Research Publications (Applied Sciences)

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Advances in synthesis of biodiesel via enzyme catalysis : Novel and sustainable approaches
(Elsevier, 2015-01) Singh, Bhaskar; Mutanda, Taurai; Permaul, Kugen; Bux, Faizal; Guldhe, Abhishek
Biodiesel, a renewable fuel has a great potential in fulﬁlling an ever-increasing transport fuel demand. The enzymatic conversion process of feedstock oil to biodiesel is greener when compared to the conventional approach of chemical conversion due to mild reaction conditions and less wastewater generation. Lipases obtained from various microbial sources have been widely applied as catalysts for the conversion of oil to biodiesel. Biodiesel and glycerol obtained by enzymatic conversion have shown a higher purity as compared to that obtained by other conversion techniques. Enzymatic conversion of oil to biodiesel is less energy intensive because of milder reaction conditions and fewer puriﬁcation steps involved in processing. Lipases, due to their catalytic efﬁciency and speciﬁcity, have emerged as a great tool for converting a wide range of feedstock oils to biodiesel. This manuscript presents an overview of the use of enzymatic conversion for making biodiesel production sustainable and environmentally-friendly. The constraints of enzymatic conversion are the high cost of the enzyme and its inhibition by alcohol and glycerol. The possible solutions to overcome these constraints are discussed. Recent advances to develop an effective process for enzymatic conversion of feedstock oils into biodiesel are critically evaluated. Prospective and challenges in scaling up of this technology are also discussed.
Biocatalytic conversion of lipids from microalgae Scenedesmus obliquus to biodiesel using Pseudomonas ﬂuorescens lipase
(Elsevier, 2015-01-31) Guldhe, Abhishek; Singh, Bhaskar; Rawat, Ismail; Perumal, Kugen; Bux, Faizal
Conversion of microalgal lipids using biocatalyst is a novel and greener approach to produce biodiesel. Free and immobilized lipases from Candida sp. and Pseudomonas fluorescens along with free lipases from porcine pancreas and wheat germ were screened for biodiesel conversion of Scenedesmus obliquus lipids. Among selected lipases from various sources immobilized lipase from P. fluorescens showed superior biodiesel conversion. Optimization of reaction parameters viz. lipase amount, temperature, methanol to oil molar ratio and water content was carried out using response surface methodology. Best conversion of 66.55% was achieved at 35 °C, methanol to oil ratio of 3:1 with 10% enzyme amount and 2.5% water content based on oil weight. To tackle methanol tolerance step-wise methanol addition was applied, which improved biodiesel conversion upto 90.81%. Immobilized P. fluorescens lipase can be used for 4 batches without much loss in conversion efficiency (>95%). Biodiesel produced has the cetane number of 51.77, Calorific value of 37.67 MJ kg−1. Most of the fuel properties of biodiesel met the specifications set by ASTM and EN standards.
Biodegradation of glycerol using bacterial isolates from soil under aerobic conditions
(Taylor and Francis, 2014) Raghunandan, Kerisha; Mchunu, Siphesihle; Kumar, Ashwani; Kumar, Kuttanpillai Santhosh; Govender, Algasan; Permaul, Kugen; Singh, Suren
Glycerol, a non-biodegradable by-product during biodiesel production is a major concern to the emerging biodiesel industry. Many microbes in natural environments have the ability to utilize glycerol as a sole carbon and energy source. The focus of this study was to screen for microorganisms from soil, capable of glycerol utilization and its conversion to value added products such as ethanol and 1,3-propanediol (1,3-PDO). Twelve bacterial isolates were screened for glycerol utilization ability in shake flask fermentations using M9 media supplemented with analytical grade glycerol (30 g/L) at various pH values (6, 7 and 8) and temperatures (30◦C, 35◦Cand 40◦C). Among these, six bacterial isolates (SM1, SM3, SM4, SM5, SM7 and SM8) with high glycerol degradation efficiency (>80%) were selected for further analysis. Highest level of 1,3-PDO production (15 g/L) was observed with isolate SM7 at pH 7 and 30◦C, while superior ethanol production (14 g/L) was achieved by isolate SM9 at pH 8 and 35◦C, at a glycerol concentration of 30 g/L. The selected strains were further evaluated for their bioconversion efficiency at elevated glycerol concentrations (50–110 g/L). Maximum 1,3-PDO production (46 g/L and 35 g/L) was achieved at a glycerol concentration of 70 g/L by isolates SM4 and SM7 respectively, with high glycerol degradation efficiency (>90). Three isolates (SM4, SM5 and SM7) also showed greater glycerol tolerance (up to 110 g/L). The isolates SM4 and SM7 were identified as Klebsiella pneumoniae and SM5 as Enterobacter aerogenes by 16S rDNA analysis. These novel isolates with greater glycerol tolerance could be used for the biodegradation of glycerol waste generated from the biodiesel industry into value-added commercial products.
Biodiesel from microalgae: A critical evaluation from laboratory to large scale production
(Elsevier, 2013) Rawat, Ismail; Ranjith Kumar, R.; Mutanda, Taurai; Bux, Faizal
The economically signiﬁcant production of carbon-neutral biodiesel from microalgae has been hailed as the ultimate alternative to depleting resources of petro-diesel due to its high cellular concentration of lip-ids, resources and economic sustainability and overall potential advantages over other sources of biofu-els. Pertinent questions however need to be answered on the commercial viability of large scale production of biodiesel from microalgae. Vital steps need to be critically analysed at each stage. Isolation of microalgae should be based on the question of whether marine or freshwater microalgae, cultures from collections or indigenous wild types are best suited for large scale production. Furthermore, the determination of initial sampling points play a pivotal role in the determination of strain selection as well as strain viability. The screening process should identify, purify and select lipid producing strains. Are natural strains or stressed strains higher in lipid productivity? The synergistic interactions that occur nat-urally between algae and other microorganisms cannot be ignored. A lot of literature is available on the downstream processing of microalgae but a few reports are available on the upstream processing of mic-roalgae for biomass and lipid production for biodiesel production. We present in this review an empirical and critical analysis on the potential of translating research ﬁndings from laboratory scale trials to full scale application. The move from laboratory to large scale microalgal cultivation requires careful plan-ning. It is imperative to do extensive pre-pilot demonstration trials and formulate a suitable trajectory for possible data extrapolation for large scale experimental designs. The pros and cons of the two widely used methods for growing microalgae by photobioreactors or open raceway ponds are discussed in detail. In addition, current methods for biomass harvesting and lipid extraction are critically evaluated. This would be novel approach to economical biodiesel production from microalgae in the near future. Glob-ally, microalgae are largest biomass producers having higher neutral lipid content outcompeting terres-trial plants for biofuel production. However, the viscosities of microalgal oils are usually higher than that of petroleum diesel.
Biodiesel synthesis from microalgae using immobilized Aspergillus niger whole cell lipase biocatalyst
(Elsevier, 2016) Guldhe, Abhishek; Singh, Poonam; Kumari, Sheena K.; Rawat, Ismail; Permaul, Kugen; Bux, Faizal
Whole cell lipase catalysis and microalgal feedstocks make overall biodiesel synthesis greener and sustainable. In this study, a novel approach of whole cell lipase-catalyzed conversion of Scenedesmus obliquus lipids was investigated for biodiesel synthesis. Microalgal biodiesel was characterized for its fuel properties. Optimization of process parameters for immobilized Aspergillus niger whole cell lipase-catalyzed biodiesel synthesis was carried out. Highest biodiesel conversion of 53.76% was achieved from S. obliquus lipids at 35 °C, methanol to oil ratio of 5:1 and 2.5% water content based on oil weight with 6 BSPs (Biomass support particles). Step-wise methanol addition was applied to account for methanol tolerance, which improved biodiesel conversion upto 80.97% and gave 90.82 ± 1.43% yield. Immobilized A. niger lipase can be used for 2 batches without signiﬁcant loss in conversion efﬁciency. Most of the fuel properties of biodiesel met the speciﬁcations set by international standards.
Display of phytase on the cell surface of Saccharomyces cerevisiae to degrade phytate phosphorus and improve bioethanol production
(Springer Verlag, 2016) Xiao, Yan; Shen, Wei; Govender, Algasan; Zhang, Liang; Xianzhong, Chen
Currently, development of biofuels as an alternative fuel has gained much attention due to resource and environ-mental challenges. Bioethanol is one of most important and dominant biofuels, and production using corn or cassava as raw materials has become a prominent technology. However, phytate contained in the raw material not only decreases the efficiency of ethanol production, but also leads to an increase in the discharge of phosphorus, thus impacting on the environment. In this study, to decrease phytate and its phos-phorus content in an ethanol fermentation process, Saccharomyces cerevisiae was engineered through a surface-displaying system utilizing the C-terminal half of the yeast α-agglutinin protein. The recombinant yeast strain, PHY, was constructed by successfully displaying phytase on the surface of cells, and enzyme activity reached 6.4 U/g wet biomass weight. Ethanol productions using various strains were com-pared, and the results demonstrated that the specific growth rate and average fermentation rate of the PHY strain were higher 20 and 18 %, respectively, compared to the control strain S. cerevisiae CICIMY0086, in a 5-L bioreactor process by simultaneous saccharification and fermentation. More im-portantly, the phytate phosphorus concentration decreased by 89.8 % and free phosphorus concentration increased by 142.9 % in dry vinasse compared to the control in a 5-L bio-reactor. In summary, we constructed a recombinant S. cerevisiae strain displaying phytase on the cell surface, which could improve ethanol production performance and effectively reduce the discharge of phosphorus. The strain reported here represents a useful novel engineering platform for developing an environment-friendly system for bioethanol production from a corn substrate.
Effect of internal woven roller shade and glazing on the energy and daylighting performances of an ofﬁce building in the cold climate of Shillong
(Elsevier, 2015) Singh, Ramkishore; Lazarus, Ian Joseph; Kishore, V.V.N.
The energy and visual performances of the façades are deﬁned by many parameters including façade size, properties of glazings and shadings, and their arrangements as well as control strategies. In this study, a number of combinations of internal woven roller shades and four double glazings have been proposed and assessed in integrated manner in order to improve the energy efﬁciency and visual comfort in new or existing ofﬁce buildings. Ofﬁce rooms facing south, east, north and west have been simulated for cold climate, by varying glazed areas and proposed glazing and shading alternatives. Results have been calculated, compared and analyzed in terms of the energy consumptions, energy saving potentials, daylight autonomy, useful daylight illuminance and discomfort glare free time, for each of the combina-tions. Simulation results show that the choice of glazing and shading alternatives can have substantial impact on energy and visual performances of the ofﬁce space. Regardless of façade orientation, the max-imum energy saving is achieved for a window-to-wall ratio (WWR) of 30%. Saving potential decreases signiﬁcantly for larger glazed area and for each façade orientation. For all façade orientations and glazed areas (except for 30% WWR in the north wall), a bare low-e coated double glazing (U = 1.616 W/m2 K, SHGC = 0.209, sv = 0.301) is found to be the most energy efﬁcient choice. For 30% north glazing, the energy efﬁciency can be maximized with a different bare low-e coated double glazing (U = 1.628 W/m2 K, SHGC = 0.370, sv = 0.581). Moreover, glare affected time, daylight autonomy and useful daylight illuminance in the ofﬁce spaces with these glazing choices are estimated P50%, between 46% and 99%and in the range of 53–88% respectively. Also, the visual comfort can further be improved just by deploy-ing even a highly transparent fabric (50% transmittance, 20% reﬂectance, 45% average openness) as an interior roller shade with these glazing choices.
Embedding undergraduate research through industry-based projects : student experiences
(Durban University of Technology, 2022) Naicker, Ashika; Singh, Evonne
Traditionally, formal training in research methodology begins in postgraduate programmes; however, potential exists to embed high-impact research skills during the undergraduate programme to develop learning by inquiry, promote critical thinking and engaged scholarship. Identifying factors that affect students’ research engagement can provide important practical implications to effectively encourage and facilitate undergraduate research opportunities. This exploratory qualitative study investigates the undergraduate student experience of the research process embedded in collaborative industry-based projects, through focus-group discussions. Using predefined domains from the interview guide, key themes emerging from the focus group discussions included a process-orientated approach to research, knowledge synthesis through data collection and handling, data collection experience, and students’ experience of a collaborative and deep approach to learning. Key enablers of the research engagement included funding for undergraduate research and transfer of research skills into higher levels of study whilst key barriers were limited foundational research knowledge and the impact of emergency situations. Other emergent themes included knowledge transfer through early initiation of research in the undergraduate programme. Institutional and programmatic engagement is required to support undergraduate students with the rigours of becoming knowledge co-constructors for their graduate destination or continuation of postgraduate studies.
Energy and daylighting performances of highly glazed buildings
(Building Simulation, 2015-12) Singh, Ramkishore; Lazarus, Ian Joseph
Glazed façades create indoor environment more attractive and pleasant but also let high solar and thermal gains in the buildings that lead to energy inefficiency. Hence, more attention needs to be given to the glazed component to improve the buildings’ energy performance and indoor visual comfort. This study aims to provide insightful on the suitable selection of the glazed components for the office buildings. In this study, a number of simulations were performed, using EnergyPlus, for the office rooms with one and two exposure wall(s) in two different climates. Results were analysed and presented in terms of the energy demands for heating, cooling, fans and lightings and daylighting performance considering useful daylight illuminance (UDI) and discomfort glare.
Enzymatic saccharification of acid/alkali pre-treated, millrun, and depithed sugarcane bagasse
(Open Journal Systems, 2016) Mkhize, Thandeka, Y.; Mthembu, Lethiwe Debra; Gupta, Rishi; Kaur, Amandeep; Kuhad, Ramesh Chander; Reddy, Prashant; Deenadayalu, Nirmala
In South Africa, approximately 3 × 106 tons of sugarcane bagasse is produced annually by 14 factories located on the north coast of KwaZulu-Natal. It is one of the most readily available lignocellulosic materials for ethanol production through enzymatic saccharification and hydrolysis. Pre-treatment enables disruption of the naturally resistant structure of lignocellulosic biomass to make the cellulose accessible to hydrolysis for conversion to biofuels. In this study, pre-treatment of depithed bagasse and mill-run bagasse was done using acid (3% H2SO4 v/v) followed by alkali (4% NaOH w/v), and the pre-treated solid was subjected to enzymatic hydrolysis. The effects of different conditions for enzymatic saccharification such as enzyme dose, reaction time, and amount of surfactant were studied in detail. The pre-treated substrate (10% w/v) when hydrolysed using 30 FPU/gds/40 FPU/g dry substrate (gds) with 0.4% (v/v) Tween® 80 for 20 h resulted in 608 mg/gds (depithed bagasse) and 604 mg/gds (mill-run bagasse) total reducing sugars.
An evaluation of the efﬁcacy of using selected solvents for the extraction of lipids from algal biomass by the soxhlet extraction method
(Elsevier, 2013-08-14) Ramluckan, Krishan; Bux, Faizal; Moodley, Kandasamy G.
The use of solvents for the extraction of lipids from algal biomass has been a method of choice for many years. The soxhlet extraction method was chosen because of its simplicity in operation, relative safety and potential for upscaling to industrial plant level. The source of algal biomass was a raceway pond. Chlorella sp. which is known to produce larger amounts of oil than other indigenous species was used for this investigation. Thirteen solvents spanning a range of polarities and solubilities were selected for this study. Extraction methodology involved the use of single solvents, selected binary solvent mixtures and time-based extractions which were varied from 1 to 5 h. Ultraviolet (UV) spectroscopy was used to determine chlorophyll content of the lipid extracts and gas chromatography was used for the identiﬁca-tion and quantitation of the lipids. Analysis showed that ethanol, chloroform and hexane were generally more efﬁcient in the extraction of lipids than the other solvents studied, producing lipid contents in excess of 10%. The time-based trials indicated that the optimum extraction time was 3 h for the solvents selected. The binary solvent mixture with the greatest extraction efﬁciency (i.e. >10% lipid extract) was obtained with the 1:1 mixture of chloroform:ethanol. Chlorophyll quantities varied for each solvent extract with chloroform and methanol producing the highest values at >1%. Chromatography was effec-tive in identifying lipids used in the production of biodiesel.
Impact of anisotropic stresses during dissipative gravitational collapse
(Springer Verlag, 2015-04) Reddy, Kevin P.; Govender, Megandhren; Maharaj, Sunil
We employ a perturbative scheme to study the evolution of a spherically symmetric stellar body undergoing gravitational collapse in the presence of heat dissipation and anisotropic stresses. The Bowers and Liang static model is perturbed, and its subsequent dynamical collapse is studied in the linear perturbative regime. We find that anisotropic effects brought about by the differences in the radial and tangential pressures render the core more unstable than the cooler surface layers. An analysis of the temperature profiles in the interior of the collapsing body shows that the temperature is enhanced in the presence of pressure anisotropy.
Improving the feasibility of producing biofuels from microalgae using wastewater
(Taylor and Francis, 2013-10-08) Rawat, Ismail; Bhola, Virthie; Ranjith Kumar, R.
Biofuels have received much attention recently owing to energy consumption and environmental concerns. Despite many of the technologies being technically feasible, the processes are often too costly to be commercially viable. The major stumbling block to full-scale production of algal biofuels is the cost of upstream and downstream processes and environmental impacts such as water footprint and indirect greenhouse gas emissions from chemical nutrient production. The technoeconomics of biofuels production from microalgae is currently unfeasible due to the cost of inputs and productivities achieved. The use of a bioreﬁnery approach sees the production costs reduced greatly due to utilization of waste streams for cultivation and the generation of several potential energy sources and value-added products while oﬀering environmental protection. The use of wastewater as a production media, coupled with CO2 sequestration from ﬂue gas greatly reduces the microalgal cultivation costs. Conversion of residual biomass and by-products, such as glycerol, for fuel production using an integrated approach potentially holds the key to near future commercial implementation of biofuels production.
The inﬂuence of initial conditions during dissipative collapse
(World Scientific Publishing Company, 2016) Naidu, N. F.; Govender, Megandhren
Starting oﬀ with two distinct initially static stellar cores (i) Florides interior (constant density, vanishing radial pressure) and (ii) Wyman interior (constant density, nonvan-ishing radial pressure), we explore the dynamics of these two models once hydrostatic equilibrium is lost. We show that although the time of formation of horizon, evolution of the mass and proper radius are independent of the chosen initially static conﬁgurations, there is a signiﬁcant diﬀerence in the temperature proﬁles of the radiating bodies as the collapse proceeds.
Integrated collector storage solar water heaters : survey and recent developments
(Springer Verlag, 2016) Souliotis, Manolis; Singh, Ramkishore; Papaefthimiou, Spiros; Lazarus, Ian Joseph; Andriosopoulos, K.
The direct conversion of solar to thermal energy is highly efﬁcient, more environmental friendly and economically viable. Integrated collector storage solar water heaters (ICSSWH) converts the solar radiation directly into heat at an appreciable conversion rate and in many cases using concentrating means. These systems are compact, aesthetically attractive and reasonable in construction and can reduce the environmental impact up to 40 %. They also have high collection efﬁciency factor and energy saving potential. Despite of many advantages, ICS solar water heaters suffer from high thermal losses in the night/overcast sky conditions. In this article, authors discuss the recently developed new and improved ICS designs and strategies used for reducing thermal losses from such devices, especially in non-collection period. The systems have been evaluated based on a followed categorization to non-concentrating, concentrating and systems with phase change materials.
Investigation of combined effect of nitrogen, phosphorus and iron on lipid productivity of microalgae Ankistrodesmus falcatus KJ671624 using response surface methodology
(Elsevier, 2015-02-15) Singh, Poonam; Guldhe, Abhishek; Kumari, Sheena K.; Rawat, Ismail; Bux, Faizal
Enhancement of lipid accumulation is essential to improve the commercial feasibility of microalgal biodiesel production. An oleaginous microalgal strain, Ankistrodesmus falcatus KJ671624 was evaluated for its potential as a biodiesel feedstock in this study. The collective effect of nutrient (nitrogen, phospho-rous and iron) stresses on the lipid productivity of the selected strain was studied by response surface methodology. The highest lipid content of 59.6% and lipid productivity of 74.07 mg L−1 d−1 was obtained under nutrient stress with nitrogen 750 mg L−1, phosphorus 0 mg L−1 and iron 9 mg L−1. The photosyn-thetic behaviour validates the high lipid productivity under combined nutrient stress condition. Saturated fatty acid composition was increased by 38.49% under selected nutrient stress condition compared to BG11 medium. The enhanced lipid accumulation with suitable lipid proﬁle (C16:0, C18:1, C18:2, C18:3) and biodiesel conversion of 91.54 ± 1.43% achieved in A. falcatus KJ671624 further conﬁrm its potential as a promising feedstock for biodiesel production.
A low cost one pot synthesis of biodiesel from waste frying oil (WFO) using a novel material, b-potassium dizirconate (b-K2Zr2O5)
(Elsevier, 2016) Singh, Veena; Bux, Faizal; Sharma, Yogesh Chandra
Biodiesel was synthesized from waste frying oil (WFO) using b-potassium dizirconate (b-K2Zr2O5)asa novel heterogeneous catalyst. Synthesized catalyst was characterized by X-ray diffractometry (XRD), thermogravimetric analysis (TGA), attenuated total reﬂectance fourier transform infrared spectroscopy (ATR-FTIR), particle size analyser, scanning electron microscopy (SEM), BET surface area and basicity. Various reaction conditions such as molar ratio of methanol: oil, catalyst amount (wt%), reaction temperature, time and reusability of catalyst were studied for transesteriﬁcation reaction with the catalyst, b-K2Zr2O5. High biodiesel conversion of 96.85% was observed at a 10:1 M ratio (alcohol: oil), 4 wt% catalyst at 65 C for 2 h. WFO was characterized by GCMS and biodiesel conversion was ascertained by Fourier transform nuclear magnetic resonance (1H and 13C FTNMR) spectroscopy. It was ﬁrst time that b-potassium dizirconate was used as a catalyst for biodiesel synthesis. The catalyst was reused up to ﬁve times without signiﬁcant loss in its activity. Physical and chemical properties of FAME such as ﬂash point, ﬁre point, cloud point, density, and kinematic viscosity were deliberated.
Physico-chemical and biotic factors influencing microalgal seed culture propagation for inoculation of a large scale raceway pond
(African Journals Online, 2014) Mutanda, Taurai; Ranjith Kumar, R.; Bux, Faizal
The growth of Chlorella vulgaris in open pond aquatic conditions poses serious challenges due to the interplay of both physico-chemical and biotic factors. We report here the monitoring of physico-chemical and biotic parameters affecting the propagation of C. vulgaris seed culture for inoculation of a large scale raceway pond (300 000 L capacity) in South Africa. The C. vulgarisstrain used for this purpose was isolated from a wastewater maturation pond and characterized for its potential for biomass and lipid production. The isolate was grown aseptically in 4 × 25 L aspirator bottles in BG-11 medium under ambient laboratory conditions and the culture was supplied with filtered air and exposed to 200 µmol photons per m2 per second using Gro-Lux agricultural fluorescent lights. The culture was transferred to a 500 L capacity portable pool under open conditions. This pond was used to further inoculate 3 more portable ponds. Physico-chemical and biotic growth parameters were monitored on a daily basis in the three ponds. The over reliance on fossil fuels will have a major impact on power supply in the near future if renewable sources of energy are not developed at a fast pace. The developed inoculum was subsequently used to inoculate an open raceway pond for large scale biomass production for biodiesel production.
The prevalence of selected emerging pathogenic species in wastewater and receiving water bodies
(2022-03-16) Govender, Reshme; Stenström, Thor Axel; Pillai, Santhosh Kumar Kuttan; Swalaha, Feroz Mahomed; Bux, Faizal
Antibiotic resistance is one of the biggest threats to global health, due to the excessive use of antibiotics, among other factors. Aquatic environments are considered hotspots for antibiotic-resistant bacteria and genes due to pollution caused by various anthropogenic activities. In this study, four emerging opportunistic pathogens viz., Acinetobacter spp., Pseudomonas spp., Aeromonas spp., and Stenotrophomonas maltophilia were investigated to understand their distribution, source, and resistance patterns in wastewater and surface water. Among these, Acinetobacter baumannii and Pseudomonas aeruginosa have been listed by the World Health Organization (WHO) in 2017 as priority bacteria for further research and development. This study focused on the Umhlangane River, located in the north of Durban, in KwaZulu Natal, South Africa. The possible effect of anthropogenic activities such as discharges from wastewater treatment plants (WWTPs), hospitals, informal settlements, and veterinary clinics on the occurrence of antibiotic-resistance, and virulence signatures of the targeted organisms, was investigated. Sixty samples (12 wastewater, 48 surface water) were collected monthly (November 2016 to April 2017). This included influent and effluent of a wastewater treatment plant (WWTP) and four additional sampling sites (upstream and downstream of the WWTP, a hospital, an informal settlement, and a veterinary clinic). In addition, to the sixty samples, further samplings of aquatic plants (n=16) and sediments (n=16) were done in October 2017, specifically for the isolation of Stenotrophomonas maltophilia. The isolation and enumeration were carried out on selective media for each bacterium. The PCR positive isolates were identified using Matrix-Assisted Laser Desorption Ionization -Time of Flight Mass Spectrometry (MALDI-TOF MS) and 16S rRNA sequencing. In addition, advanced methods such as Flow Cytometry (FCM) and Droplet Digital PCR (ddPCR) were used to detect and quantify the bacteria, in comparison to conventional methods. The multiple antibiotic resistance (MAR) index was calculated to ascertain the contribution of these pollution sources to the proliferation of antibiotic-resistant bacteria in surface water. Varying counts (log10 CFU/mL) of Aeromonas spp. (2.5±0.8 to 3.3±0.4), Pseudomonas spp. (0.6±1.0 to 1.8±1.0) and Acinetobacter spp. (2.0±1.5 to 2.6±1.2) were obtained. S. maltophilia was found in the water column only at two sites and ranged from 2.7±0.3 to 4.1±1.0 log10 CFU/mL. However, it was found abundantly in the plant rhizosphere (3.6±0.1 to 4.2±0.6 log10 CFU/mL) and sediment (3.8±0.1 to 5.0±0.1 log10 CFU/mL) samples. The major Aeromonas species identified by MALDI-TOF MS was A. hydrophila / caviae (58%) whilst P. putida (51%) was common amongst the Pseudomonas isolates. The Acinetobacter genus was dominated by the Acinetobacter baumannii complex (26%), in contrast, all Stenotrophomonas maltophilia identities were confirmed via Polymerase Chain Reaction (PCR) and MALDI-TOF MS. Aeromonas (71%) and Pseudomonas (94%) isolates displayed resistance to three or more antibiotics. Aeromonas isolates displayed high resistance against ampicillin and had higher MAR indices, downstream of the hospital. The virulence gene, aer in Aeromonas was positively associated with the antibiotic resistance gene blaOXA (χ 2=6.657, p<0.05) and the antibiotic ceftazidime (χ 2=7.537, p<0.05). Pseudomonas exhibited high resistance against third-generation cephalosporins in comparison to carbapenems. Some Pseudomonas and Aeromonas isolates were extended-spectrum β-lactamase producing bacteria as the blaTEM gene was detected in Aeromonas spp. (33%) and Pseudomonas spp. (22%). All S. maltophilia isolates were resistant to the antibiotic’s trimethoprim-sulphamethoxazole, meropenem, imipenem, ampicillin, and cefixime. Acinetobacter isolates were resistant to trimethoprimsulphamethoxazole (96%) and polymyxin (86%). The genes coding for resistance against these antibiotics were detected in both S. maltophilia and Acinetobacter. Efflux pump genes were detected in all isolates of S. maltophilia. High MAR indices were observed in isolates of Pseudomonas, S. maltophilia, and Acinetobacter at the hospital site. However, Aeromonas spp. had the highest MAR in isolates from the WWTP effluents. A comparative analysis of three different methods was performed to understand their applicability and accuracy in detecting these pathogens from wastewater samples. The total viable count using the LIVE/DEAD Baclight bacterial viability kit measured an average count (log10 bacteria per mL) of 7.8±0.03 (influent) and 6.7±0.07 (effluent) using the Flow Cytometer. The total viable count using the BacLight kit was higher than the total plate count, which was 6.46±0.02 and 4.63±0.07 log10 CFU/mLfor influent and effluent, respectively. Similarly, the concentration for each of the target bacteria determined using Flow Cytometry combined with Fluorescent-In situ hybridization (Flow-FISH) method ranged from 5.41±0.07 to 5.92±0.02 (influent) and 3.43±0.2 to 4.31±0.15 (effluent) log10 bacteria per mL which was higher than the selective plate counts (3.81±0.35 to 4.17±0.1 and 3.16±0.17 to 3.7±0.20 log10 CFU/mL, for influent and effluent respectively). The ddPCR results obtained showed the highest concentration of bacteria from both influent and effluent samples in comparison to the Flow-FISH and the plate count methods, indicating the sensitivity of this method in detecting both live and dead cells. Pseudomonas was observed to be dominant and was found in the concentration of 7.19±0.24 copies per mL (influent) and 6.48±0.20 copies per mL (effluent) while S. maltophilia (influent: 5.4 ± 0.90 copies per mL effluent: 4.53±0.57 copies per mL) was detected in the lowest concentration. A similar trend was observed in comparison to the data from the plate counts, albeit at lower concentrations. This study, therefore, makes significant contributions in several areas; firstly, it shows the abundance of opportunistic, antibiotic-resistant, and virulent bacteria in wastewater and surface water within Durban. It further demonstrates that these bacteria are mainly from anthropogenic sources such as hospitals and WWTPs. Additionally, the findings indicate the potential for community-acquired infections with these bacteria, necessitating the need for risk reduction interventions aimed at reducing environmental pollution and exposure.
Radiating collapse in the presence of anisotropic stresses
(World Scientific Publishing Company, 2016) Govender, M.; Bogadi, R. S.; Lortan, Darren Brendan; Maharaj, S. D.
In this paper, we investigate the effect of anisotropic stresses (radial and tangential pressures being unequal) for a collapsing fluid sphere dissipating energy in the form of radial flux. The collapse starts from an initial static sphere described by the Bowers and Liang solution and proceeds until the time of formation of the horizon. We find that the surface redshift increases as the stellar fluid moves away from isotropy. We explicitly show that the formation of the horizon is delayed in the presence of anisotropy. The evolution of the temperature profiles is investigated by employing a causal heat transport equation of the Maxwell-Cattaneo form. Both the Eckart and causal temperatures are enhanced by anisotropy at each interior point of the stellar configuration.