Browsing by Author "Ekama, George"

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    Open Access
    Alternative water sources for urban consumers – A novel technology for the City of Cape Town urban resident
    (2019) Yiannou, Angelos; Ikumi, David; Ekama, George
    South Africa is classified as being the 30th driest country in the world and is regarded as a water scarce country. However, for the urban residents of the City of Cape Town, the ability to reduce their municipal water consumption through initiatives, other than simply using less water, is limited. Hence, there is a need for affordable, simple and compact technical solutions which allow urban populations residing in high density developments to make use of alternative sources of water, specifically greywater, to reduce their municipal water demand. Existing commercial technologies were considered, together with the socio-economic and technical constraints of an illustrative middle-income urban household in the City of Cape Town (CoCT). It was found that each commercial technology considered satisfied some, but not all, constraints characteristic of the household. For instance, the treatment device may produce treated water of a high quality. However, it may not be financially feasible for the consumer. Of the commercial technologies considered, there is no single commercial technology which can offer a complete solution within the socio-economic and technical constraints of the household. For this reason, the opportunity exists to produce an innovative technical solution. The proposed greywater treatment device consists of four cylindrical chambers in a vertical arrangement. Raw greywater enters the top chamber and treated greywater is extracted from the bottom chamber forming the base. The treatment processes undergone as the greywater flows through the treatment device include, in the following order, pre-filtration, biological treatment (Activated Sludge), clarification, filtration and disinfection. The process is driven by a combination of gravity and electrical energy. The proposed design is constructed using readily available materials and components. It is modular in its construction, allowing for easy maintenance, assembly and an increase in design flexibility. Evaluating the design against the same evaluation criteria stipulated for the existing commercial technologies showed that the proposed design may be an appropriate solution for the illustrative middle-income household within the City of Cape Town and is a novel technical solution.
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    Design of an integrated fixed-film activated sludge (IFAS) system for possible application at the Borcherds Quarry WWTW
    (2018) Kritzinger, Marco; Ekama, George
    Nitrification can be seen as the weakness of a conventional activated sludge (CAS) process employing biological nutrient removal (BNR). Suspended nitrifiers only grow in the aerobic zone of the biological reactor but are subjected to anaerobic and anoxic conditions where no nitrifier growth takes place. To establish a nitrifier population that consistently produces low effluent ammonia concentrations, long sludge ages are required (about 15 to 25 days) in South African BNR wastewater treatment plants. This results in relatively large biological reactors. Integrated Fixed-Film Activated Sludge (IFAS) systems have been used extensively in European and Scandinavian countries. This process entails the addition of moving-bed biofilm carriers in certain zones of an activated sludge system to establish biofilm growth. The most successful application has been the addition of these carriers in the aerobic zones of activated sludge plants to facilitate the growth of nitrifiers on the biofilm. This allows nitrifiers to grow independently from the suspended sludge age since it remains stationary on the biofilm in the aerobic tank. The system is thereby relieved from the requirement of a long suspended sludge age. For the University of Cape Town (UCT) process commonly employed in South Africa, it is shown that a suspended sludge age of 5 to 7 days is adequate to meet final effluent standards when converted to an IFAS process. As a result, an UCT-IFAS process can treat 50% to 70% more wastewater in an existing process volume or reduce the size required for a new installation by 30% to 40% when compared to a conventional UCT process with a minimum wastewater temperature of 14°C. The intricacies and challenges associated with designing an IFAS process are unpacked in this thesis to gain a better understanding of what is required to harvest the potential benefits.
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    Development of a Dynamic Simulation Model for Equalization Tanks
    (2021) Simo, Eugene Fotso; Ikumi, David; Ekama, George
    The influent to a water and resource recovery facility (WRRF) generally exhibits significant diurnal variations in flow rate and load concentration. This makes determining the operating parameters and subsequently the overall operation of plants difficult, especially in developing countries due to the lack of highly skilled operators. Hence, there is an incentive for the control and operation of WRRFs in developing countries to be improved. Flow equalization tanks were identified as a potential method to attenuate the diurnal variations in flow rate and load concentration into plants. The main aim of this research was to develop a viable dynamic simulation model for the operation of flow equalization tanks, within a plant-wide framework (to allow for the evaluation of design and control strategies). The next aim was to determine the benefits of equalization tanks towards design and optimised operation of future WRRFs via scenario analyses. Finally, the effects of the equalization tank on the performance of various unit processes in a WRRF were to be investigated. The model was developed in three steps; i) the development of the required equations to model equalization tanks, ii) mass balance throughout the model for internal consistency and iii) scenario analyses to determine if the model generated reasonable and scientifically sound outputs. The model was developed using Microsoft Excel Visual Basic (VBA) and WEST®. Two scenarios were considered to assess the equalization tank modelled. Scenario One involved the comparison of the capital cost, unit process sizes and total footprint of a balanced sludge age Modified Ludzack-Ettinger (MLE) system with and without an equalization tank. Scenario Two compared the plant performance of the MLE system designed in Scenario One with and without a flow equalization tank. A dynamic simulation model replicating equalization tanks was successfully developed. From scenario analyses, it was determined that using an MLE system and only considering equalization of flow, there was a reduction in the size of several unit processes by 8-9% (primary settling tank, biological reactors, secondary settling tank, flotation unit, anoxic-aerobic digester), due to the less conservative design values that could be used as the variations of the influent were decreased. Despite this, a 13% overall increase in the footprint of the WRRF was observed due to the addition of the equalization tank. The attenuation of diurnal flow variations also resulted in reduction of various plant parameters by up to 50% (flow, OUR, VSS flux). Finally, there was a 10% improvement in the performance of various unit processes due to the presence of the equalization tank. In conclusion, the inclusion of equalization tanks in WRRFs has significant positive effects. These results were obtained with equalization of flow only. Some other limitations were experienced during the project resulting in the following recommendations: further research will be needed to validate and calibrate the model, As the model was not successfully incorporated in a plant-wide framework, further developments in that direction are required, as well as including the equalization of load in the model.
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    Development of a Dynamic Simulation Model for Equalization Tanks
    (2021) Fotso, Simo Eugene; Ikumi, David; Ekama, George
    The influent to a water and resource recovery facility (WRRF) generally exhibits significant diurnal variations in flow rate and load concentration. This makes determining the operating parameters and subsequently the overall operation of plants difficult, especially in developing countries due to the lack of highly skilled operators. Hence, there is an incentive for the control and operation of WRRFs in developing countries to be improved. Flow equalization tanks were identified as a potential method to attenuate the diurnal variations in flow rate and load concentration into plants. The main aim of this research was to develop a viable dynamic simulation model for the operation of flow equalization tanks, within a plant-wide framework (to allow for the evaluation of design and control strategies). The next aim was to determine the benefits of equalization tanks towards design and optimised operation of future WRRFs via scenario analyses. Finally, the effects of the equalization tank on the performance of various unit processes in a WRRF were to be investigated. The model was developed in three steps; i) the development of the required equations to model equalization tanks, ii) mass balance throughout the model for internal consistency and iii) scenario analyses to determine if the model generated reasonable and scientifically sound outputs. The model was developed using Microsoft Excel Visual Basic (VBA) and WEST®. Two scenarios were considered to assess the equalization tank modelled. Scenario One involved the comparison of the capital cost, unit process sizes and total footprint of a balanced sludge age Modified Ludzack-Ettinger (MLE) system with and without an equalization tank. Scenario Two compared the plant performance of the MLE system designed in Scenario One with and without a flow equalization tank. A dynamic simulation model replicating equalization tanks was successfully developed. From scenario analyses, it was determined that using an MLE system and only considering equalization of flow, there was a reduction in the size of several unit processes by 8-9% (primary settling tank, biological reactors, secondary settling tank, flotation unit, anoxic-aerobic digester), due to the less conservative design values that could be used as the variations of the influent were decreased. Despite this, a 13% overall increase in the footprint of the WRRF was observed due to the addition of the equalization tank. The attenuation of diurnal flow variations also resulted in reduction of various plant parameters by up to 50% (flow, OUR, VSS flux). Finally, there was a 10% improvement in the performance of various unit processes due to the presence of the equalization tank. In conclusion, the inclusion of equalization tanks in WRRFs has significant positive effects. These results were obtained with equalization of flow only. Some other limitations were experienced during the project resulting in the following recommendations: further research will be needed to validate and calibrate the model, As the model was not successfully incorporated in a plant-wide framework, further developments in that direction are required, as well as including the equalization of load in the model.
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    Energy optimisation on wastewater treatment plants focusing on different aeration technology
    (2020) Strassberger, Divan; Ekama, George
    With ever more pressure being exerted on South Africa to reduce its carbon emissions and their sole energy producer, Eskom, on the verge of collapse, electricity cost in South Africa are set to increase drastically. It is therefore important that electrical consumption be reduced throughout all sectors and wastewater treatment is no exception. With reduction of electrical consumption of WWTPs in mind, this thesis focused on the costing and viability of replacing less efficient aeration technology (slow speed surface aeration) with more efficient technology (fine bubble diffused aeration). The main objective of the investigation was to calculate the total cost (capital, maintenance and operational) of the two technologies, with the input of the varying inflow rates and wastewater characteristics, and find the inflow rate where the total cost of the two technologies are the same. This intersection was titled the Viability Threshold Point. With this point known it is possible to advise designers and investors as to when and where which aeration technology should be implemented. Different data groups were established with varying wastewater characteristics (see table below) as well as inflow rates varying from 1.0 Mℓ/d to 12.0 Mℓ/d. An inflow COD concentration of 750 mg/ℓ was chosen as a benchmark group and the other inflow characteristics were calculated to represent typical values based on this COD concentration.
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    Establishing the environmental and economic benefits of applying advanced thermal hydrolysis to existing anaerobic digesters in the Western Cape, South Africa
    (2021) Potts, Wesley; Ekama, George
    The treatment of sewage by wastewater treatment works (WWTW) generates a solids byproduct stream requiring treatment and disposal. The waste sludges generated are rich in essential nutrients and energy, and present an opportunity to turn a waste stream into a resource. Retrofitting a thermal hydrolysis process (THP) to existing anaerobic digestion (AD) sludge treatment has proven itself globally as a reliable means of increasing treatment capacity and creating a final product that is non-hazardous. This allows for more sustainable sludge disposal options. However, THP has not yet been proven in a South African context. This research carried out a comparative desktop case study of the existing AD facility at the Cape Flats WWTW in the Western Cape, South Africa. The facility's equipment is due for an upgrade and it was investigated if an improved process could be created. The base case of maintaining existing conventional mesophilic anaerobic digestion (MAD) was compared against the case of retrofitting THP. This would increase capacity and improve final product quality. The site would become a regional sludge facility importing additional sludge from some of the surrounding WWTWs. This would divert sludge from landfill and create more sustainable disposal options. Steady-state models were developed for the conventional MAD and THP-MAD. These models were developed to include a kinetics section, stoichiometry section and a weak acid/base chemistry section. The kinetics section used hydrolysis as the rate limiting step when applying saturation kinetics. A stoichiometry section takes input from the kinetics conversion and used the elemental compositions of both substrate and biomass while predicting the amounts of other AD products formed. The weak acid/base chemistry predicted pH and took into account corrections for ionic strength and temperature, which were found to be particularly applicable in the case of high solids THP digestion with the elevated dissolved concentrations. Many of the WWTW's in Cape Town make use of nitrification-denitrification biological excess phosphorous removal (NDBEPR) activated sludge (AS) treatment, often preceded by primary sedimentation. The modelling thus considered a 60:40 mixture of NDBEPR wasted activated sludge (WAS) and primary sludge (PS). AD modelling accounted for the breakdown of polyphosphate (PP) with the uptake of readily biodegradable COD to form poly3- hydroxybutyrate (PHB). The models also predicted the extent of spontaneous magnesium ammonium phosphate (struvite) precipitation inside the digester, and as well as the effect this would have on digester alkalinity and pH. Results showed that when THP is retrofitted 2.5 times more sludge could be processed using the existing digesters' volume i.e. without building any additional digesters. This results in sludge treatment throughput increasing from 60 dry tonnes of solids per day for conventional digestion to 153 dry tonnes per through advanced THP digestion. Modelling has shown in each case that important AD parameters, such as free ammonia concentration, pH, alkalinity, and methane production are within the correct range for stable digester operation while sludge stability was achieved. Major operating expenses and savings were evaluated. It was estimated that retrofitting THP created a saving of over R70mil/annum, largely due to savings in sludge disposal, and produce 2.7MW of surplus electrical energy. Carbon emissions were assessed for each case with THP digestion reducing significantly more emissions than conventional digestion. Additional investment required to upgrade conventional digestion to THP digestion specifically at the Cape Flats WWTW site would create a payback of between 5 to 6 years.
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    Finite element analysis of flows in secondary settling tanks
    (2002) Kleine, Dorothee; Reddy, Daya; Ekama, George
    Secondary settling tanks (SSTs) form a crucial part of wastewater treatment plants. Besides having to produce the separation of suspended solids and clarified effluent the secondary settling tank is used to concentrate and recycle the settled sludge to the biological reactor. The efficiency of the biological reactor in the waste water treatment system is determined by the efficiency of this final clarifying process. Hydrodynamic models have been developed for simulating secondary settling tanks in order to gain a better understanding of the complex flow patterns in these tanks, and to make design and optimization of the SST internal features possible. These models use mainly the finite volume method. This thesis is concerned with the development and implementation of a finite element approach to the simulation of flows in SSTs. Although it is nowadays also possible to realise an unstructured grid within the FVM, the power of the finite element method (FEM) lies in its higher flexibility in fitting irregular domains and in providing local grid refinement. Generally, unstructured mesh procedures with the FVM require essential, additional orthogonality corrections, which affect the accuracy of the solution, and these corrections increase the computational cost due to the additional computations and increased iteration requirements. Structured mesh discretization may offer significantly shorter computation time. The FEM is therefore convenient for handling arbitrarily shaped domains and adaptation of complex internal features of SSTs, such as inlet and outlet arrangements.
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    Identification of Wastewater Primary Sludge Composition using Augmented Batch Tests and Mathematical Models
    (2021) Gaszynski, Christopher; Ekama, George; Ikumi, David
    Over the past 40 years, there has been a continuous progression in generating concrete solutions in the design and operation of wastewater treatment systems. This progression has included the development of various integrated and logical-mathematical glass box models geared towards the recovery of resources. However, the accuracy of these models relies on characterising the influent waste stream accurately, which includes identifying the molecular composition of the biodegradable organics. Municipal wastewater contains an array of organics, and it is crucial to accurately identify the composition of these organics before they are fed into the virtually replicated (i.e. modelled) system. This identification of influent organics ensures that the performance of the system can be predicted, and system upset, or failure can be avoided. The overarching aim of this project was to characterise the composition of the organics present in municipal wastewater using experimental analysis and mathematical bioprocess modelling. The project extended and improved current analytical methods by developing: 1. The Augmented Biochemical Methane Potential (AugBMP) Test: A test run identically to the BMP test but extended to include the methane and carbon dioxide production, the aqueous phase volatile fatty acids (VFAs), H2CO3 and total alkalinity, ammonia and orthophosphate concentrations and the reactor pH. 2. The Augmented Biochemical Sulphide Potential (AugBSP) Test: A test aimed to improve the accuracy of the AugBMP test, as methanogenesis was replaced by Biological Sulphate Reduction (BSR), minimising the gas measurement error commonly experienced during the BMP test. The proposed AugBMP and AugBSP tests coupled with mathematical bioprocess modelling, provides a powerful tool for determining the composition of the biodegradable organics present in wastewater substrates. The project incorporated a holistic approach which included fabricating the proposed testing vessels, performing multiple experiments and as accurately as possible, simulating the observed outcome using mathematical models. The outcome of this project allowed for the composition of unknown substrates, such as the organics present in primary sewage sludge to be identified confidently. This thesis unpacks and describes this new methodology developed to characterise substrates with unknown composition.
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    Improved tracking of phosphorus in wastewater treatment works through anaerobic digestion of p-rich sludge
    (2021) Quevauvilliers, Matthieu; Ikumi, David S; Ekama, George
    This research aims at improving the tracking of phosphorus (P) in wastewater treatment works (WWTWs) by developing a model which accurately explains the intracellular processes of phosphorus accumulating organisms (PAOs). Two major models: the “Comeau-Wentzel” model (Comeau et al., 1987) and the “Mino” model (Mino et al., 1988) were developed to explain PAO intracellular processes but the failure of these models to achieve data reconciliation when modelling the anaerobic digestion of PAOs show that they are still incomplete. Ikumi and Ekama (2019) generated stoichiometry to help model PAO intracellular processes and hypothesised that an energy transfer between the activated sludge (AS) system and the anaerobic digester (AD) might take place. This research generated a steady state (SS) anaerobic digestion model (an extension of Sӧtemann et al.'s (2005) model) to model the treatment of sludge from nitrifying-denitrifying enhanced biological phosphorus removal (NDEBPR) system and assess, through data reconciliation, which of Ikumi and Ekama's (2019) stoichiometry best models PAO behaviour. The AD model generated achieved a high degree of correlation with experimental data but was unable to conclusively identify a single biochemical pathway for PAO processes.
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    Simplification of Complex WWTP Models into Simple Design and Evaluative WRRF Tool
    Nsengiyumva, Olivier; Ikumi, David; Ekama, George
    Wastewater treatment plant (WWTP) steady-state models have been used, historically, by consulting engineers and researchers for design, process optimisation, and to study and evaluate various operating scenarios. These models have, however, been generally developed for single unit process which limits their use. In addition, there have been three recent shifts in the past two decades from conventional design and modelling of WWTPs. Firstly, the shift from single unit to plant-wide modelling. Secondly, WWTPs are considered as water and resource recovery facilities (WRRFs). Lastly, there has been a growing interest to use the developed plant-wide steady-state models by stakeholders i.e., plant operators, designers and decision-makers who have limited technical expertise in WWTP modelling. These stakeholders use these models for design, evaluation and optimisation of scenarios. The later shift has raised the debate of complexity versus simplicity of the developed steady-state models. In addition to the aforementioned shifts, there has been limited research on the impact of sludge return liquors on the overall plant performance especially in the context of South African WWTPs. Wastewater treatment plants treat influent wastewater to a specified effluent quality, through several processes, before discharging it into the receiving water bodies. One of the by-products of these treatment processes is a nitrogen (N) and phosphorus (P) rich dewatering liquor (DWL). Generally, South African WWTPs recycle the DWL to the mainstream treatment process without first undergoing any side-stream treatment process (SSTP). The recycling of such N and P rich DWLs to the mainstream process, without first going through any SSTP and/or addition of organics to the mainstream process (organics have a role to play in nutrient removal, through the provision of substrate for biomass growth and provision of electron donors in the process of denitrification) poses a problem to the treatment process. Consequently, the reactor is overloaded with nutrients without sufficient organics to remove them; hence, the plant produces poor effluent quality i.e., high N and P concentrations at high operational cost. A simplified full-scale steady-state WWTP simulation tool, namely, plant performance evaluation tool (PPET), with a user-friendly interface was developed, based on principles of sound mass balance and kinetic and stoichiometric relations over the full-scale plant, to bridge the gap between the complexity of WWTP models and the lack of technical expertise of the stakeholders. This simulation tool analyses the impact of recycling sludge dewatering liquors on the overall plant performance. Furthermore, it gives the user a platform to analyse different scenarios and provides uncompromised results that enable the user to make better design and operation decisions. The bio-augmentation batch enhanced (BABE) and struvite precipitation SSTPs, and plant performance indices i.e., effluent quality and operational cost indices, EQI and OCI, respectively, were incorporated into PPET to analyse case studies on South African plants. It was found that there are added benefits of using a SSTPs to mitigate the detrimental impacts of recycled DWL when the capacity of the plant has been exceeded. However, both BABE and struvite precipitation processes achieve different results based on the composition of the DWL that is being treated i.e., for DWL from an anaerobic digester treating waste activated sludge that is not P rich (with low EBPR), then the recommended SSTP operation would be BABE process rather than struvite precipitation. Due to the different treatment systems (i.e., with variations in influent loads, system configurations and priority end products required - energy, water, phosphorus, etc.), further investigations are required on strategies for implementation of the various SSTPs.
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    The effect of a large anoxic mass fraction and concentrations of nitrate and nitrite in the primary anoxic zone on low f/m filament bulking in nutrient removal activated sludge systems
    (1992) Musvoto, Eustina V; Ekama, George
    Filamentous bulking occurs when filamentous organisms are present in excessive numbers and extend from floes into the bulk solution. They interfere with the compaction and settling of the activated sludge either by producing a very diffuse floe structure or by causing bridging between floes. This results in a sludge with poor settleability i.e., low settling velocity and low solids concentration in the return activated sludge (RAS). In severe cases overflow of the sludge with the effluent occurs. Bulking not only causes these problems in the activated sludge process, but it also causes poor dewaterability of the waste activated sludge. Clearly bulking not only adversely affects the efficiency of the secondary settling tank but also the efficiency of the sludge treatment units at the plant. While controlling or eliminating bulking at plants will certainly be beneficial for sludge handling, by far the most significant impact would be on the activated sludge process itself. It has been estimated that if the sludge settleability could be controlled at Diluted Sludge Volume Indices (DSVI) below 100 me/g, 50 to 100% more wastewater could be treated in existing plants leading to enormous savings (Ekama and Marais, 1986a). This single factor is the principal driving motive behind the research to establish the causes and control of filamentous bulking.
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    The feasibility of augmenting the Stellenbosch potable water supply by establishing a direct potable reuse plant
    (2019) Raubenheimer, Murray; Ekama, George
    The Western Cape has suffered severe droughts over the past decade which has placed severe strain on raw water resources for both agriculture and municipal use. The crisis was due to many factors including climate change, increasing urbanisation and ageing infrastructure to name a few. The water scarcity problems will persist in the future globally unless water management authorities are able to augment existing raw water resources with a mix of desalination, groundwater and reclamation of treated effluent. The town of Stellenbosch was selected as part of a case study to determine the feasibility of implementing a direct potable reuse (DPR) plant to augment the future water resource mix from a technical, social, environmental and economic standpoint. Over the past two decades there has been a global shift towards direct and indirect potable reuse schemes to augment existing surface and groundwater resources. The shift has been accelerated by advances in treatment technology, water quality monitoring and research which have reduced the costs of potable reuse when compared to conventional water resources. The effluent from the Stellenbosch Wastewater Treatment Works was investigated as a reliable raw feed water source for the Stellenbosch DPR Plant. The Stellenbosch DPR Plant treatment train followed the multiple barrier approach to ensure high quality product water and mitigate potential risks to human health. The process design favoured granular activated carbon filtration instead of reverse osmosis due to the lower costs, inland location and brine disposal issues along with the acceptable total dissolved salt levels within the source water. The process design was developed further to determine the energy consumption, chemical consumption and process monitoring and control framework for the plant. A technical feasibility was done on three scenarios which were selected based on mix of reclaimed water and current surface water resources to supply the town of Stellenbosch with potable water. Scenario A – ‘do-nothing’ approach whereby the Stellenbosch Municipality would continue to be supplied with bulk raw water from the Theewaterskloof Dam treat it at the Paradyskloof WTW Scenario B – DPR Plant which produced potable water and injected it upstream of the Paradyskloof WTW Scenario C - DPR Plant which produced potable water and injected it downstream of the Paradyskloof WTW The research found that it would be feasible to implement a DPR scheme in Stellenbosch to improve the towns’ water security to meet future demands. The technical, social and environmental issues introduced in this research would need to be considered and developed further once a decision was made to pursue DPR. The unit costs of DPR would be higher than expanding the current raw surface water allocation and conventional water treatment works, which would have a knock-on effect on consumer tariffs. These economic costs would need to be compared to the towns risk exposure to climate change and water demands from surrounding areas within the Western Cape should they continue to abstract water from surface water resource not under their control.
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    Treating wastewater in a conventional activated sludge (CAS) system or a Membrane Bioreactor (MBR). A comparison of capital and operating costs
    (2020) Smith, Delwin; Ekama, George
    More and more focus is going into the establishment of more sustainable approaches for wastewater treatment (WWT) in South Africa, as well as around the world. Governments are beginning to enforce more economical solutions for WWT, which will have less impact on costs as well as land area requirements. Effective solid-liquid separation in biological wastewater treatment is an important step in the process as it has a major impact on effluent quality. Traditionally this has been achieved using Secondary settling tanks (SSTs) for liquid/solid separation in combination with a biological reactor (for biological degradation of organic matter). SSTs, however, require a large space, which becomes onerous on land requirements. In an immersed membrane bioreactor (iMBR), solid-liquid separation takes place by the wastewater passing through membranes. As the WW flows through, at the same time solids are rejected by the membranes. These membranes are immersed in the bioreactor. iMBR thus eliminates the requirement for SSTs and are becoming more widely used to treat various types of wastewater, due to the decreasing cost of membranes and the resultant reduced plant footprint. MBR is thus becoming an attractive solution to clients due to its sustainable approach. As part of this investigation, 2 types of MBR technology were included, the Kubota FS MBR system and the Zeeweed HF MBR system. As the design of a CAS is sensitive to sludge settleability, various DSVI values were looked at as part of the CAS system. Each system was configured in an MLE and UCT process. In summary, the following systems were included in this investigation: • CAS in an MLE configuration with DSVI of 100,150 and 200 • CAS in a UCT configuration with DSVI of 100,150 and 200 • iMBR using FS membranes in an MLE configuration • iMBR using FS membranes in a UCT configuration • iMBR using HF membranes in an MLE configuration • iMBR using HF membranes in a UCT configuration Each process configuration was designed and sized using the steady state models. Each configuration was then fully costed using actual construction prices from past and current projects. Costing of the MBR systems were done in conjunction with the membrane suppliers who also provided valuable design input. The selection of design MLSS in an MBR and CAS has a significant impact on the reactor and SST size. The MLSS concentration also has an impact on the alpha factor which influences aeration efficiency. As part of this investigation, an optimum MLSS concentration (MLSSopt) cost optimization was done taking into account the effect on reactor size, SST area, membrane area, and aeration CAPEX and OPEX. This resulted in an MLSSopt of 5 500 mg/l and 6 000 mg/l for the CAS MLE and CAS UCT respectively, and 10 000 mg/l for the Zeeweed MBR and Kubota MBR system. The CAS system had the lowest total cost (CAPEX+OPEX) of the 3 systems over a lifespan of 10 years, with the Zeeweed MBR having the 2 nd lowest cost coming in at 61% higher than the CAS system. The Kubota MBR had the highest total cost with a 203% higher cost than the CAS system. In terms of land area requirement, the Kubota MBR required the least amount of land area, followed by the Zeeweed MBR which required 12% more land space. The CAS system required 127-514% more land space at the various DSVI values than the Kubota system. This was due to the additional SST area and a larger reactor requirement.
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    Water treatment analysis guide
    (2019) Morrison, Wilke; Ekama, George
    The treatment of water up to potable/drinkable standards is a complex process, with many variables and parameters impacting on each other. In South Africa drinking water delivered to consumers must meet the requirements as recorded in the South African National Standards (SANS). Today, more so than ever, there are a number water sources that can be exploited and treated to provide safe drinking water, namely; surface water (dams and rivers), sea water, ground water and treated wastewater. The focus of this dissertation is on surface water; however, reference is made in the first sections with regards to sea water and ground water. The first step in designing a treatment process begins with analysis of the raw water source. Unfortunately, there is not a one size fits all approach and it is left up to the process engineer to find the correct method of investigation. This can be a daunting task, especially if lacking in experience and available information. The first part of this dissertation focusses on just that. It prescribes the method of sampling and aims to provide the reader with context on when to and what to test for. It goes further to suggest how the results may influence the process design and how certain contaminants can be removed. It also draws the attention to the sampling timeframe required, to obtain representative information, encompassing fluctuations in water quality. The second part of this dissertation describe the methods for designing a conventional water treatment system, comprising; aeration, coagulation, flocculation, dissolved air floatation, sedimentation, filtration and disinfection. It also comments on the water quality that warrants certain process steps to assist the process engineer in choosing the correct configuration. For most steps the design approach of two or more technologies are presented. This allows the process engineer to consider which technology best suits the application at hand. The design procedures are programmed into an, excel based, software model, which permits quick and easy design. A brief description of how the software model can be used is also covered. The results given by the software model is validated through a set of examples, appended to this document. Ultimately it is concluded that although this dissertation provides a guide for designing a treatment process it is not an encompassing tool that considers all the intricacies involved. That is, there are too many factors involved and considerations required, and cannot all be captured in one dissertation such as this. As such, it is finally recommended that any design attempts should be conducted by a suitably qualified and experienced process engineer that may use this dissertation to augment their design development.