Browsing by Department "Water Research Group"

Now showing 1 - 10 of 10
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    Open Access
    Advanced water metering and its application in low income communities
    (2017) Malunga, Masoabi; Van Zyl, Jakobus E
    In South Africa, it is a legislative requirement that all water supply points be metered (van Zyl, 2011). Conventional meters are mostly used as the main means of monitoring water consumption by South African municipalities. In the last two decades, the water metering industry has seen substantial developments with new capabilities added to the conventional water meter, known as advanced meters. These advanced water meters have capability of processing, storing and communicating data without the need of human intervention. As such they come with desirable capabilities for both consumers and municipalities. These include prepaid meters which are special type of advanced water metering technology that is mostly applicable in the low income areas of South Africa. However, advanced water meters have significant drawbacks, such as higher failure rates (due to electronics, batteries and more components), higher purchase and maintenance costs and susceptibility to tampering. It is therefore necessary to make a conscious and informed consideration when deciding on which metering technology to implement for different users. This could be achieved through having a technology evaluation framework. The goal of this research was to develop an evaluation framework to help municipalities in the selection of appropriate advanced water metering technologies for application in low income communities. This goal was achieved through: determining the range of functionality of technologies both available and under development for advanced water metering; documenting case studies of both successful and failed implementation of advanced water meters, including social perception and impacts; developing an evaluation framework that can evaluate advanced water metering; and evaluating on technical, social, economic and environmental grounds. The results from literature and case studies indicate that in low income communities, advanced water metering is mainly implemented for cost recovery purposes. However, some municipalities implement advanced metering schemes for water management and debt recovery. The most advanced water metering technology being installed in low income communities is prepaid meters. Prepaid meters have a potential to fulfill all the range of objectives that municipalities install advanced metering technology for. This technology is found to have high maintenance requirements due to high failure rate. For successful implementation, it is important that municipalities have adequate budget for repairs and maintenance or seek technical support from manufacturers.
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    Aggressive water attack on carbonated cement materials
    (1991) Mackintosh, Grant Stewart; Loewenthal, Richard Eric
    Aggressive attack on samples was monitored by measuring changes in chemical characteristics of the water exposed to cement concrete samples, inter alia pH, calcium and alkalinity. Over the period of the investigation (100 days) the following observations were found to apply to both brown and white water: (i) Generally uncarbonated OPC experiences significantly higher calcium mineral dissolution rates than both carbonated OPC and 30% fly ash OPC cement concretes. (ii) Once steady dissolution rates were attained, measurements indicated that 30% fly ash OPC and carbonated OPC concrete undergo closely the same calcium mineral dissolution rates. Before these findings are implemented, the following practical considerations need to be addressed: (i) An economic assessment of the benefits of using carbonated OPC, fly ash OPC and carbonated fly ash OPC as a means of resisting aggressive attack. (ii) The investigation should be upgraded from laboratory scale to pilot scale. (iii) The influence of accelerated carbonation on corrosion of steel reinforcing.
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    The development of an ancillary textile industry waste treatment process
    (1971) Greenblau, Norman; Marais, Gerrit van Rooyen
    The objective of this thesis is twofold - (1) to design the unit processes for treating the waste from a specific industrial plant using the best practicable technology, and (2) to critically examine the theory of these unit processes for utilization in design. The industrial waste was derived from a synthetic button and textile trimmings factory producing polyester and casein buttons. The effluent has a high pH and COD; contains metallic poisons; and is highly coloured. It exceeds the limitations for effluent quality promulgated by the Cape Town Municipality before discharge to the sewers. A certain measure of pretreatment before discharge to the sewers was therefore required. The treatment process eventually selected consists of neutralization; flocculation; sedimentation; sand filtration of the sludge; and atmospheric drying of the sludge.
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    The effect of sludge age and aerobic sludge mass fraction on low F/M filament bulking in intermittent aeration nitrogen removal systems
    (1991) Warburton, Charles Arthur; Ekama, George A
    Since 1989 a wide ranging program of research has been under way to identify the factors that effect low F/M filament proliferation. Completed work has established an important factor conducive to low F /M filament proliferation - the presence of anoxic and aerobic zones, or, alternating anoxic-aerobic conditions in a system. It was also established that the presence or absence of readily biodegradable COD (RBCOD) or slowly biodegradable COD (SBCOD) were not deciding factors in their proliferation. The research presented in this thesis focuses on the effects of; • sludge age, • magnitude of the aerobic mass fraction, • magnitude of the nitrate concentration during the anoxic period, on the low F /M filaments. The experimental set-up consisted of two intermittently. aerated anoxic-aerobic (20 minute cycles, peak DO 2 to 2,5 mgO/l), single reactor completely mixed continuously fed systems. The experimental investigation was chronologically divided into 3 phases and examined the effect of the following conditions on the low F/M filaments.
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    The effect of temperature on denitrification kinetics and biological excess phosphorus removal in nutrient removal activated sludge systems in temperate climates (12°C - 20°C)
    (1995) Pilson, Richard Adair; lowe
    Filamentous bulking in nutrient (N & P) removal activated sludge systems is a problem of considerable magnitude - three quarters of 45 plants surveyed were found to have bulking sludges to the extent that sludge settleability (DSVI) was adversely affected. If filamentous organism proliferation could be controlled and thereby sludge settleability improved to below DSVI of 100 ml/g, then with provision for factors such as additional aeration capacity, between 50% and 7 5% more wastewater could be treated in existing nutrient removing activated sludge plants. Anoxic-aerobic (AA) or low F/M filaments appear to proliferate in activated sludge plants that incorporate biological nitrogen removal. From earlier research, Casey et al. (1992a) showed that the cause for AA filament proliferation lay in the denitrification behaviour of the N removal systems. They hypothesized that filamentous and floe-forming organisms have different denitrification behaviour - the former reducing nitrate only as far as nitrite whereas the latter reducing nitrate all the way to nitrogen gas via the denitrification intermediates nitrite, nitric oxide (NO) and nitrous oxide (N₂O). If nitrate and nitrite removal to nitrogen gas is not complete in the anoxic reactor, then, when conditions become aerobic, the accumulated denitrification intermediates, in particular NO, inhibit oxygen uptake in the floc-formers. The filaments do not experience this inhibition because by reducing nitrate only to nitrite, no denitrification intermediates accumulate in their cytoplasmic membrane and consequently they can successfully compete against the floe-formers and proliferate in the N removal systems. If denitrification is complete, no residual intracellular denitrification intermediates remain in the floc-formers. Therefore, when conditions become aerobic, the floc-formers are not inhibited in their oxygen uptake and can successfully compete against the filamentous organisms which cause the bulking.
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    Engineering aspects of calcium carbonate and magnesium hydroxide precipitation in waste water reclamation
    (1978) Wiechers, Hermannus Nikolaas Sybrandus; Marais, Gerrit van Rooyen
    This thesis attempts to resolve some of the major problems associated with lime treatment in waste water reclamation. The contribution to knowledge is briefly outlined below. One of the major problems associated with lime treatment is the instability of lime-treated effluent, which may result in serious calcium carbonate scale formation problems. In the thesis this instability is attributed to two fundamental causes, (1) Incomplete precipitation, i.e. a kinetic problem. (2) The unintentional absorption of carbon dioxide from the air by the highly alkaline lime-treated effluent, i.e. a contamination problem. Calcium carbonate and magnesium hydroxide precipitation are time dependent. As a consequence of this time dependency unstable effluent may be produced under reaction conditions commonly encountered in practice. An exhaustive study identified the major factors affecting the precipitation kinetics. Reaction system conditions required for producing a stable effluent are, (1) Lime slurry and sludge, in that sequence, must be thoroughly mixed with the waste water, preferably by means of in-line static mixers, before discharge to a completely stirred tank reactor. (2) A completely stirred tank reactor with a minimum mean residence time of two minutes must be provided for the dissolution and precipitation reactions to go as near to completion as possible. (3) The reactor contents must have a sludge concentration of the order of 10 000 mg l⁻¹.
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    An experimental investigation of leakage flow paths in soil surrounding leaks in water distribution systems
    (2017) Teeluckdharry, Sahil; Van Zyl, Jakobus E
    Over the last few decades, water stress has been imminent in most municipalities around the world. The problem of water losses from pipelines is a major concern due to the increasing demands. Leakage is normally responsible for a large percentage of water losses in distribution systems and results in enormous wastage of valuable resources and energy. Leaks may be developed in many forms and locations in the system and active leak detections are required to find and repair damaged pipes. Few studies have been done on the soil-leak interaction in real pipeline systems. Recent research have shown that the high velocity water jets entering the surrounding soil causes a fluidisation zone outside leaks. The fluidised zone of soil and water is responsible for dissipating most of the energy of the water jet from the pipe leak and thus, limiting the leak's ability to reach soil surface. In municipalities where active leak detections are not implemented, it is easier for municipalities to detect leaks if they appear on the surface and thus, it is crucial to understand the routes of water leaks and the factors causing them to appear above the ground. This study investigated the soil-leak interaction focusing mainly on factors affecting leakage flow paths in water distribution systems. An experimental set up was designed and built to study the different factors in a controlled environment. A series of experiments were performed where water jets from manufactured circular leaks were released in different trench set ups. Three main variables were investigated namely flow rate, leak orientation and in-situ soil to start understanding the movement of the leak flow as a preliminary study. The volumetric moisture content were measured using EC-5 moisture sensors at different locations in the tank to analyse the movement of leakage water and iPERLS smart water meters were used to measure the flow of water through the walls of the trench. The results of the experiments showed how much leakage water is actually lost through the side and bottom walls. The volumetric moisture content readings indicated the movement of the leak in the tank. The results of the study indicated that leak orientation has the greatest influence on the paths of the leaks. Also, the flow rate had to be increased to a very high value so that the leak appears above the sand surface. The permeability of the in-situ soil was found to have the least effect on the leakage flow paths.
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    The feasibility of implementing advanced metering technology in high income areas in South Africa
    (2017) Mwangi, Mburu; Van Zyl, Jakobus E
    Water is an important natural resource and a building block to all life on earth. However, substantial increase in water demand and consumption has led to numerous nations, including South Africa, to face water scarcity. Improved water demand management strategies and water monitoring approaches are imperative. In South Africa, it's a legal requirement for all water supply points to be metered. Currently, water flow is primarily measured by conventional meters. However, substantial developments have been noted in the last two decades where conventional meters with added capabilities (such as communication capabilities) added have been introduced. These meters are known as advanced water meters. These capabilities offer functions such as leakage detection and more immediate consumption feedback. However, advanced meters also have significant disadvantages such as require high start-up capital and are susceptible to higher failure rates than conventional meters. It remains to be seen if advanced metering technology is an appropriate technology to be adopted in South Africa. Due to the different dynamics of South Africa's income level groups, the metering application and effects will differ for each income level group. Therefore, the purpose of this study is to investigate the feasibility of implementing advanced metering systems in high income areas in South Africa. An evaluation framework was developed to gauge the viability of implementing advanced metering systems on four performance criteria; technical, economic, environmental and social. The composite indicator framework template was selected as it was not tailor made for a specific reason and could be adapted for this research. The necessary framework input parameter data were acquired from practitioners in the field through questionnaires and from literature. Due to lack of advanced metering case studies in South Africa (except for prepaid meter), literature from developed countries were used as proxies. The input data entailed details of the current metering system, advanced metering system and new conventional metering system with the later used as a control for comparative purposes. The typical high-income scenario was derived from typical input data. For each input parameter, there were value ranges from the low parameter value to high parameter value. These ranges were used to conduct the sensitivity analysis on the framework to access critical input parameters to the success or failure of implementation Implementing advanced metering systems in high income areas in South Africa was found to be less economically viable than conventional meters. This is due to the lack of needed infrastructure for advanced metering as well as high initial capital costs and high operating costs. Advanced meters however proved to be more environmentally viable than conventional meters as they offered higher reduction in consumption. However, the manner in which faulty batteries are disposed could lead to environmental damage. Social factors were considered negligible for high income areas as revolts to introduction to new meters arises from financial constraints that those meters might induce. Further research with more South Africa based case studies and smaller scale advanced metering systems has been recommended.
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    Primary sedimentation tank model with characterized settling velocity groups
    (University of Cape Town, 2020) Polorigni, Christian Leprince; Ikumi, David S; Ekama, George A
    Primary sedimentation involves the separation of solids and liquid in primary settling tanks (PSTs) of wastewater treatment systems. These physical processes are described by various settling conditions such as discrete and flocculent settling, along with other phenomena such as flocculation, coagulation, ammonification or hydrolysis. The modelling of primary sedimentation has often been overlooked because (i) it involves various intricacies that are difficult to replicate and (ii) primary sedimentation has been assumed to be an input to most of the main unit process models, including the activated sludge (AS) system and the anaerobic digestion (AD) models. Though there has been a wide range of proposed mathematical models to describe how PSTs function, the need to correctly disaggregate the total suspended solids (TSS) into realistic fractions of unbiodegradable particulate organics (UPO), biodegradable particulate organics (BPO) and inorganic settleable solids (ISS), remains. This is because PST models that are unable to correctly split the TSS into its characteristic components make incorrect assumptions. These assumptions lead to inconsistencies in predicting the compositions of the primary sludge (PS) that is fed to the AD unit and the settled wastewater (settled WW) that is treated in the AS system. Hence, it becomes difficult to correctly simulate the entire system (plant-wide) towards a holistic evaluation of system strategies. In this study, a realistic PST model was developed, with characterized settling velocity groups, within a plant-wide setting, for municipal wastewater. This involved the improvement of a current TSS-based model into a more accurate and realistic model that could account for the settling of raw wastewater particles. The model was therefore expected to predict the composition of the PS that is treated in the AD system and the composition of the settled WW that is going to the AS unit processes. This could be achieved by splitting the TSS into UPO, BPO and ISS fractions. In developing preparation of such a realistic PST model, the following objectives were established: 1. Disaggregate the TSS into realistic UPO, BPO and ISS fractions, by means of discrete particle settling modelling (Kowlesser, 2014) and the particle settling velocity distribution (PSVD) approach of Bachis et al. (2015). 2. Verify that the model is internally consistent with wastewater treatment plant (WWTP) data, by means of mathematical material mass balances and other specific scenarios. 3. Demonstrate the application and impact of such a model by performing steady state plant-wide simulations. Using the discrete particle settling approach of Kowlesser (2014), a discrete particle settling model was developed in Microsoft Excel and implemented into a dynamic PST framework in WEST® (Vanhooren et al., 2003). The discrete particle settling model was described using steady state and dynamic calculations and the insights obtained from these calculations were implemented in the current TSS-based PST model of Bachis et al. (2015). This was performed towards developing the University of Cape Town Primary Sedimentation Unit (UCTPSU). The influent raw wastewater TSS was fractionated into UPO, BPO and ISS fractions and settling proportions of these fractions were assigned to five settling velocity groups. In addition, a distinct settling velocity was assigned to each settling velocity group. Previous studies data from WRC (1984) and Ekama (2017), were used in the discrete particle settling model, which was able to reproduce PS and settled WW outputs, through steady state and dynamic calculations and under strict material mass balances. As a result, UPO, BPO and ISS settling proportions as well as settling velocities, were extracted from these calculations and used as input parameters into the UCTPSU model. This dynamic model was rigorously verified to be internally consistent with regards to strict material mass balances. The verification scenarios also included variations of high and low settling velocities as well as a combination of both high and low velocities and checking that the model was behaving as expected. The application and impact of the UCTPSU model were demonstrated using plant-wide scenarios in proposing a preliminary integration, under steady state conditions. It showed how incorrect disaggregation of the TSS into UPO, BPO and ISS fractions can lead to incorrect predictions in terms of the settled WW composition, the AS system capacity, the effluent quality, as well as the energy consumption and generation in the AS system and AD unit respectively. The investigation also revealed the need to measure key wastewater parameters such as particle settling velocities and the unbiodegradable particulate COD fraction, when it comes to realistically modelling of primary sedimentation of municipal wastewater, with the view of optimizing plant operations and tactical decision making. The study thereafter recommended the need to conduct an extensive experimental campaign to measure in-situ diurnal data, mainly in terms of settling velocities and settling proportions of UPO, BPO and ISS. It was also suggested to use the settleometer as a tool to extract these settling velocities and settling proportions, after performing biodegradability tests. As such, the data collected from the experimental campaign and the biodegradability tests could be used in calibrating the UCTPSU model and validation could be undertaken by means of full plant scale data.
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    The removal of nitrogen and phosphorus in anoxic-aerobic digestion of waste activated sludge from biological nutrient removal systems
    (2015) Vogts, Michelle; Ekama, George A
    Biological nutrient removal (BNR) activated sludge systems (designed and operated with an additional function of biologically removing nitrogen and phosphorus) produce a waste activated sludge (WAS) that is rich in nitrogen (N) and phosphorus (P). When digested, this nitrogen and phosphorus are released, producing a dewatering liquor high in ammonia or nitrate and phosphate. Not only does this dewatering liquor need to be treated, but the phosphate also precipitates in the digester and surrounding pipework, resulting in loss of digester capacity and pipe blockages. This investigation studies anoxic-aerobic digestion (aerobic digestion with intermittent aeration), as an alternative digestion of BNR WAS. Aerobic digestion is simple to operate – being an extension of the activated sludge process, requiring aeration and limited recycling. This compared with anaerobic digestion which is complex to operate requiring airtight containers with fire risk, heating and much recycling. In anoxic-aerobic digestion, the nitrogen is removed by nitrification-denitrification, which has the added advantages of reducing the digester's oxygen demand and recovering some of the alkalinity lost in nitrification. Phosphate is precipitated in the digester - a convenient location. This results in a digester dewatering liquor low in nitrogen and phosphorus (<5 mgNH₄-N/l, <15 mgNO₃- N/l and 20 to 30 mgPO₄-P/l) that can be returned to the activated sludge plant without overloading it.