Browsing by Author "Ojok, Walter"
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Item Facile synthesis and characterization of multi-walled carbon nanotubes decorated with hydroxyapatite from cattle horns for adsorptive removal of fluoride.(Elsevier Ltd., 2023-03-09) Ojok, Walter; Bolender, James P.; Wasswa, John; Ntambi, Emmanuel; Wanasolo, William; Moodley, BrendaDeveloping a new adsorbent for fluoride removal from cattle horn waste materials by a facile chemical method has shown great potential for fluoride removal. This paper reports the synthesis of multi-walled carbon nanotubes decorated with hydroxyapatite from cattle horns (MWCNT-CH) using a facile chemical method. Characterization studies using standard techniques showed that the composite is mesoporous with a rough morphology and contained MWCNTs uniformly encapsulated by the hydroxyapatite forming a crystalline MWCNT-CH composite. Optimization of fluoride adsorption by the as-synthesized composite using Response Surface Methodology (RSM) showed that a maximum fluoride removal efficiency of 80.21% can be attained at initial fluoride concentration = 10 mg/L, pH = 5.25, adsorbent dose = 0.5 g and a contact time of 78 min. ANOVA indicates contribution of the process variables in descending order as pH > contact time > adsorbent dose > initial fluoride concentration. Langmuir isotherm (R2 = 0.9991) best described the process, and the maximum adsorption capacity of fluoride onto the as-synthesized MWCNT-CH composite was 41.7 mg/g. Adsorption kinetics data were best fitted in the pseudo-second-order kinetic model (R2 = 0.9969), indicating chemisorption. The thermodynamic parameter ( H = 13.95 J/mol and S = 65.76 J/mol/K) showed that fluoride adsorption onto the MWCNT-CH composite was a spontaneous, endothermic, and entropy-driving process. Moreover, the adsorption mechanism involves ion exchange, electrostatic interaction, and hydrogen bonding. Fluoride was successfully desorbed (using 0.1 M NaOH) from the composite in four cycles, retaining fluoride removal efficiency in the fourth cycle of 57.3%.Item Hydrochemistry and fluoride contamination in Ndali-Kasenda crater lakes, Albertine Graben: assessment based on multivariate statistical approach and human health risk.(Elsevier, 2021-08-08) Ojok, Walter; Wanasolo, William; Wasswa, John; Bolender, James; Ntambi, EmmanuelHydrochemistry of crater lakes (n = 15) in the Ndali-Kasenda cluster was deciphered using standard methods of the American Public Health Association to understand the major ion chemistry; spatial distribution, occurrence, and non-carcinogenic health risks due to exposure to fluoride levels in the lakes in Ndali- Kasenda cluster, Albertine Graben. Numerous economic activities take place in and around the crater lakes which serve as major sources of domestic water whose origin of potential contaminants is ambiguous. In this study, WHO (2017)regulatory limit exceedance included F−, pH, Ca2+, Fe2+, Mn2+, and TDS. A strong positive correlation was observed between F− and TDS; F− and pH; F− and EC; F− and HCO3−. However, concerning hydrogeochemical signature, the lakes are mainly of Ca–HCO3 type and low in Na–K–HCO3 type due to rock water interaction in the geology of the area. Principal component analysis (PCA) performed on Ndali-Kasenda hydrogeochemical data resulted in six principal components (PCs) explaining 88.6% of the total variance. The PCs represented the primary processes that control the crater lake hydrogeochemistry in the Ndali-Kasenda area which include; weathering of rocks reactions, ion exchange, and evaporation processes. The hazard quotient (HQ) for non-carcinogenic health risks associated with exposure to Ndali- Kasenda fluoride levels via ingestion revealed that HQ for infants surpassed the acceptable HQ limit for all the lakes studied, while 86.67 % of the sampled lakes exceeded the HQ value for children via ingestion. Based on the hydrogeochemical parameters analyzed, aside from L. Murigamire and L. Wankenzi, water from the other studied lakes is chemically not acceptable for drinking purposes. An urgent need to take ameliorative action in this area to protect the inhabitants from exposure to excess fluoride in drinking water was recommended.Item Mobility of chromium, copper and arsenic in amended chromated copper arsenate contaminated soils(Asian Journal of Applied Chemistry Research, 2020-09-23) Nakiguli, Caroline Kiwanuka; Ojok, Walter; Omara, Timothy; Wasswa, John; Ntambi, EmmanuelThe use of copper-based preservatives such as chromated copper arsenate (CCA) and creosote to prolong the life of lumber present environmental concerns because they contain heavy metals and polycyclic aromatic hydrocarbons which are toxic to humans. The aim of this study was to investigate the effects of sewage sludge biosolid amendment on the distribution and mobility of chromium, copper and arsenic in chromated copper arsenate contaminated soils subjected to phytoremediation using maize (Zea maysL.). Random composite soil samples from Kitetika wood factory, Wakiso, Uganda and sewage sludge biosolid from National Water and Sewerage Corporation plant in Bugolobi, Kampala, Uganda were collected and prepared. Maize grains were obtained from FICA Seeds Limited (Uganda). The pot experiments and analysis of samples were done at Mbarara University of Science and Technology (Mbarara) and Directorate of Government Analytical Laboratory, Kampala (Uganda), respectively. The fresh CCA contaminated soils and sewage sludge biosolid were analyzed for physicochemical parameters and heavy metals (chromium, copper and arsenic). Sewage sludge biosolid was added to 1 kg of the contaminated soils at 5-25% (w/w) in 2 L plastic containers, watered and maintained at 25 °Cfor 14 days to stabilize. Controls were set up with unamended soils. Thereafter, maize was planted in the potted soils for 40 days. The concentrations of the tracemetals in the soils were determined after 20 and 40 days of maize growth by atomic absorption spectroscopy. The concentrations of chromium, copper and arsenic in fresh CCA contaminated soils were 365.8 ± 6.18 mg/kg, 109.72 ± 14.04 mg/kg and 28.22± 3.8 mg/kg, respectively. Basing on mobility factor, bioavailability of the trace metals followed the chemical sequence copper (8.9%) < chromium (17.1%) < arsenic (30.2%). The maize variety experimented could be used to phytoextract or phytostabilize the trace metals in the CCA contaminated soils without or with 5-25% amendment. Amendment with sewage sludge biosolid improved the phytoremediation potential of maize. Arsenic was the most mobile and bioavailable metal in CCA contaminated soils. Further studies should use other local maize varieties such as Longe series.Item Predicting the thermal distribution in a convective wavy fin using a novel training physics-informed neural network method(Springer Nature, 2024-03-25) Chandan, K.; Saadeh, Rania; Qazza, Ahmad; Karthik, K.; Kumar, R. S. Varun; Kumar, R. Naveen; Khan, Umair; Masmoudi, Atef; Abdou, M. Modather M.; Ojok, Walter; Kumar, RamanFins are widely used in many industrial applications, including heat exchangers. They benefit from a relatively economical design cost, are lightweight, and are quite miniature. Thus, this study investigates the influence of a wavy fin structure subjected to convective effects with internal heat generation. The thermal distribution, considered a steady condition in one dimension, is described by a unique implementation of a physics-informed neural network (PINN) as part of machine-learning intelligent strategies for analyzing heat transfer in a convective wavy fin. This novel research explores the use of PINNs to examine the effect of the nonlinearity of temperature equation and boundary conditions by altering the hyperparameters of the architecture. The non-linear ordinary differential equation (ODE) involved with heat transfer is reduced into a dimensionless form utilizing the non-dimensional variables to simplify the problem. Furthermore, Runge–Kutta Fehlberg’s fourth–fifth order (RKF-45) approach is implemented to evaluate the simplified equations numerically. To predict the wavy fin's heat transfer properties, an advanced neural network model is created without using a traditional data-driven approach, the ability to solve ODEs explicitly by incorporating a mean squared error-based loss function. The obtained results divulge that an increase in the thermal conductivity variable upsurges the thermal distribution. In contrast, a decrease in temperature profile is caused due to the augmentation in the convective-conductive variable values.Item Role of starch in one pot fabrication of mesoporous gamma-alumina with excellent fluoride sorption capacity(Elsevier Ltd., 2023-08-28) Ojok, Walter; Moodley, Brenda; Wasswa, John; Ntambi, Emmanuel; Wanasolo, William; Bolender, JamesGreen synthesis of mesoporous γ-AƖ2O3, a cutting-edge material for sustainable application in medicine, engineering, energy, and water treatment, is still challenging. Our study used a one-pot strategy for facile synthesis of γ-AƖ2O3 by sol-gel method using starch from cassava waste. AƖ(OH)3 were bound to the O-H groups of the starch molecule to form the AƖ(OH)3-starch complex in a nano-network confined in starch polymer cages. Its calcination at 500 ℃ produced a mesoporous, highly crystalline water stable γ-AƖ2O3 with a pore size of 2.07 nm and an extensive BET surface area (215 cm2/g). Using the response surface methodology (RSM), the as-synthesized γ-AƖ2O3 was optimized for efficient fluoride removal from water. A central composite design (CCD) was used to study the effect of initial fluoride concentration, pH, contact time, and sorbent dose on fluoride removal efficiency and optimization of the process. The relative importance of the sorption process variables to the fluoride removal process was assessed using ANOVA. The quadratic model showed that the predicted response was significantly correlated with the experimental response (R2 = 0.9667), with sorbent dose and pH being the process's most influential factors. Optimum conditions for 93.6% fluoride removal efficiency were sorbent dose of 0.5 g, initial fluoride concentration of 10 mg/L, pH 7, and contact time of 137.5 min. A weakly acidic medium favored fluoride removal from water, while the presence of PO43- and HCO3- retarded the process. The sorption data fitted well in the Langmuir isotherm (0.9783) and pseudo-second-order kinetic model (0.9999), indicative of a chemisorption process. The maximum sorption capacity towards fluoride was 207.5 mg/g. A thermodynamic study indicated that the sorption process was spontaneous and endothermic, with increased randomness at the solid-solution interface. Sorption, desorption, sustainability, and leaching tests showed that the sorbent could be used for sustainable fluoride removal at 8.3 USD/1000 liters of safe drinking water.Item Spatial variation in physicochemical surface water quality in River Rwizi, Western Uganda(Journal of Water Resource and Protection,, 2019) Ojok, Walter; Wasswa, John; Nakiguli, Caroline Kiwanuka; Ntambi, EmmanuelRiver Rwizi originates from the Buhweju hills. It is a major source of water for the inhabitants of Mbarara Municipality and surrounding environment. In this study, spatial variation of water quality in River Rwizi section within Mbarara Municipality was determined using cluster analysis. Laboratory analysis was conducted on water samples from five sites along the river section using standard methods for: pH, EC, TSS, TDS, turbidity, temperature, total hardness, alkalinity, salinity, colour, NH3-N, 2 SO4 − , BOD, COD, DO, Ca, Mg, Fe, and Mn. Cluster analysis grouped the study sites into slight pollution (Spencon, GBK), moderate pollution (Katete) and high pollution (BSU, Kakoba) for dry season. For rain season, order was: slight pollution (BSU, Spencon), moderate pollution (GBK) and high pollution (Kakoba, Katete), basing on similarity of water quality variables. These results show that water pollution resulted primarily from domestic waste water, agricultural runoff and industrial effluents. Thus, water from River Rwizi is not suitable for drinking in both dry and wet seasons.Item Synthesis and characterization of hematite biocomposite using cassava starch template for aqueous phase removal of fluoride(Elsevier, 2022-08-24) Ojok, Walter; Ntambi, Emmanuel; Bolender, James; Wasswa, John; Wanasolo, William; Moodley, BrendaIn this study, facile synthesis of α-Fe2O3 biocomposite was mediated by cassava starch as a soft template. Batch mode evaluated its sorption behavior for fluoride removal from aqueous media. Characterization studies using analytical techniques confirmed the existence of porous α- Fe2O3 biocomposite with heterogeneous surfaces having a varied affinity for fluoride. The sorption process was optimized using central composite design (CCD) in response surface methodology (RSM) with a good model prediction (R2 = 0.9066). A study of the interaction effect showed the synergy of process variables on fluoride removal with the result's intensity indicated by the nature of contour plot curvature. Based on the RSM optimization, an optimum fluoride removal efficiency of 85.26 % can be achieved at an initial fluoride concentration of 55 mg/L, α- Fe2O3 biocomposite dose of 0.55 g, pH of 7.5, and contact time of 95 min. Sorption equilibrium data were well modeled by Freundlich isotherm (0.9916), indicating multilayer sorption on a heterogeneous surface of the sorbent with a varied affinity for fluoride. Presence of co-existing anions reduced fluoride removal efficiency in the order PO43− > HCO3− > SO42− > NO3− > CƖ− . At the same time, its kinetics was better modeled by pseudo-second-order kinetics (R2 = 0.9764), showing that the sorption process is rate-limiting. The sorption thermodynamics study showed that the process was spontaneous, exothermic, and entropy-driven physisorption. Hence, the results signify that the green synthesized α- Fe2O3 biocomposite could be a potential sorbent for sustainable defluoridation.Item Two‑phase simulation of entropy optimized mixed convection flow of two different shear‑thinning nanomaterials in thermal and mass diffusion systems with Lorentz forces(Springer Nature, 2024-01-04) Suresha, S.; Khan, Umair; Soumya, D. O.; Venkatesh, P.; Gasmi, Hatem; Sunitha, M.; Zaib, Aurang; Al‑Naghi, Ahmed; Karoui, Hatem; Ishak, Anuar; Ojok, WalterThis research compares the momentum, thermal energy, mass diffusion and entropy generation of two shear thinning nanofluids in an angled micro-channel with mixed convection, nonlinear thermal radiation, temperature jump boundary condition and variable thermal conductivity effects. The approach was used to solve the Buongiorno nonlinear governing model. The effect of different parameters on the flow, energy, concentration, and entropy generating fields have been graphically illustrated and explained. The hyperbolic tangent nanoliquid has a better velocity than the Williamson nanofluid. The Williamson nanofluid has higher thermal energy and concentration than the hyperbolic tangent nanoliquid in the microchannel. The Grashof number, both thermal and solutal, increases the fluid flow rate throughout the flow system. The energy of the nanoliquid is reduced by the temperature jump condition, while the energy field of the nanoliquid is enhanced by the improving thermal conductivity value. The nanoliquids concentration rises as the Schmitt number rises. The irreversibility rate of the channel system is maximized by the variable thermal conductivity parameter.