Browsing by Department "Urban Water Management"

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    Open Access
    Case study review of advanced water metering applications in South Africa
    (2017) Ngabirano, Lillian; Van Zyl, Jakobus E
    Advanced water metering is part of a much larger movement towards smart networks and intelligent infrastructure. However, where advanced metering technology is focused more towards the need to obtain meter readings without human intervention in other parts of the world, in South Africa and other developing countries, advanced water metering (in the form of prepaid meters or water management devices) has been developing along a parallel path, driven by the need to provide services to previously unserved communities and deal with the problems caused by rapid urbanisation. In this report, conventional water metering is defined as systems using water meters that display their readings on the meters themselves and advanced water metering as systems that add additional components or functionality to a metering system. Advanced metering has the potential to provide substantial benefits if appropriately applied. However, compared with conventional metering, these systems are considerably more expensive and complicated, and often rely on technology that is still being developed. Advanced metering systems therefore carry a higher risk of failure, poor service delivery and financial losses unless the system is implemented with careful design and thorough planning. This report describes a number of case studies of the application of advanced metering in South Africa. The case studies were evaluated according to the evaluation framework described in Appendix A and their detailed evaluations are included in each relevant chapter. Evaluations were done in four areas: technical, environmental, social and economic. The technical evaluation is based on the systems complying with the relevant national metering standards and good metering practice, the environmental evaluations on battery disposal and water savings and the social evaluation on broad socio-economic indicators. It should be recognised that social issues are particularly complex and that no general evaluation framework can accurately predict whether an advanced metering system will be accepted by a particular community. The economic evaluations were based on reductions of the current system cost and not absolute values. Economic performance indicators included the effective surplus (income minus expenses over averaged over the meter service life) and capital repayment period. An overview of lessons learned and conclusions from the case studies are provided in Chapters 8 and 9 of the report.
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    Open Access
    Characterization of municipal waste waters
    (1995) Mbewe, Alfred; Mbewe, Alfred; Wentzel, Mark C
    Over the past 20 years there have been extensive developments in the activated sludge method of treating wastewater. The functions of the single sludge system have expanded from carbonaceous energy removal to include progressively nitrification, denitrification and phosphorus removal, all mediated biologically. Not only has the system configuration and its operation increased in complexity, but concomitantly the number of biological processes influencing the system performance and the number of compounds involved in these processes have increased. With such complexity, designs based on experience or semi-empirical methods no longer will give optimal performance; design procedures based on more fundamental behavioural patterns are required. Also, it is no longer possible to make a reliable quantitative, or sometimes even qualitative prediction as to the effluent quality to be expected from a design, or to assess the effect of a system or operational modification, without some model that simulates the system behaviour accurately. To address these problems, over a number of years design procedures and kinetic models of increasing complexity have been developed, to progressively include aerobic COD removal and nitrification (Marais and Ekama, 1976; Dold et al., 1980), anoxic denitrification ( van Haandel et al., 1981; WRC, 1984; Henze et al., 1987; Dold et al., 1991) and anaerobic, anoxic, aerobic biological excess phosphorus removal (Wentzel et al., 1990; Wentzel et al., 1992; Henze et al., 1995). In terms of the framework of these design procedures and kinetic models, the influent carbonaceous (C) material (measured in terms of the COD parameter) is subdivided into a number of fractions - this subdivision is specific to the structure of this group of models. The influent COD is subdivided into three main fractions, biodegradable, unbiodegradable and heterotrophic active biomass. The unbiodegradable COD is subdivided into particulate and soluble fractions based on whether the material will settle out in the settling tank (unbiodegradable particulate) or not (unbiodegradable soluble). The biodegradable material also has two subdivisions, slowly biodegradable (SB COD) and readily biodegradable (RBCOD); this subdivision is based wholly on the dynamic response observed in aerobic (Dold et al., 1980) and anoxic/aerobic (van Haandel et al., 1981) activated sludge systems, that is, the division is biokinetically based. Thus, as input to the design procedures and kinetic models, it is necessary to quantify five influent COD fractions, that is, to characterize the wastewater COD. From a review of the literature on existing tests to quantify the COD fractions, it was evident that the existing procedures are either too elaborate or approximate or sometimes not even available. This research project addresses these deficiencies. In this research project, the principal objective was to develop simple accurate procedures to quantify the influent wastewater COD fractions. A batch test method has been developed to quantify the five influent COD fractions; namely heterotrophic active biomass, readily biodegradable COD, slowly biodegradable COD, unbiodegradable particulate COD and unbiodegradable soluble COD. Also, the physical flocculation-filtration method of Mamais et al. (1993) to quantify RBCOD has been evaluated and refined.
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    Critical assessment of right to safe water and sanitation in a South African informal settlement: a case study of Marikana, Cape Town
    (2018) Danti, Ntomboxolo; Sanya, Tom
    The Bill of Rights in the Constitution of South Africa mandates the promotion of human dignity, equality, and freedom. To attain these three mentioned aspects, the Bill of Rights stipulates that every person has the right to safe water and sanitation and this is done to improve the welfare of every citizen. South Africa has approximately 13% (7.27 million) of its population staying in informal settlements. Most of these informal settlements were formulated during the land invasion and so on and has since been increasing throughout South Africa. This study sought to assess whether informal dwellers have access to safe water and sanitation, what is the state of the water and sanitation facilities. The assessment was conducted in terms of the Bill of Rights in the Constitution of South Africa and WHO. Marikana informal settlement in Cape Town was used as a case study. Safe water and sanitation to all remain a challenge in South Africa, notwithstanding the commendable efforts since 1994, to provide access to safe water and sanitation as a right to all people. Based on empirical findings and analysis of relevant documents, the study views the water and sanitation in SA informal settlements as unsafe. The sanitation facilities are inadequate thus contributing to existing open defecation. The coverage of the water and sanitation facilities is not enough, therefore, compromising the right to access safe water and sanitation. The findings show evidence of non-operational water supply infrastructure. The uncleanliness of the existing sanitation facilities contributes to health issues like water-borne diseases. The sanitation facilities lack the human right factor, for an example, facilities are not designed to accommodate the elderly and physical disable people. Though South Africa made commendable progress in providing access to water and sanitation nationally, the inequality in the provision of safe water and sanitation exists; there is lack of freedom due to the poor safety of public facilities and overcrowded settlements, and the protection of human dignity is still an issue in informal settlements. In general, while the study identifies the existence of comprehensive national legislative and policy frameworks in support of providing safe water and sanitation in informal settlements, there are various challenges such as availability of land, inadequate housing, policy implementation, infrastructure maintenance and so on, that hinder the right to safe water and sanitation and has a possibility to hinder the fulfillment of South Africa's vision 2030 goal to provide access to piped water and flush toilets by all people.
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    Feasibility of groundwater abstraction and treatment for urban water supply
    (University of Cape Town, 2020) Blignault, Samantha Paige; Randall, Dyllon
    Water is one of Earth's most valuable resources and one of Earth's most threatened resources. Continuously increasing population growth coupled with changing climate has resulted in the depletion of water sources. As a result, investigations into alternative water sources are being conducted worldwide. One such alternative water source is groundwater abstraction. Groundwater abstraction involves the abstraction of water from an underground source. The volume of water that can be sustainably abstracted is governed by legislation. Groundwater typically requires treatment before it can be distributed to the general population for use, and thus the implementation of large-scale groundwater abstraction projects involves large capital outlays, as well as monthly operational outlays. The feasibility into the implementation of large-scale groundwater abstraction projects is therefore of interest to stakeholders involved in the water supply industry. The lifecycle of a recently implemented large-scale groundwater abstraction project was analysed in order to determine its feasibility. The project was implemented by Drakenstein Municipality in the Western Cape in 2017. The project involved identifying groundwater abstraction points that could provide sustainable volumes of water. The water quality of each groundwater abstraction point was then investigated for any outlying parameters according to SANS 241-1:2015 guidelines for potable water. Groundwater abstraction water treatment plants were then designed in order to treat the combined sustainable flow rates of water at their specific water qualities. The treated water from each groundwater abstraction water treatment plant was then analysed in order to confirm compliance with the SANS 241- 1:2015 guidelines, before the booster pumps were commissioned and commenced with their continuous supply of potable water into the network. The capital expenditure associated with each of the groundwater abstraction water treatment plants was obtained from the Engineer, Aurecon. In addition, the estimated monthly operational expenditure was computed. These expenditures were used to determine the feasibility of the large-scale groundwater abstraction project by computing the payback period and comparing this period to the design life of each of the groundwater abstraction water treatment plants. In addition, the monthly savings applicable to the municipality as a result of the project's implementation was computed. Finally, the feasibility into varying flow rates of groundwater abstraction water treatment plants, and varying water quality of groundwater abstraction points was investigated. Two sites were identified within the municipal area, each with four groundwater abstraction points capable of delivering a combined 5.18 ML/day and 1.62 ML/day. These sites were identified as Boy Louw Sportsgrounds and Parys Sportsgrounds respectively. Although the sites were only 2.60 kilometres apart, the water quality of the combined flow rates indicated that the groundwater abstraction points were accessing two different water sources. The combined sustainable flow rate at Boy Louw Sportsgrounds required turbidity, iron and manganese removal, as well as disinfection. The combined sustainable flow rate at Parys Sportsgrounds required turbidity removal and disinfection. Groundwater abstraction water treatment plants were then designed to treat the water at Boy Louw Sportsgrounds and Parys Sportsgrounds. Boy Louw Sportsgrounds involved the distribution of equipment across seven shipping containers, whilst Parys Sportsgrounds involved the distribution of equipment across three shipping containers. It was found that the groundwater abstraction project was feasible with a payback period of three years. This payback period fell well within the 10-year design life of each groundwater abstraction water treatment plant. In addition, it was found that the municipality would be subject to a 72% monthly saving in water costs as a result of utilising the groundwater abstraction water treatment plants, as opposed to purchasing water in bulk from the City of Cape Town. It was found that the payback periods of Boy Louw Sportsgrounds and Parys Sportsgrounds were two and five years respectively. Although Boy Louw Sportsgrounds delivered almost three times the potable water flow rate than that of Parys Sportsgrounds, its payback period was three years sooner. In addition, it was found that the municipal savings as a result of Boy Louw Sportsgrounds was 8% more than that of Parys Sportsgrounds. It was therefore concluded that the larger the flow rate of water to be treated, the more financially feasible the project. In addition, it was determined that the more water quality parameters lying above the upper limits of SANS 241-1:2015 guidelines for potable water, the more treatment processes would need to be implemented resulting in additional capital and operational expenditure. It was therefore concluded that the more water quality parameters requiring treatment, the less financially feasible the project. Finally, it was determined that the feasibility of the large-scale groundwater abstraction project is limited by the rate at which the municipality purchases water in bulk from the City of Cape Town. As long as the bulk water purchase tariff remains above R 2.85/m³, the project will remain feasible. Should the bulk water purchase tariff fall below this value, the project no longer remains feasible as the payback period of the project exceeds the design life of the groundwater abstraction water treatment plants.
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    Quantifying stormwater pollutants and the efficacy of sustainable drainage systems on the R300 highway, Cape Town
    (2017) Robertson, Abby Jane; Armitage, Neil P; Zuidgeest, Mark
    Stormwater provides a direct link between urban infrastructure and the urbanised natural environment. In particular, highway drainage presents a high risk of pollution when compared to other urban land use areas (Ellis et al., 2012); introducing heavy metals, suspended solids and hydrocarbons to urban waterways. This research investigated runoff from the R300 highway, located in the greater Cape Town area. The City of Cape Town Management of Urban Stormwater Impacts Policy requires the treatment and attenuation of stormwater from developments within the city, and proposes Sustainable Drainage Systems (SuDS) as a means to achieve this (CSRM, 2009b). SuDS are structural and process controls that attenuate surface drainage, improve runoff water quality, provide amenity and deliver ecosystem services. This study characterized the R300 runoff through a sampling program and modelling exercise in order to provide an indication of the ability of SuDS to manage highway runoff in South Africa. Sediment and runoff samples were collected from the road surface and an undeveloped parcel of land adjacent to the highway. The sampling results showed that heavy metals, suspended solids and phosphorus are present in significantly greater concentrations in road runoff compared to rainwater from the same area. The concentration of aluminium, copper, lead, zinc and phosphorus exceed the Department of Water and Sanitation's water quality guidelines for aquatic ecosystems in excess of 1000%. The concentration of heavy metals, phosphorus and fats, oils and greases was significantly greater in road sediment compared to sediment from the surrounding area. Barring copper, all contaminant concentrations in the road surface sediment are less than the maximum concentration required to protect ecosystem health. The R300 rainfall-runoff response was modelled in PCSWMM to evaluate the performance of SuDS such as infiltration trenches, bioretention areas and swales for managing highway runoff in terms of quantity and quality. The modelling exercise showed SuDS to be a viable means to attain the City of Cape Town's stormwater objectives, provided that SuDS are implemented in treatment trains along the entire road length.
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    Sustainability index for integrated urban water management (IUWM) in southern African cities : case study applications : Greater Hermanus region and Maputo City
    (2007) De Carvalho, Sheilla; Armitage, Neil P
    The critical situation in the water sector continues to jeopardize developmental principles and undermine strategies for poverty eradication. On the assumption that the failure in service provision can be largely attributed to an inability to holistically address all aspects of urban water management, a systems approach was used to develop a relevant and robust sustainability index which assesses the capacity of a city or a portion thereof to be sustainable. This thesis details the process of developing the Sustainability Index (SI) for a multidimensional assessment of urban water systems. In this research, an analysis of the current problems facing developing cities, particularly in Sub-Saharan countries, was undertaken. This was done so as to provide some insight into the current developmental issues hindering sustainable development. An examination of the urban water cycle was also carried out to illustrate the links within the cycle and between the various water uses and services. A process model was developed which addresses the multi-dimensionality of sustainability and the dynamism of urban water systems. This model combines aspects of the iterative procedure for assessing environmental sustainability introduced by Lundin et al. (2002) with the step-wise process proposed by Nardo et al. (2005).
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    Sustainable water governance: An incremental approach towards a decentralised, hybrid water system
    (2018) Faragher, Tamsin; Raxworthy, Julian
    Cape Town is experiencing its worst drought in recorded history. Notwithstanding that the Western Cape has always been a water scarce region, it is this current drought that has brought home the area’s inherent vulnerability and highlighted the governance issues. The world wherein South Africa’s water governance was created is very different to the world we find ourselves in today. It is a world of uncertainty and unpredictability not contemplated in water governance comprised of legislation, policy, guidelines and practice. The current water governance constructs a conventional approach based upon predictability and certainty and is no longer appropriate to meet today’s new challenges. Consistent with this conventional approach, Cape Town’s municipal water supply is almost completely dependent upon surface water which makes it even more vulnerable to drought than if its supply was comprised of a variety of water supply options. With surface water sources fully exploited and storage opportunities within the urban edge limited alternative water supply options must be more seriously considered and the water governance reformed to accommodate its use. Water governance is the focus of reform because it is the framework for infrastructure planning and therefore controls the resultant system, infrastructure and management. This thesis interrogates the current water governance as the starting point before firstly discussing the proposed incremental approach towards a decentralised, hybrid system for water infrastructure and secondly, identifying specific areas where intervention is necessary for implementation.
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    The dual digestion of sewage sludge using air and pure oxygen
    (1995) Pitt, Andrew James; Pitt, Andrew James; Ekama, George A
    Dual Digestion is a two-stage system that combines autothermal thermophilic aerobic pre-treatment with conventional anaerobic digestion. The practicability of the system using pure oxygen is well proven. Disadvantages are the high cost of the pure oxygen and the absence of a detailed evaluation of anaerobic digester performance. This report discusses the results of a full-scale investigation into the dual digestion system (184m³ aerobic reactor and 1800m³ anaerobic digester), carried out in two phases: In the first using air alone for oxygenating the aerobic reactor and in the second using a combination of air and pure oxygen. During both phases the performance of the anaerobic digester was also monitored, but in greater detail in the second phase as far as the final sludge product is concerned. In phase I, with air, it was possible to maintain thermophilic temperatures in the aerobic reactor throughout the year. However, the required retention times were relatively long (3-6 days) in comparison with the pure oxygen reactor (~1 day) due to the high vapour heat losses. At long retention times, the volatile solids (VS) destruction was appreciable (~25%) and the reactor tended towards an autothermal thermophilic digester. Foaming, although unpredictable in its occurrence, significantly improved aerobic reactor performance by doubling the oxygen transfer efficiency. From liquid and gas mass and heat balances it was found that the specific biological heat yield and respiration quotient were approximately constant at 12.8 MJ/kg(O₂) and 0. 70 mol(CO₂)/mol(O₂) respectively over a wide range of operating conditions and consistent relationships between VS removal, heat generation, and oxygen utilisation could be established. Based on information collected, it was concluded that increased treatment capacity and greater temperature control of the aerobic reactor could be provided by supplementing air oxygenation with pure oxygen. In phase II, using a combination of air and pure oxygen, much higher loading rates on the aerobic reactor were possible. Thermophilic temperatures could be maintained at short retention times (1-2 days). Unfortunately, no foaming occurred during this period. Consequently, the benefit of improved oxygen transfer efficiency of the air oxygenation system, produced by the foam, could not be exploited. Liquid and gas mass and heat balances confirmed the specific heat yield and respiration quotient values and the relationship between oxygen utilisation, VS destruction and biological heating. During phase II, the anaerobic digester operated at a retention time of ~10 days. The sensible heat content of the hot sludge from the aerobic reactor was sufficient to force the digester into the thermophilic temperature range. The stability of the anaerobic process and final sludge product at this short retention time was monitored with % VS removal and residual specific oxygen utilisation rate tests and found to be similar to that of conventional mesophilic anaerobic digestion at 20 days retention time. Dewaterability as reflected by the specific resistance to filtration (SRF) was found to be poor, but 11ot much worse than for conventional mesophilic digestion. Sufficient information was obtained during phases I and II to allow a mathematical model to be compiled, which could reasonably reliably simulate all the main operating parameters of the dual digestion system. The model provided a means for assessing different system configurations with mesophilic or thermophilic digestion, with and without heat exchange or gas engine external heat sources, allowing technical and economical (capital and operating) feasibility to be evaluated and compared with that for conventional digestion. From both the experimental and modelled results, all the claimed benefits of the dual digestion system were verified with the exception of the claim that aerobic reactor heat pre-treatment of the sludge allows the anaerobic digester to operate at short retention times (~10 days). However, the digester can be operated at 10 days retention provided its temperature is in the thermophilic range, in which case a sufficiently stable sludge is produced; at mesophilic temperatures, a retention time of 15 days or longer is required to produce a sludge of equivalent stability to that from conventional mesophilic digestion. Consequently, it is not the stability of the anaerobic process per se that governs the minimum retention time but the quality required for the final sludge product. The aerobic reactor is an appropriate pre-treatment stage for the thermophilic digester because it provides the necessary temperature and pH buffering to allow stable operation in the thermophilic range. It is concluded that where application of conventional anaerobic digestion is contemplated, whether for new installations or for upgrading existing plants, the dual digestion system should be seriously considered as a possible option. It competes favourably both technically and economically with conventional mesophilic digestion and produces a superior sludge product which can be beneficially utilised in agriculture.
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    The viability of rainwater and stormwater harvesting in the residential areas of the Liesbeek River Catchment, Cape Town
    (2015) Fisher-Jeffes, Lloyd Norman; Armitage, Neil P
    The sustainable provision of water to South African citizens is a significant challenge facing the country. In order to avert a crisis, municipalities will need to reduce their reliance on traditional water sources. Rainwater harvesting (RWH) and stormwater harvesting (SWH) are two alternative water resources that could supplement traditional urban water supplies. To date, the potential benefits of RWH and SWH within an urban setting have not been adequately considered or investigated in South Africa. The only way to quantify the benefits and potential viability of rainwater and stormwater harvesting was to select and model a representative catchment - the Liesbeek River Catchment, Cape Town South Africa was selected. An Urban Rainwater Stormwater Harvesting Model was developed to model the use of RWH and SWH in the catchment. Additionally, a Storm Water Management Model (SWMM) of the catchment was developed to investigate the stormwater management benefits of RWH and SWH. The study found, inter alia, that: RWH was viable for only a minority of property owners; climate change would have limited impact on the performance of RWH systems; and RWH is an unreliable - even for small storm events - means of attenuating peak flows. On the other hand, SWH has the potential to reduce potable water demand in the Liesbeek River Catchment by up to 20%. However, for SWH to be viable there would need to be a high level of adoption by residents, at least for non-potable uses such as flushing toilets and outdoor irrigation. SWH is also of benefit in the attenuation of peak flows during storm events. Finally, the research found that the implementation RWH and SWH together would be unwise, as both are most cost-effective under conditions of maximum demand. The study concluded that SWH could be a viable alternative water resource for urban residential areas in South Africa - depending on the scale at which it is implemented, the end use for which it is utilised, and the population density that drives the water demand. RHW, on the other hand, has limited potential - depending on climatic conditions; it may, for example, be viable in areas with year-round rainfall.
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    The viability of using the stormwater ponds on the Diep River in the Constantia Valley for stormwater harvesting
    (2017) Rohrer, Alastair, R; Armitage, Neil P
    Harvesting stormwater to supplement water demands has attracted a growing interest in South Africa as concerns over the security of the country's water supply increase. Whilst stormwater harvesting has been shown to offer a viable alternative water resource, there are often concerns about its storage requirements due to space constraints in urban areas. Stormwater ponds offer a potential solution to these concerns. Since stormwater ponds are typically designed for the sole responsibility of attenuating the periodic peak stormwater flows that are associated with large storm events, they often remain underutilised. By introducing Real Time Control (RTC) systems to operate stormwater pond outlets, ponds could potentially be used to store stormwater. This could increase the benefits that stormwater ponds provide as well as offer a viable alternative water resource. To investigate the economic viability of harvesting stormwater from existing stormwater ponds, a case study was performed on a representative urban catchment – the Diep River subcatchment, located in Cape Town, South Africa. The catchment contains seven stormwater ponds, which could be retrofitted for harvesting purposes. Sixteen different stormwater harvesting scenarios were developed that modelled various non-potable demands in the vicinity as well as different storage and harvesting arrangements, created using RTC strategies, of the catchment's existing ponds. These scenarios were modelled using an assortment of modelling tools which include: a catchment stormwater model; water distribution network models; and a Life Cycle Cost Analysis (LCCA). The economic viability of harvesting stormwater from the Diep River subcatchment's stormwater ponds was most susceptible to the cost of the system's water distribution infrastructure. Consequently, stormwater harvesting was most economically viable if used to supply toilet, clothes washing and irrigation demands to residential properties situated in close vicinity to the system's harvesting pond as this minimised the extent of the water distribution network. The results also revealed that distributing storage amongst ponds situated throughout the catchment is an effective method of increasing the volume of stormwater a stormwater harvesting system could yield without reducing its economic viability. However, this is on the condition that the system only extracts stormwater from the most downstream pond in the catchment. Importantly, the study also revealed that the attenuation of peak flows of large storm events (up to 1-in-20 year return period), achieved when harvesting stormwater from the existing stormwater ponds would be comparable to what the ponds currently provide. The study concluded that harvesting stormwater from existing stormwater ponds is potentially viable. It also demonstrated an effective method to maximise a catchment's storage capacity using distributed storage. For stormwater harvesting to be viable however, stormwater should be used to supplement a large percentage of non-potable end-uses and requires significant uptake amongst catchment residents.