Faculty of Applied Sciences
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Item Fate and removal of emerging contaminants during chlorination in drinking water(2024-05) Hlongwa, Nhlanhla; Bux, Faizal; Kuttan, Sheena Kumari; Gyanasivan Govindsamy, RedhiThe prevalence of emerging contaminants (ECs) in drinking water is among the emerging challenges for the water industry. The problem is more complex in the developing world, where the water and sanitation facilities are underdeveloped, and the consumption of pharmaceuticals is relatively higher due to fewer healthcare facilities. Consequently, the occurrence of ECs in surface water is well reported in the literature. The presence of ECs in surface water therefore makes it necessary to investigate their removal in conventional drinking water treatment plants (DWTPs). A class of ECs known as antiretrovirals (ARVs) is commonly consumed on the African continent due to the prevalence of acquired immunodeficiency syndrome (AIDS). The chlorination process in DWTPs can have some potential for the removal of these ARVs. However, investigations on the interaction between the chlorination process and ARV removal are scarce. Therefore, the objective of this study was to investigate the removal of five ECs from conventional DWTPs. The ECs selected for the investigation were Nevirapine and Efavirenz (antiretroviral drugs), Atenolol (beta blocker), Sulfamethoxazole (antibiotic), and Carbamazepine (antiepileptic drug). Further, the chlorination process was in depth investigated to understand its kinetics, the effects of operational parameters, and the formation of disinfection by-products during the removal of two ARVs (Nevirapine and Efavirenz). To identify and measure the ECs, Ultra-High-Performance Liquid-Mass Spectrometry (uHPLC-MS) was used. In addition, laboratory studies were conducted to determine the effect of operational parameters on the removal of selected antiretroviral (Nevirapine and Efavirenz) and the formation of disinfection by products during chlorination. During optimization, the solid-phase extraction conditions for all five ECs were achieved at a pH of 3, with an average recovery rate of 64% between all selected ECs. In ascending order, the average EC concentrations detected from the influents were: Sulfamethoxazole (114.37 ng/L), Carbamazepine (118.69 ng/L), Efavirenz (156.12 ng/L), Nevirapine (164.06 ng/L), and Atenolol (197.47 ng/L), respectively. Atenolol exhibited the highest concentration levels among all the ECs in the influent Nevirapine however demonstrated the highest risk quotient (RQmax) values after post-chlorination, particularly in toddlers. The treated effluent showed a significant reduction in the amount of EC detected which was below detection and quantification level. The average removal efficiencies of ECs between the raw influent to the treated effluent where as follows: Sulfamethoxazole (87.17%), Nevirapine (85.32%), Carbamazepine (79.94%), Atenolol (76.99%), and Efavirenz (70.89%). Notably, Sulfamethoxazole exhibited significantly higher degradation and removal rates in all three DWTPs compared to the other four ECs. Using laboratory (batch) experiments, the second phase of the study examined the interaction of Nevirapine and Efavirenz with chlorination process with a prime focus on the effect of operational parameters (pH, temperature, chlorine dosage and compound concentration) and kinetics. The maximum removal of Nevirapine (97%) and Efavirenz (90%), was observed at pH=7.5 and temperature 25oC and chlorine concentration of 3 mg/L. It was further observed that Efavirenz was removed better at basic pH than acidic (37% removal at pH 5.5 versus 68% at pH 8). A threefold increase in temperature from 10oC to 30oC increased the removal of Nevirapine by 42% and Efavirenz by 39%. Higher chlorine dosages of 3 mg/L and 5 mg/L showed efficient removal of both compounds (90 - 97%). The maximum values of pseudo second order rate constant (Kapp) of Nevirapine and Efavirenz were 109.67 x 10 -2M-1 . s-1 and 95.47 x 10 -2 M-1 . s-1 at optimum conditions. The estimated the hydraulic residence time (HRT) for both ARVs was within the practical limits of 1-2 hours, considering a continuous stirred-tank reactor configuration and a chlorine dose of 2 mg/L. Further, the study investigated the formation of disinfection by-products (DBPs), specifically trihalomethanes (THMs), namely chloroform (CHCl3), dibromochloromethane (CHBr2Cl), and bromoform (CHBr3), during chlorination of the two ARVs (Nevirapine and Efavirenz). Notably, among the two drugs, Efavirenz degradation produced the highest formation of THM observed in CHCl3 (63.49 µg/L) followed by CHBr2Cl, (25.83 µg/L) and CHBr3 (11.94 µg/L). This occurred under specific conditions, including a temperature of 25 ºC, a reaction time of 6 hours, a pH of 7.5, and a residual chlorine concentration of 0.1429 μM. Furthermore, the study revealed interesting insights into the kinetics of trihalomethane formation. The highest rate Kapp for trihalomethanes was observed in CHBr2Cl, with a remarkable value of 7.722 x 10-4 M-1 ·s-1 , under the following conditions:100 µg/L efavirenz, at 25°C, chlorine concentration of 0.1426 µM, and a pH of 7.5. Conversely, the lowest Kapp value for trihalomethanes was found for CHBr3, which exhibited a Kapp value of 9.33 x 10-4 M-1 ·s -1 under the same conditions. Importantly, the investigation discovered that the Kapp for CHCl3 and CHBr2Cl formation during the degradation of Efavirenz were higher compared to those observed during the degradation of Nevirapine. This research study addressed the knowledge gap regarding EC pollution in South African drinking water by conducting a risk assessment and investigating the occurrence and removal efficiencies of specific ECs in DWTPs in KwaZulu-Natal, South Africa. The findings highlight the need for tailored approaches considering the specific characteristics and sources of ECs in the country, as complete adoption of EC management practices from developed countries may only partially mitigate EC pollution in South Africa. There is also a vital need to investigate the DPBs in an up-scale environment to assess the prevalence of DBPs in different water matrices.Item Removal of selected heavy metals from wastewater using modified agricultural waste(2023-09) Msimango, Maureen Nomaxhosa; Qwabe, L. Q.; Ntola, P.This study explores the potential of utilizing inexpensive adsorbent materials derived from agricultural waste to eliminate Zn (II), Ni (II) and Cd (II) from water-based solutions. Sugarcane bagasse was chemically modified to extract cellulose and further functionalize extracted cellulose to prepare carboxymethyl cellulose which were used as biosorbents. The biosorbents were characterized using XRD, FTIR (ATR), and SEM for confirmation of physical and chemical properties and surface morphology of the adsorbents. In batch experiments, the effect of various parameters such initial concentration (10-300 mg/L), pH (2- 8), adsorbent mass (0.1-1.7 g), and contact time (5-150 min). Adsorption was poor for all metals below pH 4 and reached maximum removal efficiency at pH 6. The increase in initial concentration favoured the increase in removal efficiency but reaches a maximum beyond 100 mg/L. The increase in biosorbent mass shows favours increase in removal efficiency for Ni (II) and Cd (II) but a decrease was observed for Zn(II). The removal efficiency increased with contact time and reached equilibrium at 60 minutes for all metals and biosorbents. The maximum adsorption capacities of Zn(II), on SCB, SCBC, and CMC were 12.3, 20.9 , and 33.5 mg/g respectively. Ni (II) adsorption capacities on SCB, SCBC, and CMC, were 41.9, 25.4, and 125.7 mg/g respectively. The maximum capacities of Cd(II) on SCB, SCBC, and CMC, were 11.3, 20.8, and 21.6 mg/g respectively. The performance of CMC superseded SCB and SCBC. Kinetic experiments showed that the adsorption process followed pseudo second order whereas the equilibrium studies showed that the adsorption process followed the Langmuir adsorption isothermItem Design and optimization of an adsorption method for the removal of textile azo dyes from aqueous solutions using Plantago lanceolata(2021) Kaunda, Thabisile Penelope; Gengan, Robert Moonsamy; Singh, T.Water is an essential commodity for human survival; however, this resource is predicted to be scarce within the 21st Century due to pollution and industrialization. Textile industries are among the many polluters of water, and hence methods to remediate textile waste-water need attention. In this study, a common garden weed Plantago Lanceolata was used for the preparation of novel activated carbon materials as an adsorbent for the degradation of textile azo dyes Reactive Blue 222 (RB), Reactive Red 195 (RR), and Reactive Yellow 145 (RY). The activated carbon was modified with four different chemical activators to produce phosphoric acid-based activated carbon (H3PQ4-AC), sulfuric acid-based activated carbon (H2SO4-AC), potassium hydroxide-based activated carbon (KOH-AC), and sodium hydroxide-based activated carbon (NaOH-AC). These materials were characterized by Fourier- transfer infrared spectroscopy (FTIR), scanning electron microscope with energy dispersive Xray (SEM/EDX), high resolution transmitting electron microscope (HRTEM), and a thermogravimetric analyzer with differential scanning calorimeter (TGA/DSC). The initial concentration of the adsorbate, adsorbent dosage concentration, contact time, temperature, and pH were optimized. The four materials adsorption capacity was studied, and H3PQ4-AC produced the best results of adsorption capacity 98,98% - 100%, with optimum agitation time of 70 minutes, the optimum dosage of 0.8 g/60 ml of adsorbent, and pH of 6. The experimental data were fitted using Langmuir (type 1- 4), Freundlich, Temkin, and Dubinin-Radushkevich isotherms. The data from this study best fitted the Langmuir isotherm type 1: RB (qm -15.58 mg g 1 ), RR (qm - 11.24 mg g 1 ) and RY (qm - 11.24 mg g 1 ). Furthermore, the reaction rate followed the pseudosecond-order kinetic model while the intraparticle diffusion model had no impact. Its thermodynamic parameters indicated the reaction as spontaneous and exothermic. Furthermore, a nanocomposite was prepared from H3PQ4-AC and iron oxide to produce an iron oxide/activated carbon nanocomposite. FTIR, SEM/EDX, HRTEM, and TGA/DSC fully characterized this novel material. The iron oxide/H3PQ4-AC nanocomposite produced slightly better results compared to H3PO4-AC: RB (99.60% - 100%), RR (99.59 - 100%) and RY (99.48% - 100%). The experimental data fitted Langmuir isotherm type 1, and the reaction followed the pseudo-second-order kinetic reaction model.