Potato peels which are a low cost, renewable agroindustry by-product were used for the removal of hexavalent chromium from aqueous effluents. Batch experiments were carried out with an artificial effluent comprising of potassium dichromate in deionised water. The effects of the initial hexavalent chromium concentration, dose of biosorbent, and removal kinetics were explored. An adsorbent dosage of 4 g/L was effective in complete removal of the metal ion, at pH 2.5, in 48 minutes. The kinetic process of Cr(VI) adsorption onto potato peel powder was tested by applying pseudo-first-order and pseudo-second-order models as well as the Elovich kinetic equation to correlate the experimental data and to determine the kinetic parameters. The adsorption data were correlated by the Langmuir and Freundlich isotherms. A maximum monolayer adsorption capacity of 3.28 mg/g was calculated using the Langmuir adsorption isotherm, suggesting a functional group limited adsorption process. The results confirmed that potato peels are an effective biosorbent for the removal of hexavalent chromium from effluent.

The production of biodiesel from dairy effluent scum using calcined egg shell as the transesterification catalyst has been explored. Eggshell powder was calcined at 900 °C for 3 h and used as catalyst. The influence of methanol-oil molar ratio, catalyst concentration and reaction temperature were studied using Response Surface Methodology employing a Central Composite Rotatable Design. An empirical model that relates the yield of biodiesel to the studied factors was obtained. The model has high statistical significance at 95% confidence interval with R2 and adjusted R2 values of 96.31% and 95.75% respectively. Results showed that among the three studied factors, the methanol-oil molar ratio had the greatest contribution to the yield of dairy effluent scum derived biodiesel followed by reaction temperature and finally, the catalyst concentration. Significant interaction effects were also present between methanol-oil ratio and catalyst, catalyst and reaction temperature and methanol-oil ratio and reaction temperature. Accordingly, the optimal variable settings were 14.355:1 methanol-oil molar ratio, 3.09% catalyst loading by weight of pre-treated dairy scum oil and 55.20°C reaction temperature; with a corresponding yield of 92.72%.

The equilibrium adsorption of pyrethrin onto aggregates formed by the flocculation of micelles of the surfactant sodium dodecyl sulphate (SDS) with aluminium sulphate is reported. The experimental results were analysed using different adsorption isotherms (Langmuir, Freundlich, Redlich-Peterson, Sips, Radke-Prausnitz, Temkin, linear equilibrium, and the Dubin-Radushkevich isotherms). The Freundlich and linear equilibrium isotherms best describe the adsorption of pyrethrin onto SDS micellar flocs, with the Freundlich adsorption constant,KF, and the mass distribution coefficient,KD, of 64.266 ((mg/g)(L/mg)1/n) and 119.65 L/g, respectively. Applicability of the Freundlich adsorption model suggests that heterogeneous surface adsorption affects the adsorption. The mean free energy value estimated using the Dubinin-Radushkevich isotherm was 0.136 kJ/mol indicating that physisorption may be predominant in the adsorption process.

The production of oxalic acid from sawdust using a mixture of strong nitric acid and concentrated sulphuric acid with coal fly ash as a catalyst has been explored. Operating parameters affecting the reaction were determined to be temperature, mesh size and amount of fly ash catalyst, time and the $${\text{HNO}}_{3} :{\text{H}}_{2} {\text{SO}}_{4}$$ HNO 3 : H 2 SO 4 ratio. A maximum oxalic acid yield of 84% was obtained using a mixture of 60% $${\text{HNO}}_{3} {\text{ and }}40 \%{\text{ H}}_{2} {\text{SO}}_{4}$$ HNO 3 and 40 % H 2 SO 4 at 70 °C and a reaction time of 150 minutes. Coal fly ash with particle size of 50–100 μm proved to be a suitable and efficient catalyst, and the optimum quantity of catalyst employed was 5g of fly ash for every 100g of sawdust.