Doctoral Degrees (Chemical Engineering)

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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.
The Chemical removal of sulphates using barium salts.
(1988) Trusler, Graham Errol.; Buckley, Christopher Andrew.; Edwards, R. I.; Brouckaert, Christopher John.
Abstract available in PDF copy.
Decentralised sanitation to fill the gap in urban wastewater treatment within the eThekwini Municipality: a focus on tertiary treatment in vertical down-flow constructed wetlands.
(2022) Arumugam, Preyan.; Pocock, Jonathan.; Brouckaert, Christopher John.
South Africa’s bulk sanitation infrastructure is failing, and there is an urgent need to look at other appropriate sanitation solutions. Moreover, there is no data on the proportion of population with access to safely managed sanitation services, an indicator for the United Nation’s Sustainable Development Goal (SDG) 6.2.1a. In a safely managed sanitation service, the user is provided with an improved facility, not shared with other households, and the excreta is safely disposed in situ or transported and treated off-site. In the city of eThekwini, informal settlements spring up faster than services can be delivered, severely impacting on public health, the environment, and the social well-being of these communities. The eThekwini Municipality sees the benefits of decentralised sanitation solutions for in situ informal settlement housing upgrades, but the selected system needs to produce fully compliant effluent with the Department of Water and Sanitation’s (DWS) Revised General Authorisation (GA) limits for safe discharge to a water resource. Since 2010, a modular-designed demonstration-scale decentralised wastewater treatment system (DEWATS) for raw domestic wastewater from 84 households has been in operation in eThekwini. The DEWATS operates with no electricity or chemicals for treatment, but was designed according to European best practice, and not according to the community served (such as influent characterisation and hydraulic loading). This study evaluated the applicability of vertical downflow constructed wetlands (VFCWs) as the tertiary treatment module in DEWATS in four design configurations, to determine an appropriate design that can be applied for the formal housing upgrades where safe discharge of the final effluent is required. These designs, all receiving anaerobically treated domestic wastewater from the demonstration-scale DEWATS and operating in the field, were: 1. A single-stage demonstration-scale VFCW (design 1) compared to its hybrid configuration with a horizontal flow CW (HFCW) (design 2). 2. VFCWs with extended filter depths (1 m) consisting of 2-3 mm coarse sand media (at pilot-scale) (design 3). 3. Two-stage VFCWs (at pilot-scale, operating under field conditions) (design 4): a. First stage: 0.5 m filter depth consisting of 2-3 mm coarse sand media. b. Second stage: 0.6 m filter depth with 0.5-2 mm fine to coarse sand media. Neither design was able to produce fully compliant effluent for safe discharge to a water resource. Depth had no impact on the treatment efficiency of the pilot-scale single-stage VFCWs; although the design with a two-stage VFCW, adapted from the Austrian design, did achieve higher total nitrogen removal compared to single-stage VFCWs with/without extended filter depths. Overall, design 2 with the demonstration-scale hybrid CW design (VFCWHFCW) produced the highest quality effluent. However, nitrate-N removal was limited in the HFCW due to low residence times, mixed aggregate media, high dissolved oxygen (DO) concentrations and lack of available carbon as an energy source for denitrification. A plantbased carbon source from dried plant material of the invasive Giant reed, Arundo donax L., was used to augment the carbon availability for denitrifying bacteria within the HFCW. However, it is surmised that the DO concentration above 0.5 mg L-1 limited NO3-N removal. It is recommended that the DEWATS design with the hybrid CW system be redesigned according to the raw wastewater characterisation and media gradation within both CWs to ensure sufficient residence times, natural aeration in the VFCW, limited diffusion of oxygen into the HFCW, and increased availability of biodegradable chemical oxygen demand carbon for denitrification. Moreover, if the upgraded households are installed with urine diversion flushing toilets, then the nutrient load to the DEWATS will be reduced, potentially resulting in fully compliant effluent. Consequently, DEWATS will then be considered a safely managed sanitation service, allowing South Africa to track their progress against SDG 6.2.1a.
An integrated computational fluid dynamics an kinetics study of ozonation in water treatment.
(2005) Huang, Tzu Hua.; Buckley, Christopher Andrew.; Brouckaert, Christopher John.
Computational fluid dynamic (CFO) modelling has been applied to examine the operation of the prc-ozonation system at Wiggins Waterworks, operated by Umgeni Water in Durban, South Africa. Ozonation is employed in water treatment process primarily to achieve the oxidation of iron and manganese, the destruction of micro-organisms and the removal of taste and odour causing compounds. It also aids in the reduction of the colour of the final water, enhancement of algae removal and possible reduction of coagulant demand. A hydrodynamic model has been satisfactorily verified by experimental tracer tests. The effect of the gas injection was modelled by increasing the level of turbulence intensity at the ozone contactor inlet. The model prediction of the overall tracer response corresponded closely to the experimental results. The framework of ozone reaction modelling was subsequently established using values of rate constants from the literature. An accurate prediction of the ozone concentration profile requires the application of the correct ozone kinetics involved. In raw waters, the depletion of ozone is influenced by the presence of natural organic matters (NOM). The observed ozone decay was found in good agreement using the pseudo first-order rate law. By measuring the total organic carbon (TOC) as a surrogate for NOM, the experimentally determined rate constants can be calculated to account for the effects of the ozone doses and the water quality. The characterisation study also aimed to provide sufficient information on ozone depletion and to be operated easily, without the lengthy and costly analyses ofa detailed kinetics study. The predicted profile of residual ozone concentration suggests the current operating strategy can be improved to optimise the ozone utilisation. The proposed monitoring point was suggested to be at the end of second companment where most ozone reactions have been completed. By coupling the transport equations of the target compounds with their chemical reaction rates, the concentration profile of these compounds such as ozone can be predicted in order to assist the understanding of an operation and to attain better interpretation of experimental results.
Modelling municipal wastewater treatment plants for industrial effluent discharge permitting: focusing on how modelling can be carried out in cases where measurements and resources are limited.
(2016) Mhlanga, Farai Tafangenyasha.; Buckley, Christopher Andrew.; Brouckaert, Christopher John.
Abstract available in PDF file.

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Browsing Doctoral Degrees (Chemical Engineering) by Author "Brouckaert, Christopher John."