(2016) Science of the Total Environment_Enhanced thermal destruction of toxic microalgal biomass by using CO₂

Jung J.-M., Lee J., Kim J., Kim K.-H., Kim H.-W., Jeon Y.J., Kwon E.E.

(Elsevier B.V.) Science of the Total Environment ISSN: 489697 Vol.566-567 Issue. Article No. DOI: 10.1016/j.scitotenv.2016.05.161

This work confirmed that dominant microalgal strain in the eutrophic site (the Han River in Korea) was Microcystis aeruginosa (M. aeruginosa) secreting toxins. Collected and dried microalgal biomass had an offensive odor due to microalgal lipid, of which the content reached up to 2 ± 0.2 wt.% of microalgal biomass (dry basis). This study has validated that the offensive odor is attributed to the C_3–6 range of volatile fatty acids (VFAs), which was experimentally identified by the non-catalytic transformation of triglycerides (TGs) and free fatty acids (FFAs) in microalgal biomass into fatty acid methyl esters (FAMEs). In particular, this study mechanistically investigated the influence of CO₂ in the thermal destruction (i.e., pyrolysis) of hazardous microalgal biomass in order to achieve dual purposes (i.e., thermal disposal of hazardous microalgal biomass and energy recovery). The influence of CO₂ in pyrolysis of microalgal biomass was identified as 1) the enhanced thermal cracking behaviors of volatile organic compounds (VOCs) from the thermal degradation of microalgal biomass and 2) the direct gas phase reaction between CO₂ and VOCs. These identified influences of CO₂ in pyrolysis of microalgal biomass significantly enhanced the generation of CO: the enhanced generation of CO in the presence of CO₂ was 590% at 660 °C, 1260% at 690 °C, and 3200% at 720 °C. In addition, two identified influences of CO₂ (i.e., enhanced thermal cracking and direct gas phase reaction) occurred simultaneously and independently. The identified gas phase reaction in the presence of CO₂ was only initiated at temperatures higher than 500 °C, which was different from the Boudouard reaction. Lastly, the experimental work justified that exploiting CO₂ as a reaction medium and/or chemical feedstock will provide new technical approaches for controlling syngas ratio and in-situ air pollutant control without using catalysts. © 2016 Elsevier B.V.

This work was supported by a National Research Foundation of Korea ( NRF ) Grant funded by the Korean Government (MSIP) (no. NRF-2014RA1A004893 and NRF-2015H1D3A1066513 ). This work was also supported by the Pukyong National University Research Fund in 2013 ( CD20131333 ).