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The kinetics of citric acid fermentation from corn starch hydrolysate using Aspergillus niger ATCC 9142 was studied in a batch fermenter. A general model for citric acid production was formulated. Four kinetic models, Monod, Haldane, logistic and hyperbolic for describing the growth of the fermenting microorganism were explored. The validity of the models in terms of predicting growth of the fermenting organism was determined by fitting each kinetic model to experimental data collected in the course of this work. Comparison of experimental results to model predicted results showed 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 µ max , Y x/s , Y p/x , K s and K p as calculated by the hyperbolic model are 0.01320h -1 , 0.711g/g, 13.6708g/g, 0.0006g/dm 3 , and 0.2572 g/dm 3 respectively. The validated model was implemented in an advanced equation oriented modelling software to determine the effect of key process parameters on the production of citric acid.Results of simulating the model show that the production of citric acid is a growth associated process. Optimum pH, initial sugar concentration and temperature of for citric acid production were 5.5, 40w/v and 30 o C respectively.

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This paper considered the toxicity assessment of some crude oil contaminated soils in Niger Delta areas. The soil samples were collected from different horizontal distances, vertical depths and contaminated soil of different ages. The heavy metals in the contaminated soils were digested and extracted using di-acid digested and DTPA extraction methods respectively. The physiochemical parameters (moisture content, pH, N, P and heavy metals (Ni, Pb and Cd) were analysed with APHA method. The heavy metals concentration was determined using atomic absorption spectrophotometer (AAS). The results show that the metals concentration decreased with the age of the contaminated soil and with increased vertical depths. However, the metals concentrations were almost constant at different horizontal distances. Similar trend was observed for the moisture content, pH, N, P and K.

The potential use of waste tyre rubber granules (WTRG) for the batch adsorption of naphthalene from aqueous solutions was investigated. The effect of various operational variables such as contact time, initial naphthalene concentration, adsorbent dose, size of adsorbent particles, and temperature of solution on the adsorption capacity of WTRG was evaluated. The adsorption of naphthalene by WTRG was a fast kinetic process with an equilibrium contact time of 60 min. A low temperature (5°C), small adsorbent particle size (0.212 mm) and higher adsorbent dosage favored the adsorption process. Results of isotherm studies revealed that adsorption of naphthalene was best described by the Langmuir isotherm equation (R 2 =0.997) while the kinetics of the process was best described by the Lagergren pseudofirst order kinetic equation (R 2 =0.998). This study has demonstrated the suitability of WTRG for the removal of naphthalene from aqueous solution.Contributions: FAA, in collaboration with ANA, designed the study; AIA performed the experiments while ANA and SAA managed the literature searches; ANA wrote the first draft of the manuscript; FAA provided analytical advice and manuscript correction. All authors read and approved the final manuscript.

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