Browsing by Author "Tenza, Ntombiphumile Perceverence."

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Harnessing the power of Microalgae and Daphnia for bioremediation of nutrients, pharmaceuticals, and heavy metals in wastewater.
(2024) Tenza, Ntombiphumile Perceverence.; Mahlambi, Precious Nokwethemba.
Excess nutrients in aquatic ecosystems promote eutrophication, which significantly affects oxygen-dependent organisms. Furthermore, toxic microalgae, such as microcystin, cylindrospermopsis, etc., thrive during eutrophication, releasing poisonous compounds harmful to human health and other aquatic organisms. Pharmaceutical compounds and heavy metals in aquatic environments further exacerbate these global concerns. Thus, addressing such problems is paramount and aligns with Sustainable Development Goals (SDGs) 6 - Clean Water and Sanitation, 12 - Responsible Consumption and Production, and 14 - Life Below Water. Bioremediation of wastewater with biological microorganisms such as microalgae and daphnia provides an excellent solution due to their remarkable properties that enable them to efficiently eliminate many contaminants, including heavy metals, nutrients, and pharmaceuticals. So, this study explored the novel approach to nutrient removal by combining Chlorella spp. and Daphnia magna (D. magna). Chlorella spp. completely removed nitrate and nitrite from wastewater by converting them into compounds like amino acids, proteins, and lipids. When D. magna was employed alone, it faced significant challenges due to the absence of primary producers like bacteria and microalgae, which they mainly feed on. However, combining it with Chlorella spp. proved exceptionally effective, as 100% removal was obtained for nitrate and nitrite, possibly driven by D. magna grazing on Chlorella spp. that had assimilated nitrate and nitrite into their biomass. Challenges arose for ammonia and phosphate removal as they achieved up to 27% removals. This can be ascribed to nutrient release, Chlorella’s saturation capacity, and environmental changes such as pH. For pharmaceuticals, the study successfully developed and validated the LC-PDA method for separating sulfamethoxazole, nevirapine, and efavirenz. The optimum conditions were a mobile phase (90:10% acetonitrile: water with 0.1% formic acid), run time (8 minutes), flow rate (0.4 mL/min), and wavelength (220 nm). The study also developed and validated the solid-phase extraction (SPE) method for extracting analytes of interest in water matrices. The optimum conditions were conditioning solvent (mixture of acetonitrile and methanol in a 70:30 (v/v) ratio), sample volume (50 mL), and pH 7. The study then assessed Chlorella's capacity to remove sulfamethoxazole, nevirapine, and efavirenz. The obtained removal efficiencies for efavirenz, nevirapine, and sulfamethoxazole ranged from 0–60%, 5–51%, and 10–50%, respectively. Furthermore, the results exhibited lower removal efficiency (up to 15%) for higher concentrations (1 and 5 mg/L), whereas lower initial concentrations (0.5 and 0.25 mg/L) showed higher removal rates (up to 60%). Low removals could be due to factors like toxic metabolite accumulation and pharmaceutical toxicity. This study also explored copper, lead, and zinc adsorption capacity on Chlorella spp. biomass. Batch cultures were assessed in triplicate at 150 rpm in an orbital shaker under different biomass dosages, pH levels, contact times, and metal concentrations. The optimum conditions were pH 7, 60 minutes contact time, biomass dosage of 12.5 mg, and 0.5 m/L concentration. The optimal conditions yielded complete removal of lead and zinc, with copper reaching up to 80% removal. The study also assessed the adsorption of target heavy metals employing Freundlich, Langmuir, and Temkin isotherms, with the Langmuir isotherm better fitting copper (R2 = 0.9888) while the Freundlich isotherm best-fitted lead (R2 = 0.976) and zinc (R2 = 0.968). Lead and zinc favoured the pseudo-first-order kinetic model, whereas copper favoured the pseudo-second-order kinetic model. Thermodynamic studies exhibited an endothermic and spontaneous process for copper and zinc. The results of this PhD underscored Chlorella's potential as an environmentally safe and effective option for removing nutrients, pharmaceutical compounds, and heavy metals. Mechanisms for removal included surface adsorption, photodegradation, bioaccumulation, and enzymatic degradation. The Fourier transform infrared spectroscopy (FTIR) confirmed the existence of functional groups like alkene, amide, carbonyl, carboxyl, ethers, hydroxyl, and methyl, which participate in the adsorption of these contaminants through various interactions. Surface morphology analysis through scanning electron microscopy (SEM) shows changes in Chlorella spp. cells after exposure to target compounds (nutrients, pharmaceutical compounds, and heavy metals), suggesting the possibility of interaction that aids their removals. Thus, this study contributed valuable insights for improving wastewater treatment strategies and addressing water scarcity concerns. Additionally, it promotes a circular economy as Chlorella spp. and daphnia biomass can be harvested at the end of the treatment process for diverse uses, including biogas production, organic fertiliser, animal feed, etc. Going forward, future research should focus on optimising bioremediation by exploring different combinations of microalgae and other biological agents to enhance the removal efficiencies of heavy metals and pharmaceuticals. Moreover, genetic modification of Chlorella spp. to improve resilience and uptake capacity is crucial, and integrating advanced monitoring technologies like biosensors are promising directions. In-depth studies on removal mechanisms, such as adsorption, photodegradation, bioaccumulation, and enzymatic degradation, are essential. Also, scaling up to pilot and full-scale applications is crucial for evaluating feasibility and economic viability. Lastly, collaboration with industrial partners and policymakers can help develop regulatory frameworks and incentives. These efforts can advance bioremediation and support global SDGs related to clean water, responsible production, and life below water.
Macroinvertebrates as ecological indicators of the wellbeing of the lower uMvoti and Thukela Rivers, KwaZulu-Natal, South Africa.
(2018) Tenza, Ntombiphumile Perceverence.; O'Brien, Gordon Craig.; Downs, Colleen Thelma.
The excessive use of water resources and climate change stressors is impacting the quality and quantity of surface aquatic ecosystems in South Africa, a semi-arid country. Although South Africa is considered to be a developing nation, riverine ecosystems have already been transformed and impacted on to meet human needs. This has altered the ecological characteristics of the rivers of which more than 70% are now threatened. The National Water Act (NWA) of South Africa and associated National Water Resource Strategy (NWRS) advocates the establishment of a suitable balance between the use and protection of water resources to ensure sustainability. The implementation of NWA and NWRS is limited in some South African rivers and the quality of these vulnerable ecosystems continues to deteriorate. Knowledge is needed to evaluate the response of the riverine ecosystems to changes in environmental variables so that we can understand the socio-ecological consequences of the continued deterioration of our resources and best manage them when resource demand exceeds supply. This study focusses primarily on lower uMvoti and Thukela Rivers along with their associated tributaries (Ntchaweni and Mandeni Streams). These rivers are among the highly threatened ecosystems and that can be attributed to water resource use stressors including overexploitation, invasion by exotic species, industrial pollution and effluents, extensive agricultural practices, mining activities, increased urbanization as well as social and economic development in peri-urban and urban centres. These stressors have been identified as determinants of the degradation of aquatic biodiversity and they result in the loss of key ecosystem services. Aquatic macroinvertebrates are good ecological indicators that have been used internationally to establish robust bio-monitoring lines of evidence or tools for the monitoring and management of river ecosystems. Today a suite of international and local lines of evidence incorporating macroinvertebrates are available to evaluate the wellbeing of macroinvertebrates communities, their response to environmental variable changes and the wellbeing of the rivers they occur in. To implement the use of macroinvertebrate communities as ecological indicators of the evaluation of the wellbeing of the uMvoti and Thukela Rivers, aquatic insects, mollusks, fresh water crustaceans, annelids, and other aquatic invertebrate communities were characterised. These use of these ecological indicators is well established due to: (1) the knowledge of the tolerances of taxa to different water quality, quantity and habitat stresses, (2) the high diversity of taxa that are representative of a wide range of river ecosystem types and (3) they are abundant, easy to collect (visible to the naked eye) and easy to identify. Two community metric measure tools namely the South African Scoring System (SASS, version 5) and the Macroinvertebrate Response Assessment Index (MIRAI) were used to evaluate the wellbeing of macroinvertebrate communities of the lowland uMvoti and Thukela Rivers in this study. The ecological integrity of both rivers were found to be adversely impacted and their integrity state ranged mostly from class C (moderately modified) to class E/F (seriously or extremely modified). Reduced habitat heterogeneity and altered water quality were found to be driving factors that cause the degradation in macroinvertebrate communities. Multivariate statistical analyses were used to evaluate the responses of macroinvertebrate communities to water resource use activities associated with the uMvoti and Thukela Rivers. In the early part of the study period many intolerant macroinvertebrate taxa contributed to the structure of communities. However, towards the latter part of the study, pollution tolerant taxa dominated communities. Both rivers also showed a decreasing trend in estimated macroinvertebrates estimated abundance and number of taxa. In the uMvoti River this can be attributed to the combined effect of the urban runoff, effluence discharge from the Gledhow sugar mill and Sappi Stanger Mill, informal settlements and agricultural activities. Results reported from the Thukela River can be ascribed to the synergistic effects of water quality stressors associated with the Isithebe Industrial complex, wastewater treatment works, effluent from the Sappi mill, sugarcane plantations as well as domestic use by local communities. The outcomes of this study showed that there is not sufficient protection and management measures afforded to the systems. The requirements of the National Water Act to establish a sustainable balance between the use and protection of the water resources in the system is not being achieved. No action is being taken to mitigate pollution from major sources in the study area. Thus, an appropriate management plan and its implementation is urgently needed, with monitoring activities, to mitigate these stressors and attain a balance between use and protection of these socio-ecologically important ecosystems. Failure to implement effective management plans may result in continued deterioration of the wellbeing of the ecosystem and potential loss of biodiversity, ecosystem services and functions that these rivers provide.