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The vast range of applications for enzymes in the production of biofuels has led to a major increase in market demand in recent years. Cellulase's high cost and poor catalytic efficiency are two key barriers to the industrial usage of lignocellulosic biomass as feedstocks for fuels in biorefineries. In this study, the economic evaluation of cellulase production in solid-state fermentation was done by designing two process routes (batch and semi-batch) to optimize the process. SuperPro Designer Software has been used to create a process model that assessed the economics of fermentation operations while Monte Carlo Software was used to conduct the sensitivity analysis investigation. The impacts of cellulase yield, productivity, aeration rate and specific power input on the unit production cost (UPC) of cellulase enzyme were studied. The batch procedure requires more sterilized air for the aerobic fermentation process than the semi-batch approach, according to the results. In comparison to the batch fermentation process, the semi-batch approach had a payback period of less than 2 years, an internal rate of return of 39.14% and a net present value of $142 089 000. The semi-batch process approach has a higher economic feasibility when compared with the batch fermentation process since it is more certain to attain its base case value of UPC at the maximum. This research was key to developing a process pathway that reduces cellulase production costs in solid-state fermentation while improving market supply for its use in a biorefinery to produce sustainable fuel.

Increasing industrialization and urbanization has led to increased wastewater effluents, which affect the environment if not properly treated before discharge into water bodies. Hence, it is important to adopt an efficient technique for treating wastewater before discharge into water bodies. This study investigated the interaction of initial concentration, pH, adsorbent dosage, and particle size with orange peels for the biosorption of Cu2+ and Pb2+ from aqueous solution using the response surface methodology (RSM) with the central composite design (CCD). The regression model ascertained the validity of the second-order polynomial equation for the biosorption of Cu2+ and Pb2+ using orange peels. The coefficient of determination (R2) obtained from the analysis of variance (ANOVA) for Cu2+ and Pb2+ are 0.9852 and 0.9433, respectively. The maximum adsorption uptakes of Cu2+ and Pb2+ were 54.94 mg/g and 65.14 mg/g respectively, which suggests that orange peels have a higher affinity for Pb2+ than for Cu2+. The maximum efficiencies of Cu2+ and Pb2+ under the optimum conditions of the process variables are 88% and 90%, respectively. The agreement between the experimental and predicted values shows that the quadratic model developed can be used to adequately determine the interaction between process parameters in the bio-sorption of Cu2+ and Pb2+ onto orange peels. The study contributes to the search for eco-friendly and sustainable solutions to the treatment of water contaminated with low concentrations of Cu2+ and Pb2+ metal ions.

Subcritical water extraction (SWE) technology, as an environmentally sustainable technique, was applied to optimize the recovery of polyphenolic compounds from apple pomace (AP). Box–Behnken experimental design approach was used to investigate the effects of four process variables; extraction temperature (100-220 ºC), extraction time (30-120 min), mean sample particle size (500-1000 µm) and solid to solvent ratio (1-10 g/100 mL) on total polyphenolic compounds (TPC) yield. The SWE conditions for the optimal TPC of 39.08 ± 1.10 mg GAE per g of AP on dry basis (db) were determined to be temperature of 203.71 ºC, time of 75 min, solid to solvent ratio of 1 g/100 mL and a mean sample particle size of 500 µm. The temperature and solid to solvent ratio were determined as the most statistically significant process variables that influenced TPC yield. At the optimum conditions, antioxidant activity (% DPPH inhibition activity) of the polyphenolic extract was found in the range of 15.38–92.90% as compared to ascorbic acid (8.64–95.90%). The findings of this study proposed that SWE as a green and efficient technology provided significant advantage in term of polyphenolic compounds yield, and AP could be utilized as potential raw material for SWE of valuable antioxidant polyphenolic compounds.

The response surface methodology was used to investigate the removal of Pb (II) from an aqueous solution using banana peel with varying operating parameters in a batch mode. The central composite design was used to study the interactive effects of the operating parameters (initial concentration, pH of the solution, adsorbent dosage and the particle size). The banana peel was characterized by FTIR which showed the functional groups, while SEM and EDS were used to study morphology and elemental composition. The optimum removal of Pb(II) was 98.146 % at initial concentration 100 mg/L, pH 5, adsorbent dosage 0.55 g and particle size 75 ��m. The deviation between the experimental and the model predicted percentage removal was 5.17 %. The analysis of variance showed that the regression model was significant with a low probability and the correlation coefficient R2 value of 0.9153. The results showed that the biosorption of Pb(II) was highly influenced by the pH and the adsorbent dosage, while the particle size had little effect on the biosorption process.

This study investigates Marula (Sclerocarya birrea) seed oil (SBSO) as a novel feedstock for biodiesel production through the transesterification process catalysed by heterogeneous bio-alkali derived from banana (Musa acuminata) peels. Response surface methodology (RSM) and artificial neural network (ANN) tools were used for the modelling and optimization of the process variables. The reaction process parameters considered were methanol/SBSO molar ratio, catalyst loading levels, reaction time and temperature. Central composite design (CCD) was espoused to generate 30 experimental conditions which were deployed in investigating the individual and synergetic effect of the process input variables on Sclerocarya birrea oil methyl ester (SBOME) yield. Appropriate statistical indices were adopted to investigate the predictive aptitude of the two models. Analysis shows that ANN model obtained for the transesterification process has a higher coefficient of determination (R2) of 0.9846 and lower absolute average deviation (AAD) of 0.07% compared to RSM model with R2 of 0.9482 and AAD of 0.12%. The process modelling outcome also confirmed ANN performance to be more precise than RSM. At methanol/SBSO ratio of 6:1, catalyst loading level of 2 wt%, process reaction time of 50 min and temperature of 55°C, the experimental maximum SBOME yield was observed to be 96.45 wt % following the ANN predicted yield of 96.45 wt % and RSM predicted yield of 96.65 wt % respectively. The analysed fuel properties of SBOME was found satisfactory within the biodiesel stipulated standard limit(s). The study establishes that SBSO is a good source for biodiesel production and its biodiesel methyl ester is a potential substitute for petroleum diesel and a bioenergy fuel.

The amount of tyres generated around the world has been on the rise. This has prompted the need to explore ways in which waste tyres can be disposed. One of the ways of recycling waste tyres is through pyrolysis, a process that has the potential to produce oil products with high calorific value. However, the oil produced from waste tyre pyrolysis has a high sulphur content, resulting in high levels of toxic emissions during combustion. This research study focuses on two aspects associated with waste tyre pyrolysis. The first aspect deals with the establishment of the kinetics of scrap tyre pyrolysis while the second aspect involves the oxidative desulphurisation (ODS) of tyre-derived oil (TDO). The ODS was carried out with incorporation of the central composite design (CCD) technique of the response surface methodology (RSM) in order to model the desulphurisation process. In order to study the kinetics of the scrap tyre pyrolysis, three different models were applied to thermogravimetric data. The thermogravimetric (TG) experiments were carried out in a nitrogen environment and a temperature range of 20°C to 600°C at heating rates of 2, 5, 10, and 20 °C min-1. The models used to determine the activation energy (Ea) were Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and Friedman (FR) whereas the Coats-Redfern (CR) model aided in the determination of the pre-exponential factor. The FWO model had the highest average value (R2 = 0.9847) of the coefficient of determination, and therefore the Ea values from this model were loaded into the CR model to determine the pre-exponential factors and the order of the reaction model. The thermal decomposition started at a mean temperature of about 285°C and was complete at about 482 °C for the four heating rates. Results indicate that the mass losses become greater with increasing heating rates. The thermogravimetric analysis results revealed that tyre pyrolysis involves three stages i.e. removal of lubricants and oil in the scrap tyre, breakdown of natural rubber and breakdown of butadiene rubber and styrene-butadiene rubber. The average activation energies obtained were 206.01 kJ mol-1, 206.08 kJ mol-1 and 204.82 kJ mol-1 using KAS, FWO and FR models respectively. A mean pre-exponential factor of 1.27E+10 min-1 was obtained. In addition, the results showed that the pyrolysis of the tyre crumb conforms to the second order reaction model (F2). The second objective of the study involved the use of the CCD methodology to investigate the interaction of parameters during the ODS of tyre-derived oil. The oxidative desulphurisation involved the investigation of the interaction of formic acid and hydrogen peroxide amounts, reaction time and temperature. The liquid-liquid extraction was carried out using two different solvents. In addition, for one of the solvents (acetonitrile), two solvent to oil ratios were used, bringing the total number of solvent extraction scenarios to three. The three extraction scenarios were acetonitrile to oil ratio of 1:1, acetonitrile to oil ratio of 1:2 and dimethylformamide to oil ratio of 1:1. The ODS for each of the solvent extraction scenarios consisted of 21 experiments. Therefore, the total number of experiments for the three solvent extraction scenarios was 84 i.e. 21 runs for the oxidation stage and 63 runs for the solvent extraction. The maximum sulphur removal achieved was 86.05, 52.77 and 35.00 % respectively for oxidised oils extracted using 1:1 acetonitrile to oil ratio, 1:2 acetonitrile to oil ratio and 1:1 dimethylformamide to oil ratio while the corresponding minimum sulphur removal values were 34.02, 27.91 and 3.8 %. The results of the sulphur removal in which extraction was carried out at 1:1 acetonitrile to oil ratio were further analysed and modelled. From the analysis of variance (ANOVA), the reduced cubic model was found to be the best predictor of sulphur removal during the ODS process. Coefficient of determination (R2 = 0.9776), adjusted R2 = 0.9254, predicted R2 = 0.8356 all showed that the model was significant. Moreover, the p-value for the lack of fit was 0.8926, which is indication of its insignificance relative to pure error. In summary, the data obtained from the kinetic study of the scrap tyre pyrolysis could play an important role in the design and optimisation of industrial scale scrap tyre pyrolysis units. The findings could provide an insight for improvement of the general operability of scrap tyre thermal conversion processes via pyrolysis. Further research should be carried out to obtain thermogravimetric data at higher heating rates, which can then be used to model the process via the non-isothermal means. On the other hand, the findings from the oxidative desulphurisation of tyre-derived oil obtained from this research can play a key role in minimising the levels of emission during the combustion of oils obtained from the pyrolysis of waste tyres. In addition, the knowledge from the present study could be useful in commercialisation of efficient sulphur removal technology in tyre-derived oils, which can then be blended with other fuels such as diesel for use in real combustion processes. Further work with incorporation of a different organic acid, such as acetic acid and hydrogen peroxide as part of the oxidation system may be carried out to investigate the change in the extent of sulphur removal.

The aim of this study was to apply the central composite design technique to study the interaction of the amount of formic acid (6-12 mL), amount of hydrogen peroxide (6-10 mL), temperature (54-58°C) and reaction time (40-60 min) during the oxidative desulphurisation (ODS) of tyre-derived oil (TDO). The TDO was oxidised at various parametric interactions before being subjected to solvent extraction using acetonitrile. The acetonitrile to oil ratios used during the extraction were 1:1 and 1:2. The content of sulphur before and after desulphurisation was analysed using ICP-AES. The maximum sulphur removal achieved using a 1:1 acetonitrile to oxidised oil ratio was 86.05%, and this was achieved at formic acid amount, hydrogen peroxide amount, temperature and a reaction time of 9 mL, 8 mL, 54°C and 50 min respectively. Analysis of variance (ANOVA) indicated that the reduced cubic model could best predict the sulphur removal for the ODS process. Coefficient of determination (R2 = 0.9776), adjusted R2 = 0.9254, predicted R2 = 0.8356 all indicated that the model was significant. In addition, the p-value of lack of fit (LOF) was 0.8926, an indication of its insignificance relative to pure error.

Agricultural waste materials have been proven to be efficient for heavy metal sequestration from wastewater. In this paper, the interactive effects of initial concentration, adsorbent dosage, and particle size on the removal of copper and lead ions in a binary system onto orange peels were investigated using a central composite design. The pHpzc of orange peels was determined to be 3.85. The Fourier transform infrared (FTIR) and energy dispersive x-ray (EDX) revealed the functional groups and elemental composition present on the surface of the bio-sorbent, respectively, before and after adsorption. The ANOVA showed a good fit with a coefficient of determination (R2) of 0.973 and 0.993 for Cu and Pb, respectively. The bio-sorption of Cu and Pb increased with increasing adsorbent dosage while the percentage removal of Pb was consistently higher than Cu. The highest percentage removal of Cu and Pb gave 86.27% and 98.85%, respectively. The kinetic and isotherm studies showed that pseudo-second-order and Langmuir isotherm models fitted the experimental data suggesting chemisorption and monolayer adsorption, respectively. The treatment of wastewater is very essential to avoid water scarcity and to achieve the Sustainable Development Goals (SDGs). This study demonstrates the potential of utilizing orange peels as bio-sorbent for the treatment of wastewater containing Cu and Pb ions.

The presence of acid mine drainage (AMD) poses health risks to humans and other living organisms. While much research on AMD has been conducted, the absence of a widely accepted AMD treatment technology makes it an ongoing topic for further exploration. The present study explored the potential of nano-clay adsorbents for the removal of iron and manganese from AMD. The two nano-clay adsorbents used in this study were synthetic hydrotalcite (HT) and modified bentonite (MB) clays. The adsorption media were characterised before and after adsorption using X-ray diffraction (XRD), Fourier transforms infrared (FTIR) spectroscopy, Brunauer–Emmett–Teller (BET), and Scanning Electron Microscope (SEM) to explain the adsorption mechanisms. To investigate the efficiency of the clays, batch adsorption studies were carried out by varying the concentration, pH, and time. To establish the kind of adsorption mechanism that occurred, Langmuir and Freundlich isotherms were applied. It was found from characterisation results that HT and MB contained hydroxyl and carbonyl functional groups responsible for surface complexation mechanisms; XRD showed that isomorphic substitution and precipitation also occurred in adsorption using HT. The specific surface area for modified bentonite and hydrotalcite as determined by BET was 3.13 and 44.7 m2/g respectively. The XRD and the SEM results showed that HT was crystalline while MB was amorphous, probably due to the irregular stacking of the surfactant. It was observed that the adsorbent deprotonated as pH increased, resulting in an increase in metal removal. The Langmuir isotherm provided the best monolayer adsorption capacity with RL < 1 and correlation coefficients ranged from 0.95 to 0.99 for both adsorbents.

In the search for a technically efficient and abundant adsorbent in water treatment processes, a bio-composite adsorbent derived from agricultural wastes has been identified as a potential candidate. In this study, eggshells and sugarcane bagasse were combined in varied proportions (1:0, 1:3, 1:1, 3:1 and 0:1) and applied as biosorbents in a lab-scale adsorption column. The effect of bed depth (4–12 cm) of the biosorbents was investigated which enabled the prediction of breakthrough curves for the removal of Pb (II) ions. The life span of the column was extended by increasing the bed depth of the column. The binary adsorbent of 1:3 weight ratio of

This study investigates Marula (Sclerocarya birrea) seed oil (SBSO) as a novel feedstock for biodiesel production through the transesterification process catalysed by heterogeneous bio-alkali derived from banana (Musa acuminata) peels. Response surface methodology (RSM) and artificial neural network (ANN) tools were used for the modelling and optimization of the process variables. The reaction process parameters considered were methanol/SBSO molar ratio, catalyst loading levels, reaction time and temperature. Central composite design (CCD) was espoused to generate 30 experimental conditions which were deployed in investigating the individual and synergetic effect of the process input variables on Sclerocarya birrea oil methyl ester (SBOME) yield. Appropriate statistical indices were adopted to investigate the predictive aptitude of the two models. Analysis shows that ANN model obtained for the transesterification process has a higher coefficient of determination (R

It is very rare to have the ions of only one metal ion in wastewater. Hence, the removal of copper and lead ions from aqueous solution in single and binary systems using natural banana peels was investigated in a batch mode. Banana peels were characterised using FTIR, which gave the functional groups present. The spectra of banana peels loaded with Pb(II) had a higher percentage transmittance after adsorption. The point of zero charge pHpzc of banana peel was found to be 4.83 which makes it suitable for the adsorption of cations. Kinetic and isotherm studies were carried out at a pH of 5.5, concentration range of 10���100 mg/ L, and adsorbent dosage range of 0.1���1 g. A pseudo-second order model is fitted to the kinetic data suggesting chemical adsorption. The Langmuir isotherm performed well with the experimental data which means adsorption occurred as a monolayer on the surface of banana peels. The maximum adsorption capacity of Pb(II) for Langmuir isotherm was 66.67 mg/g. This indicated that in the single system banana peels have more affinity for Pb(II) than for Cu(II). At higher concentrations, the experimental data for the isotherm study showed the effect of a competitive phe-nomenon which affected only Cu(II) in the binary system. Natural banana peels are efficient agricultural waste materials that can be used for the treatment of waste-water contaminated with copper and lead ions.

PURPOSE: Banana peel was used as a low-cost adsorbent for the removal of Cu and Pb ions from aqueous solution in a binary system. METHODS: The interactive effects of the operating parameters such as initial concentration, pH, adsorbent dosage and particle size were studied in a batch mode using central composite design. The characterizations of banana peels were done using point of zero charge (pHpzc), Fourier infrared transform (FTIR), scanning electron microscopy (SEM) and elemental composition (EDS). RESULT: The point of zero charge of banana peels was determined to be 4.83. The FTIR, SEM and EDS showed the functional groups, surface morphology and elemental composition respectively before and after the adsorption process. The analysis of variance (ANOVA) showed a good fit of coefficient of determination (R(2)) for Cu and Pb being 0.998 and 0.988 respectively. The percentage removal of Cu and Pb increased with increasing adsorbent dosage, however, the bio-sorption capacity of Pb was greater than Cu. The optimized variable conditions for the bio-sorption of Cu and Pb using banana peel gave 99.79% and 88.94% removal for Pb and Cu respectively with initial concentration of 100 mg/L, pH 5, adsorbent dosage of 1 g and particle size of 75 μm. The above condition gave desirability of 0.959, which denotes that the optimum conditions are acceptable. CONCLUSION: The regression model and the agreement between the experimental and predicted values confirmed the validity of second-order polynomial equation for the bio-sorption of Cu and Pb using banana peels. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40201-021-00632-x.

The extraction of oil from Croton gratissimus seeds was studied using the three-factor five-level full-factorial central composite rotatable design (CCRD) of the response surface methodology (RSM). The effect of the three factors selected, viz., extraction time, extraction temperature and solvent-to-feed ratio on the extraction oil yield was investigated when n-hexane and ethyl acetate were used as extraction solvents. The coefficients of determination (R2) of the models developed were 0.98 for n-hexane extraction and 0.97 for ethyl acetate extraction. These results demonstrated that the models developed adequately represented the processes they described. From the optimized model, maximum extraction yield obtained from n-hexane and ethyl acetate extraction were 23.88% and 23.25%, respectively. In both cases the extraction temperature and solvent-to-feed ratio were 35°C and 5 mL/g, respectively. In n-hexane extraction the maximum conditions were reached only after 6 min whereas in ethyl acetate extraction it took 20 min to get the maximum extraction oil yield. Oil extraction of Croton gratissimus seeds, in this work, favoured the use of n-hexane as an extraction solvent as it offered higher oil yields at low temperatures and reduced residence times.

This study investigates the effectiveness of a base heterogenous catalyst derived from waste Carica papaya peels in the transesterification of used vegetable oil (UVO). The calcined Carica papaya peels (CCPP) were characterised using scanning electron microscope-energy dispersive X-ray (SEM-EDX), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The EDX result indicated that the ash contains various minerals with potassium (K) as the main active element in remove for the charge of the high catalytic activity. Response surface methodology (RSM) based on the Box Behnken design (BBD) was used to optimise and investigate the effect of the critical process parameters which include: the reaction time (50 – 70 min), catalyst loading (2.5 – 4.5 wt%) and methanol-to-oil molar ratio (9:1 – 15:1). The optimal reaction condition for the transesterification process was found to be catalyst loading of 3.5 wt%, methanol/oil molar ratio of 12:1, process reaction time of 60 min at constant reaction temperature of 65 oC which resulted in the maximum biodiesel yield of 97.5 wt%. The quality of the produced biodiesel was in agreement with ASTM standards. The catalyst was reused up to three times with minimal decrease in the catalytic activity in the biodiesel conversion. The study demonstrates the potential of waste biomass feedstocks in the production of sustainable biodiesel fuel.

The extraction of oil from Croton gratissimus seeds was studied using the three-factor five-level full-factorial central composite rotatable design (CCRD) of the response surface methodology (RSM). The effect of the three factors selected, viz., extraction time, extraction temperature and solvent-to-feed ratio on the extraction oil yield was investigated when n-hexane and ethyl acetate were used as extraction solvents. The coefficients of determination (R

Mixing efficiency in stirred tanks is an important consideration in the design of many industrial processes. Computational fluid dynamics (CFD) techniques have been employed in the present work to study the hydrodynamics in a tank stirred by a Rushton turbine. The effect of the impeller clearance on the velocity field and mixing has been investigated. It has been shown that at a low impeller clearance, the Rushton turbine generates a flow field that evolves from the typical two loops to a single loop flow pattern similar to that of an axial impeller. This single loop flow pattern resulted in an increase in axial flow and a decrease in mixing time at a constant power number. It has been found that a draft tube can be used with a single Rushton turbine, at a low clearance to aid axial flow and mixing, and this resulted in 50% reduction in mixing time. There was a good comparison between laser Doppler velocimetry (LDV) experimental and CFD simulation flow fields, both of which showed that the draft tube improved mixing in the tank by suppressing secondary circulation loops.

Based on a purposive sample of 15 second‐year chemical engineering students, this study investigates students' conceptions of evaporation, condensation and vapour pressure. During individual interviews the students were questioned on three tasks that had been designed around these topics. Qualitative analysis of student responses showed a range of conceptions in each area, including some misconceptions. A key underlying misconception was the belief that evaporation and condensation require a temperature gradient in order to take place. Many students changed their initial (incorrect) answers when presented with further physical evidence as the interview progressed. The study points to the importance not only of practical work, but of associated conceptual discussions that allow students to reflect on and refine their conceptions.

Kilishi is a sun-dried, spiced and roasted traditional African meat product of long shelf-life and high consumer acceptability. This study reports on contributions made to the understanding of the drying and infusion processes. The production process involves two drying stages. The average critical moisture content of the first stage (before infusion) was 1·24 kg H2O/kg solid. The critical moisture content of the second stage (after infusion) was found to vary as a function of the degree of infusion. Values obtained ranged from 0·16 to 1·59 kg H2O/kg solid. Three periods of the drying curves (one constant rate and two falling rate periods) were observed in both stages. The degree of infusion was found to increase with time and varied inversely with moisture content before infusion. An optimum time of 35 min is proposed for the infusion process on the assumption that the higher the ingredient uptake, the higher the consumer acceptability.

Lead and cadmium are amongst some of the most hazardous and carcinogenic heavy metals to contaminate water sources in the industrial sector. As such, there have been several research efforts to remediate this worldwide environmental concern. The main objective of this study was to determine the efficacy of using two natural agricultural waste materials, sugarcane bagasse and eggshells, in removing Pb (II) and Cd (II) from aqueous solutions. The biosorbents were characterized using Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD). The functional groups present in eggshells was carboxylic and carbonyl groups with hydroxyl and carbonyl groups present for bagasse. Crystallographic information revealed both an amorphous and a crystalline phase for bagasse with a crystalline phase for eggshells. The effect of particle size and pH was investigated where a higher removal rate was obtained with increasing pH with no significant difference observed with the particle size. Sorption equilibrium and kinetics were also studied by varying the initial concentration and contact time, respectively. The Langmuir and Freundlich models were applied for the mathematical description of the isotherms. The applicability of the Langmuir isotherm implied a monolayer formation of metal ions onto the surface of the adsorbents. The maximum amounts of Pb and Cd adsorbed based on 1 g of biosorbent were found to be 277.8 and 13.62 mg/g for eggshells and 31.45 and 19.49 mg/g for bagasse, respectively. The pseudo-second order model was used to describe the kinetics of the adsorption process for Pb and Cd ions. Based on the above findings, this study has demonstrated the efficacy of both adsorbents and presents it as a viable adsorbent for the biosorption process.