Water SA

A simple calibration of Hobo 4 channel analogue dataloggers for use with Watermark 253-L soil water potential sensors

The combination of granular matrix sensors with a Hobo 4 analogue channel datalogger provides a relatively inexpensive continuous soil water monitoring system. However, the datalogger excites all 4 channels concomitantly as it reads the sensor measurement of each channel in sequence. This results in localised electrolysis causing measurement bias error in Channels 2, 3 and 4. To evaluate this channel bias, Watermark granular matrix sensors were connected to Hobo 4 channel dataloggers to measure electrical conductance of the soil. This study formed part of a larger study aimed at understanding water use by Eucalyptus plantations at different soil depths. The measured soil conductivity was calibrated against the gravimetric method in soil derived from Natal Group Sandstone and Dwyka Tillite that occur in southern KwaZulu-Natal. The channels of a Hobo 4 channel datalogger were successfully calibrated against the gravimetric method for both soil types (R² > 0.92). The voltage measurements of each channel increased in the order 1 < 2 < 3 < 4 for both soil types at a soil water content range of 12 to 44% and 6 to 46% for Dwyka Tillite and Natal Group Sandstone soils, respectively. Channel measurements were similar at soil water content ranges below 12 and 6% for tillite and sandstone soils, respectively. The study showed that Channels 2, 3 and 4 of the Hobo 4 channel datalogger are affected by electrolysis. If this analogue datalogger is used with these types of sensors, these channels need to be calibrated back to Channel 1.

Domestic water meter optimal replacement period to minimize water revenue loss

Water meter under-registration results in apparent losses and lost revenue for municipalities. Municipalities should scientifically determine the optimal replacement periods for the meters in their particular municipality, as this would result in the formulation and implementation of appropriate meter replacement strategies and a reduction of apparent losses due to water meter inaccuracies. A water meter management database was analysed using the relative meter error method to determine if a relationship exists between domestic water meter age, total registered volume and accuracy, as well as the volume of apparent water losses caused by inaccuracies due to domestic water meter age and total registered volume. The net present value chain (NPVCn) method was used to determine the optimal domestic water meter replacement period. This study found no relation between water meter age and total registered volume. A relation was found between water meter age and accuracy and well as between total registered volume and accuracy. The median relative meter error was found to decrease with increasing water meter age and to increase from under-registration to over-registration as the total registered volume increased. The study also determined the volume of apparent water losses caused by domestic water meter inaccuracies due to age and total registered volume for this particular municipality to be 1.814 kL∙meter−¹∙month−¹, which translated to 2.81% of the municipality's total system input volume. The optimal water meter replacement period of the municipality was determined using the NPVCn method to be at water meter ages of 9, 12 and 16 years and total registered volumes of 3 971, 5 162 and 6 750 kL at discount rates of 10%, 8% and 6%, respectively. This means that the municipality can now proactively replace its water meters so as to minimize the impact of meter inaccuracies on non-revenue water.

Assessment of apparent losses due to meter inaccuracy – a comparative approach

The empirical method for the determination of apparent water losses, using the assessment of consumption patterns and the laboratory testing of water meters, is compared against alternative methods of comparative billing and meter change analyses for one of the largest water utilities in South Africa. Using the empirical method, apparent losses are estimated to have an average value of 12% of the billed volume with a range from 9.4% to 14.6% that is dependent on meter size ratios. This overlaps with the estimates, of 8%−10% for a utility with direct feed good quality water but high meter age (> 10 yr) and low accuracy, currently proposed in some studies and used by industry. The estimate from the comparative billing analysis method is 14% and it is sensitive to how the data is processed and analysed. The meter change method yielded an estimate of 4.7% for only a subset of the data. Both results of the alternative methods are in line with previous studies, with the comparative billing analysis performing better, but requiring further refinement for better accuracy and repeatability. The empirical method remains the gold standard in assessing apparent water losses but is undoubtedly very laborious, expensive and out of reach of the budget of many utilities. The development and validation of alternative methodologies therefore holds great promise but these are substantially reliant on comprehensive meter information and credible billing datasets which are rarely available in most utilities in Africa.

Determination of isotopic composition of rainwater to generate local meteoric water line in Thohoyandou, Limpopo Province, South Africa

Hydrogen (D) and oxygen (18O) isotopic compositions of precipitation are useful tools to delineate the nature of precipitation, groundwater recharge and climatological investigations. This study investigated the isotopic composition of 12 rainfall occurrences at Thohoyandou, with the objective of generating the local meteoric water line (LMWL) and determining the factors controlling the isotopic composition of the rain. The delta (δ) values for D and 18O of the samples were determined using a Thermo Delta V mass spectrometer connected to a Gasbench. Thohoyandou rainwater showed a wide range of stable isotope values; δD values of the rainwater varied from −76.3‰ to +22.7‰ (SMOW) with a weighted mean of −9.8‰ and δ18O values ranged from −10.78‰ to +3.07‰ (SMOW) with a weighted mean of −2.7‰. δ-values of rainwater were more enriched during winter and more depleted during summer, due to the amount of rainfall and seasonal effect. The LMWL in Thohoyandou is defined by δD = 7.56δ18O + 10.64, which shows a similar slope to the global meteoric water line (GMWL) but with a slightly higher intercept, of 10.64‰ instead of 10‰. This implies that the process of rain formation in Thohoyandou occurred under equilibrium conditions which are not significantly affected by evaporation. The slightly higher d-intercept value above the GMWL reflects an additional supply of recycled moisture across the regions. This implies that there is no continental effect but inland moisture from various water bodies and vegetation.

Assessment of probable causes of chlorine decay in water distribution systems of Gaborone city, Botswana

Gaborone city water distribution system (GCWDS) is rapidly expanding and has been faced with the major problems of high water losses due to leakage, water shortages due to drought and inadequate chlorine residuals at remote areas of the network. This study investigated the probable causes of chlorine decay, due to pipe wall conditions and distribution system water quality in the GCWDS. An experimental approach, which applied a pipe-loop network model to estimate biofilm growth and chlorine reaction rate constants, was used to analyse pipe wall chlorine decay. Also, effects of key water quality parameters on chlorine decay were analysed. The water quality parameters considered were: natural organic matter (measured by total organic carbon, TOC; dissolved organic carbon, DOC; and ultraviolet absorbance at wavelength 254, UVA-254, as surrogates), inorganic compounds (iron and manganese) and heterotrophic plate count (HPC). Samples were collected from selected locations in the GCWDS for analysis of water quality parameters. The results of biofilm growth and chlorine reaction rate constants revealed that chlorine decay was higher in pipe walls than in the bulk of water in the GCWDS. The analysis of key water quality parameters revealed the presence of TOC, DOC and significant levels of organics (measured by UVA-254), which suggests that organic compounds contributed to chlorine decay in the GCWDS. However, low amounts of iron and manganese (< 0.3 mg/L) indicated that inorganic compounds may have had insignificant contributions to chlorine decay. The knowledge gained on chlorine decay would be useful for improving water treatment and network operating conditions so that appropriate chlorine residuals are maintained to protect the network from the risks of poor water quality that may occur due to the aforementioned problems.

A bivariable coupling model for river channel routing developed from the flow continuity equation and its application

In this study, a bivariable coupling model for river channel routing is presented. The proposed model is developed from the Priessmann 4-point implicit differential scheme with a weight coefficient of river flow continuity equation. It is based on the transformation of two different expression forms of river channel storage equation. Furthermore, we consider the impact of lateral inflow along the study river channel from another perspective. In this paper we deduct lateral inflow from the lower section instead of adding lateral inflow to the upper section. In order to be representative of geographical range, river channel characteristics, flood magnitude, hydraulic characteristics and time, the proposed model is tested in 38 river channels of 6 river systems in China by using observed data during flood season. The rationality of model structure and the validity of model simulation are examined comprehensively. Comparison between the proposed model and Muskingum model shows that the proposed model can improve the simulation accuracy. The results show that the simulation accuracy and stability of the bivariable coupling model is much better than that of the Muskingum model.

Development of an empirical formula for estimation of bioretention outflow rate

Urbanization of a watershed affects both surface water and groundwater resources. When impervious area increases, the excess runoff and volume of water collected at the downstream end of the watershed also increases, due to the decrease in groundwater recharge, depression storage, infiltration and evapotranspiration. Low-impact development (LID) methods have been developed in order to diminish adverse effects of excess stormwater runoff. Bioretention is one of the LID types which is used to prevent flooding by decreasing runoff volume and peak flow rate, and to manage storm-water by improving water quality. In this study, an empirical formula is derived to predict the peak outflow out of a bioretention column as a function of the ponding depth on bioretention, hydraulic conductivity, porosity, suction head, initial moisture content and height of the soil mixture used in the bioretention column. Coefficients of the empirical formula are determined by using meta-heuristic algorithms. For analyses, the experimental data obtained from rainfall-watershed-bioretention (RWB) system are used. The reliability of the empirical formula is evaluated by calculating the absolute per cent error between the peak value of the measured outflow and the calculated outflow of the bioretention columns. The results show that the performance of the empirical formula is satisfactory.

Variable water quality of domestic wells emphasizes the need for groundwater quality monitoring and protection: Stinkwater, Hammanskraal, Gauteng

Groundwater is a critical water resource in many peri-urban areas without municipal water supply, a common situation globally, but especially in Africa. These areas contain multiple water pollution risks from various human activities, including small industry, dumping, stock and pet animals, and pit latrines. Stinkwater village, 40 km north of Pretoria in Gauteng Province, that has only partial municipal water supply, was sampled for water quality from municipal taps, boreholes and open hand-dug wells. The water quality varied greatly, with few obvious geographic or geochemical correlations, other than high bacterial counts in the open wells. The key health concerns were nitrate, fluoride and coliform bacteria (including E. coli), some at dangerous levels. Relatively subtle variations in land use, including water use and pollution sources, as well as vadose zone character, including depth to water table, permeability and recharge pathways, could account for much of the variation in water quality. The study reveals the risk of relying upon a single water quality analysis to determine groundwater conditions for an area. In areas with multiple possible pollution sources, thorough groundwater monitoring is needed to determine the usability of water resources.

Leachate seepage from landfill: a source of groundwater mercury contamination in South Africa

Mercury has been used for many centuries in the production of consumer products such as thermometers, electrical switches, fluorescent light bulbs, batteries, biocides and pesticides, cosmetics and dental amalgam filling, among others. After use, these mercury-containing consumer products form part of the municipal solid waste (MSW). As a result of an unseparated solid waste collection system, mercury-containing wastes tend to end up in landfills where mercury and other pollutants can leach out of products into landfill leachates. The present study, therefore, was conducted with the aim of determining the total mercury (THg) concentrations in leachate and sediment samples collected from 4 selected landfill sites (3 sites in Gauteng Province - Soshanguve, Hatherly, Onderstepoort and 1 site in Limpopo Province - Thohoyandou). Groundwater samples were collected from the monitoring boreholes at the four selected landfill sites in the summer and winter periods. An acid digestion method was employed for sample preparation and this was followed by analysis using cold vapour atomic absorption spectrophotometry (CVAAS). The concentration range of total mercury in the Thohoyandou leachate, sediment and groundwater samples was 0.12-2.07 µg/L, 0.03-0.48 µg/g and 0.09-2.12 µg/L, respectively. In Soshanguve, the concentration range of total mercury in leachate, sediment and groundwater samples was 0.10-1.20 µg/L, 0.04-0.62 µg/g and nd -1.66 µg/L respectively, Hatherly concentration range was 0.42-1.31 µg/L and 0.06-0.78 µg/g in leachate and sediment, respectively and in Onderstepoort the concentration range was 0.12-2.41 µg/L, 0.03-0.50 µg/g and 0.05-2.44 µg/L, in leachate, sediment and groundwater, respectively. The findings from this study suggest that there is a likelihood of groundwater pollution by mercury from landfill leachate seepage, particularly for landfills that are not lined with a geomembrane.

Neuro-fuzzy systems to estimate reference evapotranspiration

Routine and rapid estimation of evapotranspiration (ET) at regional scale is of great significance for agricultural, hydrological and climatic studies. A large number of empirical or semi-empirical equations have been developed for assessing ET from meteorological data. The FAO-56 PM is one of the most important methods used to estimate evapotranspiration. The advantage of FAO-56 PM is a physically based method that requires a large number of climatic parameter data. In this paper, the potential of two types of neuro-fuzzy system, including ANFIS based on subtractive clustering (S_ANFIS), ANFIS based on the fuzzy C-means clustering method (F_ANFIS), and multiple linear regression (MLR), were used in modelling daily evapotranspiration (ET0). For this purpose various daily climate data - air temperature (T), relative humidity (RH), wind speed (U) and insolation duration (ID) - from Dar El Beidain Algiers, Algeria, were used as inputs for the ANFIS and MLR models to estimate the ET0 obtained by FAO-56 based on the Penman-Monteith equation. The obtained results show that the performances of S_ANFIS model yield superior to those of F_ANFIS and MLR models. It can be judged from results of the Nash-Sutcliffe efficiency coefficient (EC) where S_ANFIS (EC = 94.01%) model can improve the performances of F_ANFIS (EC = 93.00%) and MLR (EC = 92.12%) during the test period, respectively.

Assessing the accuracy of ANN, ANFIS, and MR techniques in forecasting productivity of an inclined passive solar still in a hot, arid environment

Solar still productivity (SSP) essentially describes the performance of solar still systems and is an important factor to consider in achieving a reliable design. This study presents the use of artificial neural networks (ANN), adaptive neuro-fuzzy inference systems (ANFIS), and multiple regression (MR) for forecasting the SSP of an inclined solar still in a hot, arid environment. The experimental data used for the modelling process included meteorological and operational variables. Input variables were relative humidity, solar radiation, feed flow rate, and total dissolved solids of feed and brine. The models were assessed statistically using the correlation coefficient (CC), root mean square error (RMSE), overall index of model performance (OI), mean absolute error (MAE), and mean absolute relative error (MARE). Overall, ANN was shown to be superior (CC = 0.98, RMSE = 0.05 L·m−²·h−¹, OI = 0.95, MAE = 0.03 L·m−²·h−¹, and MARE = 8.92%) to ANFIS and MR for SSP modelling. The relatively low errors obtained by the ANN technique led to high model predictability and feasibility of modelling the SSP. Thus, our findings indicate that ANN can be applied as an accurate method for predicting SSP.

Characterization of the performance of venturi-based aeration devices for use in wastewater treatment in low-resource settings

Low-cost aerators relying on the venturi principle to entrain air into flowing water have the notable advantage of contributing both to water mixing and oxygen transfer, making them attractive for wastewater treatment in low-resource settings. This study aimed to characterize the performance of such aerators by describing the impact of different design characteristics, including water flow rate, the number of nozzles used, and the nozzle depth. The study also explored the effect on aeration performance of temperature, total dissolved solids (TDS) concentration, and addition of the archetypal surfactant sodium dodecyl sulphate (SDS). Tests were conducted in a 200 L reactor with 2, 3 or 4 nozzles, at depths of 20, 40 or 60 cm, while circulating water through the aeration device at a rate of 400, 600 or 800 L/h. The configuration that yielded the highest mass transfer coefficient (K La20 of 20.8 h-1) had both the highest flow rate (800 L/h) and the smallest number of nozzles (2). Nozzle depth had no detectable effect on performance. The configuration with the highest standard aeration efficiency (SAE) had a low flow rate (400 L/h) and 4 nozzles. The effect of TDS concentration was not detected in the concentration range typical of domestic wastewater (300-1 250 mg/L). The effect of temperature on K La followed a first-order exponential curve, as reported in the literature (θ = 1.02). Addition of SDS was found to increase the K La20 of the tested aerator design by up to 60% of its value in tap water, in contrast to results from literature. The performance data obtained herein was compared to other types of aerators. Though venturi nozzles were found to be less efficient than other available technologies, it is proposed that using plunging rather than immersed venturi nozzles could increase performance to an attractive level for low-resource applications.

Seasonal variation in waterbird assemblage in the Mahango Game Reserve, north-eastern Namibia

There are few African studies on seasonal changes in the waterbird assemblages in river ecosystems. Tropical freshwater ecosystems are regarded as more stable habitats over the year than terrestrial ones. The same could be expected in regard to the bird fauna associated with such ecosystems. In order to test if waterbird asembalges followed the stable ecosystem paradigm a study was undertaken in the Okavango River, in the Mahango Game Reserve, north-eastern Namibia. Counts of all waterbirds were conducted in wet and dry seasons during 2001-2006. In total, 88 waterbird species were recorded. In wet seasons the number was slightly lower (N = 75) than in dry seasons (N = 78) (chi-square test: χ² = 0.06; p > 0.05). The total number of individuals of all resident species recorded in wet seasons was unexpectedly much lower in wet (N = 9 979) than in dry seasons (N = 15 501) (chi-square test: χ² = 1 196; p < 0.01). In wet seasons, Collared Pratincole, Blacksmith Lapwing, African Openbill Stork and African Darter dominated (58.8%), while in the dry season: White-faced Duck, Spur-winged Goose, African Skimmer, African Reed Cormorant, African Darter and Squacco Heron contributed 60.8% to the overall abundance. Diversity indices were similar in both seasons.

Urinals for water savings and nutrient recovery: a feasibility study

This research investigates the feasibility of implementing waterless urinals at a public university in Cape Town, South Africa. Two analytical approaches were adopted to assess the feasibility of the proposed systems: a social study in the form of an online survey and an economic evaluation of four separate water savings and nutrient removal systems. In terms of the online survey, 87% of respondents claimed they would use urine- diverting technology and 79% stated they would eat food that was grown using urine-recycled phosphorus as fertilizer. It was found that merely reducing the number of times a urinal could be flushed to 3 times per day could save approximately 18 ML of water annually. Additionally, the University of Cape Town requires 3 600 kg of fertilizer for its sports fields, while the urine collected in waterless systems has the potential to produce 6 700 kg of fertilizer. This work has shown that a significant amount of water can be saved by installing waterless urinals in public institutions such as a university. It also shows that there is potential to recover valuable resources from our 'waste' streams, thus closing various nutrient cycles through on-site fertilizer production.

Application of VOF and k-ε turbulence model in simulation of flow over a bottom aerated ramp and step structure

A three-dimensional numerical model of ANSYS, Fluent (2011) was employed for studying mid to high discharge supercritical two-phase flow over a single slope spillway with a single step for aeration of the flow. In this study 18 simulations were conducted using the Volume of Fluid (VOF) method for air-water interface tracking and simple k-ε model for turbulence closure. Submerged circular shaped pipes located at the bottom of the step were utilized as aerators. Analyses concentrate on the air-entrainment phenomenon and jet-length of the flow from the step to the re-attachment point. The variables considered in the study are discharge, aerator size, different aerator arrangements, Froude number of the flow, presence of a ramp before the step and its angle. Observed jet-length values in this study were compared with two sets of empirical formulae from literature for code validation. Cross-sectional average of air concentration due to bottom aeration was determined in the streamwise direction downstream of the re-attachment of the jet. The air concentration is observed to follow a logarithmic decay in the flow direction within the de-aeration zone.

Requirements for sustainable operation and maintenance of rural small-scale water infrastructure in Limpopo Province, South Africa

This study assessed the presence of key requirements for sustainable O and rehabilitation of rural small-scale water infrastructure in Makhudutamaga Municipality in South Africa. The study found a significant correlation between the requirements for sustainable O and rehabilitation of rural small-scale water infrastructure and continuity of service provision (p < 0.001) by the small-scale water infrastructure as well as functionality (p < 0.001) of the small-scale water infrastructure hardware. The study concludes that the presence of the key requirements varies as a function of social dynamics of communities and the presence of these requirements has an impact on the functionality and continuity of the small-scale water infrastructure hardware.