Research Articles (Chemical Engineering)

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Hydrothermal synthesis of Aragonite from acid mine drainage (AMD) of the Witwatersrand basin in Gauteng, South Africa
(Elsevier, 2025-12) Khumalo, Recardo D.S.; Brink, Hendrik Gideon; Chirwa, Evans M.N.; evans.chirwa@up.ac.za
Hydrothermal urea hydrolysis has been extensively used for homogenous precipitation processes mainly because the resulting products are generally of high crystallinity, uniform particle size and shape, as well as not generating waste brine. In this study, acid mine drainage water samples from the three Witwatersrand goldfields basins (Eastern, Central and Western, Gauteng, South Africa) were subjected to hydrothermal urea hydrolysis to investigate if any mineral(s) could be recovered. In these experiments, three urea concentrations (3.3, 4.0 and 10.0 [urea]/[total metal] ratio) were used while the reaction time (3 h) and temperature (80 °C) were kept constant. The resulting materials were characterised to reveal their chemical compositions, crystalline phases and morphologies. The bulk properties as determined using the Fourier Transform Infrared Spectroscopy, Thermogravimetric Analysis and X-ray Diffraction Spectroscopy showed that the obtained products were predominantly calcium carbonate, the aragonite polymorph, for all three basins. The particles obtained from the polluted mine water samples displayed different morphologies, while mostly were characterised by needle and/or rod-like morphologies with varying lengths and diameters in nanometre range (average aspect ratios ranged from 3.1 to 13.2) as shown by the Scanning Electron Microscope images. Other morphologies, cauliflower-, bouquet- and urchin-like particles were obtained without the use of organic additives. The method was demonstrated to be effective in the removal of calcium (more than 98 % on average) and some evidence of heavy metals, manganese in particular, also being removed from the polluted water. The findings highlighted a possibility of a single method that can be adopted for the remediation of acid mine drainage of the three basins to recover aragonite calcium carbonate, an industrially valuable mineral. HIGHLIGHTS • Hydrothermal urea hydrolysis was used to treat acid mine drainage. • Aragonite CaCO3 was recovered from all three Witwatersrand gold field basins. • Diverse aragonite super-structures were obtained without utilising organic additives.
CO conversion to liquid fuel over a bi-functional Co/H-ZSM-5 catalyst: effect of support desilication and catalyst promotion
(Taylor and Francis, 2025) Mudau, Tsireledzo L.; Sadare, Olawumi Oluwafolakemi; Iwarere, Samuel Ayodele; Daramola, Michael Olawale; michael.daramola@up.ac.za
Please read abstract in the article.
Improving the thermal stability of fly ash-based geopolymer materials through cellulose nanocrystal reinforcement
(Springer, 2025-12) Roopchund, Rishen; Fajimi, Lanrewaju; Seedat, Naadhira; Andrew, Jerome
Prior to this study, the thermal stability of fly ash-based geopolymer (FAG) construction materials as a function of cellulose nanocrystal (CNC) concentration and the optimal CNC dosage leading to thermal stability have not been investigated. This study investigates the influence of CNC reinforcement and curing duration on the thermal stability of FAG geopolymer. A series of samples incorporating CNC dosages ranging from 0 to 1.86 wt.% were prepared and subjected to 24- and 48-h curing regimes to evaluate their thermal degradation behaviors. Thermogravimetric analysis (TGA) revealed that 24-h-cured samples exhibited steeper weight losses compared to 48-h-cured ones, particularly in the 100–600 ℃ range. This trend was attributed to incomplete stabilization of organics in shorter curing times. Among all dosages, the 48-h-cured 1.7 wt.% CNC sample demonstrated the lowest total weight loss (~ 9.6% lower than the control), indicating enhanced thermal resistance. Derivative weight analysis further confirmed this, showing the lowest peak weight change rate (0.105%/℃) for the 1.7 wt.% CNC sample cured for 48 h, compared to 0.304%/℃ for the unreinforced control. Additionally, differential scanning calorimetry (DSC) indicated reduced exothermic heat flow in 48-h-cured samples, especially in the 1.7 wt.% CNC formulation, suggesting minimal phase transitions and improved thermal reliability. The novelty of this work lies in demonstrating the synergistic enhancement of thermal resistance through CNC addition and extended curing. Unlike prior studies that primarily focused on mechanical reinforcement, this research establishes an optimal CNC dosage (1.7 wt%) that minimizes thermal degradation, offering critical insights for thermally stable, bio-reinforced geopolymer development. These findings support the application of CNC–geopolymer composites in fire-resistant, sustainable construction materials.
MXenes as sustainable functional nanomaterials for photocatalytic degradation of dye pollutants : performance, effect of process parameters, stability and re-useability evaluation – a critical review
(Elsevier, 2025-12) Emmanuel, Stephen Sunday; Adesibikan, Ademidun Adeola; Tichapondwa, Shepherd Masimba; Rayaroth, Manoj P.; Boscá, Francisco; Marín, M. Luisa; Samejo, Bakhtiar Ali; Boczkaj, Grzegorz
Please read abstract in the article. HIGHLIGHTS • Good MXENE stability and possibility of its regeneration for long-term applications. • Importance of scavenging tests and proper identification of radical species in the process. • Degradation studies must be evaluated, including the final mineralization rate of the pollutant. • Optimization of pollutant concentration must include the aspect of photocatalyst capacity. • Controversial, not confirmed, conclusions about CO2 formation during treatment.
Influence of carbon sources and biosurfactants on selenite and lead bioremediation by Enterococcus sp
(Elsevier, 2026-01) Tendenedzai, Job Tatendan; Chirwa, Evans N.M.; Brink, Hendrik Gideon; job.tendenedzai@tuks.co.za
Please read abstract in the article.
Ultrahigh-efficiency zinc-air batteries enabled by defect-engineered biomass carbon and dynamic nickel redox mediation
(Wiley, 2025) Huang, Yongfa; Li, Tingzhen; Wu, Zhenzhen; Yang, Wu; Liu, Zhendong; Gan, Jianyun; Zou, Ren; Iwuoha, Emmanuel; Feleni, Usisipho; Ren, Jianwei; Ocakoglu, Kasim; Zhong, Linxin; Peng, Xinwen
Coupled zinc-air batteries (CZABs) are promising in future energy storage and conversion solutions because of their potential for enhanced energy efficiency and boosted power density. However, sluggish reaction kinetics at the cathode remain a key challenge, leading to cycling instability and insufficient battery performance. In this study, a rational interfacial etching method is developed to fabricate nitrogen-doped and defect-rich carbon catalysts from the low-cost eucalyptus waste. The precise formation of carbon vacancies, driven by synergistic spatial confinement domains and oxygen-containing functional groups exposed on eucalyptus precursors, promotes the reconstruction of pyridinic nitrogen (Py-N) coordination. This induces local electron redistribution, enhancing charge transfer efficiency at adjacent Py-N sites, and optimizing *O/*OH adsorption–desorption kinetics, thereby significantly boosting the electrocatalytic activity for the oxygen reduction reaction. Additionally, the integration of self-adaptive Ni2+/Ni3+ redox pair into the cathode effectively mitigates the oxygen evolution reaction and thus reduces voltage delay by 0.12 V. The resulting CZABs achieve 82% energy efficiency at 5 mA cm−2 and 77% after 400 h, which is rarely reported. This work elucidates the intricate mechanism of defect formation during biomass pyrolysis and presents a scalable, cost-effective strategy for producing high-efficiency catalysts, offering a promising strategy toward advanced energy storage systems.
Antibiotic removal in South African water using artificial neural networks and adaptive neuro-fuzzy inference system models : a review
(Elsevier, 2025-10) Keitemoge, Molly Katlo; Onu, Matthew Adah; Sadare, Olawumi Oluwafolakemi; Seedat, Naadhira; Moothi, Kapil
The growing occurrence of antibiotic residues in South African water systems poses serious environmental and public health risks, owing mostly to pharmaceutical discharge, agricultural runoff, and poor waste management. Conventional water treatment procedures frequently fail to properly remove these micropollutants, needing new predictive and analytical approaches. This review critically investigates the implementation of Artificial Neural Networks (ANN) and Adaptive Neuro-Fuzzy Inference System (ANFIS) models to forecast and optimize antibiotic removal from South African water bodies. To the best of our knowledge, little or no research compares the models’ respective performances in the context of the urban water cycle in South Africa. Therefore, this review elaborates on some of the pharmaceuticals (such as diclofenac sodium and tetracycline) that have been studied, as well as the challenges associated with their removal. It also emphasizes studies on modeling and predicting pharmaceutical removal from wastewater using ANN and ANFIS models. Additionally, this review considered the comparisons between ANN and ANFIS models in predicting the removal of emerging contaminants, as well as the challenges and limitations associated with these modeling techniques. The studies established that AI models achieved higher R² and lower error metrics compared to classical statistical or isotherm models.
Mixture models inspired by the Kolmogorov-Arnold representation theorem
(Elsevier, 2025-10) Focke, Walter Wilhelm; walter.focke@up.ac.za
Physical property models were developed to predict temperature-dependent multicomponent data using only temperature-independent binary parameters and pure component property temperature dependence. The Kolmogorov-Arnold representation theory was used to extend the linear blending rules and the Padé-like expressions describing the variation of physical properties of ideal solutions with composition. The effectiveness of correlating density, viscosity, refractive index and surface tension using this concept was tested. Ten ternary systems at either three or four different temperatures were regressed and compared to an ideal solution case. It was found that the four-parameter Kolmogorov-Arnold (KA) model performed excellently when the data regression included the full datasets. Unfortunately, the KA model may be too flexible, leading to overfitting binary data when applied to predicting ternary data.
Degradation of rhodamine B Dye on BiOIO3/Bi12O17Cl2 heterostructure photocatalyst under visible light activation
(Elsevier, 2025-10) Ogbeifun, Osemeikhian; Tichapondwa, Shepherd Masimba; Chirwa, Evans M.N.
Dye pollution resulting from industrial waste poses a substantial threat to both human health and the environment. Heterostructure composites of BiOIO3 and Bi12O17Cl2 with varying mass ratios (BiOIO3/Bi12O17Cl2-y:x) were fabricated to enhance the degradation abilities of the individual material towards dye contaminants. The rapid recombination of photogenerated electron-hole pairs in Bi12O17Cl2 and the limited photon utilisation of the visible light wavelengths by BiOIO3 were addressed in the heterojunction. The heterojunction formed between the material provides for spatial charge separation and boost of redox power of photogenerated electrons and holes. The degradation rate constant of Rhodamine B dye on BiOIO3/Bi12O17Cl2–1:1, the best performing material, under visible light in 6 h was 0.4 h−1, which is 2.7 and 4.3 times the rate constants for Bi12O17Cl2 (0.149 h−1) and BiOIO3 (0.093 h−1), respectively. The results demonstrate the contribution of heterostructure formation in improving the photocatalytic degradation process. The main species in the degradation step are hydroxyl (•OH) and superioxide (•O2–) radicals. BiOIO3/Bi12O17Cl2–1:1 has good photocatalytic stability, as 96 % efficiency retention is reported after four cycles. Thus, BiOIO3/Bi12O17Cl2–1:1 is a promising material for the degradation of dyes.
Superstructure-based optimization of membrane gas separation processes : a review
(American Chemical Society, 2025-07) Chiwaye, Natsayi; Majozi, Thokozani; Daramola, Michael Olawale
Membrane technology for gas separation has apparent advantages such as compactness, ease of operation, and the possibility of incorporation into hybrid systems. This review analyzes the superstructure-based optimization models for membrane gas separation systems reported in the literature. The review describes and analyzes the membrane permeation models embedded in the optimization models and solution approaches, the superstructures presented, the objective functions adopted, and outcomes for different application cases. The progress is reported, and challenges and opportunities for future research are suggested. The presented review would be useful to researchers and engineers in membrane technology research and development and could lead to the deployment and adoption of membranes in various applicable industries, such as carbon capture.
Incorporating PET-MIL-101(Fe) within cellulose acetate membrane for thin film microextraction of neonicotinoid insecticides in water
(Nature Research, 2025-09) Jakavula, Silindokuhle; Mpayipheli, Neliswa; Nqombolo, Azile; Ren, Jianwei; Nomngongo, Philiswa Nosizo
Herein, cellulose acetate membrane modified with polyethylene terephthalate derived MIL-101(Fe) (PET-MIL-101(Fe)) was used as an extraction phase for the direct immersion-thin film microextraction method (DI-TFME) of neonicotinoid insecticides in water samples. The quantitative analysis of clothianidin, imidacloprid, thiacloprid and thiamethoxam was carried out using high-pressure liquid chromatography (HPLC-DAD). The morphological and structural characteristics of the materials were studied using transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and energy dispersive X-ray spectrometry (EDX). Under optimum conditions, acceptable analytical performance for the developed DI-TFME/HPLC-DAD method was attained. The linearity of the method ranged from 0.04 to 500 µg/L with R2 ranging from 0.9981 to 0.9989. The detection limits, quantification limits and relative standard deviation (%RSD) of the DI-TFME/HPLC-DAD method were in the range of 0.013–0.016 µg/L, 0.043–0.053 µg/L and 1.2–3.9%, respectively. The method was applied in the analysis of real water samples, and the spiking recoveries of the target analytes were 95.6–102%, 91.2–98.6% and 79.2‒98.7% for river water, effluent and influent samples, respectively, with %RSDs ranging from 1.8 to 4.8%. These findings demonstrated that the developed DI-TFME/HPLC-DAD method had high precision, accuracy, sensitivity and enrichment factor (73–88). The DI-TFME/HPLC-DAD method proved sustainable for the simultaneous quantification of trace neonicotinoid insecticides in real samples.
Performance evaluation of gold (III) bio-reduction by bacterial strains and a consortium isolated from gold mine effluent
(Elsevier, 2026-01) Mpeta, Miranda; Tendenedzai, Job Tatenda; Tichapondwa, Shepherd Masimba; Chirwa, Evans M.N.; u24054276@tuks.co.za
The bioreduction of Au (III) to Au (0) offers a sustainable and eco-friendly alternative to conventional gold recovery methods, reducing environmental impacts associated with chemical processing. This study investigated the bioreduction capabilities of indigenous bacterial strains and a microbial consortium isolated from gold tailings and mine wastewater. Aerobic batch experiments were conducted at pH 7 and 35 ± 2°C over 24 h, with initial Au (III) concentrations of 3 and 6 ppm, to compare the reduction efficiencies of individual strains and a mixed consortium. Gram-negative bacteria (Stenotrophomonas maltophilia, Klebsiella pneumoniae, Acinetobacter bereziniae) achieved superior reduction efficiencies of 98.33–99.8 %, outperforming the Gram-positive Bacillus cereus (92.9 %), likely due to differences in cell wall structure, with Gram-negative strains leveraging outer membrane proteins and efficient extracellular electron transfer mechanisms, while B. cereus relies on biosorption via its thicker peptidoglycan layer. The consortium, combining all four strains, reached 94.5 % efficiency, reflecting synergistic interactions through resource partitioning and metabolite recycling. Scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDS), X- ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed the formation of Au (0) nanoparticles, with an 8.5 % crystalline gold content in the consortium despite low starting concentrations. These findings highlight the potential of indigenous bacteria for efficient gold bio- recovery from mining effluents and tailings, demonstrating a viable bio- hydrometallurgical process that integrates waste treatment with precious metal extraction. The technology offers significant advantages for mining operations through reduced chemical consumption, lower energy requirements, and simultaneous environmental remediation, supporting the industry’s transition toward sustainable extraction practices and circular resource utilization in mineral processing operations. HIGHLIGHTS • Indigenous bacteria from mine waste achieve >98 Au (III) reduction within 24 h. • Gram-negative bacteria outperformed Gram-positive by 6% via electron transfer. • Mixed consortium reached 94.5% Au (III) reduction through synergistic interactions. • Effective bioreduction of low-grade gold solutions (3–6 ppm) typical of mining effluents.
Artificial intelligence-assisted modelling of heavy metal adsorption using cellulose-based and bio-waste adsorbents : a focus on ANN and ANFIS architectures
(Elsevier, 2025-12) Kumari, Binu; Seedat, Naadhira; Moothi, Kapil; Roopchund, Rishen
This review explores the application of artificial intelligence (AI) models, specifically artificial neural networks (ANN) and adaptive neuro-fuzzy inference systems (ANFIS), in predicting heavy metal adsorption performance using bio-based adsorbents. Focus is placed on sustainable materials such as cellulose nanocrystals (CNCs), agricultural waste-derived biochar, and microbial biomass. The review compiles more than 60 studies over the past decade, analysing model structures, input-output variables, training algorithms, and validation strategies. Performance metrics reveal that most ANN models achieve R² > 0.98, with NARX-ANN reaching as high as 0.9998 in time-resolved batch adsorption simulations. ANFIS models offer added interpretability through fuzzy rule extraction, though their adoption remains limited. Optimization techniques such as particle swarm optimization (PSO) and genetic algorithms (GA) improved RMSE by 5–15%.Comparative evaluation shows variability in model generalization depending on input complexity and adsorbent type. Despite promising results, the review identifies gaps in dataset standardization, model validation, and real-world applicability under multicomponent or noisy conditions. The novelty of this review lies in its cross-comparative benchmarking of ANN and ANFIS architectures applied specifically to bio-adsorbents, and its recommendations for engineering-grade AI deployment in environmental remediation systems. Future research should incorporate deep learning, sensor integration, and regulatory-informed optimization to enhance model robustness and scalability in wastewater treatment applications. HIGHLIGHTS • AI techniques such as ANN and ANFIS model heavy metal adsorption with high accuracy. • Bio-based adsorbents (e.g., CNC, biomass) are central to eco-friendly water treatment. • NARX-ANN achieves R² = 0.9998 in modeling batch adsorption kinetics. • ANFIS improves interpretability using fuzzy rule-based logic. • Key gaps include cross-validation, regulatory constraints, and dataset diversity.
Adsorption of tetracycline using silica nanoparticles : a comparative study of sodium silicate-derived and fly ash-derived silica nanoparticles
(Elsevier, 2025-09) Houghton, Eric Emmanuel; Yapi, Litha; Tichapondwa, Shepherd Masimba; shepherd.tichapondwa@up.ac.za
Fly ash (FA), a fine particulate residue produced from the combustion of coal in thermal power plants, is generated in substantial quantities and presents significant challenges related to its environmental management and disposal. Repurposing FA can mitigate waste accumulation while contributing to sustainable environmental solutions. One promising approach is utilising FA as an adsorbent for removing pollutants from aqueous solutions, particularly emerging contaminants (ECs). In this study, silica nanoparticles were synthesised from FA (FA-SiNPs) and subsequently modified with iron to produce Fe-SiNPs. As a control, silica nanoparticles were synthesised directly from a sodium silicate solution (SSSNPs). The different silica nanoparticles were used as adsorbents to remove tetracycline (TC) from aqueous solutions under identical conditions, to compare their adsorption performance. Under the identical conditions, Fe-SiNPs demonstrated superior performance, achieving 59 % removal of TC, compared to 30 % and 20 % removal by FA-SiNPs and SSSNPs, respectively. The enhanced adsorption capacity of Fe-SiNPs was attributed to the presence of iron, which facilitated TC removal through chelation. Upon optimisation of experimental parameters, a maximum TC removal efficiency using Fe-SiNPs of 86 % was observed at the optimal dosage of 5 g/L within a pH range of 4 to 5. The adsorption kinetics were best described by the Elovich model, whereas the equilibrium data fitted the Langmuir isotherm model with a maximum adsorption capacity of 32.31 mg/g at 30 °C. Thermodynamic analysis revealed that the adsorption process was both spontaneous and exothermic in nature. The adsorption of TC on Fe-SiNPs involved chemisorption, electrostatic attraction and hydrogen bonding. This study highlights the potential of FA-derived silica nanoparticles, particularly Fe-SiNPs, as cost-effective and sustainable adsorbents for TC removal from contaminated water. HIGHLIGHTS • Silica nanoparticles synthesized from fly ash (FA-SiNPs) and sodium silicate (SSSNPs). • FA-SiNPs were modified with iron to produce Fe-SiNPs. • Fe-SiNPs showed the highest tetracycline (TC) removal efficiency. • TC adsorption capacity of Fe-SiNPs reached 32.31 mg/g. • Adsorption on Fe-SiNPs involved electrostatic forces, chemisorption, and H-bonding.
Defect-free Bi-Sn@C composites with high capacity and long cycle life for superior sodium storage
(Springer, 2025-10) Tian, Jiabei; Guo, Siguang; Gao, Biao; Liu, Min; Zhou, Yi; Ren, Jianwei; Javanbakht, Mehran; Omidvar, Hamid; Li, Zhuo; Song, Hao; Huo, Kaifu
Binary alloys have garnered significant attention for the development of the sodium-ion battery due to their ability to combine the advantages of single-phase alloys. However, these materials often demonstrate limited electrochemical performance, and the relationship between their crystallization states and their sodium storage properties remains poorly understood. Here, we synthesize Bi-Sn binary alloys with various compositions via phase-separation metallurgy to explore the sodium storage properties of different crystalline structures. The results indicate that hypo- and hyper-eutectic Bi-Sn alloys readily form a “dendritic” primary phase at the non-eutectic interface, which aggravates structural degradation and increases internal resistance. In contrast, Bi-Sn alloys with optimized eutectic interfaces effectively control dendritic growth and reduce defects, resulting in enhanced microstructural stability and superior electrochemical performance. As results, the eutectic p-Bi57Sn43@C anode achieves a record-high specific capacity of 470.3 mAh g−1 at 1 C and exhibits remarkable long-term cycling stability, retaining 95.2% of its capacity after 1000 cycles at 20 C. The defect-free eutectic concept presented here establishes a valuable foundation for future studies of binary and polycrystalline eutectic alloys in electrochemical applications.
Biomolecular mechanism in the uptake of Pt(IV) by Saccharomyces cerevisiae EBY100 cells expressing platinum binding peptides
(Elsevier, 2024-08) Mashangoane, Boitumelo Francina; Chirwa, Evans M.N.; Gidudu, Brian; bmashangoane@tuks.co.za
Platinum group metals (PGMs) are currently under increased demand due to limited availability and their unique properties; therefore, their limited availability presents an economically attractive opportunity to recover these metals from waste. The recovery of PGMs from effluents using conventional techniques such floatation, precipitation and ion exchange results in large volumes of hazardous waste as well as high operating costs and low efficiencies. Biosorption using biomass such as microorganisms as adsorbents can offer a cheap, efficient and environmentally friendly alternative for the recovery of PGMs. Despite previous research on the use of biosorption techniques for the recovery of PGMs; there is still room for improvement in the way that microorganisms absorb metals. Such advancements can be achieved through the use of genetically engineered peptides for inorganics (GEPI) for cell surface display purposes. In this work, Saccharomyces cerevisiae EBY100 cells were genetically engineered for cell surface display of platinum binding peptides to enable Pt(IV) adsorption from an aqueous solution. The transformed Saccharomyces cerevisiae EBY100 cells attained the maximum adsorption of 40 % for Pt(IV) after 3 h at the optimal pH = 3. As the initial metal concentration rose from 10 ppm to 50 ppm, the biosorption Pt(IV) increased as well, reaching a biosorption capacity of 85 mg/g. The findings also showed that the Freundlich model best explained the Pt(IV) biosorption isotherm onto P3.1, while the pseudo-second-order model best explained the Pt(IV) adsorption kinetics onto P3.1. HIGHLIGHTS • Saccharomyces cerevisiae EBY100 cells express platinum binding peptides. • Genetically engineered Saccharomyces cerevisiae EBY100 cells adsorb Pt(IV). • Increase in initial Pt(IV) concentration increases biosorption capacity of the cells.
Liquid-liquid equilibrium studies for potential solvents/cosolvents for the separation of aromatics and alkanes
(American Chemical Society, 2025-06) Paile, Blessing Mcebo; Narasigadu, Caleb; Seedat, Naadhira
Liquid–liquid equilibria (LLE) data for ternary systems of n-heptane + a solvent mixture + toluene were measured at 298.15 and 313.15 K and 101.3 kPa. The solvents investigated are mixtures of N-methylpyrrolidone and glycerol, with ratios of N-methylpyrrolidone to glycerol of 90:10, 70:30, and 50:50. LLE measurements were carried out using the direct analytical method, and the composition analysis was performed using gas chromatography. The effectiveness of the solvent mixtures of N-methylpyrrolidone and glycerol in extracting toluene from n-heptane was evaluated by determining the solvent selectivity and capacity and evaluating the extent of the two-phase region. All systems investigated were found to exhibit type I LLE behavior. The binodal curves were correlated to the Hlavatý β function and log γ equations. The tie-lines were correlated with the NRTL and UNIQUAC activity coefficient models. A comparison of the root-mean-square deviation (rmsd) showed that the NRTL model provided a better correlation for all systems.
Technical and financial evaluation of an emerging thermochemical technology for sustainable management of municipal wastewater sludge
(IWA Publishing, 2024-12) Zvimba, John Ngoni; Musvoto, Eustina; Kholisa, Buyisile; buyisile.kholisa@tuks.co.za
The management of municipal wastewater sludge is a significant challenge for wastewater management, particularly the need to manage and dispose of the sludge in an environmentally friendly and sustainable manner. The emergence of stricter regulations regarding landfill disposal of wastewater sludge necessitates the need for alternative options for municipal wastewater sludge management, with thermochemical technologies potentially contributing towards achieving carbon neutrality goals and fostering sustainable development. This study sought to address these challenges through a technical and financial evaluation of a pilot-scale emerging thermochemical technology, the enhanced hydrothermal polymerization to provide adequate understanding of the technology's feasibility regarding its application for municipal wastewater sludge volarization into a multi-use hydrochar. The study findings indicated that the enhanced hydrothermal polymerization-generated hydrochar exhibited significant energy content compared to wastewater sludge, suggesting the potential use of the hydrochar as an energy source. The preliminary designs of a full-scale greenfield installation and retrofit processing 50 t/d and 35 t/d dry sludge, respectively, were evaluated to be technically feasible. Furthermore, on the basis of preliminary designs, the enhanced hydrothermal polymerization technology was determined to be the most financially feasible option, also offering other unique advantages over well-established technologies currently used within municipal wastewater services.
Usage of silica xerogel from African sugarcane leaves as a catalyst in biodiesel production through transesterification
(American Chemical Society, 2025-06) Maseko, Ncamisile Nondumiso; Enke, Dirk; Owolawi, Pius Adewale; Iwarere, Samuel Ayodele; Oluwafemi, Oluwatobi Samuel; Pocock, Jonathan
Biodiesel was produced through transesterification from canola oil and methanol in the presence of silica xerogel derived from sugar cane leaves as a solid catalyst. The transesterification reaction was carried out at 65 °C in a batch-type reactor where a three-neck round-bottom flask was used as a reaction vessel with a reflux setup. Reaction time, methanol to oil ratio, and weight percentage of the catalyst were varied to optimize the biodiesel yield. The xerogel catalyst was characterized by inductively coupled plasma-optical emission spectroscopy (ICP-OES), nitrogen physisorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The produced biodiesel was characterized using gas chromatography-mass spectroscopy (GC-MS), Fourier transform infrared spectroscopy (FTIR), and a viscometer. The synthesized catalyst was found to operate as a true heterogeneous catalyst, since it preserved its solid nature and did not leach into the reaction medium. A biodiesel yield of 96.9% was achieved under optimal reaction conditions of 60 min reaction time, 6:1 methanol to oil ratio, and 3 wt % catalyst loading. The produced biodiesel was found to have a mixture of both saturated and unsaturated fatty acid methyl esters and had physical properties that met the ASTM and EN standards. The investigated catalyst was found to have a potential of being recycled up to 3 times, which positively affects the biodiesel production costs.
Melt processing of cellulose acetate for controlled release applications - a review
(Wiley, 2025-09) Mphateng, Thabang N.; Mapossa, António Benjamim; Mokhena, Teboho; Ray, Suprakas Sinha; Sundararaj, Uttandaraman
Cellulose acetate (CA) has garnered considerable industrial and research interest due to its sustainable properties, such as biodegradability and biocompatibility. Despite these attractive properties, CA is difficult to process using traditional melt processing techniques. This is due to its high crystallinity and a glass transition temperature that exceeds the thermal degradation temperature. Therefore, different additives have been explored to overcome these issues. This review explores recent trends in the use of melt-processed CA materials for encapsulating and controlling the release of active compounds. It highlights the advancements made over the past decade in processing CA-based materials using thermoplastic techniques. Additionally, the review discusses the properties of these materials, including biodegradation, photodegradation, and solubility, which are important for delivering active agents. Finally, it provides an overview of the challenges and prospects for CA-based materials processed through thermoplastic processing methods.

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