Treatment of biodiesel wastewater by adsorption with commercial chitosan flakes: Parameter optimization and process kinetics

• Effect of parameters on biodiesel wastewater treatment by adsorption was investigated.
• Four repetitive adsorptions gave acceptable properties of treated wastewater, except oil & grease.
• NaOH could partially regenerate the used commercial chitosan.
• Adsorption kinetics was controlled by diffusion and adsorption during the first 1.5 h.
• Adsorption kinetics was solely controlled by the adsorption process after 2 h.

The possibility of using commercial chitosan flakes as an adsorbent for the removal of pollutants from biodiesel wastewater was evaluated. The effect of varying the adsorption time (0.5–5 h), initial wastewater pH (2–8), adsorbent dose (0.5–5.5 g/L) and mixing rate (120–350 rpm) on the efficiency of pollutant removal was explored by univariate analysis. Under the derived optimal conditions, greater than 59.3%, 87.9% and 66.2% of the biological oxygen demand (BOD), chemical oxygen demand (COD) and oil & grease, respectively, was removed by a single adsorption. Nevertheless, the remaining BOD, COD and oil & grease were still higher than the acceptable Thai government limits for discharge into the environment. When the treatment was repeated, a greater than 93.6%, 97.6% and 95.8% removal of the BOD, COD and oil & grease, respectively, was obtained. The reusability of commercial chitosan following NaOH washing (0.05–0.2 M) was not suitable, with less than 40% efficiency after just one recycling and declining rapidly thereafter. The adsorption kinetics of all pollutant types by the commercial chitosan flakes was controlled by a mixed process of diffusion and adsorption of the pollutants during the early treatment period (0–1.5 h) and then solely controlled by adsorption after 2 h.