that waste margarine can be used to produce biodiesel as a low-cost feedstock. The core of the study was performed using EasyMax Mettler Toledo reactor equipped with a DiComp (Diamond) probe. The quantitative monitoring of the biodiesel production was performed by building a quantitative model with multivariate calibration using iC Quant module from iC IR 7.0 software. Fourteen samples of known concentrations were used for the modelling which were taken in duplicate for model calibration and cross-validation, data were pre-processed using mean centring and variance scale, spectrum math square root and solvent subtraction. These pre-processing methods improved the performance indexes from 7.98 to 0.0096, 11.2 to 3.41, 6.32 to 2.72, 0.9416 to 0.9999, RMSEC, RMSECV, RMSEP and R2Cum, respectively. The R2 values of 1 (training), 0.9918 (test), 0.9946 (cross-validation) indicated the fitness of the model built. The model was tested against the univariate model; small discrepancies were observed at low concentration due to unmodelled intermediates but were quite close at concentrations above 18%. The software eliminated the complexity of the Partial Least Square (PLS) chemometrics. It was concluded that the model obtained could be used to monitor transesterification of sunflower oil at industrial and lab scale. The model thus obtained, a batch reactor setup, EasyMax Mettler Toledodo reactor was used, the experiments were designed and monitored using iControl software. The results were recorded and quantified using iC IR software based on the biodiesel calibrated monitoring model built. The optimisation of the biodiesel was performed using three key parameters (methanol to oil ratio, catalyst ratio and temperature) while keeping time at 60 minutes and mixing rate at 150RPM. The highest yield of 97.85 % was obtained at 60 oC, 0.85 wt % catalyst ratio and 10.5 methanol to oil mole ratio. The analysis of variances of biodiesel production showed the values of 0.9847, 0.9674 and 0.8749, for R-squared, adjusted R-squared and predicted R-squared, respectively. A quadratic mathematical model was developed to predict the biodiesel conversion in the specified parameters ranges. Using the Arrhenius equation, activation energy (Ea) and frequency factor were found to be 41.279 kJ.mole-1 and 1.08 x10-4 M-1. s-1, respectively. The proposed kinetics model was a pseudo-first-order reaction. It was concluded that the model obtained can be used for industrial and laboratory-scale biodiesel production monitoring.
Synthesis of gelatin-cellulose hydrogel membrane for copper and cobalt removal from synthetic wastewater
(Vaal University of Technology, 2021-04) Lukusa, Tresor Kabeya; Shoko, Lay, Dr.; Tshilenge, John Kabuba, Dr.
Heavy metal ions are one of the most toxic materials in the environment. Adsorption is the most used process for the removal of heavy metals from wastewater. Much research has been conducted into processes to remove heavy metals using different adsorbents. Various adsorbents have been used to remove heavy metal ions from wastewater especially those that are harmful to mankind. Zeolite, clay, activated carbon and biopolymers are the most common adsorbents used. In this research, gelatin, and cellulose nanocrystals (CNCs) were used to synthesize a hydrogel membrane to remove Cu(II) and Co(II) metal ions from mining processes wastewater. The synthetic wastewater was prepared in the laboratory to conduct the experiments. Batch experiments were conducted to obtain the optimum conditions for the Cu(II) and Co(II) metal ions. The effect of parameters such as pH, ratio, contact time, and temperature were also determined. The optimum conditions obtained were 120 min contact time for both metal ions at the temperature of 30oC, pH 5 for copper and pH 7 for cobalt. The high removal of both metals ions was obtained using the ratio 3:1 (75% Gelatin and 25% CNCs) at the temperature of 303K. The maximum adsorption capacity of Cu(II) and Co(II) was 7.6923 mg/g and 10.988 mg/g, respectively. The high percentage removal of Cu(II) and Co(II) metal ions obtained was found to be 70.5% for Cu(II) at pH 5 and 74.5% for Co(II) at pH 7. The experimental data fit well to Pseudo-first-order kinetic and Freundlich isotherm models (KF= 1.89x103 mg/g for copper and 3.7x102 mg/g for cobalt) for both metal ions. The values of energy (E) from D-R model have shown that the adsorption of both metal ions was of physical nature (E<8kJ/mol) then confirmed by the thermodynamic results (ΔH°). The kinetic diffusion models have shown that the experimental data fit well with the film diffusion (R2= 0.977 and 0.989) for both metal ions at pH 5. Negative values of ΔG°obtained for both metal ions indicate that the adsorption process was spontaneous. The positive values of ΔH° obtained showed a physical adsorption process and also indicate that the adsorption process of both metal ions was endothermic. The positive values of ΔS° indicate an increase in randomness at the solid/solution interface during adsorption.
Desulphurization of diesel fuel using carbon-based metal oxide nanocomposites
(Vaal University of Technology, 2021-04) Cherubala, Rusumba Bienvenu; Rutho, L., Prof.; Tshilenge, J. K., Dr.
This thesis presents a slight on desulphurization process of the commercial diesel fuel using the carbon-based metal oxide nanocomposites such as graphene oxide, ZnO, rGO as a nano-adsorbent, activated carbon (PAC and AC) and charcoal Granular active carbon (GAC) to produce a fuel of less than 10 ppm sulphur content. Due to the high percentage of sulphur compounds in the fuel causing air pollution, acid rain and other problems related to combustion process. The synthesised of sorbents were achieved using incipient impregnation, microwaved-assisted and chemical exfoliation methods. The materials were characterized using Thermogrametric Analyzer (TGA), Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometer (XRD), Brunauer, Emmett and Teller (BET). The examination effect of operating conditions on the adsorption capacity with DBT and Sulphur compounds adsorption, the isotherms and the adsorption kinetic models were evaluated. The experimental data for PAC and AC were well suited to Freundlich isotherm and pseudo second-order kinetic models. The results shown that the sulphur feed concentration, the space velocity and the functional groups of the adsorbents have a considerable effect on the adsorption. In addition, it was observed that the temperature in the range of 30 to 80oC has a significant effect on the adsorption of Sulphur compounds from diesel fuel using 20 wt.% of sorbents. The rGO substrate which contained abundant oxygen functional groups was confirmed to promote the dispersion metal oxide and increased the adsorption efficiency of sulphur compounds (H2S and SO2) by providing oxygen ions weakly bound to the sulphur molecules. For the desulfurization process by adsorption, PAC and AC exhibited a better affinity for 80% removal of sulphur compared to the GAC and GO. The effects of metal species such as zinc oxide (ZnO) and reduced graphite oxide (rGO) composite on the adsorption capacity of hydrogen sulphide (H2S) were investigated. It was found that depending on the copper load, the adsorption capacity of H2S increased up to 20 times compared to pure ZnO. To study the oxidation changes on copper and zinc oxides, crystallite analysis by XRD and chemical state analysis by XPS were performed.
Development of sulfonated chitosan membranes modified with inorganic nanofillers and organic materials for fuel cell applications
(Vaal University of Technology, 2021-07-06) Zungu, Nondumiso Petunia; Ofomaja, A., Prof.; Osifo, P. O., Prof.
Fuel cell technology is a promising clean energy source compared to internal combustion engines and electricity generating plants which are associated with high emissions of greenhouse gases. The aim of this study was to modify chitosan into polymer electrolyte membranes suitable for use in PEMFC and DMFC fuel cells. Chitosan modification was done with 2-aminoethanesulfonic acid (2-AESA), dimethylformamide (DMF) and silica nanoparticles. The effect of the modification on the properties of the developed chitosan membranes was studied using FTIR, XRD, SEM-EDS and TGA. The performance of the membrane electrode assemblies was investigated. The formation of electrostatic interactions in the developed sulfonated chitosan membranes was confirmed via the Fourier transform infrared (FTIR) analysis, indicating a shift in the wavenumber of the N-H bonds from 1581 cm-1 on the chitosan spectrum to a lower wavenumber of 1532 cm-1 in the FTIR spectra of the membranes and by the new peak at the wavenumber of ~1260 cm-1 attributed to the asymmetric O=S=O stretching vibrations of the sulphate groups and sulfonic acid groups from the cross-linking sulphuric acid solution and 2-aminoethanesulfonic acid incorporated on the chitosan polymer chain during the modification. Notably, the FTIR spectra of the developed sulfonated chitosan membranes lacked the peak at the wavenumber of ~1153 cm-1 attributed to the stretching of C-O-C bonds of the polysaccharide ring of chitosan. A reaction mechanism was proposed in this study illustrating the possible conversion of the polysaccharide rings of chitosan into a poly (cyclohexene-oxide) thermoplastic rings in the developed membranes. The TGA/DTGA results of the developed sulfonated chitosan membranes showed three degradation stages. The initial weight loss occurred at temperatures ˂100 °C due to the evaporation of volatile components and water molecules inside the membranes. The second degradation phase of the membranes occurred at 208 ℃ with a loss in weight of >30% resulting from the decomposition of cross-linking networks. The third degradation stage was associated with the decomposition of the main polymer backbone of the membranes and occurred at 263°C for the chitosan membranes modified with 2-aminoethanesulfonic acid and at 266 °C for the chitosan membrane modified with silica nanofiller. The TGA/DTGA curves of Nafion 117 showed a small loss in weight of ~ 5% before a sharp decomposition that occurred between 346–505 °C. The XRD diffractograms of the developed sulfonated chitosan membranes showed amorphous phases, the crystal peaks of chitosan at 2theta of 10° and 20° were flattened on the membranes. The SEM images showed a homogenous surface morphology for the sulfonated chitosan membrane with a higher weight percentage of 2-aminoethanesulfonic acid (13,6 wt.%). The SEM images performed on the surface of the sulfonated chitosan membrane modified silica nanoparticles showed a slight agglomeration associated with the migration of the unbonded silica to the surface. The methanol permeability coefficient of the developed sulfonated chitosan membrane modified with 2-aminoethanesulfonic acid was calculated to be 2.29x10-6 cm2/s. This value was close to the methanol permeability coefficient of 2.33x10-6 cm2/s associated with unfavourable depolarisation at the cathode in direct methanol fuel cells when using Nafion 117. The proton diffusion coefficient of Nafion 117 was calculated to be 1.64x10-5 cm2/s and that of the developed sulfonated chitosan membrane modified with 2-aminoethanesulfonic acid was found to be 6.56x10-6 cm2/s, respectively. The fuel cell performance of the developed sulfonated chitosan membrane modified with 2AESA was investigated in a hydrogen fuel cell (PEMFC) supplied with H2 and O2 directly from the electrolyser. The sulfonated chitosan membrane modified with 2-aminoethanesulfonic acid (13.6 wt.%) achieved an open-circuit voltage of ~0.9 V and a maximum power output of 64.7 mW/cm2 at a maximum current of 70 mA. The current produced by the developed chitosan membrane was applied into the load and was able to turn (power) the electric fan. The sulfonated chitosan membrane modified with silica nanoparticles (2 wt.%) yielded an open-circuit voltage of ~0.9 V and attained a maximum power output of 58 mW/cm2 at a maximum current output of 60 mA/cm2. The current generated by the membrane was also able to turn the electric fan. The Nafion 117 membrane was also investigated under similar conditions and obtained an open-circuit voltage of 0.6 V and a maximum power output of 130 mW/cm2 at the maximum current output of 308 mA. The current produced by Nafion 117 was supplied into the load and was able to turn the electric fan.
Biogas production from solid food waste and its use for electricity production
(Vaal University of Technology, 2021-10-15) Khune, Selebogo Mervyn; Ochieng, Aoyi, Prof.; Otieno, Benton, Dr.; Osifo, Peter, Prof.
An enormous amount of food waste (FW) is generated worldwide. Most of this waste is discarded in landfills, where it undergoes uncontrolled anaerobic digestion (AD) process, which emits excessive amounts of greenhouse gases, (methane and carbon dioxide), thereby contributing to global warming. A controlled AD of FW is key for organic waste management with a positive impact on the environment and economy. In South Africa (SA) there is little uptake of biogas technology for FW management due to little research on biogas potential at small to large scale. Furthermore, there is an over reliance on foreign data, which leads to misfit parameters to local raw materials; consequently, producing biogas of low quality and quantity with low degradation of waste. Biogas with poor quality reduces the efficiency of biogas conversion to energy and the low production rate makes the system less feasible. Considering the challenges faced with FW management and the little uptake of the AD technology in SA, this study aimed to treat FW through AD and convert the biogas produced to electricity. A complete-mix biogas pilot plant (VUT-1000C) was designed, constructed and commissioned. The materials used for constructing the pilot plant were sourced locally to prove the applicability of the AD technology in SA. The biodigester was operated at mesophilic temperature, 37 oC, aided by a solar system. A stand-alone 1 m3 plug-flow ambient biodigester (STH-1000A) was operated semi-continuously as well as a control. Cow dung (CD) was used to inoculate the biodigesters, which were then operated semi-continuously at their optimum organic loading rate (OLR). The STH-1000A digester was operated at 0.446 kgVS/m3/day OLR, according to the manufacturer’s specification, while for VUT-1000C, the OLR was determined. The highest biogas and methane yields obtained were 582 and 332 L/kgVS/m3, respectively, at the determined optimal OLR of 1.5 kgVS/m3/day for the VUT-1000C digester this was supported by the modified Gompertz model with an R2 value of 0.9836. VUT-1000C produced 1200 L/day while STH-1000A produced 150 L/day. VUT-1000C proved to be a more effective biodigester than STH-1000A owing to the digester design and operation at mesophilic conditions. The key design findings are higher reactor working volume and high digester temperature. From the 1000 L of biogas produced from VUT-1000C, 1.8 kW of electricity was generated, which is equivalent to powering 300 6W light bulbs for 1 hour. The energy balance of the pilot plant showed that only 10 percent of the energy output was required to operate the plant. These results show that SA has a 475 GWh energy potential based on the current FW figures. Furthermore, the study has shown that biogas technology is readily available for South Africans and that the designed biogas plant was very efficient in FW-to-energy conversion.
Electrocatalytic degradation of industrial wastewater using iron supported carbon-cloth electrode via Electro-Fenton oxidation process
(Vaal University of Technology, 2022-02) Emeji, Ikenna Chibuzor; Ama, O. M., Dr.; Osifo, P. O., Prof.
Human immunodeficiency virus (HIV) and acquired immune deficiency syndrome (AIDS) causes morbidity and mortality in infected patients. These epidemics are significantly reduced and treated globally with antiretroviral drugs (ARVDs). However, the eventual disposal of the ARVDs, either by excretion or otherwise, enables them to end up as emerging hazardous contaminants in our environment. Of all the available methods to remove ARVDs from our water bodies, electrochemical methods are reckoned to be one of the most effective. As a result, it is imperative to acknowledge the interactive behavior of these pharmaceuticals on the surface of the electrode. In this study, iron nano-particles were deposited on the carbon cloth electrode by electrodeposition using chronoamperometry techniques. The synthesized electrode was characterized using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), and x-ray photoelectron spectroscopy (XPS) microanalysis. The electrochemical characterization of the material was also carried out using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrode's electrocatalytic activity toward the generation of hydrogen peroxide (H2O2) through a two-electron oxygen reduction reaction was assessed. Furtherance to this is the electrochemical degradation of nevirapine (NVP), lamivudine (LVD), and zidovudine (ZVD) in wastewater as a pharmaceutical model compound for organic pollutants in 50 mM K2SO4 electrolyte at a pH of 3. The SEM and EDX analysis showed the formation of iron nanoparticles within the matrix structure of the carbon cloth (CC) electrode. The XPS enlightened the presence of oxygen functional groups in the electrode's structure. EIS results are indicative that the modified electrode has a decreased charge transfer resistance (Rct)value as compared to the bare CC electrode. On the other hand, the CV result fosters good conductivity, enhanced current and large surface area of the modified electrode. More active and anchor sites were discovered on the iron-supported CC electrode which resulted in higher catalytic activity for the generation and accumulation of H2O2. The concentrations of “in-situ” generated H2O2 were found to be related to the current density supplied to the device after quantification. Although the accumulated H2O2 concentration appears to be low, it's possible that side reactions depleted the amount of H2O2 produced. As a result, the oxygen reduction reaction (ORR) through 2e- has a higher electrocatalytic activity with the improved iron assisted CC electrode than bare CC electrode. The electrochemical degradation studies conducted with the modified CC electrode by electro-Fenton process show a decrease in the initial ARVDs concentration (20 mg/L) as compared with the bare electrode. Their rate constants were 1.52 x 10-3 mol-1min-1 for ZVD, 1.20 x 10-3 mol-1min-1 for NVP and 1.18 x 10-3 mol-1min-1 for LVD. The obtained removal efficiencies indicate that the iron nanoparticle in the synthesised improves the degradation efficiency.

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