Inhibition of residual n-hexane in anaerobic digestion of lipid-extracted microalgal wastes and microbial community shift

Yun, Yeo-Myeong; Shin, Hang-Sik; Lee, Chang Kyu; Oh, You-Kwan; Kim, Hyun Woo

Inhibition of residual n-hexane in anaerobic digestion of lipid-extracted microalgal wastes and microbial community shift

2016

Yun, Yeo-Myeong | Shin, Hang-Sik | Lee, Chang Kyu | Oh, You-Kwan | Kim, Hyun Woo

Converting lipid-extracted microalgal wastes to methane (CH₄) via anaerobic digestion (AD) has the potential to make microalgae-based biodiesel platform more sustainable. However, it is apparent that remaining n-hexane (C₆H₁₄) from lipid extraction could inhibit metabolic pathway of methanogens. To test an inhibitory influence of residual n-hexane, this study conducted a series of batch AD by mixing lipid-extracted Chlorella vulgaris with a wide range of n-hexane concentration (∼10 g chemical oxygen demand (COD)/L). Experimental results show that the inhibition of n-hexane on CH₄ yield was negligible up to 2 g COD/L and inhibition to methanogenesis became significant when it was higher than 4 g COD/L based on quantitative mass balance. Inhibition threshold was about 4 g COD/L of n-hexane. Analytical result of microbial community profile revealed that dominance of alkane-degrading sulfate-reducing bacteria (SRB) and syntrophic bacteria increased, while that of methanogens sharply dropped as n-hexane concentration increased. These findings offer a useful guideline of threshold n-hexane concentration and microbial community shift for the AD of lipid-extracted microalgal wastes.

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