Showing papers by "Bhekie B. Mamba published in 2022"

Emerging remediation potentiality of struvite developed from municipal wastewater for the treatment of acid mine drainage.

Abstract: The valorisation of wastewaters for minerals recovery and their potential beneficiation has gained enormous attention recently. In this study the removal of phosphate and ammonia from municipal wastewater using activated magnesite resulted in the formation of struvite. The optimum conditions for the synthesis of struvite were 60 min of mixing, 300 rpm mixing speed, 1 g of activated magnesite and room temperature, whilst optimum conditions for the treatment of acid mine drainage (AMD) using the synthesized struvite were 45 min of mixing, 20 g of struvite dosage, 1000 mL, and 300 rpm mixing speed. The efficacy of struvite for neutralisation of AMD and attenuation of inorganic contaminants were ≥98.99% for metals (Al3+, Fe3+, and Mn2+) and ≥30% for SO42-. Traces of other metals such as Zn, Cu, Ni, Pb, and Cr were significantly attenuated. Phosphate was fully attenuated from the aqua-sphere. PHREEQC predicted the removal of minerals as oxy-(hydro)-sulphates, oxy-(hydro)-phosphate, metals hydroxides, and other complexes. FE-SEM equipped with FIB and an EDX, XRD, XRF, and FTIR confirmed the synthesis of struvite and fate of chemical species after treatment. This study confirmed the feasibility of recovering phosphate and ammonia as struvite which can be employed for the treatment of AMD.

The application of photoelectrocatalysis in the degradation of rhodamine B in aqueous solutions: a review

Abstract: The pollution of the water environment by industrial effluents is an ongoing challenge due to the rate of industrialisation and globalisation. Photoelectrocatalysis (PEC), an electrochemical advanced oxidation process, has proven to be an effective method for removing organics from wastewater. Photoelectrocatalysis is environmentally benign, cost-effective and easy to operate. In this present review, we examine the recent progress in the removal of rhodamine B dye, a common constituent of textile effluent released into the environment, through photoelectrocatalytic degradation. We present a detailed discussion on the use of different kinds of unmodified and modified photoanodes that have been explored for the photoelectrocatalytic removal of this dye. More importantly, discussions are presented on the mechanisms and kinetics of the degradation of rhodamine B dye using these photoanodes. Hence, this review will be beneficial for researchers in developing future projects in the area of wastewater treatments through photoelectrocatalysis.

S-Scheme Bi2S3/CdS Nanorod Heterojunction Photocatalysts with Improved Carrier Separation and Redox Capacity for Pollutant Removal

Abstract: Constructing step scheme (S-scheme) heterojunctions makes it possible for promoting the separation and transfer of photoinduced carriers, as well as maintaining strong photoredox capacities. Herein, S-scheme Bi2S3/CdS heterojunctions were designed and constructed by the in situ substitution of Bi3+ on CdS nanorods. The S-scheme 10%-Bi2S3/CdS heterojunction with intense interfacial contacts shows not only an optimal photoreduction rate toward Cr(VI) (3.18 and 7 times that of pure CdS and Bi2S3, respectively) but also a high photodegradation rate of ciprofloxacin (1.94 and 8.75 times that of pure CdS and Bi2S3, respectively). Meanwhile, the S-scheme 10%-Bi2S3/CdS heterojunction could efficiently prevent itself from photoetching. It is confirmed that the S-scheme 10%-Bi2S3/CdS heterojunction is produced by a built-in electric field between CdS and Bi2S3, which not only improves the charge transfer and separation efficiencies but also maintains strong redox capacities. The present study will provide distinguished insight into fabricating an S-scheme heterojunction with strong photoredox capabilities for the removal of pollutants.

Magnetically separable samarium doped copper ferrite-graphitic carbon nitride nanocomposite for photodegradation of dyes and pharmaceuticals under visible light irradiation

Abstract: Photocatalysis suffers two major drawbacks, namely the separation of the photocatalyst from treated water and the utilisation of expensive UV light. This has limited its application on an industrial scale. A novel nanocomposite of CuSm0.06Fe1.94O4@g-C3N4 with exceptional magnetic, electrochemical, and optical properties was synthesised using the hydrothermal method. The ratio of CuSm0.06Fe1.94O4 and g-C3N4 was optimised. Sm-CFGNC-3 (3: 1) was found to exhibit the highest photodegradation efficiency of 95.7% towards methyl orange (MO) in 90 min at pH 3.5, using visible light. In addition, 90.1% degradation of MO was observed in the scaled-up experiment, while high MO degradation efficiencies were also obtained for the spiked raw water from the Rand water treatment plant (83.4%) and Hazelmere treatment plant (76.6%). Furthermore, good removal efficiencies were obtained during the photodegradation of dyes (Congo red, tartrazine, Metanil yellow) and pharmaceuticals (carbamazepine, zidovudine, acetaminophen). The influence of various reaction parameters, such as catalyst amount, pH, dye concentration, oxidant effect, trapping experiments, catalyst reusability, and reaction mechanism, were investigated. Lastly, the reusability study showed a minimal loss in photocatalytic performance after 4 cycles, and the nanocomposite was easily separated from the treated water using a magnet. Thus, the synthesised nanocomposite is a potential candidate for the application of photocatalysis at an industrial scale.

In Situ Generation of Fouling Resistant Ag/Pd Modified PES Membranes for Treatment of Pharmaceutical Wastewater

Abstract: In this study, Ag and Pd bimetallic nanoparticles were generated in situ in polyethersulfone (PES) dope solutions, and membranes were fabricated through a phase inversion method. The membranes were characterized for various physical and chemical properties using techniques such as FTIR, SEM, AFM, TEM, EDS, and contact angle measurements. The membranes were then evaluated for their efficiency in rejecting EOCs and resistance to protein fouling. TEM micrographs showed uniform distribution of Ag/Pd nanoparticles within the PES matrix, while SEM images showed uniform, fingerlike structures that were not affected by the presence of embedded nanoparticles. The presence of Ag/Pd nanoparticles resulted in rougher membranes. There was an increase in membrane hydrophilicity with increasing nanoparticles loading, which resulted in improved pure water permeability (37–135 Lm2h−1bar−1). The membranes exhibited poor salt rejection (<15%), making them less susceptible to flux decline due to concentration polarization. With a mean pore radius of 2.39–4.70 nm, the membranes effectively removed carbamazepine, caffeine, sulfamethoxazole, ibuprofen, and naproxen (up to 40%), with size exclusion being the major removal mechanism. Modifying the membranes with Ag/Pd nanoparticles improved their antifouling properties, making them a promising innovation for the treatment of pharmaceutical wastewater.

The synergistic effect of peracetic acid activated by graphene oxide quantum dots in the inactivation of E. coli and organic dye removal with LED reactor light

Abstract: Abstract This study presents a low-impact process that uses the synergy of peracetic acid (PAA) and graphene oxide quantum GQDs to degrade poorly biodegradable organic compounds and potentially substitute chlorination in wastewater treatment. The role of GQDs in GQDs/PAA activity and the effect of GQDs loading were examined. The results showed that increasing GQDs loading in the GQDs/PAA system greatly improved the photodegradation efficiency. Conversely, increasing the PAA concentration slightly enhanced efficiency due to few active sites being available. GQDs acted as catalysts and radical scavenging experiments confirmed that the degradation occurred via generation of hydroxyl (•OH) and peroxy (CH3C(=O)OO•)) radicals. A probable degradation mechanism of the organic dye was presented based on the reaction by-products detected after HPLC-MS studies. The E. coli inactivation mechanism was elucidated by monitoring the morphological changes of E. coli using scanning microscopy. The proposed antimicrobial mechanism includes the initial diffusion of PAA through the cell membrane which caused damage and induced cellular matter leakage, resulting in cell death. Bacterial regrowth studies confirmed GQDs/PAA were able to bypass the natural mechanisms of microorganisms that enables them to repair any damages in their DNA.

Interdependence of Kinetics and Fluid Dynamics in the Design of Photocatalytic Membrane Reactors

Abstract: Photocatalytic membrane reactors (PMRs) are a promising technology for wastewater reclamation. The principles of PMRs are based on photocatalytic degradation and membrane rejection, the different processes occurring simultaneously. Coupled photocatalysis and membrane filtration has made PMRs suitable for application in the removal of emerging contaminants (ECs), such as diclofenac, carbamazepine, ibuprofen, lincomycin, diphenhydramine, rhodamine, and tamoxifen, from wastewater, while reducing the likelihood of byproducts being present in the permeate stream. The viability of PMRs depends on the hypotheses used during design and the kinetic properties of the systems. The choice of design models and the assumptions made in their application can have an impact on reactor design outcomes. A design’s resilience is due to the development of a mathematical model that links material and mass balances to various sub-models, including the fluid dynamic model, the radiation emission model, the radiation absorption model, and the kinetic model. Hence, this review addresses the discrepancies with traditional kinetic models, fluid flow dynamics, and radiation emission and absorption, all of which have an impact on upscaling and reactor design. Computational and analytical descriptions of how to develop a PMR system with high throughput, performance, and energy efficiency are provided. The potential solutions are classified according to the catalyst, fluid dynamics, thickness, geometry, and light source used. Two main PMR types are comprehensively described, and a discussion of various influential factors relating to PMRs was used as a premise for developing an ideal reactor. The aim of this work was to resolve potential divergences that occur during PMRs design as most real reactors do not conform to the idealized fluid dynamics. Lastly, the application of PMRs is evaluated, not only in relation to the removal of endocrine-disrupting compounds (EDCs) from wastewater, but also in dye, oil, heavy metals, and pesticide removal.

Modeling the antifouling properties of atomic layer deposition surface-modified ceramic nanofiltration membranes

Abstract: Abstract This work investigates the enhancement of antifouling properties of ceramic nanofiltration membranes by surface modification via atomic layer deposition (ALD) of TiO2. Feed solutions containing bovine serum albumin (BSA), humic acid (HA) and sodium alginate (SA) were used as model foulants. The classic fouling mechanism models and the modified fouling indices (MFI) were deduced from the flux decline profiles. Surface roughness values of the ALD coated and uncoated membranes were 63 and 71 nm, respectively, while the contact angles were 34.2 and 59.5°, respectively. Thus, coating increased the water affinity of the membrane surfaces and consequently improved the anti-fouling properties. The MFI values and the classic fouling mechanism correlation coefficients for cake filtration for the ALD coated and the uncoated membrane upon SA fouling were 42,963 (R 2 = 0.82) and 143,365 sL−2 (R 2 = 0.98), respectively, whereas the correlation coefficients for the combined foulants (SA + BSA + HA) were 267,185 (R 2 = 0.99) and 9569 sL−2 (R 2 = 0.37), respectively. The study showed that ALD can effectively enhance the antifouling properties of ceramic membranes. Graphical Abstract

Delayed Solvent–Nonsolvent Demixing Preparation and Performance of a Highly Permeable Polyethersulfone Ultrafiltration Membrane

Abstract: Membrane performance optimization is a critical preparation step that ensures optimum separation and fouling resistance. Several studies have employed additives such as carbon and inorganic nanomaterials to optimize membrane performance. These particles provide excellent results but are rather costly, unstable and toxic to several biological organs. This study demonstrated that performance enhancement can also be achieved through delayed solvent–nonsolvent demixing during phase inversion membrane preparation. The rate of solvent–nonsolvent demixing was delayed by increasing the concentration of the solvent in the coagulation bath. This study employed synthetic and real water samples and several analytical techniques to compare optimized performances and properties of membranes prepared in this study with that of nanoparticle-embedded membranes in the literature. Pure water flux and BSA rejection of the membranes prepared in this study were comparable to those of nanoparticle embedded membranes. This study also shows the influence of delayed solvent–nonsolvent demixing on membrane properties such as morphology, wettability, surface roughness and porosity, thereby showing the suitability of the technique in membrane optimization. Furthermore, fouling studies showed that membranes prepared in this study have high flux recovery when fouled by humic acid feed water (>95%) and above 50% flux recovery with real water samples.

Amorphous Nickel-Iron Hydroxide Nanosheets for Effective Electroreduction of Nitrate to Ammonia

Abstract: Nitrate emitted from agricultural runoff and industrial wastewater seriously pollutes surface and underground water. Converting nitrate (NO3-) into ammonia (NH4+) by electrochemical method not only addresses the water pollution issues...

Rejection of trace organic compounds by membrane processes: mechanisms, challenges, and opportunities

Abstract: Abstract This work critically reviews the application of various membrane separation processes (MSPs) in treating water polluted with trace organic compounds (TOrCs) paying attention to nanofiltration (NF), reverse osmosis (RO), membrane bioreactor (MBR), forward osmosis (FO), and membrane distillation (MD). Furthermore, the focus is on loopholes that exist when investigating mechanisms through which membranes reject/retain TOrCs, with the emphasis on the characteristics of the model TOrCs which would facilitate the identification of all the potential mechanisms of rejection. An explanation is also given as to why it is important to investigate rejection using real water samples, especially when aiming for industrial application of membranes with novel materials. MSPs such as NF and RO are prone to fouling which often leads to lower permeate flux and solute rejection, presumably due to cake-enhanced concentration polarisation (CECP) effects. This review demonstrates why CECP effects are not always the reason behind the observed decline in the rejection of TOrCs by fouled membranes. To mitigate for fouling, researchers have often modified the membrane surfaces by incorporating nanoparticles. This review also attempts to explain why nano-engineered membranes have not seen a breakthrough at industrial scale. Finally, insight is provided into the possibility of harnessing solar and wind energy to drive energy intensive MSPs. Focus is also paid into how low-grade energy could be stored and applied to recover diluted draw solutions in FO mode.

Comparative analysis of performance of fabricated nitrogen-doped carbon-nanotubes, silicon/germanium dioxide embedded polyethersulfone membranes for removal of emerging micropollutants from water

Abstract: The occurrence of emerging micropollutants (EMPs) in water is a new challenge to scientific community and ecosystems health worldwide. There remains widespread data gaps regarding effective removal of EMPs from water. In this study, nitrogen-doped carbon nanotubes/polyethersulfone (N-CNT/PES), silicon dioxide (silica) (SiO2) and germanium dioxide (GeO2) embedded polyethersulfone (PES) membranes were fabricated using phase inversion method. A comparative multivariate statistical analysis was done to comprehend major underlying factors behind the performance of the membranes in the removal of EMPs from water using the cross flow filtration system. The EMPs were detected and quantified using GC xGc-HRTOFMS Strong statistically significant positive correlations were observed between removal efficiency of all analytes, namely carbamazepine (CBZ), tonalide (AHTN), galaxolide (HHCB), caffeine (CAF), technical 4-nonylphenol (NP) and bisphenol A (BPA) and various membrane characteristics such as pore density number, ultimate tensile strength, Young's modulus, flux recovery ratio (p-value < 0.05, 95% confidence level). Statistically significant negative corrections were observed between the removal efficiency of the EMPs with pore size, contact angle and surface roughness. The EMPs were observed to be removed from real water samples in the following order: HHCB > NP > AHTN > BPA > CBZ > CAF. The removal of the EMPs followed the order of the decrease in hydrophobicity. It was also observed that modification of PES membranes with N-CNTs, SiO2 and GeO2 nanoparticles enhanced the fouling resistance of the membranes. Generally, the performance of the fabricated membranes in the removal of all analytes followed the following order: SiO2/PES > GeO2/PES > N-CNT/PES > pristine PES. The order of increase in water flux (L/m2/h) was observed to be PES (200.60 ± 0), N-CNT/PES (265.01 ± 0), GeO2/PES (300.01 ± 0) and SiO2/PES (305.88 ± 0). However, lower nanoparticle loadings were required to bring statistically significant improvements in performance and characteristics of the N-CNT/PES membranes than that in the SiO2/PES and GeO2/PES membranes. The results showed that the capability fabricated membranes in removing EMPs from water was superior to the majority of methods reported in the literature.

Electrode Materials for Pharmaceuticals Determination

Abstract: The presence of pharmaceuticals in surface waters called for urgent concern in recent years due to their prospective environmental effects. Various analytical methods including chemiluminescence, high-performance liquid chromatography, capillary electrophoresis-mass spectrometry, spectrophotometry and liquid chromatography have been employed for the determination of various pharmaceuticals. However, all these techniques are time-consuming, complicated and require expensive equipment. On the contrary, the electrochemical technique resolved these problems owing to its low cost, fast response, simplicity and ease of on-site application. Considering this, various electrodes have played significant roles in the determination of different drugs in biological, urine and pharmaceuticals formulations. Various electrodes are modified with various nanomaterials to improve the sluggish electron migration and electrode fouling, which reduces their selectivity and sensitivity. Considering this, the present chapter discusses the applications of various electrodes for different electrochemical analyses.