Statistical Optimization of Process Variables for Osmotic Dehydration of Okra (Abelmoschus esculentus) in Sucrose Solution

The objective of this study was designed to elucidate the effects of temperature, solute concentration, and size diameter and process time on the osmotic dehydration of okras in sucrose solution. Response Surface Methodology (RSM) with Central Composite Rotable Design (CCRD) was used with five levels and four factors (temperature, sucrose concentration, size diameter and process time) as independent variables, while water loss and solute gain as dependent (response) variables. The osmotic dehydration data was well fitted to a second-order quadratic polynomial regression model with high correlation coecient (R2 > 0.90) using the Statistica program (v. 6.08). The quadratic regression models for the water loss and solute gain yielded signicant (p < 0:05) and predictive results. The osmotic dehydration process was optimized for water loss and solutes gain. The predicted optimum conditions to achieve 39. 78 percent water loss and 10.16 percent solute gain were found to be: solute concentration, 49.28(% w/w); solution temperature, 40.79; sam- ple size diameter, 15mm and process time, 4.49hr. At this predicted optimum point, the observed water loss and solute gain were found to be 38.87 and 10.65(g/100g initial sample), respectively.Keywords: okra, optimization, osmotic dehydration, process variables, response surface, sucros

Thin Layer Drying Kinetics of Pineapple: Effect of Blanching Temperature – Time Combination

Drying is an energy intensive unit operation and long drying periods tend to increase the energy requirements for the production of a unit dry product. In this study, the effect of blanching temperature - time combinations treatment conditions on the drying behavior of pineapple slices was investigated. Slices of pineapple were blanched at different temperature-time combinations before being dried in an oven dryer at adry bulb temperature of 70oC. Four thin-layer drying models were fitted to the experimental drying data. The results show that drying rates and drying times were affected by the blanching temperature-time combinations. Drying times increased as blanching temperature-time combinations increased. The predominant drying regime of the blanched pineapple was observed to be in the falling rate period. The logarithmic model best describe the drying behaviour of blanched pineapple slices with goodness of fit (R2 > 0.99). The effective moisture diffusivity of blanched samples decreased with increase in blanching temperature-time combinations. This implied enhanced mass transfer activities of blanched pineapple slices at decreasing blanching temperature-time combinations. Therefore, blanching pretreatment at lower temperature-time combinations in the drying of fruits and vegetables reduces the drying time and energy cost of drying.Keywords: Blanching; drying; drying models; effective diffusivity; pineapple; temperatur

Kinetics of batch microbial degradation of phenols by indigenous binary mixed culture of Pseudomonas aeruginosa and Pseudomonas fluorescence

The potential of various organisms to metabolize organic compounds has been observed to be a potentially effective means in disposing of hazardous and toxic wastes. Phenolic compounds have longbeen recognized as one of the most recalcitrant and persistent organic chemicals in the environment. The bioremediation potential of an indigenous binary mixed culture of Pseudomonas aeruginosa andPseudomonas fluorescence was studied in batch culture using synthetic phenol in water in the concentration range of 100 –500 mg/L as a model limiting substrate. The effect of initial phenol concentration on the degradation process was investigated. Phenol was completely degraded at different cultivation times for the different initial phenol concentrations. Increasing the initial phenol concentration from 100 to 500 mg/L increased the lag phase from 0 to 18 h and correspondinglyprolonged the degradation process from 24 to 96 h. There was decrease in biodegradation rate as initial phenol concentration increased. Fitting data into three different kinetic models (Monod, Haldane, andYano and Koga) showed that the difference in fit between the models was very small and thus statistically insignificant. Thus, the Yano and Koga model has been used to interpret the free cell dataon phenol biodegradation. The kinetic parameters have been estimated up to initial phenol concentration of 500 mg/L. The rsmax decreased, while Ks and Ki increased with higher concentration of phenol. The rsmaxhas been found to be a strong function of initial phenol concentration

Energetics of binary mixed culture of Pseudomonas aeruginosa and Pseudomonas fluorescence growth on phenol in aerobic chemostat culture

Bioenergetic analysis of the growth of the binary mixed culture (Pseudomonas aeruginosa and Pseudomonas fluorescence) on phenol chemostat culture was carried out. The data were checked for consistency using carbon and available electron balances. When more than the minimum number of variables are measured, and measurement errors are taken into account, the results of parameter estimation depend on which of the measured variables are chosen for this purpose. Similar parameter estimates were obtained using Pirt’s model based on the Monod equation approach and a modified model based on substrate consumption being rate limiting. Coupled with the covariate adjustmentestimation technique, the best estimates were the maximum likelihood estimates (MLE) based on when all the measured data were used. For the aerobic growth of the mixed culture on phenol, ηmax = 0.396 and me= −0.020 h-1. From the 95% confidence intervals, a maximum of about 38 – 41.3% of the energy contained in phenol is incorporated into the mixed culture biomass. The balance (58.7 – 62%) is evolved as heat with little or no energy needed for the maintenance of organisms.Keywords: Binary mixed culture, biomass energetic yield, chemostat culture, energetic analysis, maintenance coefficient, Pirt’s mode

Substrate inhibition kinetics of phenol degradation by binary mixed culture of Pseudomonas aeruginosa and Pseudomonas fluorescence from steady state and wash- out data

Steady states of a continuous culture with an inhibitory substrate were used to estimate kinetic parameters under substrate limitation (chemo stat operation). Mixed cultures of an indigenous Pseudomonas fluorescence and Pseudomonas aeruginosa were grown in continuous culture on phenol as the sole source of carbon and energy at dilution rates of 0.01 – 0.20 h-1. Using different dilution rates several steady states were investigated and the specific phenol consumption rates were calculated. In addition, phenol degradation was investigated by increasing the dilution rate above the critical dilution rate (washout cultivation). The results showed that the phenol degradation by mixed culture of P. fluorescence and P. aeruginosa can be described by simple substrate inhibition kinetics under substrate limitation but cannot be described by simple substrate inhibition kinetics under washoutcultivation. The phenol consumption rate (degradation rate) increased with increase in dilution rate. Fitting of the steady state data from continuous cultivation to six inhibition models resulted in the bestfit for Haldane, Yano and Koga, Aiba et al. and Teissier models, respectively. The rsmax value of 0.322 mg/mg/h obtained from these model equations was comparable to the experimentally calculated rsmax value of 0.342 mg/mg/h obtained under washout cultivation

BIOELECTRICITY PRODUCTION FROM CASSAVA MILL EFFLUENTS USING MICROBIAL FUEL CELL TECHNOLOGY

A Microbial Fuel Cell (MFC) is a biochemical-catalyzed system that generates electricity by oxidation of biodegradable organic substance in the presence of microorganisms or enzymes. Microbial fuel cell technology is a new form of renewable and sustainable technology for electricity generation as it recovers energy from renewable materials such as organic wastes and wastewaters that can constitute environmental pollution if not disposed without proper treatment. This work therefore investigated the possibility of electricity generation from cassava mill effluent using MFC. The cassava mill effluent was found to generate voltage and current to the maximum of 275 mV and 2.75 mA, respectively, corresponding to a maximum power density of 189 mW/m2. The voltage and current generation was respectively and significantly influenced with change in temperature, pH, concentration (strength) of effluent and addition of nutrient. Thus, it can be concluded that bioelectricity can directly be generated from cassava mill effluent using the MFC technology. http://dx.doi.org/10.4314/njt.v35i2.1

Bioremediation of Atrazine Herbicide Contaminated Soil Using Different Bioremediation Strategies

This study evaluated the bioremediation of atrazine herbicide contaminated agricultural soil under different bioremediation strategies using indigenous Pseudomonas aeruginosa, Bacillus subtilis and Aspergillus niger as bioaugmentation agents and poultry droppings as biostimulation agent. The results showed that bioaugmentation with Pseudomonas aeruginosa, bioaugmentation with Bacillus subtilis, bioaugmentation with Aspergillus niger, bioaugmentation with bacterial-fungal consortium (Pseudomonas aeruginosa, Bacillus subtilis and Aspergillus niger), biostimulation with poultry droppings, and combined biougmentation and biostimulation (Pseudomonas aeruginosa, Bacillus subtilis, Aspergillus niger and poultry droppings) resulted in maximum atrazine biodegradation of about 97%,95%, 84%, 99%, 100% and 100%, respectively. The kinetics of atrazine biodegradation in the soil were modelled using first-order kinetic model and the biodegradation half-life estimated. The first order kinetic model adequately described the kinetics of atrazine biodegradation in soil under the different bioremediation strategies. The rate constants ( k1 ) of atrazine biodegradation in soil subjected to bioaugmentations with  Pseudomonas aeruginosa, Bacillus subtilis, Aspergillus niger, and bacterial-fungal consortium ranges between 0.059 day-1 and 0.191 day-1 while for that subjected to natural bioattenuation, biostimulation and combined bioaugmentation and biostimulation are 0.026 day-1, 0.164 day-1 and 0.279 day-1, respectively. The half-life ( 2 t1/ ) of atrazine biodegradation in soil under natural bioattenuation was obtained to be 26.7 days. This was reduced to between 2.5 and 11.7 days under the application of bioaugmentation, biostimulation and combined bioaugmentation and biostimulation strategies. The bioremediation efficiencies of the different bioremediation strategies in influencing atrazine biodegradation or removal is of the following order: Combined bioaugmentation and biostimulation > Bioaugmentation with bacterial-fungal consortium > Biostimulation with poultry droppings > Bioaugmentation with Pseudomonas aeruginosa > Bioaugmentation with Bacillus subtilis > Bioaugmentation with Aspergillus niger > Natural bioattenuation.Keywords: Atrazine; Bioaugmentation; Bioremediation; Biostimulatio

Modelling of Thermal Degradation Kinetics of Ascorbic Acid in Pawpaw and Potato

Ascorbic acid (vitamin C) loss in thermally treated pawpaw and potato was modelled mathematically. Isothermal experiments in the temperature range of 50 -80 oC for the drying of pawpaw and 60 -100 oC for the blanch-drying of potato were utilized to determine the kinetics of ascorbic acid loss in both fruit and vegetable. Changes in ascorbic acid degradation followed first-order reaction kinetics. Temperature dependence of the rate constant during thermal processing of pawpaw and potato obeyed the Arrhenius relationship with activation energy of 12.1 and 19.3 KJ/ mole for pawpaw and potato, respectively. A correlation between the loss of ascorbic acid and moisture loss in pawpaw was established with satisfactory statistical predictions(R= 0.996)

Modelling of thermal degradation kinetics of ascorbic acid in pawpaw and potato

Ascorbic acid (vitamin C) loss in thermally treated pawpaw and potato was modelled mathematically. Isothermal experiments in the temperature range of 50 -80 oC for the drying of pawpaw and 60 -100 oC for the blanch-drying of potato were utilized to determine the kinetics of ascorbic acid loss in both fruitand vegetable. Changes in ascorbic acid degradation followed first-order reaction kinetics. Temperature dependence of the rate constant during thermal processing of pawpaw and potato obeyed the Arrhenius relationship with activation energy of 12.1 and 19.3 KJ/ mole for pawpaw and potato, respectively. A correlation between the loss of ascorbic acid and moisture loss in pawpaw was established with satisfactory statistical predictions(R= 0.996