Digital Knowledge Collection:

Effects of temperature, substrate-to-inoculum ratio, nutrient augmentation, and inoculum acclimation on the anaerobic digestion of primary winery wastewater sludge

Thu, 01 Jan 2026 00:00:00 GMT

Title: Effects of temperature, substrate-to-inoculum ratio, nutrient augmentation, and inoculum acclimation on the anaerobic digestion of primary winery wastewater sludge Authors: Kaira, Walusungu Maclean Abstract: The wine industry generates substantial volumes of organic-rich primary winery wastewater sludge (PWWS), posing both economic and environmental challenges if not managed effectively. Currently, only 17% of wineries surveyed in the Western Cape province of South Africa employ anaerobic digestion (AD) for treatment of their PWWS, with others opting for composting and off-site disposal. With rising energy costs and increasingly stringent environmental regulations, circular waste management practices are essential for achieving long-term economic and environmental sustainability. This study addresses the need for a circular bioeconomy approach by evaluating the feasibility of AD as a waste management and energy solution for wineries, aligned with South Africa’s National Development Plan 2030 and UN Sustainable Development Goals (SDGs 7, 12, and 13). This thesis investigated the variability of PWWS from six wineries (designated AF) and the optimization of anaerobic digestion (AD) of the PWWS for methane (CH₄) production. The study evaluated the influence of key parameters such as inoculum acclimation, substrate composition, operational temperature, inoculumto-substrate ratio (ISR), and micronutrient supplementation on CH₄ yields and process stability. The variability of PWWS from winery A during the crush and post-crush seasons was examined. Results revealed significant intra-site variability (p<0.05), likely due to differences in winery operations during those periods. The total solids (TS), volatile solids (VS), and chemical oxygen demand (COD) content of post-crush PWWS were found to be 74%, 171%, and 132% higher, respectively, than those of crush-season PWWS. Inter-site variability was also assessed across PWWS from wineries B through E, as well as lees from winery F. Substantial variation was observed, with COD, total organic carbon (TOC), TS, and VS concentrations ranging between 33.0–181.7 g/L, 6.8–20.2 g/L, 32.8–153.1 g/L, and 26.0–123.5 g/L, respectively. Theoretical biomethane yields at standard temperature and pressure (STP) were Theoretical biomethane yields at standard temperature and pressure (STP) were determined based on the COD:VS ratio of each sample. The estimated CH₄ yields were 567 mLCH₄/gVSadded and 490 mLCH₄/gVSadded for winery A crush and post- crush season PWWS, respectively, 654 mLCH₄/gVSadded for winery B PWWS, 251 mLCH₄/gVSadded for winery C PWWS, 470 mLCH₄/gVSadded for winery D PWWS, 544 mLCH₄/gVSadded added for winery E PWWS, and 1 434 mLCH₄/gVSadded for lees from winery F. The actual CH4 yields achieved at 37oC without added nutrients were 204 mLCH₄/gVSadded, 65 mLCH₄/gVSadded, 43 mLCH₄/gVSadded, 53 mLCH₄/gVSadded, and 765 mLCH₄/gVSadded for PWWS from wineries A-E and lees from winery F, respectively. With the addition of nutrients at 37°C, the CH4 yields achieved were 154 mLCH₄/gVSadded, 28 mLCH₄/gVSadded, 114 mLCH₄/gVSadded, 62 mLCH₄/gVSadded, and 584 mLCH₄/gVSadded for PWWS from wineries A-E and lees from winery F, respectively. This study found that in comparison to ambient temperatures, when the temperature was elevated to 37°C, CH₄ production was enhanced and time required to reach maximum yield was reduced. However, heating is only justified when the increase in CH₄ production exceeds 30 mL CH₄/g VS compared to unheated conditions. For small-scale wineries, lower-cost strategies such as insulating digesters or painting them black to enhance solar heat absorption may be more appropriate and cost-effective than active heating. The addition of a micronutrient blend containing 14 trace elements produced mixed results, likely due to substrate-specific nutrient imbalances and potential synergistic effects with temperature. These findings suggest that nutrient supplementation strategies must be tailored to the specific characteristics of the PWWS substrate and the operating conditions of the digester. The study also highlighted the critical role of inoculum acclimation and substrate type in determining methanogenic pathways and overall process performance. When the inoculum was switched from a municipal waste-activated sludgeacclimated inoculum (MWASi) to a PWWS-acclimated inoculum (PWWSi), biomethane yields increased from 0 to 49 mL CH₄/g VS added. Moreover, analysis revealed that the dominant methanogenic populations in PWWSi were composed of both acetoclastic and hydrogenotrophic communities, indicating active methanogenesis through multiple metabolic routes. Kinetic modelling showed that the Chen and Hashimoto and Cone models provided the best fit for predicting AD performance of PWWS from wineries B through E at 37°C. At ambient temperature, the Cone and Logistic models were more accurate. For the digestion of lees from winery F, the Logistic model consistently provided the best prediction regardless of temperature or nutrient supplementation. These findings reveal significant variability in PWWS characteristics across wineries and seasons, underscoring the importance of a tailored approach to AD. Effective AD of PWWS requires optimization of process parameters based on specific substrate properties and the use of a well-acclimated inoculum. The study emphasizes the need for customized, site-specific strategies to enhance biogas production and improve the overall feasibility of AD in the wine industry. Description: Thesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2026

Green synthesis of CuO/CQD nanocomposites for printed electrochemical glucose sensor

Thu, 01 Jan 2026 00:00:00 GMT

Title: Green synthesis of CuO/CQD nanocomposites for printed electrochemical glucose sensor Authors: Atson, Ryal Abstract: Enzymatic electrochemical glucose sensors are widely used to monitor glucose levels and effectively manage diabetes. However, these sensors suffer from poor environmental stability and complex enzyme immobilisation procedures. Additionally, many traditional nanomaterial synthesis routes used in the development of electrochemical glucose sensors rely on toxic reagents and harsh reaction conditions, raising concerns about sustainability. To address this, non-enzymatic glucose (NEG) sensors can be realised through plant-mediated green synthesis. In this approach, plant phytochemicals drive the formation of nanomaterials that function as the active sensing elements, avoiding enzyme-related issues and providing a more sustainable alternative to conventional methods. Among candidate nanomaterials, CuO offers strong catalytic activity toward glucose oxidation, and its performance can be enhanced by integrating conductive carbon quantum dots (CQDs) into a hybrid nanocomposite. For this, plant extracts can serve as both reducing agents for synthesising CuO nanoparticles and carbon sources for synthesising CQDs. However, despite its phytochemical abundance, Aloe arborescens has not previously been explored for the green synthesis of a NEG sensor. The strategy used to deposit these nanomaterials onto sensor substrates also plays a decisive role in shaping sensor performance. Yet, the influence that microplotting (a digitally controlled printing technique) has on the electrochemical performance of green-synthesised glucose sensors has not been systematically investigated previously. To this end, this study aimed to synthesise CuO/CQD nanocomposites via a green hydrothermal route using A. arborescens extract as a reducing agent and carbon source, and to evaluate their performance as an electrochemical NEG sensor. A secondary aim was to assess the effect of microplotting deposition on the overall sensing performance of the fabricated sensor electrodes. Optimisation of the A. arborescens phytochemical extraction temperature and time maximised the phenolic content, and optimisation of the hydrothermal synthesis conditions (i.e., temperature, time, pH, precursor concentration, and extract concentration) ensured the reproducible formation of CuO/CQD nanocomposites. Structural characterisation (SEM, EDS, FT-IR, Raman, XRD, TGA/DTA) confirmed the formation of quasi-spherical CuO nanostructures decorated with CQDs. Electrochemical characterisation of pristine CuO and CuO/CQD films drop-cast on fluorine-doped tin oxide (FTO) glass revealed that the CuO/CQD/FTO platform improved charge-transfer kinetics, electroactive surface area, and catalytic efficiency. Drop-casting was employed as a benchmark method before the development of microplotted sensors. A comparative study of deposition techniques demonstrated that microplotting yields CuO/CQD electrodes with more application-relevant electrochemical behaviour than dropcasting. Accordingly, CuO/CQD ink was microplotted onto screen-printed gold electrodes (SPGEs) and evaluated for glucose detection in 0.1 M NaOH. The resulting CuO/CQD/SPGE platform exhibited a wide linear range of 0.9–17.1 mM (R2 ≥ 0.995), a detection limit of 0.33 mM, and sensitivities of 0.131–0.0826 mA·mM-1·cm-2, with a rapid steady-state response (<6 s). The wide linear range spans hypoglycemic, normoglycemic, and hyperglycemic states, confirming its clinical relevance. The CuO/CQD sensor also demonstrated excellent repeatability, reproducibility, stability, and selectivity under the influence of common interferents, chelating agents, and physiologically relevant chloride concentrations. Comparative benchmarking against state-of-the-art CuO-based NEG sensors highlights the role of electrode geometry, deposition precision, and material compatibility in extending the linear range. Proof-of-concept testing in serum showed <6% deviation from a commercial glucose meter, affirming the clinical potential of the CuO/CQD/SPGE platform. These findings illustrate how green-synthesised nanomaterials and precision microfabrication can enable sustainable, high-performance glucose sensing platforms for clinical and point-of-care applications Description: Thesis (ChemEng) - Masters Degrees

The extraction of platinum group metals from catalytic converters: non conventional solvents and pressure effects

Wed, 01 Jan 2025 00:00:00 GMT

Title: The extraction of platinum group metals from catalytic converters: non conventional solvents and pressure effects Authors: Griffiths, Clive Vinee O’niell Abstract: Secondary sources of precious metals, such as catalytic converters, contain up to 200 times higher concentrations of platinum group metals (PGMs) compared to natural ores, making them increasingly important for sustainable metal recovery. Catalytic converters contain platinum, palladium, and rhodium in approximate ratios of 4:4:1, with market values in the ratio of 1:1:4, respectively. Current recovery methods using conventional organic solvents achieve high recoveries for platinum and palladium but significantly lower yields for rhodium, while also posing environmental, health, and safety concerns. Deep eutectic solvents (DES) have emerged as environmentally benign alternatives to conventional organic solvents for metal extraction. However, their high viscosity limits mass transfer efficiency, reducing extraction kinetics and overall recovery yields. This study investigates, for the first time, the combination of DES with supercritical CO₂ (sCO₂) to overcome viscosity limitations and enhance PGM recovery from spent catalytic converters. Conductor-like Screening Model for Real Solvents (COSMO-RS) identified choline chloride and oxalic acid as the optimal hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) pair for DES formulation. Extraction experiments were conducted using both water bath and pressure-assisted processes with compressed CO₂. The effect of water addition on DES viscosity and the influence of compressed CO₂ on extraction efficiency were systematically investigated. The combined DES-sCO₂ approach achieved unprecedented recovery yields from the solid residue: 86.5% for platinum, 84.7% for palladium, and above 77% for rhodium. This represents the first time such high rhodium recovery has been achieved using compressed CO₂-assisted extraction. However, a significant challenge was identified in the poor absorption of metals into the DES phase, with only 17.8%, 17.3%, and 20.5% absorption for platinum, palladium, and rhodium, respectively. This work demonstrates that while DES-sCO₂ systems can effectively leach PGMs from catalytic converter matrices, future research must focus on optimizing metal-DES complex formation to improve absorption efficiency. The findings provide a foundation for developing more sustainable PGM recovery processes and highlight the potential of pressure-assisted extraction using environmentally benign solvents. Description: Thesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2025

Iron precipitation kinetics during microbial ferrous-ion oxidation

Mon, 01 Jan 2024 00:00:00 GMT

Title: Iron precipitation kinetics during microbial ferrous-ion oxidation Authors: Swami, Kevin Nzuzi Abstract: The formation of ferric-ion precipitates, such as jarosite, has been extensively documented during the bioleaching process. These precipitates serve as pathways for unwanted iron to escape from the system in various processes. However, a significant accumulation over an extended period can hinder reaction kinetics and reduce the overall efficiency of bioleaching. Therefore, this study sought to investigate the kinetics of the ferric-ion precipitates that are formed through bacterial oxidation. Experiments were conducted using a mixed mesophilic culture in shake flasks, with temperatures set at 30, 35, and 40 °C in a shaking incubator maintained at a constant pH of 1.7. The experiments lasted 14 days, with an agitating speed of 120 rpm. Upon analysing the quantification results, the maximum quantity of ferric-ion solid precipitates that developed was 2.48 grams at a temperature of 40 °C. Additionally, the data indicated that ferric-ion precipitation began 24 hours into the process. The precipitates generated were characterized by dense, light ochreous yellow residues. The patterns created by the X-ray powder diffraction (XRD) of these crystals were identified as potassium jarosite (K-jarosite), with its chemical formula being [KFe3(SO4)2(OH)6]. The scanning electron microscopy (SEM) analysis of their shape showed clusters of spherical, oval, and/or rectangular, powdery particles, all without clear, sharp edges. The Fourier transform infrared (FTIR) spectra of these crystals revealed the vibrational frequencies of SO42−, H2O, OH, and Fe–O in the jarosite. Furthermore, the thermogravimetric analysis (TGA) tests indicated the loss of hydroxyl groups from K-jarosite and the complete decomposition of yavapaiite when heated. The formation of ferric precipitates occurred according to first-order kinetics. The estimated activation energy was 117.2 kJ/mol with a frequency factor (K) of 2.94 X 1020 mmol Fe3+.h-1, indicating that the process was endothermic, with an average [Fe3+] of threshold 1.22 g/L. The thermodynamic parameters obtained were entropy (ΔS) = 0.25 kJ/mol K, Gibbs free energy (ΔG) = 43.89, 42.64, and 41.39 kJ/mol at 30, 35, and 40 °C, respectively, and Enthalpy (ΔH) = 120 kJ/mol. These values suggest that the formation of ferric precipitates was non-spontaneous and required a considerable amount of energy to proceed towards spontaneity. This study revealed that the generation of iron precipitation during microbial ferrous-ion oxidation by mesophilic consortia follows first-order kinetics. This process is endothermic and non-spontaneous, necessitating energy to transition to a spontaneous state. The findings could provide valuable insights for biohydrometallurgical processes aimed at managing and controlling jarosite formation and accumulation, thereby minimizing metal losses. Description: Thesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2024