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 Prevalence and fate of antibiotics and its derivatives in sewage treatment in Durban and the receiving environment(2019) Faleye, Adekunle Christopher; Stenström, Thor-Axel; Ramluckan, Krishan; Adegoke, Anthony Ayodeji; Bux, FaizalAntibiotics are released to the environment either directly in an unchanged form or partially metabolized. The discharge is usually through untreated waste or through wastewater treatment effluents. The stable antibiotics in reduced amounts persist through the wastewater treatment processes and end up in receiving waters, where they may impact crops through irrigation or affect drinking water intakes. Antibiotics in the waste and sludge fractions may similarly impact crops and arable land through their use as fertilizers. Conventional wastewater treatment plants are not designed for the removal of antibiotics but may to a varying extent reduce their concentrations. Their quantitative occurrence within the water matrices depends on the frequency and quantities of use for therapeutic purposes or as growth promoters in animal production. Additional inputs may emanate from individual waste discharges. Antibiotics present in sub-inhibitory concentrations may predicate for resistance among the resident bacteria in the water matrix, biofilms or in humans and animals. In South Africa antibiotics are extensively used both in human therapy and in animal husbandry without clearly followed regulations and are sometimes readily available. The available studies have focused on the presence of antibiotic resistant bacteria in wastewater influent and effluent but there is a paucity of information relating to these antibiotics as emerging contaminants in South Africa wastewater. In this thesis a rapid and sensitive analytical methodology was initially assessed and applied, based on the use of HPLC/diode array UV detector for six antibiotics (ethionamide (ETI), metronidazole (MET), trimethoprim (TRI), ciprofloxacin (CIP), sulfisoxazole (SUF) and albendazole (ALB). Validation of the method was performed by screening assessment in selected wastewater treatment plants (WWTPs) with the aim of determining the sensitivity of the equipment (Shimadzu 2020), assess the limit of detection, optimize the extraction procedure (solid phase extraction) and screen for the most prevalent antibiotics. The percentage recovery for the optimized method using wastewater sample was above 65 % for all antibiotics of interest. The limit of detection, which ranges from 0.03 to 0.48 mg L-1, enables the determination of a range of concentration of antibiotics in polluted sample such as the wastewater influent sample. Furthermore in this thesis, a more advanced, online solid phase extraction – high performance liquid chromatography mass spectrometry (SPE-HPLC-MS) method, was applied to measure the concentration of these and an additional seven antibiotics, norfloxacin (NOR), ofloxacin (OFL), clindamycin (CLI), sulfamethoxazole (SUL), erythromycin (ERY), clarithromycin (CLA), azithromycin (AZI) and roxithromycin (ROX) in ng L-1 concentrations. The quantity and occurrence of the selected antibiotics was assessed in untreated wastewater in four wastewater treatment plants in Durban, KwaZulu-Natal (KZN), at different treatment stages and in the effluent and recipient surface water environment. In the influent the additive concentration of the antibiotics associated to the separated sediment fraction through centrifugation and in the supernatant of samples collected were accounted for and analyzed. The limit of detection (LOD) and the limit of quantification (LOQ), ranged from 0.07 – 0.33 ng L-1 and 0.23 – 1.09 ng L-1, respectively for the 13 assessed antibiotics and the percentage recovery were in the range of 51 to 111 %. The percentage of antibiotics recovered from the sediment (centrifuged) samples, which would have been lost to filtration if not analyzed in parallel, were in the range of 2.6% – 97% (n = 32), while the frequency of detection in the influent samples for the sampling period ranges from 62.5 – 100 % (n = 32). All the studied antibiotics were detected in the influent of each WWTP and the concentration was in the rage of 1.3 ng L-1 (AZI) – 81748 ng L-1 (CIP). The antibiotics with the highest concentrations (median) detected in the receiving water (downstream) for each of the four WWTPs in KZN, were TRI (217 ng L-1), SUL (239 ng L-1), CIP (708 ng L-1) and ALB (325 ng L-1) respectively. The overall percentage removal efficiency for the four WWTPs ranged from 21 % - 100 %. The most effective treatment steps were assessed with the focus on activated sludge filter and trickling filter. Within these, it was actually the sedimentation treatment stages (secondary clarifier), after these steps that played the most vital role in the reduction of antibiotics where > 70 % of the antibiotics was removed. Finally, the impact of post chlorination was analyzed for the effluent of the WWTPs. The presence of transformation product as a result of post chlorination was examined in a parallel study using a controlled experiment and full scale analysis. The efficiency of chlorine in the reduction of antibiotics was more of transformation of antibiotics than degradation. The oxidative ability of chlorine enhances its reaction with antibiotics thereby transforming the antibiotics. The percentage reduction of antibiotics in relation to chlorination was >85 % (pilot experiment) and ranged between 14 % - 97 % in the field experiments. Likewise, UV was effective in the degradation of antibiotics, with longer exposure time producing higher degradation. Future research should focus on determining the toxicological impact of these transformation products. The concentration of the antibiotics in the downstream samples were generally low when compared to their influent concentrations.