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Chemical Engineering

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Browsing Chemical Engineering by SDG "SDG6"

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    A framework for modelling the interactions between biochemical reactions and inorganic ionic reactions in aqueous systems.
    (2022) Brouckaert, Christopher John.; Lokhat, David.
    Bio‐processes interact with the aqueous environment in which they take place. Integrated bio‐process and three‐phase (aqueous–gas–solid) multiple strong and weak acid/base system models are being developed for a range of wastewater treatment applications, including anaerobic digestion, biological sulphate reduction, autotrophic denitrification, biological desulphurization and plant‐wide wastewater treatment systems. In order to model, measure and control such integrated systems, a thorough understanding of the interaction between the bio‐processes and aqueous‐phase multiple strong and weak acid/bases is required. This thesis is based on a series of five papers that were published in Water SA during 2021 and 2022. Chapter 2 (Part 1 of the series) sets out a conceptual framework and a methodology for deriving bioprocess stoichiometric equations. It also introduces the relationship between alkalinity changes in bioprocesses and the underlying reaction stoichiometry, which is a key theme of the series. Chapter 3 (part 2 of the series) presents the stoichiometric equations of the major biological processes and shows how their structure can be analysed to provide insight into how bioprocesses interact with the aqueous environment. Such insight is essential for confident, effective and reliable use of model development protocols and algorithms. Where aqueous ionic chemistry is combined with biological chemistry in a bioprocess model, it is advantageous to deal with the very fast ionic reactions in an equilibrium sub‐model. Chapter 4 (part 5 of the series) presents details of how of such an equilibrium speciation sub‐model can be implemented, based on well‐known open‐source aqueous chemistry models. Specific characteristics of the speciation calculations which can be exploited to reduce the computational burden are highlighted. The approach is illustrated using the ionic equilibrium sub‐model of a plant‐wide wastewater treatment model as an example. Provided that the correct measurements are made that can quantify the material content of the bioprocess products (outputs), the material content of the bioprocess reactants (inputs) can be determined from the bioprocess products via stoichiometry. The links between the modelling and measurement frameworks, which use summary measures such as chemical oxygen demand (COD) and alkalinity, are described in parts 3 and 4 of the series, which are included as appendices to the thesis. An additional paper, presenting case study on modelling an auto‐thermal aerobic bio‐reactor, is included as a third appendix, as it demonstrates the application of some of the principles developed in the series of papers.
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    The effect of microwave treatment on the physicochemical characteristics of faecal sludge and implications for sludge treatment.
    (2023) Mdolo, Principal.; Pocock, Jonathan.; Velkushanova, Konstantina Veselinova.
    Faecal sludge (FS) is generated from non-sewered sanitation technologies such as pit latrines and septic tanks. Over time, FS needs to be emptied from the pit latrine and processed. Resource recovery from FS is growing because it contains organic matter and other materials that can be valorized to plant nutrients and biofuels. Drying, hydrothermal carbonization (HTC) and anaerobic digestion (AD) are some technologies used to treat FS and recover resources from it. Drying is achieved through solar, thermal, infrared or microwave heating. Microwave (MW) treatment is a technology of interest because of its efficient heating mechanism and versatility. It can efficiently meet several treatment objectives, such as volume reduction, nutrient recovery, or pathogen inactivation in a single operation. It can be incorporated into other treatment processes like pyrolysis, hydrothermal carbonization, and biological degradation to improve process efficiency. This study evaluated the effect of MW treatment on FS characteristics and the subsequent anaerobic digestion. A response surface modelling was used to study the MW operating parameters that influenced FS solubilization. The FS was collected from active ventilated improved pit (VIP) latrines and was treated in a domestic MW oven at 630W, 720W and 810W for 1 to 10 minutes. Changes in the properties of the treated FS were analyzed using ultraviolet-visible (UV/VIS) spectrophotometry, carbon, nitrogen and sulfur (CNS) elemental analyzer, Fourier transform infrared (FTIR), scanning electron microscopy (SEM) imaging, flow cytometry (FCM) and Automatic Methane Potential Test System (AMPTS II). The change in chemical oxygen demand (COD) provided a means of evaluating the effect of MW treatment on FS solubilization. The untreated FS had a high soluble COD (sCOD) to total COD (TCOD) ratio (10%), which indicated that the FS underwent stabilization in the pit latrine and during storage. A high sCOD/TCOD ratio was expected because the average age of VIP latrine FS in eThekwini is approximately five years. Although the FS showed properties of stabilization, MW treatment increased the sCOD, showing an initial sCOD release phase (phase 1), degradation of sCOD (phase 2) and a second slight sCOD release (phase 3). The sCOD release profiles were similar to the temperature profiles. In all the treatments (630W, 720W and 810W), the maximum sCOD release was recorded when the FS reached the boiling temperature (~96°C). The highest sCOD/TCOD achieved was 27% when a microwave power (MP) of 630W was applied for 4 minutes. The highest sCOD release was achieved in all treatments during the first phase. Although there was a second sCOD release (phase 3), it did not result in additional sCOD. Therefore, the microwave operation could be stopped after the first phase if the treatment aims to solubilize organic matter. Soluble proteins (sProt) and soluble carbohydrates (sCarbs) also increased after MWtreatment and followed a similar trend to the sCOD release. A correlation heat map revealed at the centre configuration had the least amplitude at high flowrates. This can be used online to check for particle breakage and the resulting maldistribution in flow in packed bed reactors. A model was developed to analyse pressure fluctuations in packed bed reactors. The model was developed using equations, found from literature, for non-ideal flow in packed beds. MATLAB software was used to solve and analyse the model. The pressure fluctuations obtained from experimental work agreed with the simulated data. The uniform packing had the highest amplitude while the nonuniform (large and small at the centre) had the least amplitude. The model was in agreement with experimental data, as it was seen that the amplitude of pressure fluctuations can be used for diagnosing flow maldistribution in packed bed reactors.