Optimisation of Solid State Fermentation of Banana Peels for Citric Acid Production

In this study, design of experiment (DOE) for response surface methodology (RSM) was used to analyse and optimise the simultaneous effect of solid substrate loading, initial pH and inoculum density on citric acid production from banana peels via solid state fermentation using Aspergillus niger. A three-variable, three-level Box-Behnken design was used to develop a statistical model to describe the relationship between citric acid concentration and the chosen independent variables and to optimise the production of citric acid using RSM. The model was statistically significant (p<0.0001) with a low standard deviation (0.43) and did not show lack of fit (R2=0.999). Citric acid production was significant at high levels of solid loading, low levels of pH and intermediate levels of inoculum density. Solid loading positively influenced citric acid production while the reverse was the case for initial pH. The optimum values of solid loading, pH and inoculum density were 20 g/L, 8 and 4.97×106 spores/mL respectively. Under these conditions, the citric acid concentration was obtained as 49.9 g/L. Validation of the statistical model showed an insignificant difference between experimental and model predicted results.http://dx.doi.org/10.4314/njt.v34i4.

Optimising the Effect of Stimulants on Citric Acid Production from Cocoyam Starch Using Aspergillus Niger

Additives such as low molecular weight alcohols, trace metals, phytate, lipids etc have been reported to stimulate citric acid production. Hence the objective of this study was to investigate the effect of stimulating the metabolic activity of Aspergillus niger for the purpose of improved citric acid production from cocoyam starch. A  three-variable,  three-level  Box-Behnken  design  (BBD)  was  used  to develop  a  statistical  model  to study the effects of Zinc (II) ion, Iron (III) ion and methanol on the production of citric acid. Response surface methodology (RSM) was used to optimise the effects of these stimulants. The results of analysis of variance (ANOVA) carried out on the model showed that the model was statistically significant (p< 0.0001) and did not show lack of fit (R2=0.997). The results also showed that citric acid production increased when the levels of zinc and methanol were increased. Intermediate levels of iron were required to produce citric acid at optimum levels. Results obtained from RSM showed that the optimum levels of zinc, iron and methanol were 4.5 g/L, 6.87 g/L and 3.0 %v/v respectively. Under these conditions, the maximum citric acid concentration was obtained as 108 g/L. Validation of the model indicated no significant difference between predicted and experimental values.http://dx.doi.org/10.4314/njt.v34i4.

Effect of Acid mixtures on the Hydrolysis of Coconut Coir for Recovery of Fermentable Sugars

In this study, coconut coir was hydrolysed to produce fermentable sugars using dilute nitric and acetic  acid. The hydrolysis process was carried out according to a four variable Box-Behnken design which was used to develop a statistical model to describe the relationship between the concentration of fermentable sugars produced (dependent variable) and the independent variables (time, temperature, nitric acid concentration and acetic acid concentration). Results of analysis of variance (ANOVA) performed to determine the fit of the statistical model showed that the model was statistically significant (p<0.0001) with a low standard deviation (1.77) and non-significant lack of fit (R2=0.93). The concentrations of nitric and acetic acid as well as the hydrolysis time and temperature all positively influenced the hydrolysis process as evident in the increase in the amount of fermentable sugars produced when the values of these variables were increased. When both acids were combined together, the amount of fermentable sugar produced was increased by as much 54%. Optimisation of the statistical model showed that the maximum sugar concentration was 32.7 g/L and this was obtained for coconut coir catalysed by 0.50 %w/v nitric acid, 0.40 %w/v acetic acid at 160 oC for 30 minutes. Validation of the statistical model showed that there was no significant difference between predicted and observed values.Keyword: Coconut coir, Lignocellulosic feedstock, Response Surface Methodology, Optimisatio

Application of Experimental Design Method for the Optimisation of Xanthan Gum Production from Pineapple Peels Using Xanthomonas Campestris via Submerged Fermentation

Xanthan gum is a major biopolymer which finds a lot of applications industrially and domestically. Biotechnological production of xanthan gum from waste biomass has been reported to be sustainable in terms of economics and viability. In this study, xanthan gum was produced from pineapple peels using Xanthomonas campestris by submerged fermentation. A  three-variable,  three-level  Box-Behnken  design  (BBD)  was  used  to develop  a  statistical  model  to study the effects of fermentation time, concentration of nitrogen (NH4NO3) and phosphorus (KH2PO4) on the amount of xanthan gum produced. Response surface methodology (RSM) was used to optimise these process variables. Results obtained showed that the model was statistically significant (p<0.0001) and did not show lack of fit (R2=0.989). The results also showed that xanthan gum production was positively influenced by high levels of phosphorus and low levels of nitrogen. Increasing the fermentation time also favoured the production of xanthan gum. Results obtained from RSM revealed that the optimum fermentation time, nitrogen and phosphorus concentration were 3 days, 2 g/L and 15 g/L respectively. Under these conditions, the xanthan concentration was obtained as 8.48 g/L. Validation of the model indicated no significant difference between predicted and experimental values.http://dx.doi.org/10.4314/njt.v34i3.1

Modelling and Simulation of the Batch Hydrolysis of Acetic Anhydride to Produce Acetic Acid

The kinetic modelling of the batch synthesis of acetic acid from acetic anhydride was investigated. The kinetic data of the reaction was obtained by conducting the hydrolysis reaction in a batch reactor. A dynamic model was formulated for this process and simulation was carried out using gPROMS® an advanced process modelling and simulation software. The developed model was validated against experimental data by estimating the kinetic parameter (reaction rate constant k=0.11302 min-1) and comparing simulation results with experimental data. Results obtained show that the formulated model was able to predict the experimental data to a high level of confidence. The dynamic behaviour of the reaction process was assessed by simulating the validated model at the initial state to obtain time trajectories of all the variables of interest. The model developed in this work will provide insight as to how the process responds under dynamic conditions and its amenability to control

Statistical Optimisation of Fermentation Conditions for Citric Acid Production from Pineapple Peels.

This study investigated the optimisation of fermentation conditions during citric acid production via solid state fermentation (SSF) of pineapple peels using Aspergillus niger. A three-variable, three-level Box-Behnken design (BBD) comprising 17 experimental runs was used to develop a statistical model for the fermentation process while response surface methodology (RSM) was used for the optimisation of fermentation conditions. Increasing the fermentation temperature and the moisture content of the solid substrate enhanced the production of citric acid. Increasing the broth pH did not favour citric acid production as higher citric acid concentrations were recorded at low pH values. These results showed that citric acid production was influenced by these variables (i.e. temperature, moisture content and pH). The optimal fermentation conditions were determined as follows: fermentation temperature, 35oC; broth pH, 2 and initial moisture content, 84.56%. The maximum concentration of citric acid produced under these conditions was 72.41 g/l. These results imply that the metabolic activity of the fermenting organismn (Aspergillus niger) used in this study was maximum at these optimised conditions. Validation of the statistical model indicated no difference between predicted and observed values as seen in the high correlation between model predicted results and experimental results.Keywords: Box-Behnken Design, Solid State Fermentation, Aspergillus niger, Citric Aci

Dynamic Modelling and Simulation of Citric Acid Production from Dilute Acid Hydrolysed Corn Starch Using Aspergillus Niger

The modelling of batch production of citric acid from corn starch hydrolysate using Aspergillus niger ATCC 9142 was carried out in this work. A validated mathematical model was developed to describe the process. Four kinetic models, Monod, Haldane, logistic and hyperbolic for simulating the growth of the Aspergillus niger cells were explored. The validity of the models in terms of predicting the growth of Aspergillus niger cells was determined by fitting each kinetic model to experimental data. Comparison of experimental results to model predicted results revealed that only the hyperbolic model was able to accurately replicate the experimental results. This was evident from the high level of correlation between the experimental and model predicted results. The kinetic parameters for cell growth, substrate consumption and product formation µmax, Yx/s, Yp/x, Ks and Kp as calculated by the hyperbolic model were 0.0130h-1, 0.711g/g, 13.671g/g, 0.001g/L, and 0.257 g/L respectively. Results of simulating the model showed that the production of citric acid was a growth associated process.  Optimum pH, initial sugar concentration and temperature for citric acid production obtained were5.5, 40w/v and 30oC respectively.http://dx.doi.org/10.4314/njt.v33i2.1

Optimisation of Dilute Sulphuric Acid Hydrolysis of Waste Newspaper for High Yields of Fermentable Sugars

Dilute sulphuric acid hydrolysis of waste paper was investigated in this study. The effects of acid  concentration, time, temperature and liquid to solid ratio on the total reducing sugar concentration were studied over three levels using a four variable Box-Behnken design (BBD). A statistical model was developed for the optimisation of the process variables using response surface methodology (RSM). The optimal hydrolysis conditions that resulted in the maximum total reducing sugar concentration were: acid concentration, 1.49 %w/w; temperature, 200°C; time, 20 min and liquid to solid ratio, 30 mL/g. Under these conditions, the total reducing sugar concentration was obtained to be 20 g/L. Validation of the model revealed no difference between predicted and experimental results.Keywords: Bioethanol, Waste paper, Response Surface Methodology, Pretreatment, Biomas

Application of Box-Behnken Design for Optimum Citric Acid Production from Cocoyam Starch Hydrolysate using Aspergillus niger

This study investigated the use of design of experiment (DOE) for response surface methodology (RSM) to analyse and optimise the production of citric acid from cocoyam starch hydrolysate. The effect of three factors, temperature, pH and inoculum density on citric acid production was determined using a three variable Box-Behnken design (BBD). The BBD was used to develop a statistical model to describe the production of citric acid and the fermentation conditions were then optimised using RSM. The model was statistically significant (p<0.0001) with a low standard deviation (0.52) and did not show lack of fit (R2=0.997). Citric acid production was favoured by intermediate levels of temperature, high levels of pH and low levels of inoculum density. The initial pH positively influenced citric acid production while the reverse was the case for inoculum density. The optimum values of temperature, pH and inoculum density were 32.98 oC, 8.0 and 0.5×106 spores/mL respectively. Under these conditions, the citric acid concentration was obtained as 26.2 g/L. Validation of the statistical model showed no significant difference between experimental and model predicted results.Keywords: Citric acid, Submerged fermentation, Box-Behnken design, Optimisation, ANOV