Water SA https://www.ajol.info/index.php/wsa <p>This journal publishes refereed, original work in all branches of water science, technology, engineering and policy. &nbsp;This includes: water resource development; the hydrological cycle; surface hydrology; geohydrology, hydropedology and hydrometeorology; limnology; freshwater and estuarine ecology; salinisation; treatment and management of municipal and industrial water and wastewater; treatment and disposal of sewage sludge; environmental pollution control; environmental and drinking water quality; drinking water treatment; water services, including domestic water supply and sanitation services; agricultural water; aquaculture in terms of its impact on the water resource; water policy and governance; water economics; water as a social good.&nbsp; <em>Water SA</em> is intended to serve both international and Southern African readers and authors. &nbsp;Contributions which are not of broad international interest must make a specific contribution to Southern Africa (defined for this purpose to include the countries of South Africa, Swaziland, Lesotho, Namibia, Botswana, Zimbabwe and Mozambique). &nbsp;Submissions of predominantly local interest outside of Southern Africa will not be considered.</p> <p>&nbsp;</p> <p>Contributions may take the form of a paper, a critical review, a short communication, a rapid communication, a technical note or comments on papers already published. &nbsp;A <strong>paper </strong>is a comprehensive contribution to the subject, including introduction, experimental information and discussion of results. &nbsp;(Technical accounts involving application of well-known techniques, and situation assessment/observation/sampling papers reporting results of work not carried out as a research activity, cannot be considered.) &nbsp;A <strong>review </strong>is an authoritative, critical account of recent and current research in a specific field to which the author has made notable contributions. &nbsp;A <strong>short communication </strong>is a concise account of new and significant findings to inform readers of preliminary or limited research results. &nbsp;A <strong>rapid communication </strong>is an original contribution which merits prompt publication to publicise the findings of very recent research with immediate significance. &nbsp;A <strong>technical note </strong>describes an original process or technique without necessarily including extensive data, theory or critical evaluation. &nbsp;<strong>Comments </strong>on papers already published are sent to the authors of the paper for reply and both the comments and the authors’ reply will be published in the upcoming issue of <em>Water SA</em>. Preference is given to concise contributions.</p> <p style="line-height: 140%; background: white;">Other websites related to this journal: <span style="line-height: 140%; font-family: Arial; color: #111111; font-size: 9.5pt;"><a href="http://www.wrc.org.za/" target="_blank" rel="noopener"><span style="color: #337755;">http://www.wrc.org.za </span></a></span></p> <p style="line-height: 140%; background: white;"><em><span style="line-height: 140%; font-family: Arial; color: #111111; font-size: 9.5pt;">WaterSA</span></em><span style="line-height: 140%; font-family: Arial; color: #111111; font-size: 9.5pt;"> is also available electronically through SABINET Online&nbsp;<a title="http://reference.sabinet.co.za/sa_epublication/waters" href="http://reference.sabinet.co.za/sa_epublication/waters" target="_blank" rel="noopener">http://reference.sabinet.co.za/sa_epublication/waters</a></span></p> en-US Copyright for articles published in this journal is retained by the Water Research Commission. watersa@wrc.org.za (Water SA Editor) watersa@wrc.org.za (Ms Tamsyn Sherwill) Wed, 12 May 2021 10:01:56 +0000 OJS 3.1.2.4 http://blogs.law.harvard.edu/tech/rss 60 Optimizing water and resource recovery facilities (WRRF) for energy generation without compromising effluent quality† https://www.ajol.info/index.php/wsa/article/view/207044 <p>The primary separation unit (PSU) splits the organic load on the water and resource recovery facility (WRRF) between the primary sludge (PS) anaerobic digester (AD), where energy can be generated, and the biological nutrient removal (BNR) activated sludge (AS) reactor, where energy is consumed. With a CHONP element massbalanced plant-wide stoichiometric and kinetic steady-state model, this paper explores quantitatively the impact of four cases of increasing organics removal efficiencies in the PSU on (i) settled wastewater characteristics, (ii) balanced solids retention time (SRT) of the Modified Ludzack-Ettinger (MLE) and University of Cape Town/ Johannesburg (UCT/JHB) systems for lowest economical effluent N and P concentrations, (iii) reactor volume, (iv) energy consumption for aeration, pumping and mixing, (v) energy generation by AD of PS and waste activated sludge (WAS), (vi) N&amp;P content of the PS and WAS AD dewatering liquor (DWL) and (vii) final effluent N and P concentrations with and without enhanced biological P removal (EBPR), and looks for an optimum WRRF layout for maximum energy recovery without compromising effluent quality. For the low biogas yield from the WAS AD, decreasing as the SRT of the BNRAS system gets longer and with the added complexity of N&amp;P removal from the digested sludge DWL, makes AD of WAS undesirable unless P recovery is required. Because the wastewater&nbsp; biodegradable particulate organics (BPO) have a low N&amp;P content, it is better to divert more biodegradable particulate organics to the PSAD with enhanced primary separation than digest WAS – the PSAD DWL can be returned to the influent with relatively small impact on final effluent N and P concentration. </p> George A. Ekama Copyright (c) https://www.ajol.info/index.php/wsa/article/view/207044 Wed, 12 May 2021 00:00:00 +0000 Performance intensification of the coagulation process in drinking water treatment https://www.ajol.info/index.php/wsa/article/view/207049 <p>Surface water pollution has increased, owing to industrial development and population growth. Consequently, it is important to find alternative drinking water treatment strategies, which cater for changes in the quality of raw water. This study compared the efficiency of different coagulants in treating raw water that feeds a drinking water treatment plant (WTP). Using jar testing equipment and a number of physicochemical parameters, an investigation was conducted to establish optimum conditions for aluminium chloride (A),&nbsp; ferric chloride (B), and chitosan (C), and their performance compared with aluminium sulphate (D), which is the coagulant used at the WTP. The turbidity removal efficiencies for the single coagulants were in the order: B (95.7%) &gt; A (94.7%) &gt; C (94.4%), at optimum coagulant doses of 60, 50, and 0.6 mg/L, respectively. The coagulants achieved high removal efficiencies for turbidity, total dissolved solids (TDS), ultraviolet absorbance at 254 nm (UV254) and conductivity under acidic conditions. For dual coagulants, there was a&nbsp; gradual increase in the removal efficiencies of the tested parameters with increasing pH. Combined coagulants were more effective compared to single coagulants, with highest removal efficiencies being exhibited by the A/C combination. Overall, the coagulants proved to be suitable alternatives to D, since they had comparable performances. </p> Nhamo Chaukura Copyright (c) https://www.ajol.info/index.php/wsa/article/view/207049 Wed, 12 May 2021 00:00:00 +0000 Can CHIRPS fill the gap left by the decline in the availability of rainfall stations in Southern Africa? https://www.ajol.info/index.php/wsa/article/view/207050 <p>Rainfall is the most important input to any hydrological or water resources study. The decline in the number of suitable rainfall stations since the 1970s is a cause for concern, plus there is an additional complication in that – for a number of catchments – mean annual precipitation (MAP), as derived from a recent study by Pegram, differs substantially from those adopted by the Water Resources of&nbsp; South Africa, 2012 study (WR2012) (mostly as derived by Dent). Rainfall data sourced by the Climate Hazards Group InfraRed&nbsp; Precipitation with Station data (CHIRPS) satellite database was selected as a basis for comparison, both for catchment MAP and time series of monthly rainfall as used for input to the Pitman hydrological model (WRSM/Pitman, previously called WRSM2000). The analyses revealed that the WR2012 method of constructing the time series yielded the best results overall, but the difference was not marked, except in the winter rainfall region, where CHIRPS (and to a lesser extent, Pegram) performed poorly. It is concluded that CHIRPS will have a role to play in future water resources studies. It is recommended that the study be extended to cover a larger sample of catchments with up-to-date rainfall and that the possibility of CHIRPS data being recalibrated for the winter rainfall area be investigated. </p> W.V. Pitman Copyright (c) https://www.ajol.info/index.php/wsa/article/view/207050 Wed, 12 May 2021 00:00:00 +0000 Assessing the frequency of drought/flood severity in the Luvuvhu River catchment, Limpopo Province, South Africa https://www.ajol.info/index.php/wsa/article/view/207051 <p>The Luvuvhu River catchment experiences rainfall variability with a high frequency of extremely dry and wet conditions. Understanding the frequency of drought and floods in this catchment area is important to the agriculture sector for managing the negative impacts of these natural hazards. This study was undertaken to investigate the frequency and severity of drought/floods and linkages with the El Niño Southern Oscillation (ENSO) phenomenon. Poor and resource-limited small-scale farmers in the Luvuvhu River catchment area struggle to adjust due to decreasing crop yields and livestock mortality caused by drought and floods. Monthly rainfall data from 15 grid points (0.5° × 0.5°) was used to compute the Standardised Precipitation Index (SPI) for the period between 1979 and 2016. The 3-month SPI was calculated for the December–January– February (DJF) period. The second half of the agricultural season was selected because the influence of ENSO is high during the late summer season (DJF) in the catchment. The SPI results indicate that the&nbsp; agricultural seasons 1982/83, 1991/92 and 2015/16 were characterised by extreme drought. Conversely, the SPI values also show that the wettest seasons were recorded in 1998/99 and 1999/00. The catchment experiences a high frequency of moderate to severe drought in the north and north-eastern parts. Spatially, the occurrence of moderate to severe dry conditions covers large areas in the north and south-western parts. Severe to extreme wet conditions cover large areas in the north and south-eastern parts of the catchment. The SST index (Niño 3.4) shows a strong influence on rainfall variability in the catchment, resulting in either dry or wet conditions. Therefore, this study recommends further research focusing on more climatic modes that influence rainfall variability, as well as further development of drought and flood forecasting to improve farmers’ adaptations options and reliability of weather forecasts used as a tool to manage crop production. </p> <p>&nbsp;</p> S.M. Mazibuko, G. Mukwada, M.E. Moeletsi Copyright (c) https://www.ajol.info/index.php/wsa/article/view/207051 Wed, 12 May 2021 00:00:00 +0000 The effect of veld fires on the hydrological response of streamflow https://www.ajol.info/index.php/wsa/article/view/207052 <p>Veld fires are natural occurrences with the potential to impact thousands of hectares of vegetation, and in doing so, changes soil characteristics, for both urban and rural areas. It is therefore reasonable to assume that the hydrological response of a catchment could be affected by fire. The main aim of this research was to investigate the hydrological changes caused by fire on a catchment scale using a case study. On 9 March 2015, a wildfire which started in Jonkershoek nature reserve destroyed indigenous fynbos vegetation and afforested areas. Within the nature reserve, there are multiple rainfall and runoff stations, which provided a means of measuring any possible hydrological changes due to these fire events. Four catchments were used for this research, one main catchment (fynbos area) and three sub-catchments (afforested areas). Fifty-six percent of the main catchment burned, while two sub-catchments were completely burned and the other primarily unaffected by the fire. The main catchment’s hydrological response was analysed by&nbsp; comparing the hydrographs of comparable pre- and post-fire runoff events. Eighteen comparable events were used for the analysis. The mean runoff volume increased by approximately 7% after the fire and mean peak flow by 50%. The change was even more noticeable when comparing the two sub-catchments affected by the veld fire and the unburned sub-catchment with each other. All the sub-catchments were similar in size and were located close enough to each other to be represented by one rainfall station. Before the fire, the average daily streamflows between the unburned (control) and burned catchments were similar; however after the fire the<br>average daily streamflow of the two burned catchments in comparison to the control catchment increased by 45% and 50%, respectively. The mean runoff volume from the two affected/burned catchments, after the fire, for individual events increased by approx. 72% and 52% in comparison to the control catchment. The mean peak flows increased by approximately 173% and 110% in comparison to the control catchment.</p> J.A. du Plessis, H. van Zyl Copyright (c) https://www.ajol.info/index.php/wsa/article/view/207052 Wed, 12 May 2021 00:00:00 +0000 The use of Radon (Rn<sup>222</sup>) isotopes to detect groundwater discharge in streams draining Table Mountain Group (TMG) aquifers https://www.ajol.info/index.php/wsa/article/view/207053 <p>Environmental isotopes have been used for decades as natural tracers in studies aimed at understanding complex hydrogeological processes such as groundwater and surface water interactions. Radon (Rn<sup>222</sup>) is a naturally occurring, radioactive isotope which is produced from radium (Ra<sup>226</sup>) during the radioactive decay series of uranium (U<sup>238</sup>). Since U<sup>238</sup> is present in most geological substrates, Rn<sup>222</sup> is produced in various lithological structures and subsequently transported with groundwater through fractures and<br>pore spaces in an aquifer towards surface water discharge points in rivers and springs. This study aimed to determine (i) the concentration of Rn<sup>222</sup> within both surface water and groundwater in Table Mountain Group (TMG) aquifer systems, and (ii) the feasibility of using Rn<sup>222</sup> isotopes as a natural tracer in groundwatersurface water interaction studies. This study was conducted in a highly fractured TMG aquifer system near Rawsonville, South Africa. Surface water from two perennial rivers (i.e. Gevonden and Molenaars), together with groundwater from a nearby borehole, were sampled and their corresponding Rn<sup>222</sup> concentrations measured. Our study found median Rn<sup>222</sup> concentrations in the Gevonden River of 76.4 Bq∙L<sup>-1</sup> and 67.2 Bq∙L<sup>-1 </sup>in the dry and wet seasons, respectively. Nearly 12% of surface water samples exceeded 100 Bq∙L<sup>-1</sup>. These abnormally high Rn<sup>222</sup> concentrations can only be attributed to the influx of groundwater with extremely high Rn<sup>222</sup> concentrations. Under ambient (no pumping) conditions, Rn<sup>222</sup> concentrations in groundwater range between 130–270 Bq∙L<sup>-1</sup>. However, when the borehole was pumped, and inflowing water from the surrounding aquifer was sampled, even higher Rn222 concentrations (391–593 Bq∙L<sup>-1</sup>) were measured. These extremely high<br>Rn<sup>222</sup> concentrations in groundwater are believed to be attributed to the underlying granitic geology and the prevalence of faults. The use of Rn222 isotopes as an environmental tracer in groundwater–surface water interaction studies is therefore regarded as a feasible option in similar highly fractured aquifer systems.</p> T. Strydom, J.M. Nel, M. Nel, R.M. Petersen, C.L. Ramjukadh Copyright (c) https://www.ajol.info/index.php/wsa/article/view/207053 Wed, 12 May 2021 00:00:00 +0000 Integration of ANFIS with PCA and DWT for daily suspended sediment concentration prediction https://www.ajol.info/index.php/wsa/article/view/207054 <p>Quantifying sediment load is vital for aquatic and riverine biota and has been the subject of various environmental studies since sediment plays a key role in maintaining ecological integrity, river morphology and agricultural productivity. However, predicting sediment concentration in rivers is difficult because of the non-linear relationships of flow rates, geophysical characteristics and sediment loads. It is thus very important to propose suitable statistical methods which can provide fast, accurate and robust prediction of suspended sediment concentration (SSC) for management guidance. In this study, we developed coupled models of discrete wavelet transform (DWT) with adaptive neuro-fuzzy inference system (ANFIS), named DWT-ANFIS, and principal component analysis (PCA) with ANFIS, named PCA-ANFIS, for SSC time-series modeling. The coupled models and single ANFIS model were trained and tested using long-term daily SSC and river discharge which were measured on the Schuylkill and Iowa Rivers in the United States. The findings<br>showed that the PCA-ANFIS performed better than the single ANFIS and the coupled DWT-ANFIS. Further applications of the PCA-ANFIS should be considered for simulation and prediction of other indicators relating to weather, water resources, and the environment</p> <p>&nbsp;</p> Nguyen Mai Dang Copyright (c) https://www.ajol.info/index.php/wsa/article/view/207054 Wed, 12 May 2021 00:00:00 +0000 Increasing nutrient influx trends and remediation options at Hartbeespoort Dam, South Africa: A mass-balance approach https://www.ajol.info/index.php/wsa/article/view/207055 <p>The Hartbeespoort Dam, located 40 km west of Tshwane on the Crocodile River, is an extremely eutrophic water body. Situated in one of the most economically active areas of South Africa, it receives a high nutrient input from wastewater treatment works (WWTW), leaking sewers, as well as urban and agricultural runoff. The Metsi a Me programme, which ran from 2006 to 2016, aimed to mitigate in-lake nutrient stocks using biomanipulation, including the physical removal of Eichhornia crassipes (water hyacinth) and Microcystis aeruginosa (blue-green algae). Using Department of Water and Sanitation water quality and flow data, the annual influxes and outfluxes of total nitrogen (TN) and total phosphorus (TP) to the Hartbeespoort Dam were calculated. Through literature review and comparison with previous studies, the relative importance of nutrient removal from biomass harvesting in relation to retained nutrients was assessed. The average nutrient influx from rivers during hydrological years 2010/11 to 2016/17 was 582 t∙a<sup>−1</sup> TP and 4 687 t∙a<sup>−1</sup> TN, with trends for both TN and TP being significantly positive over this period. TP influx increased by 77.8 t∙a<sup>−1</sup> every year and TN influx increased by 456 t∙a<sup>−1</sup>, reversing a long-term negative trend. Average annual dam retention + removal (calculated as the difference between river inputs and outputs, i.e., including sedimentation, biomass removal and denitrification losses) was 358 t P and 2 195 t N. A best estimation of nutrient removal from water hyacinth and algal harvesting was 2.1 t∙a<sup>−1</sup> P and 11.5 t∙a<sup>−1</sup> N, and 3.9 t∙a<sup>−1</sup> P and 40 t∙a<sup>−1</sup> N, respectively. An estimated 341 t∙a<sup>−1</sup> P and 674–1 288 t∙a<sup>−1</sup> N was sedimented. Denitrification losses are poorly quantified but<br>are possibly comparable to sedimentation. River outfluxes increased by 28.4 t∙a<sup>−1</sup> TP and 110 t∙a<sup>−1</sup> TN, smaller rates than the influxes, suggesting increasing retention per annum. Upgrading WWTWs in the catchment and refurbishing leaking and overflowing sewers is the most appropriate long-term solution. </p> A.S.D. Carroll, C.J. Curtis Copyright (c) https://www.ajol.info/index.php/wsa/article/view/207055 Wed, 12 May 2021 00:00:00 +0000 Temporal and spatial variations of organochlorine pesticides (OCPs) and phthalates affecting the quality of water and sediment from Loskop Dam, South Africa https://www.ajol.info/index.php/wsa/article/view/207056 <p>Organochlorine pesticides (OCPs) and phthalates are amongst the most emphasized man-made environmental contaminants, due to their prevalence, persistence and potential to induce adverse effects in organisms. In addition to prevailing industrial and domestic activities, their presence in the environment is exacerbated by leaching from associated materials, run-off and emissions. The Loskop Dam in the Mpumalanga Province, South Africa, is located on the Olifants River, which flows through a hub of industrial and agricultural activities. Research aimed at monitoring the levels of OCPs and phthalate contamination in South Africa, particularly in the Olifants catchment, has been limited and is restricted to short-term monitoring. In this study, the spatial and temporal variations of 21 OCPs and 7 phthalates in water and sediments from Loskop Dam were evaluated over a 3-year period (2015–2017). Annual average OCP levels ranged from 0.013±0.006 to 0.36±0.13 μg/L in water and from below the limit of detection to 2.4±1.2 µg/kg in sediments.&nbsp; Phthalates were present at average concentrations ranging from 0.023±0.041 to 2.1±1.5 μg/L and 20±0.63 to 55±6.9 µg/kg in water and sediments, respectively. The levels of OCPs and phthalates were greatest in autumn, attributed to higher input sources and concentration effects due to lower water levels. Phthalates were present at greater quantities at the inlet, while OCP accumulation was observed at the upper reaches of the dam. This may be an indication of the differences in input sources and translocation of these compounds, related to the topography of the dam and variability in water flow rates. These findings are important in highlighting the environmental and health concerns that may arise in the Olifants catchment area. After considering the outcomes of this study, we propose the implementation of regular and stringent monitoring strategies, which include surveys of OCPs and phthalates for Loskop Dam and similar water systems globally. </p> Mathapelo P. Seopela, Robert I. McCrindle, Sandra Combrinck, Wilma Augustyn Copyright (c) https://www.ajol.info/index.php/wsa/article/view/207056 Wed, 12 May 2021 00:00:00 +0000 Development of a flowchart method for source detection of illicit discharges into stormwater drainage systems in Cape Town https://www.ajol.info/index.php/wsa/article/view/207058 <p>Stormwater drainage systems discharging non-storm water add substantial pollution to urban watercourses, with negative impacts to water quality and aquatic ecosystems. Thus, the elimination of these discharges can be a highly effective non-structural best&nbsp; management practice (BMP) to improve water quality. This study aimed to guide local municipalities whose task it is to control polluted non-storm water entries into the stormwater drainage system. The study evaluated procedures, methodologies and techniques of&nbsp; illegal discharge detection and elimination (IDDE) programme components, as practised internationally, and applied these in a local condition to verify their feasibility and challenges. The paper provides guidance to identify and prioritise investigations for controlling illegal discharges into stormwater drainage systems. Challenges encountered in the study included lack of legal authority to undertake inspection, surveillance and monitoring at private and corporate properties, and to undertake requisite enforcement measures to remove sources of illegal discharges. It is recommended that local governments include in their stormwater management plan a control measure for an IDDE programme. More work is needed to better quantify the pollutant prevention and removal strategies and associated costs.</p> Yaw Owusu-Asante Copyright (c) https://www.ajol.info/index.php/wsa/article/view/207058 Wed, 12 May 2021 00:00:00 +0000 Fabrication of smartphone-based colorimetric device for detection of water leaks https://www.ajol.info/index.php/wsa/article/view/207059 <p>South Africa is a water-scarce country due to the shortage of rainfall. This scarcity is further exacerbated by the loss of water through leakage from faulty pipes. This paper reports on the use of a simple microfluidic device in the early detection of water leakages. The microfluidic paper-based device (µPADs) were prepared by printing patterns of wax (100 μm width) on the paper surface and melting the wax into the paper to form hydrophobic barriers. Solutions of lower to higher pH were also prepared and were introduced to the chlorophenol red test strips and a range of colours from yellow (lower pH) to purple (higher pH) were obtained. The digital images obtained with the μPADs were analysed using the CIELab colour system. The optimized pH range was wider than the typical grayscale-based image analysis and was successful for a wide pH range of 2–12. The QR codes attached to the strips enable tracking to obtain the real-time location from which leakage was detected. The study conclusively shows that the combination of digital image analysis and a μPAD device is highly efficient for quantitative analysis, and thus useful for the detection of household water leaks. </p> Zodidi Gcolotela, Stanley Chibuzor Onwubu, Sindisiwe Fortunate Muthwa, Phumlane Selby Mdluli Copyright (c) https://www.ajol.info/index.php/wsa/article/view/207059 Wed, 12 May 2021 00:00:00 +0000 The emergence of collectively owned self-supply water supply systems in rural South Africa – what can we learn from the Tshakhuma case in Limpopo? https://www.ajol.info/index.php/wsa/article/view/207060 <p>Despite the rapid extension of public service delivery since the end of Apartheid, many rural citizens in South Africa still rely on their own initiatives and infrastructure to access water. They construct, improve, operate and maintain infrastructure of different&nbsp; complexities, from individual wells to complex collectively owned water schemes. While most of these schemes operate without legal recognition, they provide essential services to many households. In this article we will first provide an overview of the growing international body of literature describing self-supply as an alternative pathway for public service delivery. We then take a historical perspective on the role of communities and self-supply in South Africa and describe the emergence of six collectively owned, gravity-fed, piped schemes in Tshakhuma, Limpopo Province. We describe and compare these systems using key characteristics like resource access, investment, construction, operation, maintenance and institutional governance. We further assess their performance with regard to coverage, service level, reliability, governance structure, accountability and water quality. We do so because we are convinced that lessons learned from studying such schemes as locally adapted prototypes have the potential to improve public approaches to service delivery. The described cases show the willingness of community members to engage with service delivery and their ability to provide services in cases where the state has failed. The assessment also highlights problematic aspects of self-supply related to a lack&nbsp; of accountability, technical expertise and the exclusion of disadvantaged community members. By describing and assessing the performance of rural self-supply schemes, we aim to recognize, study and learn from such schemes. We consequently do not conclude this article by providing answers, but by raising some pertinent, policy-relevant questions.</p> Moritz Hofstetter, Barbara van Koppen, Alex Bolding Copyright (c) https://www.ajol.info/index.php/wsa/article/view/207060 Wed, 12 May 2021 00:00:00 +0000 Scholarship on urban Africa’s water crisis narratives: the state of the art https://www.ajol.info/index.php/wsa/article/view/207061 <p>Water crises present a global water governance challenge. To date, scholarship has tended to focus on technological and policy-based solutions, while ignoring the influence of narratives on public buy-in during such crises. Africa is expected to become hotter and drier in future, while its cities experience high levels of informal population growth and inequality. These factors combine to make African cities particularly vulnerable to times of water stress. The aim in this paper is to investigate the state of the 'art' on narratives framing domestic water use in African cities during periods of acute water stress and 'crises', using a systematic literature review of peer-reviewed academic journal articles. The findings revealed a small population of recently published papers that engage critically with state-generated narratives framing the crisis, limited to case studies on Cape Town and Windhoek. We recommend, however, a greater critical engagement with the anti-establishment narratives that can flourish during periods of acute water stress, and tend to be<br>inflammatory and divisive in nature.</p> D.W. Olivier, C. Vogel, B.F.N. Erasmus Copyright (c) https://www.ajol.info/index.php/wsa/article/view/207061 Wed, 12 May 2021 00:00:00 +0000 Parameters to characterize the internal recirculation of an oxidation ditch https://www.ajol.info/index.php/wsa/article/view/207063 <p>Mixed liquor circulates ceaselessly in the closed-loop corridor in an oxidation ditch (OD), which is significantly different from other wastewater treatment processes. The internal recirculation ratio (IRR), i.e., the ratio between circulation flow rate (Q<sub>CC</sub>) and influent flow rate (Q<sub>In</sub>), and the circulatory period (T), i.e. the time consumed for the mixed liquor to complete one lap in the circular corridor, was used to quantify the internal recirculation characteristics of the OD system. In order to elucidate the characteristics and&nbsp; applicability of IRR and T, this study obtained the numerical relationship between IRR and T by formula derivation. It also discusses the factors influencing IRR and analyses the applications of IRR and T. The results showed that IRR = Q<sub>CC</sub>/Q<sub>In</sub> = HRT/T = HRT • IRF (HRT = hydraulic retention time of the mixed liquor in the circular corridor; IRF = internal recirculation frequency). Moreover, three kinds of parameters had an effect on IRR: Q<sub>In</sub>; reactor dimensions, i.e., length (Lmid), width (B), and height (H) of the circular corridor; and horizontal velocity of the mixed liquor in the circular corridor (v). Q<sub>In</sub> changed IRR by altering HRT. However, B, H, L<sub>mid</sub>, and v changed IRR by altering IRF and T. Furthermore, the same IRR corresponded to many different HRT and IRF. Therefore, when Q<sub>In</sub> and Q<sub>CC</sub> varied in the OD system, using HRT and IRF to evaluate the variation of QIn and Q<sub>CC</sub>, respectively, was better than using IRR to evaluate their synthetical variation. IRF and T were useful for directly and precisely characterizing the circulation speed and circulation flow rate in the circular corridor, while IRR was more useful for evaluating the dilution effect of reflux on influent. </p> Shao Po Wang, Jing Jie Yu, Hua Ji Ma Copyright (c) https://www.ajol.info/index.php/wsa/article/view/207063 Wed, 12 May 2021 00:00:00 +0000