Browsing by Author "Brouckaert, Christopher John."

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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.
Analysis of nutrient requirements for the anaerobic digestion of Fischer-Tropsch reaction water.
(2013) Mathir, Aarefah.; Foxon, Katherine Maria.; Brouckaert, Christopher John.
Nutrients play an important role in the functioning of microorganisms during anaerobic digestion. The anaerobic treatment of industrial wastewaters, such as Fischer-Tropsch Reaction Water (FTRW), requires the addition of nutrients suitable for micro-organisms (micronutrients) since these wastewaters are devoid of essential metals. However, the dosing of nutrients is only effective if the metals are in a bioavailable form which in turn is dependent on the chemical speciation of the system. This study aimed to investigate and model the influence of precipitation on bioavailability by considering the extent to which precipitation can sequester metals into forms that are not bioavailable and the extent to which this sequestration can describe biological effects in an anaerobic system. Visual MINTEQ and Excel were used to develop a combined mass balance and chemical-equilibrium speciation model that considered the soluble and the precipitate metal phases. The model was compared to two sets of experimental analysis. Experiment A included metal analysis on the sludge and supernatant from glucose and ethanol fed ASBRs while Experiment B included similar analysis on FTRW fed ASBRs while biological parameters were monitored during a micro-metal washout experiment. Precipitation was found to sequester Al, Zn and Fe to a large extent making them non-bioavailable in Experiment A, while sulphide precipitates were predicted to dominate the metal speciation in Experiment B. In Experiment A, the organically bound metals phase was also a significant phase that sequestered metals. Furthermore, the rates of washout of most of the metals (excluding Mg) were over-predicted, which may have been due to the absence of other solid related phases in the model. This may also be attributed to kinetic effects in the system. Although there were reasonable correlations between the model predicted and the experimentally determined concentrations, it is recommended that the model should include the organically bound phase and consider mass transfer effects in the system. After 12 cycles without dosing micro-metals in Experiment B, the biogas production decreased by 43%. A decline in the predicted and determined soluble concentrations of a variety of metals were observed during this time, suggesting that there may be an agreement between predicted metals washout and reduction in anaerobic activity. Since the soluble metal concentrations did not decrease as rapidly as predicted by the model, a lag period between the two parameters was observed. Therefore, although the model provides an improved understanding of metal speciation and bioavailability such that recommendations may be made for prudent micro-metal dosing, further development is required for more accurate representations of the system.
Application of pinch technology in an integrated pulp and paper mill.
(2003) Naylor, Gladys M.; Brouckaert, Christopher John.
The objective of this investigation was to utilise water pinch analysis as a tool for the optimisation of fresh water use in an integrated pulp and paper mill. The investigation was carried out at Mondi Paper in Merebank, south of Durban. The pulp and paper manufacturing process is a large consumer of fresh water and minimising the amount of fresh water used in the processes is beneficial from both a cost and environmental point of view. There are examples of mills which have "closed" their water systems to the extent that fresh water make up is minimal and most of the water is recycled and reused in a closed loop. These examples provide guidance on the basis of proven methods for reducing water consumption in the pulp and paper industry and can be used as a reference for mills wishing to reduce water consumption by making use of tried and tested methods. This investigation sought to provide an alternative method to identifying potential savings in fresh water consumption by making use of water pinch analysis. This was done at Mondi Paper by analysing individual parts of the mill and then a larger section of the mill which included both pulp and paper production. Flow rates of water streams and fibre content in those streams were obtained from plant data, where available, and this data was used to produce.a mass balance using the Linnhoff-March software, Water Tracker. The balance produced using Water Tracker provided the missing flow and fibre content data and this data was used as the input for the Linnhoff-March software, Water Pinch , to perform the water pinch analysis. The results achieved when analysing the individual parts of the mill did not demonstrate potential for significant savings in fresh water consumption, however the analysis of the integrated section of the mill identified a potential reduction in fresh water. It was found that the application of a single contaminant analysis to the larger section of the mill identified a possible reduction in the freshwater requirement of 8.1% and a reduction in effluent generated of 5.4%. This is a savings of R1 548 593 per annum based on 2003 costs of fresh water and effluent disposal. This analysis was conducted using the most simplified representation possible to produce meaningful results in order to evaluate the effectiveness of water pinch analysis in optimising the fresh water consumption in an integrated pulp and paper mill. It is demonstrated that water pinch analysis is potentially a useful tool in determining the minimum fresh water requirement of a site.
The application of water pinch analysis at AECI bioproducts.
(2002) Schneider, Janos Pal Zsigmond.; Buckley, Christopher Andrew.; Brouckaert, Christopher John.
AECI Bioproducts (Bioproducts) is part of an industrial complex located at Umbogintwini, approximately 26 km south of Durban, Kwazulu-Natal. This system was selected for water pinch investigation, as it is one of the major users of freshwater on the complex and hence discharges a related quantity of wastewater, amounting to approximately 400 ML per annum. Bioproducts is a manufacturer of l-lysine, which is an animal feed additive. Water stream flowrate and purity data, as well as operating cost information, were obtained from plant records at AECI Bioproducts. Limiting flowrate and purity conditions for the water-using operations were established from a mass balance over the entire system using the Linnhoff-March software, WaterTracker. Subject to the specified constraints and operating costs, the problem was to determine the design of the water-using subsystem. No treatment plants were included in the study, as none exist at the facility. Three scenarios were investigated, which examined the operating variability of one of the evaporators on the site (the AS evaporator), which produces a condensate source of variable purity. The operating cost target and network design for each scenario was determined using the Linnhoff-March software, WaterPinch. Alterations from current operating practice were identified and associated savings (water-using network operating cost and freshwater flowrate) were highlighted. A robust optimal design was identified, with a recycle, which was consistent for all scenarios investigated. The degree of reuse of the AS evaporator condensate source was determined to be dependent on the purity of the source. The limiting constraint was identified at the sea pipeline, for suspended solids (SS): a prohibitively low discharge concentration constraint was identified as posing the major obstacle for saving. The potential for saving was investigated by incrementing the SS concentration constraint and subsequently the free and saline ammonia (FSA) constraint and allowing for the broth effluent to be discharged via the sea pipeline (which was previously disallowed by an effluent exemption). Although relatively small savings were identified through process integration (from 0.61% to 1.56% of the water-using network operating cost), the analysis identified a potential saving of over 70% of the water-using network operating cost, with relaxation of the sea pipeline SS and FSA constraint.
Assessing the treatability of textile effluents in an activated sludge system.
(2014) Mashava, Arnold.; Buckley, Christopher Andrew.; Brouckaert, Christopher John.
Assessing the treatability of a textile effluent through the activated sludge process required the development of analytical protocols and evaluating their suitability in providing receiving municipal wastewater treatment plants with systematic methodologies for predicting: (i) soluble dye effluent decolourisation through the activated sludge process (ii) impact of surfactants on oxygen transfer in the activated sludge system (iii) subsequent biodegradability of these surfactant effluents. Decolourisation was assessed through spectrophotometric computations of the mass of dye remaining in the activated sludge supernatant. Oxygen transfer was quantified from estimates of volumetric oxygen transfer coefficients which were computed from the modified form of the Lewis-Whitman interfacial mass transfer model which took into account the oxygen uptake rate from the respiring microbial species Biodegradability of the surfactant effluent was computed from the mass of soluble biodegradable substrates assimilated by the active sludge system during exogenous respiration The mass of the dye particles removed from solution attained an asymptotic value after 1 h and this implied adsorption equilibrium. A comparison between the adsorption equilibrium attained after 1 h and the municipal activated sludge system hydraulic residence time of 6 h led to the conclusion that soluble colour removal in receiving municipal activated sludge systems is not rate limited and it was therefore not necessary to accurately predict the adsorption kinetics. Instead, the adsorptive capacity of the activated sludge and extent of dye effluent decolourisation is of greater significance. Instantaneously after dosing the activated sludge system with the surfactant effluent, computed estimates of the volumetric oxygen transfer coefficient exhibited sudden and pronounced increments which simultaneously coincided with pronounced increments in the non-linear regression confidence level error bounds associated with each mass transfer coefficient computation. It was theorised that the surfactant effluent imparted some form of interference to the Clark dissolved oxygen sensor’s dissolved oxygen measurement mechanism and this resulted in erratic data points that did not fit onto the model. Comparative computations of volumetric oxygen transfer coefficients in the presence of a non-surfactant substrate such as CH3COOH should be conducted for purposes of elucidating increments in the mass transfer coefficients as a result of reaction-enhanced mass transfer from increments resulting from the impact of the surfactant effluent on either the liquid film mass transfer coefficient or the interfacial area or both. Further refinements are required in automating the methodology for computing volumetric oxygen transfer coefficients and generating scatter plots of the mass transfer coefficients as a function of time from automated real-time feeds of dissolved oxygen time series data logged by dissolved oxygen online instrumentation. Biodegradability numerical estimates were all far less than the estimates reported in literature by surfactant manufacturers and it was postulated that the erratic dissolved oxygen time series data points resulting from the dosing of the surfactant effluent were also extended to the biodegradability computations. It is also highly probable that the pronounced dissimilarities in biodegradability estimates were a result of either the presence of toxic components in the surfactant effluent which resulted in the gradual inhibition of microbial activity or a significant presence of slowly biodegradable and inert soluble substrates in the surfactant effluent which were not depleted through aerobic utilisation by heterotrophic microbial populations.
CFD modelling of a novel clarifier design for use in sugar cane juice clarification.
(2008) Govender, Thishen.; Brouckaert, Christopher John.; Davis, S. B.
The purpose of clarification in the sugar industry is to remove soluble, insoluble and colloidal matter from cane juice. Efficient clarification is required to produce high quality sugar and to prevent entrainment of solids in downstream equipment. The objective of this study is to produce a Computational Fluid Dynamics (CFD) model of the Magra Ultrasep clarifier. This was accomplished by: • Modelling the hydrodynamics of a laboratory scale clarifier In the Fluent CFD program. • Incorporating the flocculation process into the CFD model. • Performing experiments on a pilot scale clarifier to obtain parameter values for the flocculation model. The hydrodynamic model of the clarifier showed the presence of a recirculation zone above the baffle plate. Particle injections using Fluent's discrete phase modelling option determined that particles within the size range of IOOj..Lm to 4mm would circulate in this region, forming the bed of floc particles required for the Magra Ultrasep to work efficiently. The flocculation process in Fluent was represented using three different solid phases of different particle sizes. Small and medium sized particles were allowed to combine to form larger particles by changing the volume fractions according to three rate equations. A fibre glass laboratory scale model was set up at Maidstone Sugar Mill and fed the same sugar cane juice that enters the Rapi-Dorr clarifiers. The experimental results were then fed into a simplified flocculation model in MATLAB. An overall rate constant (k) of 5kg.m-3.s-) for the flocculation kinetic equation satisfied the experimental result.
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.
Co‐digestion of industrial and domestic wastewater.
(2020) Tanyanyiwa, Jimson Itai.; Buckley, Christopher Andrew.; Brouckaert, Christopher John.
This study is part of an extensive project studying the possibility of co-digestion of industrial and domestic wastewater at Amanzimtoti Wastewater Treatment Plant in Durban, South Africa. The focus of this study was to develop a model-based procedure to dose the 2 000 m3 full-scale Amanzimtoti pilot co-digestion plant with expired fruit juice. Modelling and experiments were used to create a six-stage feedback control loop. Experiments were conducted in 6.5 L batch reactors in the laboratory and in the 2 000 m3 plant that was operated at room temperature with intermittent mixing. The laboratory reactors were used in the first stage loop for data acquisition at 35°C and 25°C with digester sludge from the 2 000 m3 plant and expired fruit juice. pH values and biogas flowrate were measured continuously for 24 h during the experiments. The experimental data collected was used to calibrate a model of the laboratory reactor in the second stage. The WEST modelling platform was used for all modelling activities. The model was a UCT adaptation of the ADM1 model, and it used glucose as a representative of expired fruit juice as indicated in earlier work. Extensive kinetic parameters from the second stage were used to develop a model of the 2 000 m3 plant in the third stage. Expired fruit juice was dosed into the 2 000 m3 plant, and pH data was collected continuously over 24 h in the fourth stage. The pH data was used in the fifth stage to calibrate the model of the 2000 m3 plant model to the dosing of expired fruit juice. Extensive kinetic parameters from the fifth stage were used to develop the 6.5 L batch reactor model in the sixth stage. The 35°C experimental data was successfully used in the development of the 2 000 m3 plant model. The feedback control loop can be used to guide how much expired fruit juice can be dosed in the 2 000 m3 plant. Although the feedback control loop was successful, various components of the 2 000 m3 digester were not functional, which resulted in the feedback control loop being completed only once.
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.
The development and application of combined water and materials pinch analysis to a chlor-alkali plant.
(1989) Gianadda, Paolo.; Buckley, Christopher Andrew.; Brouckaert, Christopher John.
Pinch Analysis, in the broadest sense, is concerned with the optimal use of resources (material or energy) in a multi-process system. Pinch Analysis based techniques have emerged for water systems over the past decade. A major assumption that has been made in applying these techniques is that a process system can be segregated into a set of process streams and a set of water streams. With this distinction in place, only the water streams are considered in the Pinch Analysis with the process streams represented implicitly. This approach has obvious limitations in situations where a clear distinction between process streams and water streams cannot be made. The chlor-alkali process is an example of a system in which the clear distinction between process streams and water streams cannot be made. Water is intrinsically involved in the process, serving as a carrier medium for raw materials and eventually becoming part of the products produced by the complex. Hydrochloric acid and caustic soda are reagents which are both used within and produced by the complex. These reagents are required by the process at a range of concentrations and the concentrated reagent is diluted to the required concentrations using demineralised water. Within the chlor-alkali complex, a number of effluents containing the reagent species are available and are typically sent to drain. It is conceivable that these effluents might be recovered and used for dilution purposes instead of demineralised water. This would bring about a reduction in the amount of water and concentrated reagent used and the amount of effluent produced by the complex. Given the economic value of these reagents relative to water, their recovery, if feasible, is likely to dominate the optimal water-use and effluent generation strategy. Current Water Pinch Analysis theory relies on the distinction being made between process streams and water streams and does not consider the recovery of reagents or the presence of desirable species within the system. In addition, the assumption is made that species are non-reactive; reactive species such as hydrogen chloride and sodium hydroxide, fall outside the scope of the current theory. The objectives of this study have included the development of an approach which is able to address these limitations of the existing theory. This approach, termed Combined Water and Materials Pinch Analysis seeks to identify optimal use strategies for raw materials and reagents, in addition to water-use and effluent generation. The approach combines mathematical programming with conceptual insights from Water Pinch Analysis. The approach is based on the optimisation of a superstructure which represents the set of all possible flow configurations for water, reagents and raw materials between the various operations within the process system; this problem is solved as a nonlinear programming (NLP) problem using standard optimisation tools. The application of the developed approach to the Sasol Polymers chlor-alkali complex at Umbogintwini, south of Durban, has been a further objective of this study. Given the variety of process operations present within the complex, which differ both in terms of their physical structure and function, individual process models for these operations were required. These models were described in terms of four basic functional elements, namely, mixing, flow separation, component separation and reaction, and incorporated into the superstructure. Given the complexity of the problem, the process system was divided into three subsystems which were optimised in isolation from each other. These results were subsequently integrated to reflect the performance of the subsystems in combination with each other. The results showed a potential reduction of 14% in water-use and 42% in effluent production by the complex, relative to the existing operating configuration. Amongst other savings in material use, the results indicated a 0.2% reduction in the use of salt, a 1.6% reduction caustic soda use and an 8.3% reduction in the use of hydrochloric acid. Economically, the potential saving identified was R 945 727 per annum, based on operating costs in the year 2000. The final objective of this study was the interpretation of the pinch as it relates to the Combined Water and Materials Pinch Analysis problem. A general definition of the pinch was proposed; according to this definition, the pinch corresponds to that constraint or set of constraints which limits the performance of the system, that is, prevents it from further improvement. For the Combined Water and Materials Pinch Analysis problem, this performance is measured in terms of the operating cost. This definition is thus a departure from its usual thermodynamic interpretation of the pinch; in addition, the pinch is defined in terms of a constraint or a set of constraints instead of a point. These constraints are identified by an analysis of the marginal values provided by the optimisation algorithm. Marginal values are also used as a means of identifying process interventions which may be effected such that the performance of the system may be improved further.
Development of a model of the aerobic membrane bioreactor treating Illovo wastewater.
(2014) Kay, Liam Grant.; Foxon, Katherine Maria.; Brouckaert, Christopher John.
The Membrane Bioreactor (MBR) at Sezela, KwaZulu-Natal treats a process effluent emanating from a sugar industry by-products plant. Depending primarily on the effluent feed rate to the MBR as well as other less significant factors, the MBR tends to operate at a temperature that fluctuates between 40 and 50 °C. As a result of the temperature fluctuations the MBR may operate at either mesophilic or thermophilic temperatures. In an attempt to avoid the operational instability that accompanies the transition between temperature regimes, it would be conceivable to maintain mesophilic operation through either the removal of heat during feed increases or by continuously maintaining a low feed rate; alternatively to maintain thermophilic operation by providing auxiliary heat to the MBR when low feed rates are experienced, or by maintaining a high feed rate, possibly in conjunction with a buffer tank. A solution to the problem was sought through the formulation of a coupled dynamic mass and energy balance model, with an attached speciation routine. Development of a simulation model allowed the prediction of key operating parameters, namely the temperature, pH, substrate concentration, and volatile suspended solids (VSS) concentration. The sources of data used for modelling were laboratory experiments, historical MBR data, and literature data. Kinetic and stoichiometric coefficients of the model were determined from batch respirometric tests on the MBR furfural plant effluent feed and the activated sludge. The final model yielded a dynamic temperature (Root Mean Square Deviation (RMSD) of 1.61 and 1.34 °C) and pH (RMSD of 0.36 and 0.47) prediction over a continuous 69 day interval, where only the furfural plant effluent feed and sludge wasting rates were required as model inputs. The prediction of the substrate concentration and VSS concentration were found to be unreliable. The results of the comparison of mesophilic to thermophilic operation, through the final calibrated model, indicated that thermophilic operation was advantageous, however a rigorous economic analysis is required to substantiate this outcome. Thermophilic operation at 50 °C can handle feed rates 2.2 times higher than mesophilic operation at 40 °C, but may be more susceptible to process upsets.
Dynamic modelling of anaerobic digestion of Fischer-Tropsch reaction water.
(2013) Lees, Crispian McLintock.; Foxon, Katherine Maria.; Brouckaert, Christopher John.
Fischer-Tropsch Reaction Water (FTRW) is a high organic strength wastewater produced as a by-product in Sasol’s Fischer-Tropsch Reactors. Typically it has an organic load of 18000 mgCOD/L and is highly acidic with a pH of approximately 3.8. It is deficient in nutrients (N and P and other micronutrients). This dissertation deals with the biological and physico-chemical model development of a dynamic anaerobic digestion model, and explores two different approaches to representing the physico-chemical processes that complement and interact with the bioprocesses. The performances of the resultant two dynamic models (ADFTRW1 & AD-FTRW2) were compared in order to assess to what extent the more detailed and rigorous ionic speciation modeling in AD-FTRW2 addressed the shortcomings attributed to the simplified physicochemical modeling in AD-FTRW1. The ionic speciation model used in AD-FTRW2 uses a classic equilibrium formulation along the same lines as in the UCTADM2 model for anaerobic digestion of municipal wastewater sludges (Brouckaert et al., 2010), while AD-FTRW1 uses a simplification of the approach developed by Musvoto et al. (2000) in order to represent short chain fatty acid (SCFA) dissociation and the weak acid base chemistry of the inorganic carbon system. A 44 day extract from a 700 day laboratory-scale dataset (Van Zyl et al. 2008) was used as the basis for comparing the models. During this period the membrane bio-reactor was subjected to varying flow and load conditions. To validate the models, the experimentally measured and model predicted process variables of reactor alkalinity, reactor pH, biogas production and effluent SCFA concentration were compared. It was found that AD-FTRW2 provided superior agreement with pH data, but predictions of alkalinity, gas production rate and effluent short-chain fatty acids were not significantly improved in AD-FTRW2 relative to AD-FTRW1. This outcome was hypothesized since pH is strongly dependent on physico-chemical processes such as ionic interactions in solution and gas exchange which were the components to the models (AD-FTRW1 versus AD-FTRW2) which differed most significantly. Alkalinity, which is also highly influenced by physico-chemical model representations showed substantial improvement however statistical analysis could not show this improvement to be significant. The other two variables that were compared, biogas production and effluent SCFA concentration, displayed very similar agreement with experimental data. These variables depend more on mass balance effects and biological kinetics and were therefore not significantly altered by the more rigorous handling of aqueous chemistry in AD-FTRW2. It was concluded that AD-FTRW2 constitutes an improvement in model predictive power over AD-FTRW1 at a small cost in computing time.
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.
An investigation into the application of multiple criteria decision analysis as a decision support tool for municipal engineers.
(2015) Salisbury, Frances.; Buckley, Christopher Andrew.; Brouckaert, Christopher John.
A Multiple Criteria Decision Analysis (MCDA) was developed for the selection of sanitation systems. This decision support system was aimed at assisting municipal engineers to design and implement sustainable solutions to meet the municipality’s obligation to provide Free Basic Sanitation (FBS). The literature review investigated the factors which determine the success of sanitation projects and the sustainability framework in which the MCDA would be structured. Different multiple criteria methods were investigated with particular reference to those which have been applied to sanitation. Multi-Attribute Value Theory (MAVT) was selected as the method most suited to the problem under consideration. This requires the selection of indicators for which alternatives can be evaluated as well as the development of a multi-attribute value function which aggregates the partial values assigned to the indicators to arrive at an overall value for each alternative. The implementation of FBS by the eThekwini Municipality and the research projects carried out by the University of KwaZulu-Natal on the sanitation systems used by the municipality were analysed. Data from this research informed the allocation of indicator values to the sanitation alternatives under consideration: initially Ventilated Improved Pit latrines (VIPs) and Urine Diversion Dehydrating Toilets (UDDTs). Later a third option, the pour-flush latrine, was added. Criteria which determine the sustainability of sanitation were selected and a spreadsheet-based MCDA with stakeholder and expert user interfaces was developed. Stakeholders will determine the weighting of each indicator and expert users will determine the values to be entered for the alternatives against each indicator. The partial values are aggregated using a weighted sum function. The MCDA was populated with values derived from the eThekwini research. Sensitivity analysis was carried out for the weighting of the three main criteria: environmental, financial/technological, and socio-cultural. An innovative scenario analysis method was used to determine the effect of different weightings and/or values. The MCDA was found to provide a guiding framework for municipal engineers in their efforts to implement sustainable sanitation. The process of deriving values for the MCDA is likely to prove even more useful than the overall value scores of the options under consideration.
Modelling and control of potable water chlorination.
(2003) Pastre, Amelie.; Mulholland, Michael.; Brouckaert, Christopher John.; Buckley, Christopher Andrew.; Le Lann, Marie Veronique.
In potable water preparation, chlorination is the last step before the potable water enters the distribution network. Umgeni Water Wiggins Waterworks feeds the Southern areas of Durban. A reservoir at this facility holds treated water before it enters the distribution network. To ensure an adequate disinfection potential within the network, the free chlorine concentration in the water leaving the reservoir at the Umgeni Water Wiggins Waterworks should be between 0.8 and 1.2 mg/L. The aim of this study was to develop an effective strategy to predict and control the chlorine concentration at the exit of the reservoir. This control problem is made difficult by the wide variations in flow and level in the reservoirs, together with reactive decay of the chlorine concentration. A Computational Fluid Dynamic study was undertaken to gain understanding of the physical processes operating in the reservoir (FLUENT software). As this kind of modelling is not yet applicable for real-time control, compartment models have been created to simulate the behaviour of the reservoir as closely as possible, using the results of the fluid dynamic simulation. These compartment models were initially used in an extended Kalman filter (MATLAB software). In a first step, they were used to estimate the kinetic factor for chlorine consumption and in a second step, they predicted the chlorine concentration at the outlet of the reservoir. The comparison between predictions and data, allowed the validation of the compartment models. A predictive control strategy was developed using a Dynamic Matrix Controller, and tested offline on the compartment models. The controller manipulated the chlorine concentration in the inlet of the reservoir in order to control the chlorine concentration in the outlet of the reservoir. Finally, the simplest compartment model was implemented on-line, using the Adroit SCADA system of the plant, in the form of a Kalman filter to estimate the chlorine decay constant, as well as a predictive model, using this continuously-updated decay parameter. The adaptive Dynamic Matrix Controller using this model was able to control the outlet chlorine concentration quite acceptably, and further improvements of the control performance are expected from ongoing tuning.
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.
Modelling of ionic interactions with organic components in wastewater.
(2014) Westergreen, Sarah.; Foxon, Katherine Maria.; Brouckaert, Christopher John.
In current biological wastewater treatment models, physico-chemical processes (ionic speciation reactions, gas-liquid exchange, and liquid-solid interactions such as precipitation and adsorption) either are not explicitly considered, or are incorporated as simplified descriptions. This may result in an inaccurate prediction of digester behaviour. Specifically, the ionic behaviour of biomass is not explicitly included in standard models. The objectives of this study were to develop a model component that describes ionic behaviour of biomass, use this to predict the overall solution pH buffering capacity and determine its impact in an anaerobic digester’s operating range (pH 6-8). The study hypothesises that the ionic behaviour of biomass can be described in terms of glycine equivalence; alternatively, it can be described by a model component consisting of functional groups characterised by concentration per unit mass of sludge and pKₐ value for each group, either at equilibrium conditions, or considering kinetic effects. The methodology involved constructing a mass balance / ionic speciation model capable of simulating alkaline and acidimetric experimental titrations with modifications for each hypothesis. Varying concentrations of glycine or suspensions of biomass (particulate organic matter) in background salt solutions were titrated and the model was fitted to the data by changing the parameters associated with the biomass description and, (where appropriate) associated kinetic terms, with associated estimation of parameter uncertainty. A model component, UKZiNe was developed consisting of 4 functional groups; 2 carboxyl groups, 1 phosphate group and 1 amine group. Kinetic effects including carbon dioxide exchange and pH probe lag were explored. The hypothesis that glycine could represent the ionic behavior of biomass was not supported. The alternate hypothesis, considering UKZiNe at equilibrium conditions, required further testing to evaluate the effects of kinetic reactions; the second alternate hypothesis that non-equilibrium effects significantly influence the measured experimental pH value, was supported. All model formulations predicted that the biomass contribution to the overall buffer capacity in the operating region of an anaerobic digester was insignificant. The study implies that the inclusion of an ionic description of biomass does not considerably improve the pH prediction in digester simulations and can be excluded in future model development.
Modelling of the Marianridge wastewater treatment plant.
(2008) Mhlanga, Farai Tafangenyasha.; Brouckaert, Christopher John.
One of the consequences of the social and economIc change due to industrialisation is the generation of industrial wastewater which requires treatment before being released into the natural aquatic environment. The municipality has wastewater treatment plants which were initially designed for the treatment of domestic wastewater. The presence of industrial wastewater in these treatment plants introduces various difficulties in the treatment process due to the complex and varying nature of the industrial wastewater. A means needs to be developed, that will allow the municipality to evaluate if a wastewater treatment plant can adequately treat a particular composition or type of wastewater to a quality suitable for release to the environment. Developing a simulation model for a wastewater treatment plant and calibrating it against plant operating data will allow the response of the wastewater treatment plant to a particular wastewater to be evaluated. In this study a model for the Mariamidge Wastewater Treatment Plant is developed in the WEST (Worldwide Engine for Simulation, Training and Automation) software package. The sources of data for modelling were laboratory experiments, historical data from the municipal laboratory and modelling of experiments. Dynamic input files representing the properties of the influent wastewater were generated by characterising the influent wastewater through the use of batch respirometric tests and flocculation filtration on composite samples of wastewater. Kinetic and stoichiometric coefficients of the model were determined from batch respirometric tests on wastewater and activated sludge, and simulation of the batch respirometric experiment. To make the model plant-specific it is calibrated against plant operating data. Influent characterisation and reliable ASM3 model parameters were determined from the respirometric batch test and modelling of experiments. The resulting plant model was able to closely predict the trends of the effluent COD concentration in the plant. Hence it was concluded that the use of laboratory experiments, historical data from the municipal laboratory and modelling of experiments in order to generate information for the modelling of wastewater treatment plants makes up a methodology which can be adopted and improved by additional experiments.
Modelling the distribution of micro-nutrient metals in the anaerobic digestion for fischer-tropsch reaction water.
(2017) Ntuli, Nomalungelo Thembeka.; Brouckaert, Christopher John.
Sasol, one of South Africa’s largest petrochemical producers; derives water from the Fischer Tropsch process and is referred to as Fischer-Tropsch Reaction Water (FTRW). FTRW has high hydrocarbon content and a very low pH, hence, it must be treated prior reuse in the system. In the purification process, the organic content in the FTRW is mainly broken down to CO2 and CH4 by microorganisms which use the organic content as nourishment, bringing about its decomposition. Macro and micronutrients are necessary for survival of microorganisms, and this study is focused on the optimisation of micronutrients (micro-metals) to supplement the treatment of FTRW. This study was aimed at developing a model to predict the distribution of micronutrients in the various phases present in anaerobic digester sludge: soluble ions, precipitates and an adsorbed phase. The aim was to introduce an adsorbed phase to the precipitates-soluble phase model to reduce the deviation between model and experimental sludge concentrations. The model would thereafter be used for optimization of micronutrients dosing techniques employed by Sasol to reduce operating costs of anaerobic treatment of FTRW. The model was sufficiently extended to include the adsorbed phase by ionic representation of the biomass, however, the accuracy to which the model represents reality could not be tested by model validation due to these crucial limitations: incomplete set of experimental soluble phase concentrations, imprecise experimental data for metals entrapped in precipitates only and in the adsorbed phase only, to allow for regression of governing equations, as well lack of experimental representation of the relationship between sulphide and sulphate by concentrations. The integrated Ionic speciation model was used to point out the importance of the sulphatesulphide system, as the phase control varies between the precipitates and the adsorbed phase, depending on the behaviour of the anions, specifically the sulphides. A series of further experimental work needs to be completed to ensure a robust model outcome, such that the model best represents the speciation of metals in an anaerobic digester. The hypothesis therefore could not be proven to be true based on the data at hand. The next steps will be to carry out detailed experimental work; showing initial conditions, sulphate and sulphide concentration as well as experimental partitioning of metals in the various phases. In the meantime, Sasol can look into incorporation of a donor cation with a greater affinity to sulphide ions and adsorption on biomass while not impacting the decomposition reaction, such that the metal cations essential for anaerobic digestion are kept in solution to enhance the microbial activity for the treatment of FTRW.
Optimal operation of a water distribution network by predictive control using MINLP.
(2004) Biscos, Cedric P. G.; Mulholland, Michael.; Buckley, Christopher Andrew.; Brouckaert, Christopher John.; Le Lann, Marie Veronique.
The objective of this research project is to develop new software tools capable of operational optimisation of existing, large-scale water distribution networks. Since pumping operations represent the main operating cost of any water supply scheme, the optimisation problem is equivalent to providing a new sequence for pumping operations that makes better use of the different electricity tariff structures available to the operators of distribution systems. The minimisation of pumping costs can be achieved by using an optimal schedule that will allow best use of gravitational flows, and restriction of pumping to low-cost power periods as far as possible. A secondary objective of the operational optimisation is to maintain the desired level of disinfectant chlorine at the point of delivery to consumers. There is a steady loss of chlorine with residence time in the system. If the level drops too low there is a risk of bacterial activity. Re-dosage points are sometimes provided in the network. Conversely, too high a level produces an unacceptable odour. The combinatation of dynamic elements (reservoir volumes and chlorine concentration responses) and discrete elements (pump stati and valve positions) makes this a challenging Model Predictive Control (MPC) and constrained optimisation problem, which was solved using MINLP (Mixed Integer Non-linear Programming). The MINLP algorithm was selected for its ability to handle a large number of integer choices (valves open or shut / pumps on or off in this particular case). A model is defined on the basis of a standard element, viz. a vessel containing a variable volume, capable of receiving multiple inputs and delivering just two outputs. The physical properties of an element can be defined in such a way as to allow representation of any item in the actual network: pipes (including junctions and splits), reservoirs, and of course, valves or pumps. The overall network is defined by the inter-linking of a number of standard elements. Once the network has been created within the model, the model predictive control algorithm minimises a penalty function on each time-step, over a defined time horizon from the present, with all variables also obeying defined constraints in this horizon. This constrained non-linear optimization requires an estimate of expected consumer demand profile, which is obtained from historical data stored by the SCADA system monitoring the network. Electricity cost patterns, valve positions, pump characteristics, and reservoir properties (volumes, emergency levels, setpoints) are some of the parameters required for the operational optimisation of the system.