Water SA

A baseline study on the prevalence of microplastics in South African drinking water: from source to distribution

2023-11-01T14:08:27+00:00

Due to the worldwide increasing prevalence of microplastics in the aquatic environment, this study aimed to perform a screening of the source and drinking water of South Africa’s largest bulk drinking water supplier to determine the extent to which microplastics occur in the water. Source water samples, samples immediately after treatment, and samples in the distribution network (Johannesburg, Mabopane, Garankua and Pelindaba) were analysed. Microplastics concentrations in the source water ranged from 0.24 to 1.47 particles/L, immediately after treatment from 0.56 to 0.9 particles/L, and in the distribution network from 0.26 to 0.88 particles/L. Most of the microplastics found in the water were classified as ‘fragments’ and a few as ‘fibres’. The control sample (indicating contamination during sample preparation and analysis) showed 0.34 particles/L, which was higher than some of the samples taken, indicating very low microplastics concentrations in these samples. Little evidence was found that the drinking water treatment processes reduced the number of microplastics from the source to the final treated water. No evidence could be found that the pipes in the distribution network contribute to microplastics in the tap water. The most frequently found polymer in the samples was rubber. Based on mass, however, as a function of particle size and polymer density, ethylene-vinyl-acetate (a polymer commonly used as foam in sporting equipment and flip-flops) comprised 54% of the microplastics and polyethylene (standard and chlorinated) 25%.

Cape Town residents’ willingness to pay for a secure and ‘green’ water supply

2023-11-01T14:16:09+00:00

The City of Cape Town experienced a serious drought between 2016 and 2018 which led to severe water shortages and concerns for the environment. This study took advantage of a period of unprecedented levels of awareness about water security in order to investigate households’ willingness to pay (WTP) for reliable water supply and their WTP to avoid environmental damages in securing this supply. Increasing the supply of water from dams and groundwater will ultimately impact on aquatic ecosystems, but alternatives are more expensive. We surveyed 248 households from 105 suburbs and used contingent valuation methods to investigate WTP for both secure and less damaging or ‘greener’ ways of supplying water. Depending on income level, households were willing to pay 63–127% more for their normal levels of consumption in order to have security of supply, and a further 35–68% more to ensure its environmental sustainability. Based on the relationship between WTP for 7 income categories, the overall WTP for secure water supply under nondrought conditions amounted to some 2.8 billion ZAR/year, which is about 90% higher than pre-drought revenues. Aggregate WTP for securing this supply using options that ensured the protection of the region’s rivers and estuaries was 3.3 billion ZAR. These results have an important bearing on water investment and pricing decisions over the longer term.

Assessment of long-term water demand for the Mgeni system using Water Evaluation and Planning (WEAP) model considering demographics and extended dry climate periods

2023-11-01T14:23:26+00:00

The Mgeni System is recognised as the main source of water supply for the Durban and Pietermaritzburg region in South Africa. This area is regarded as the primary economic hub of KwaZulu-Natal Province, and this brings about a high level of demographic pressure, with potential water supply problems in the future. This study investigates the water resource situation in the Mgeni System and evaluates future supply and demand accounting based on the (Water Evaluation and Planning) WEAP software. WEAP was used to analyse the study area for the period 2009–2050 to assess the impacts of various scenarios on future water supply shortfalls. Four scenarios were used, which take into account changing population growth rates and extended dry climates. The study found that the catchment is relatively sensitive to changes in population growth and extended dry climates, and this will alter the water availability significantly, causing a water supply deficit. In response to the projected future water demands, one technique to overcome the unmet demand is by introducing water conservation and demand management (WC/DM) strategies to reduce the water losses and shortfall encountered. By implementing adequate measures, water losses can be reduced, preventing water scarcity and giving decision makers time to provide further solutions to water supply problems.

Endogenous irrigation in arid Zimbabwe: farmer perceptions of livelihood benefits and barriers to scaling

2023-11-01T14:28:14+00:00

In Zimbabwe, farmer-led irrigation is far more widespread than planners and policy makers realise. Along the Shashani sand river, in the arid to semi-arid lands of south-western Zimbabwe, diverse farmer-initiated irrigation ventures exist. This qualitative case study focuses on bucket irrigation, in which very small vegetable fields of up to 450 m² are fenced by tree branches, and irrigated with water from scoop holes in sandy river beds. Farmers initiate and operate their fields with no external assistance. This study presents the benefits of bucket irrigation as an often-overlooked form of farmer-led irrigation development. Through this qualitative and strongly observational study, 26 bucket irrigation farmers and 4 non-irrigators were interviewed using semi-structured interviews where farmers’ perceptions and experiences were captured. We investigate what drives and sustains bucket irrigation, its significance to rural livelihoods under harsh economic and climatic conditions, and the barriers towards scaling this type of farmer-led irrigation development. The results show that drivers for bucket irrigation stem from economic hardship and are gendered. Women are motivated to irrigate mainly by the need to produce vegetables for household consumption, whereas men pursue irrigation due to a lack of employment. Bucket irrigators experience enhanced food security, and have more secure income, contributing to improved wellbeing. Furthermore, despite the desire to scale, the farm size is mainly constrained by fencing and energy for transporting water, which is a result of a persistent lack of financial capital to invest in irrigation technologies. We conclude that bucket irrigation acts as an important livelihood strategy, and that it significantly enhances farmers’ resilience to economic and climatic shocks. Bucket irrigation should not be overlooked in policies that advocate scaling of irrigation. Bucket irrigators have the potential to expand and benefit significantly if supported with innovative financial mechanisms that enable investments in the required technology and knowledge.

The effects of deficit irrigation on water use efficiency, yield and quality of drip-irrigated tomatoes grown under field conditions in Zimbabwe

2023-11-01T14:38:07+00:00

Water availability in the root zone directly affects the yield and quality of tomatoes yet in most cases in subSaharan Africa water is either expensive or scarce. It is therefore important to establish and utilise suitable irrigation strategies in order to produce the crop in a sustainable way. In this study the effect of conventional and deficit irrigation treatments on yield, fruit quality and water use efficiency (WUE) were determined. Four trials were conducted at the University of Zimbabwe Farm from 2014-2017 with four treatments per trial: T1 = 100%, T2 = 80%, T3 = 60%, and T4 = 50% of crop water requirements (ETc). Treatments had equal number of plants per trial with an in-row plant spacing of 0.3 m and 0.5 m between adjacent rows. ETc was determined daily for each treatment and the corresponding volume applied through one drip emitter per plant. Fruits from each treatment were gathered while ripening and the total yield obtained. WUE was calculated by dividing the total fresh yield by total irrigation water applied. Maximum yield was obtained where 100% ETc was applied, with no significant difference between yield of plants at 80% and 60% ETc, except in 2016. Yield decreased with 50% ETc in 2014, 2015, and 2017 with no significant difference in yield between 60% and 50% ETc treatments in 2016. The 2015 season recorded the highest yield when compared to other trials showing that we can save 40% of water resulting in high WUE with minimum loss in yield. Deficit irrigation reduced fruit water but increased fruit soluble solids (°brix), vitamin C and fruit acid concentrations. Firmness was best when 60% ETc was applied. These results show that deficit irrigation is feasible for crop water management options for the production of high-quality field-grown tomatoes without major yield reductions.

Experimental study on optimum performance of two-stage air-heated bubble-column humidification–dehumidification system

2023-11-01T14:46:06+00:00

An experimental investigation of a small-scale air-heated humidification–dehumidification (HDH) desalination system with bubble- column humidification and dehumidification units was conducted. The study addressed the performance of the multistage air-heated bubble-column HDH system, which has limited coverage in the literature, by operating two bubble-column humidifiers in series for the air humidification process with air reheating. The effect of operating parameters such as airflow rate, air temperature, and saline water levels in both humidifiers on the performance metrics of the system were investigated. The product distillate rate, energy consumption, gain output ratio (GOR), and specific energy consumption (SEC) are the main indicators of performance for the proposed desalination system. Response surface methodology (RSM) was applied to the current system using the design of experiment (DoE) for the prediction of variables that greatly affect productivity and energy input. The airflow rate, air temperature, and water level of the second humidifier have a favourable effect on the distillate rate and GOR of the system. In contrast, the effect of the water level inside the first humidifier is insignificant. Furthermore, the RSM optimization approach was used to obtain the optimum distillate productivity. An optimized distillate rate of 0.45 L/h and a GOR of 0.4 are achieved at 1.5 SCFM (standard cubic feet per minute) of airflow rate, and 6.5 cm of water level in the second humidifier with 140°C air inlet temperature. The numerical optimization reveals the optimal operating parameters, that correspond to maximum distillate production of 0.3 L/h with minimum input energy of 0.71 kW, to be 139°C air temperature, 1.13 SCFM of airflow rate, 6.5 cm and 3 cm water levels of second and first humidifier, respectively.

Effects of leachate concentration, carbon dioxide and aeration flow rate on chlorophyll and carotenoid productivity and bioremediation potential of the microalga Chlorella minutissima

2023-11-01T15:00:43+00:00

The use of microalgae cultures to process effluents from industries, leachates, and tanneries, among others, quantified by the reduction of metallic materials in the medium and the reduction of chemical oxygen demand (COD), helps reduce the environmental impact caused by human development. In addition, with the growth of the culture, it is possible to produce a significant amount of chlorophyll, a carotenoid of high value in the cosmetics and food industries that are used as a natural pigment. In this context, this work presents a study conducted to verify the bioremediation and chlorophyll production potential of the cultivation of the microalgae Chlorella minutíssima, using the Taguchi method. The microalgae Chlorella minutissima has given good results in the bioremediation of leachate, as a mean reduction of 33% in COD was obtained, as well as a 92% reduction in the toxic components. In addition, statistical analysis revealed that the four process factors were significant factors for chlorophyll a, chlorophyll b and carotenoid productivity (p < 0.05). Finally, it was observed that the maximum chlorophyll a (111.9 ± 0.8 mg·L−1·d−1), chlorophyll b (66.1 ± 1.7 mg·L−1·d−1), and carotenoid (31.9 ± 0.03 mg·L−1·d−1) values obtained occurred in Experiment 8, which is closer to the ideal conditions identified by statistical analysis, revealing the effectiveness of the use of the Taguchi method for the design of experiments.

Occurrence of multidrug-resistant Escherichia coli and antibiotic resistance genes in a wastewater treatment plant and its associated river water in Harare, Zimbabwe

2023-11-01T16:37:38+00:00

Wastewater treatment plants (WWTPs) have been identified as point sources of antibiotic-resistant bacteria (ARB) and antibiotic- resistance genes (ARG). Due to variations in antibiotic use and prescribing patterns in different countries, it is imperative to establish the presence of ARB and ARGs in water environments on a country-by-country basis. This study investigated the occurrence of 11 antibiotic- resistance genes (QNRB, DFR14, CTX-M, KPC, Sul1, QNRA, Sul2, ERMB, ERMA, SHV, NDM), and antibiotic-resistant Escherichia coli in a WWTP and its associated river water in Harare, Zimbabwe. 24 water samples were collected across 3 sites: upstream and downstream of the WWTP; final effluent of the WWTP. The samples were collected weekly for 8 weeks. Pure cultures of the E. coli isolates were obtained by membrane filtration (0.45 µm) and repeated streaking on Tryptone Bile X-glucuronide followed by biochemical tests (indole test; citrate test; motility, indole, and ornithine). Antibiotic resistance profiling was done for 12 antibiotics using the disc diffusion method. Total genomic DNA was extracted from the 21 water samples and the occurrence of 11 antibioticresistant genes investigated using conventional PCR. 86 E. coli isolates were obtained from the sampled sites: 28 from the upstream site, 26 from the WWTP effluent, and 32 from the downstream site. The results from chisquared analysis showed a significant association (p < 0.05) between the sampling site and the percentage of antibiotic-resistant E. coli for all 12 antibiotics investigated. The percentage of E. coli isolates resistant to the tested antibiotics varied from 29% (ertapenem) to 80.2% (ciprofloxacin). 81 (94.2%) E. coli isolates were resistant to antibiotics from ≥3 classes. Eight (8/11, 72.7%) ARGs were detected in the WWTP effluent and river water samples. Results indicate that the investigated WWTP and associated river water are reservoirs of ARGs and antibiotic-resistant E. coli, which is a public health concern.

Effect of water stratification and mixing on phytoplankton functional groups: a case study of Xikeng Reservoir, China

2023-11-01T16:45:05+00:00

A shift in reservoir stratification and mixing significantly affects the water column ecosystem, which in turn leads to changes in phytoplankton abundance and community structure. To explore the effects of stratification and mixing on the phytoplankton community structure of a diversion reservoir, a 1-year survey was divided into a stratification period in 2020, a mixing period in 2020, and a stratification period in 2021, and redundancy analysis (RDA), variance partitioning analysis (VPA) and Pearson correlation analysis were used to analyse the key drivers affecting the phytoplankton functional groups, using Xikeng Reservoir as a case study. During the study period, 8 phyla, 69 genera and 9 major functional groups were observed in this reservoir. The dominant functional groups varied significantly, being X1 in the stratified period in 2020; P and D in the mixing period in 2020; and D, X1, and M in the stratified period in 2021. The phytoplankton diversity index was greater in the mixing period than in the stratification period, in agreement with the results of the aquatic ecological status evaluation (Q index, higher in the mixing period than in the stratification period). However, phytoplankton diversity of Xikeng Reservoir was of limited value in assessing the degree of water pollution, so should be considered in combination with the Q index. Water temperature (WT), mixing depth (Zmix), nitrogen–phosphorus ratio (N/P), and total nitrogen (TN) were important drivers of phytoplankton functional group dynamics in different periods. The study provides a valuable reference for assessing the relationship between environmental factors and phytoplankton communities, as well as for the evaluation and conservation of aquatic ecosystems in southern China’s water diversion reservoirs.

Antibiotics in water bodies, cyanobacterial toxicity and odorous compounds release: a review

2023-11-01T16:48:34+00:00

The present study aimed to propose a new cause of odorous compounds release, i.e., the presence of antibiotics in water bodies and its toxicity to cyanobacteria, known to be the main producer of geosmin (GEO) and 2-methylisoborneol (2-MIB). Therefore, a literature review was carried out regarding the problems caused by antibiotics in aquatic environment, including cyanobacterial blooms and GEO and 2-MIB release. In addition, a bibliometric analysis was performed using the VOSviewer software based on the results obtained from the Web of Science (WOS) database. This review aims to build a scientific understanding of the problem, presenting interesting points that converge with the proposed association. It is worth mentioning that no work has been found in the literature that has proposed this relationship. Thus, based on the bibliographic survey, observations and information acquired in recent years about cyanobacterial blooms and environmental contamination by pharmaceutical drugs, one of the main causes of an earthy and musty flavour and odour in a drinking water supply is the toxicity imposed by the presence of antibiotics in aquatic environments on cyanobacteria.