Adsorption of pollutants from biodiesel wastewater using chitosan flakes

• Effect of parameter for adsorption of pollutant from biodiesel wastewater by chitosan was studied.
• Adsorption capacity of pollutant by chitosan increase with adsorption time or agitation speed.
• Adsorption kinetics of chitosan fitted very well with the Langmuir isotherm via physical process.
• NaOH was more effective at regenerating the used chitosan than HNO3.

This work was carried out to evaluate the possibility of using commercial chitosan flakes as an adsorbent for the removal of pollutants from biodiesel wastewater. The effect of varying the adsorption time (0.5–5 h), initial wastewater pH (2–8), dosage of adsorbent (1.5–5.5 g/L) and mixing rate (120–350 rpm) on the adsorption capacity of pollutants, measured in terms of biological oxygen demand (BOD), chemical oxygen demand (COD) and oil & grease levels, was explored by univariate analysis. Under the derived optimal conditions (adsorption time of 3 h, initial wastewater pH of 4.0, chitosan at 3.5 g/L and agitated at 300 rpm), the adsorption capacity of BOD, COD and oil & grease levels were 236, 4503 and 140 mg/g, respectively. This corresponds to a reduction in the initial BOD, COD and oil & grease levels of around 76, 90 and 67%, respectively. To facilitate a higher reduction level in the investigated pollutants, the repetitive treatment of the wastewater was performed with satisfactory water quality levels being obtained after four successive treatments. The adsorption kinetics fitted very well with the Langmuir isotherm and the adsorption of all pollutants onto chitosan flake occurs via a physical process. Finally, the reusability of used chitosan by HNO3 or NaOH treatment was explored.