Photocatalytic degradation of geosmin: Reaction pathway analysis

The presence of geosmin in drinking water imparts a musty odour which leads to consumer complaints. Geosmin and other unwanted organics can be treated using photocatalysis. However, the intermediates formed during the photocatalytic degradation process and their degradation pathways have not previously been described. In this study, the degradation profile, as well as the intermediates formed during the photocatalytic degradation of geosmin was monitored in an effort to obtain a better understanding of the degradation kinetics and pathway. Photocatalytic degradation of geosmin in the presence of radical scavengers was shown to be inhibited, as evidenced by the reduction in reaction rate coefficient (k’) from 0.055 to 0.038 min-1. The hydroxyl radical reaction was thus shown to be the predominant process over direct photolysis by incident UV energy. Results from mass spectrum analysis of degradation intermediates indicate rapid fission of sp3─sp3 (C─C) bonds resulting in ring opening of the cyclic geosmin structure. Bicyclic compounds that could be expected from dehydration and dehydrogenation of geosmin’s ringed structure were not found among the detected intermediate products. Intermediates identified consisted of acyclic unsaturated alkenes, carbonyl compounds and some organic acids. Although the identified degradation products are not seen to be directly harmful, chlorine disinfection of water containing these compounds could produce potentially harmful halogenated hydrocarbons.The research was funded by the Water Research Commission (WRC) of South Africa through WRC Project No. K5/1717 awarded to Prof Evans MN Chirwa of the University of Pretoria.http://www.wrc.org.zaai201

A finite velocity simulation of sedimentation behaviour of flocculating particles – A real-time model evaluation

A mechanistic velocity model is developed to simulate the behaviour of flocculating colloidal particles in turbid water. The current model is based on one-dimensional mass transport in the vertical direction as an integrated form of the model derived by Ramatsoma and Chirwa. The percentile removal model achieved more accurate simulation of physical experimental data than known models such as the Ozer’s model and San’s model. In this study, an integrated velocity form was used to estimate flocculent settling velocity of fine suspended particles under near quiescent conditions. Model closeness to experimental measurements was determined as a function of the sum of squares error (SSE) between model data and experimental data. The proposed velocity model offers a distinctive advantage over the interpolated-isopercentile based models which are prone to numerical errors during interpolation. The results contribute towards the ultimate goal of achieving full automation of the design of gravitational particle separation devices for water and wastewater treatment.The research was funded partially through the National Research Foundation (NRF). Incentive Funding for Rated Researchers, Grant No. IFR2010042900080 awarded to Evans MN Chirwa of the University of Pretoria.http://www.wrc.org.zaam201

Applications of proxy system modeling in high resolution paleoclimatology

AbstractA proxy system model may be defined as the complete set of forward and mechanistic processes by which the response of a sensor to environmental forcing is recorded and subsequently observed in a material archive. Proxy system modeling complements and sharpens signal interpretations based solely on statistical analyses and transformations; provides the basis for observing network optimization, hypothesis testing, and data-model comparisons for uncertainty estimation; and may be incorporated as weak but mechanistically-plausible constraints into paleoclimatic reconstruction algorithms. Following a review illustrating these applications, we recommend future research pathways, including development of intermediate proxy system models for important sensors, archives, and observations; linking proxy system models to climate system models; hypothesis development and evaluation; more realistic multi-archive, multi-observation network design; examination of proxy system behavior under extreme conditions; and generalized modeling of the total uncertainty in paleoclimate reconstructions derived from paleo-observations

Modelling U(VI) reduction by Pseudomonas stutzeri

Pseudomonas stutzeri, a facultative anaerobe sourced from soil in a uranium mine in Limpopo, South Africa, reduced uranium-6 (U(VI)) to uranium-4 (U(IV)) in batches under a relatively high initial U(VI) concentration ranging from 30 to 400 mg/L (pH 5 to 6). U(VI) reduction was rapid during the first 4 to 6 h of incubation followed by slower reduction rates at incubation times longer than 6 hours. Equilibrium conditions were only obtained after incubation for 24 h. The reduced U(VI) was recovered in solution as a hydroxide which was determined to consist of U(IV). A kinetic model based on enzyme kinetics produced the best fit of the optimised model to experimental data of U(VI) versus time in batch cultures of Pseudomonas stutzeri. The parameters: maximum specific uranium-6 reduction rate coefficient (ku), half velocity concentration (Ku), and uranium-6 reduction capacity of cells (Tc) were estimated using the data from the 200 mg/L batch. The parameters obtained in the 200 mg/L batch were then used to simulate the concentration in the other batches at lower and higher initial U(VI) concentrations. The reduction capacity Tc remained stable but a loss of accuracy was observed with increasing initial U(VI) concentration. Numerous batch experiments were conducted to establish kinetic parameters that will be used later for scale-up purposes. The knowledge gained from such processes will be of practical value in predicting effluent response to diverse loading conditions.http://www.aidic.it/cetam2013ai201

The Influence of Different Amendments in Parental Materials in Early Development of Technosols Bioremediation

The aim of this study was to develop a topsoil with ecological functionality to meet mine rehabilitation and re-establishment of the desired final ecosystem considering different technosols bioremediation configurations. The substrates were amended with compost and malt residue to provide the organic fraction of the soil. In terms of nutrient requirements for fertile soils to sustain plant cover, the best configurations were attained, and this implies that the different amendments were necessary in influencing soil properties. The presence of Eragrostic tef ensured absence of metal mobilisation and an improved soil structure. The results showed that amendments and pH have direct linear correlations to plant growth. It was identified that dolomite (3%), calcite (5%) and gypsum (4%) are indicative of both higher biomass accumulation and degree of germination. Technosols have an improved soil-plant-water relations compared to that of stockpiled soil, therefore displaying potential for land rehabilitation and repurposing of coal waste

The role of pH, electrodes, surfactants, and electrolytes in electrokinetic remediation of contaminated soil

Electrokinetic remediation has, in recent years, shown great potential in remediating polluted environments. The technology can efficiently remove heavy metals, chlorophenols, polychlorinated biphenyls, phenols, trichloroethane, benzene, toluene, ethylbenzene, and xylene (BTEX) compounds and entire petroleum hydrocarbons. Electrokinetic remediation makes use of electrolysis, electroosmosis, electrophoresis, diffusion, and electromigration as the five fundamental processes in achieving decontamination of polluted environments. These five processes depend on pH swings, voltage, electrodes, and electrolytes used in the electrochemical system. To apply this technology at the field scale, it is necessary to pursue the design of effective processes with low environmental impact to meet global sustainability standards. It is, therefore, imperative to understand the roles of the fundamental processes and their interactions in achieving effective and sustainable electrokinetic remediation in order to identify cleaner alternative solutions. This paper presents an overview of different processes involved in electrokinetic remediation with a focus on the effect of pH, electrodes, surfactants, and electrolytes that are applied in the remediation of contaminated soil and how these can be combined with cleaner technologies or alternative additives to achieve sustainable electrokinetic remediation. The electrokinetic phenomenon is described, followed by an evaluation of the impact of pH, surfactants, voltage, electrodes, and electrolytes in achieving effective and sustainable remediation.The University of Pretoria, Sedibeng Water Chair in Water Utilisation Engineering, RandWater Chair in Water Utilisation and National Research Foundation.https://www.mdpi.com/journal/moleculesam2023Chemical Engineerin

Biosorption and desorption potential of gold(III) by freshwater microalgae scenedesmus obliquus as-6-1

Biosorption is an eco-friendly and cost-effective way for recovering gold from high-volume and lowconcentration wastewater. In this study, the freshwater microalgae Scenedesmus obliquus AS-6-1 were used as biosorbent for gold(III) in short-term batch tests. For an initial gold(III) concentration of 5 mg/L, the optimum condition of gold(III) adsorption was 0.10 g/L biomass dosage, the temperatures in the range of 20 - 25 °C, pH 2.0 within 30 min. The level of Au (III) uptake by S. obliquus AS-6-1 could approach 15 % of the organism’s dry weight at the optimum conditions with an initial concentration of 20 mg/L. The gold-loaded biomass of S. obliquus AS-6-1 was able to be regenerated by 0.1 M thiourea at pH 2.0 and its desorption efficiency retained 95 %, 94 % and 88 %, respectively, in three alternating adsorption/desorption cycles. The current experiments suggest that the freshwater microalga S. obliquus AS-6-1 is a promising and efficient biosorbent for gold recovery.The Sedibeng Water, South Africa and the Water Utilization and Environmental Engineering Division at the University of Pretoria.http://www.aidic.it/cetam2018Chemical Engineerin

Biosurfactant facilitated emulsification and electro-osmotic recovery of oil from petrochemical contaminated soil

Petroleum industries are burdened with the problem of handling petroleum products, petroleum waste products and refinery byproducts such as large quantities of oil waste. Improper management of these products and their wastes present an environment hazard when they end up in the atmosphere, water and land due to their hazardous constituents. An evaluation to determine the possibility of enhancing the electrokinetic process by application of a biosurfactant producing strain for remediation of petroleum contaminated soil through oil recovery and hydrocarbon degradation was studied at a bench scale. A DC powered electrokinetic reactor consisting of electrode/electrolyte compartments and a medium chamber was used under voltage variations of 10 V and 30 V with an electrode spacing of 185 mm. Biosurfactant with its producing microbes and biosurfactant free cells were introduced in the soil chamber after which the reactor was left to run for 10 days under the electric field. The technology was able to achieve the highest oil recovery of 75.15 % from the soil in 96 hours at 30 V. The microorganisms were able to survive under the electric field there by leading to further reduction of the carbon content in the reactor.The National Research Foundationhttp://www.aidic.it/cetam2020Chemical Engineerin

Pathway analysis of phenol degradation by UV/TiO2 photocatalysis utilising the C-13 isotopic labelling technique

Photocatalysis is a green technology for the degradation of persistent organic compounds in water and has been successful in the removal of several water pollutants. Degradation of organic compounds in water is often accompanied by the formation of several intermediate compounds, some of which are feared to be more toxic than the original compound being treated. In this study, aromatic intermediates formed during the photocatalytic degradation of phenol were profiled in a batch system. The carbon-13 isotopic labelling technique was used to track the degradation pathway. Photocatalytic degradation of phenol was conducted in 1L solutions of phenol (20mg/L) in ultrapure water in a batch system. Catalyst concentration was constant at 8mg/L Titanium dioxide (TiO2). Concentration of phenol and detection of the aromatic intermediates of phenol degradation were monitored on a Waters High Performance Liquid Chromatograph (HPLC) and Gas Chromatogram- Mass Spectrometer (GC-MS), respectively. Aromatic intermediates identified during the course of photocatalysis of the phenol include hydroquinone, benzoquinone catechol and resorcinol. The concentration of phenol was determined from the calibration curve of standards of phenol. Photocatalysis is a promising technology for the complete mineralization of aromatic organic pollutants as it has been demonstrated that both the pollutant and its direct intermediates can be completely removed from solution. Phenol degradation produces first aromatic dihydroxy substituted compounds that are further degraded forming cycling compounds on cleavage of the aromatic ring. The distribution of the degradation intermediates confirms that the dominant degradation pathway is via hydroxyl radical mechanism.http://www.aidic.it/cetam2019Chemical Engineerin

Equilibrium and kinetic modeling for biosorption of Au(III) on freshwater microalgae

Microalgae have been considered as a promising biosorbent for recovery of precious metal ions from diluted aqueous solutions; especially the self-flocculating microalga has the potential for cost-effective harvesting of tiny microalgae. In this study, the adsorption of Au(III) by the self-flocculating microalgae Tetradesmus obliquus and non-flocculating T. obliquus as a control was studied in different initial Au(III) concentrations, temperatures, and pH. The adsorption equilibrium by the tested microalgae fitted well to the Langmuir model at different temperatures. The maximum adsorption capacity from the Langmuir model for T. obliquus AS-6-1 was 169.49 mg g−1 obtained at pH 2.0 and 30 °C, which was higher than that observed by the non-flocculating T. obliquus with 153.85 mg g−1. Furthermore, all the Kd values above 5000 mL g−1 at 30 °C for T. obliquus AS-6-1 showed that the flocculating microalgae had a stronger adsorption affinity to Au(III). The initial Au(III) concentration and solution pH significantly affected the adsorption capacity of Au(III) on algal species. While, their adsorption of Au(III) was slightly influenced at temperature from 30 to 40 °C but significantly influenced and decreased at low (≤ 7 °C) or high temperature (≥ 60 °C). The experimental data fitted well to the second-order kinetic model, which indicated that the adsorption reaction on the surface of adsorbent was the rate-limiting step, instead of mass transfer.The Sedibeng Water, South Africa and the Water Utilization and Environmental Engineering Division at the University of Pretoria.https://link.springer.com/journal/108112019-12-01hj2018Chemical Engineerin