Development of integrated process based on fenton reaction for lipid recovery from chlorella sp.

Abstract

Biofuel produced from microalgae is one of the promising renewable energy sources. Although there has always been a controversy about economic feasibilities in biofuel production, overall production cost is expected to be reduced by improving the downstream process. Even though there are many useful methods of harvesting and lipid extraction, the practical application has been limited due to its own issues like energy consumption and scale-up. Since drying process is considered to be a heavy burden to the industrial-scaled production, wet lipid extraction directly from wet microalgal biomass without drying process has been recently researched to improve entire production efficiency. This study developed the wet lipid extraction process combining electro‐coagulation–flotation (ECF) which is classified as a low-energy $1^{st}$ harvesting technology using ferric ions as coagulants, and Fenton process which uses ferric ions for cell disruption, in order to simplify the process by omitting the second harvesting and drying process. Firstly, effects of various experimental factors such as oxidant concentration, reaction time, and temperature were evaluated. The lipid yield reached up to 85.4 % at 90 ℃ with the oxidant concentration of 0.6%, which indicated that high reaction temperature requiring high energy consumption was inevitable to achieve sufficient lipid yield. Thus, in order to overcome the temperature issue, two-step disruption process connecting Fenton reaction and the physical disruption, high shear mixer or microwave, was established, and it enabled to achieve high lipid yield over 90% while reducing energy consumption by 42.6% at the low temperaure of 50 ℃. Finally, the one-step disruption process obtaining high lipid yield with low energy consumption was established to achieve process intensification by combining simultaneous operation of Fenton reaction and the high shear mixer showing the high energy-efficiency in the two-step disruption process. Moreover, in the one-step disruption process, the fractional feeding of the oxidant reduced its total usage by half with obtaining sufficient lipid extraction efficiency. Thus, it is expected that overall production cost of microalgae-based biofuel could be reduced by the integrated process based on Fenton reaction.