Biological utilization of pyrolytic acetic acid for lipid-rich algal biomass production: Substrate detoxification, inhibition mechanism, and fermentation optimization.

摘要

Acetic acid derived from fast pyrolysis of lignocelulosic biomass is a promising substrate for microalgae Chlamydomonas reinhardtii fermentation for producing lipid-rich biomass. However, pyrolytic-acetate-containing substrate has an extremely complex composition and highly inhibitory to microorganism due to the various toxic contaminants. In this dissertation, this work is to improve the C. reinhardtii fermentation performance through various detoxification practice for enhancing the fermentability of the C. reinhardtii. The inhibitory mechanisms of toxic compounds to the algal culture were also studied. Finally, the algal fermentation on pyrolytic acetic acid was optimized though the development of various fermentation strategies. When growing in raw bio-oil without any detoxification treatment, the algae can only tolerate up to 0.1 wt% of pyrolytic acetic acid stream. Alkaline treatment and oxidative treatment were applied to detoxification of pyrolytic acetic acid substrate. Addition of KOH, NaOH or Ca(OH)2 can significantly reduce the toxicity and improved algal fermentability by 20, 40 and 55 times, respectively. Alkali species used, treatment pH and treatment temperature were found all influencing the effectiveness of the alkali treatment. When oxidative treatment was further applied to NaOH-treated pyrolytic acetic acid substrate, the maximum cell density and biomass productivity was improved under each level inclusion of treated pyrolytic substrate although the cell still cannot tolerate the higher inclusion of the pyrolytic substrate. It was also found that directed evolution of algal strain increased the tolerance of algae strain; the maximum tolerance level of pyrolytic substrate by the evolved strain increased to 5.5wt% as comparted to the maximum tolerant level of 4% by the wild type strain.