Scielo RSS <![CDATA[Water SA]]> vol. 48 num. 1 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Integration of complete elemental mass-balanced stoichiometry and aqueous-phase chemistry for bioprocess modelling of liquid and solid waste treatment systems -Part 3: Measuring the organics composition</b>]]> Bioprocesses transform the components of the material entering single or multiple reactor systems from one kind to another without a change in total material exiting the system(s) in the solid, aqueous or gas phases. Provided that the correct measurements are made that can quantify the material content of the bioprocess products (outputs), the material content of the bioprocess reactants (inputs) can be determined from the bioprocess products via stoichiometry. Based on this principle of mass conservation, the augmented biomethane (AugBMP) and biosulphide (AugBSP) potential test procedures are proposed, which change the BMP from a stand-alone test to a bio-reactor on which a range of additional tests are made to determine the composition of biodegradable organics. The AugBSP, which is based on biological sulphate reduction, can replace the inaccurate gas measurements in the BMP with the more accurate aqueous sulphate and sulphide measurements. The suitability of these two procedures is evaluated from a theoretical and modelling perspective. The analytical tests required to determine the composition of influent organics, expressed as QHyOzNaPbSc, are identified. Examples of the calculation procedure from the test results are given. It is concluded that the augmented BMP (AugBMP) and BSP (AugBSP) test procedures, supplemented by anaerobic digestion dynamic modelling, are as accurate as the analytical measurements for determining the composition of biodegradable organics, and also allow the hydrolysis rate of the biodegradable organics and the unbiodegradable fraction of the organics to be determined. Knowing these characteristics of organics fed to anaerobic digesters is important to predict the anaerobic digester performance and stability. <![CDATA[<b>Integration of complete elemental mass-balanced stoichiometry and aqueousphase chemistry for bioprocess modelling of liquid and solid waste treatment systems -Part 4: Aligning the modelled and measured aqueous phases</b>]]> Completely mass-balanced biological, physical and chemical process stoichiometry ensures that the CHONPS material and charge content entering and exiting bioprocess system models is conserved, which is a requirement for pH prediction in integrated physical, chemical and biological process models. Bioprocesses transform the material content from reactants to products, exchanging material between the aqueous, gaseous and solid phases, which cause pH changes in the aqueous phase. By measuring the material content of the aqueous phase, the progress of bioprocesses can be monitored. Alkalinity is an important aqueous-phase property that can be used to track aqueous-phase changes caused by physical, chemical and biological processes. Alkalinity is a stoichiometry property of the components in solution (i.e., a linear function of the amounts present). Its uptake from, and release to, the aqueous phase can both be modelled with bioprocess stoichiometry, and measured in physical bioprocess systems, and so aid in linking the modelled and measured aqueous-phase compositions. Changes in the concentrations of components containing the elements C, H, O, N, P and S result in changes in six weak acid/bases systems in the aqueous phase, all of which affect the total alkalinity. These are: inorganic carbon (IC), ortho-phosphate (OP), free and saline ammonia (FSA), volatile fatty acids (VFA), free and saline sulphide (FSS) and the water itself. Characterization of the aqueous phase to quantify the material content of the aqueous phase containing these six weak acid/base systems using the 5-point titration method is described. While several alkalinity titration based methods are available for anaerobic digestion bioprocess monitoring, only the 5-point titration is sufficiently accurate for aqueous-phase characterization to quantify the aqueous-material content for pH prediction in bioprocess models. <![CDATA[<b>Integration of complete elemental mass-balanced stoichiometry and aqueous-phase chemistry for bioprocess modelling of liquid and solid waste treatment systems -Part 5: Ionic speciation</b>]]> Where aqueous ionic chemistry is combined with biological chemistry in a bioprocess model, it is advantageous to deal with the very fast ionic reactions in an equilibrium sub-model, as was frequently mentioned in the preceding papers in this series. This last paper in the series presents details of how such an equilibrium speciation sub-model can be implemented, based on well-known open-source aqueous chemistry models. Specific characteristics of the speciation calculations which can be exploited to reduce the computational burden are highlighted. The approach is illustrated using the ionic equilibrium sub-model of a plant-wide wastewater treatment model as an example. <![CDATA[<b>The effects of dry versus wet season on the performance of a wastewater treatment plant in North West Province, South Africa</b>]]> The study was conducted at a wastewater treatment plant (WWTP) in the North West Province of South Africa (SA), to investigate the effect of seasonal variations of rainfall and temperature on the fate of Escherichia coli (E. coli) and on chemical parameters. Both seasons showed variations in terms of rainfall levels and temperature. The average temperatures measured at the final effluent were 14 and 22°C for the dry and wet season, while the rainfall averages ranged between 0.0 and 69.0 mm and 16.0 and 258.9 mm for the dry and wet season, respectively. The impact of rainfall within the two seasons presented a variation in the plant inflow rate of 34 000 and 48 000 m³ during the dry and wet season, respectively. Higher E. coli concentrations were detected before and after chlorination in the wet season (1.86 x 10(5) and 8.40 x 10¹ MPN/100 mL) than in the dry season (2.26 x 10(4) and 5.10 x 10¹ MPN/100 mL). The recorded values for the chemical parameters in the dry and wet season were within the following ranges: ammonia (0.27 and 3.68 mg/L), chemical oxygen demand (COD) (29.53 and 22.10 mg/L), nitrate (9.21 and 2.40 mg/L) and ortho-phosphate (0.46 and 0.39 mg/L). Though the detections of these indicator parameters were affected differently by the seasonal variations, it is important to note that the efficiency of the WWTP in reducing these indicator parameters proved to be consistent across all seasons, except in the case of ammonia and nitrate. The majority of the studied parameters showed effective compliance when measured against SA regulatory standards (general limits) in both the dry and wet season, with the exception of ammonia during the wet season. <![CDATA[<b>A comparison of oil and grease removal from automobile workshop stormwater runoff using gravel, granular activated carbon, rice husk and conventional oil and grease (O& G) trap</b>]]> Oil and grease (O) removal efficiencies using 4 automobile stormwater treatment systems were investigated and compared. The treatment systems used were: low-cost granular activated carbon-rice husk (GAC-RH) filter system, river gravel-granular activated carbon (GR-GAC) filter system, rice husk only (RH) filter system and the conventional PVC O trap (COT). Sampling of automobile stormwater from the five selected automobile workshops was carried out using the manual grab sampling methods. The treatment involved filtration using the low-cost technologies and O separation from stormwater. GAC-RH exhibited the highest O removal with an average removal efficiency of 43.2% from all the automobile workshops, followed by RH with an average removal efficiency of 31%. O removal using GR-GAC and COT resulted in average removal efficiencies of 28.6% and 26.8%, respectively. Further studies need to be carried out to optimize the GAC and RH low-cost filter materials for the purpose of achieving the USEPA and Nigerian effluent standards of 0.1 mg/L, since all the treatment systems produced effluents with minimum concentrations ranging between 0.8 mg/L and 3.6 mg/L. <![CDATA[<b>Predicting the head leakage behaviour of cracks in pipe elbows</b>]]> In this study, finite element analysis (SAP2000 program) was used to investigate the relationship between the pressure and leakage area in 90° pipe elbows with longitudinal, spiral, and circumferential cracks. The results show that leakage areas expand linearly as the internal pressure increases and its inclination is called the pressure-area slope (m). A sensitivity study was conducted to recognize the influence of different parameters (inside diameter, wall thickness, modulus of elasticity, longitudinal stress, Poisson's ratio, and finally crack orientation) on both m and leakage exponent (N). The results reveal that the elasticity modulus has the dominant impact on m, followed by elbow wall thickness, and then elbow inside-diameter. The Poisson's ratio and the longitudinal stress have an insignificant influence on m. Moreover, the slope m varies more in the longitudinal and spiral cracks than the circumferential cracks. The amount of leakage through the different cracks is a function of the internal pressure raised to an exponent ranging from 0.5 to 1.01. An attempt was made to find empirical equations to express the pressure-area slope as a function of elbow properties and crack orientation. The study's findings were checked against numerical and experimental results and good correlations were obtained. <![CDATA[<b>Framework for implementation of the Pitman-WR2012 model in seasonal hydrological forecasting: a case study of Kraai River, South Africa</b>]]> Hydrological forecasting becomes an important tool in water resources management in forecasting the future state of the water resources in a catchment. The need for a reliable seasonal hydrologic forecast is significant and is becoming even more urgent under future climate conditions, as the assimilation of seasonal forecast information in decision making becomes part of the short and long-term climate change adaptation strategies in a range of contexts, such as energy supply, water supply and management, rural-urban, agriculture, infrastructure and disaster preparedness and relief. This work deals with the framework for implementation of the Pitman-WR2012 model in a hydrological forecasting mode. The Pitman-WR2012 model was forced with 10-member ensemble seasonal climate forecast from Climate Forecast Systems v.2 (CFSv2), which is downscaled using the principal components regression (PCR) approach. The generated seasonal hydrological forecast focused on the summer season, in particular on the Dec-Jan-Feb (DJF) period, which is the rainy season in the studied catchment (Kraai River catchment in the Eastern Cape Province of South Africa). The hydrological forecast issued at the end of November showed skill in December and February (assessed through Receiver Operating Characteristic (ROC) and Ranked Probability Skill Score (RPSS)), with poorer skill in January. Importantly, the skill of streamflow forecast was better than that of rainfall forecast, which likely results from the influence of the initial conditions of the hydrological model. In conclusion Pitman-WR2012 model performed realistically when implemented in seasonal hydrological forecasts mode, and it is important that in that mode the model is run with near-real-time rainfall data in order to maximize forecast skill arising from initial conditions. <![CDATA[<b>Deriving the maximum extent and hydroperiod of open water from Sentinel-2 imagery for global sustainability and biodiversity reporting for wetlands</b>]]> The monitoring of wetland extent is a global imperative, considering loss of ecosystem services and conservation value. To date, the understanding of the variation in the extent of lacustrine (inundated) wetlands has been limited, based on intermittently available, coarse-scale imagery. The aim of this study was to assess the capabilities of the freely available Sentinel-2 sensor in monitoring inundated wetlands. In particular, to demonstrate the ability to determine the maximum extent of inundation for reporting on the Sustainable Development Goal (SDG) 6.6 (Clean Water and Sanitation) and SDG 15.1 (i.e., halting biodiversity loss), the functional diversity and the hydrological regime of depressions were explored in the Mpumalanga Lake District (MLD) of South Africa. Using the monthly inundation data derived from Sentinel-2 images between January 2016 and May 2018, the results showed that the maximum extent of open water can be successfully reported for SDG 6.6. Lacustrine wetlands constituted about 47 of the 416 (but 66% of the total areal extent of) depressions in the MLD, while others were predominantly palustrine (vegetated). The functional diversity varied from predominantly (61% of the extent of) inundated depressions to seasonally (3%) inundated depressions. The Sentinel-2 sensor was able to detect intra- and inter-annual variation of the extent of inundation, making it suitable to monitor these wetlands for global and climate change impacts. <![CDATA[<b>Crop response and water productivity of sunflower <i>(Helianthus annuus </i>L.) drip-irrigated with magnetically treated and non-magnetically treated water with variable salinity</b>]]> To compare the effect of magnetic drip irrigation and conventional irrigation with different salinity levels on water productivity and yield of sunflower (Helianthus annuus L.), a factorial experiment was conducted using a completely randomized design with 6 treatments and 3 replicates at the Research Station of the Faculty of Water Sciences Engineering, Shahid Chamran University of Ahvaz, Iran. The experiment was executed over the crop year 2018-19. The treatment variables consisted of 2 types of water (magnetically treated and non-magnetically treated) and 3 salinity levels (Karun River water (S1), 4 dS/m (S2), and 6 dS/m (S3)). The use of magnetically treated irrigation water increased the biomass water use efficiency, and the weight of 100 seeds by 13.9%, and 5.48%, respectively. With the conventional irrigation method, increased salinity reduced the seed yield. The highest seed yield and irrigation water productivity were observed at 4 459 kg/ha and 0.73 kg/m³ for grain yield at a water salinity level of S1 (the control treatment). The application of water with salinity of 4 dS/m and 6 dS/m (S2 and S3) caused a reduction in seed yield by 9.3 and 21.8%, respectively, in comparison to that of the control treatment. Moreover, irrigation water productivity for the biomass yield decreased by 14.57 and 29.23%, respectively. Based on the results of this study, the use of magnetically treated water can reduce the effects of salinity stress under conditions of salt stress. Therefore, magnetically treated water can increase the yield and productivity of irrigation water. <![CDATA[<b>Smallholder farmer coping and adaptation strategies for agricultural water use during drought periods in the Overberg and West Coast Districts, Western Cape, South Africa</b>]]> Drought is one of the most significant disasters affecting farm productivity in South Africa, with the Western Cape Province among the most affected areas. Smallholder farmers usually suffer the most due to limited resources. The study identified agricultural water use coping and adaptation strategies adopted by both crop and livestock smallholder farmers in the West Coast and Overberg districts during the recent 2015-2018 drought. Interviews were conducted with 100 smallholder farmers and 11 focus group discussions were held in the two districts. Quantitative data were analysed using the Statistical Package for Social Sciences, while qualitative data were analysed using Atlas.ti. Furthermore, the Hyogo Framework of Action was used to analyse the support that smallholder farmers had received and to understand how smallholder farmers could be effectively supported to promote the adoption of proactive strategies to deal with drought in the short and long term. It was found that the 2015-2018 drought occurred when smallholder farmers from both districts were least expecting it and were unprepared. In the West Coast District, the main coping strategies included using borehole water and selling livestock. In the Overberg District, smallholder farmers coped by purchasing fodder and transporting water from sources such as the river and dam to the farms. Several smallholder farmers in both districts did not implement any adaptation strategies. They were largely unaware of proactive agricultural water use strategies that could bolster their resilience to drought. Recommendations for the future include the adoption of drip irrigation, mulching, growing vegetables with shorter growing periods and changing planting dates. For livestock farmers, adaptation strategies include drilling boreholes and grazing management. There is also a need for early warning systems to improve the drought preparedness of smallholder farmers.