# High Cell Density Fermentation of Yarrowia lipolytica on n-Hexadecane for the Valorization of Pyrolyzed Plastic Waste

## TL;DR

This study explores using the yeast Yarrowia lipolytica to convert plastic waste into valuable biomass through high-density fermentation.

## Contribution

The study demonstrates high cell density fermentation of Yarrowia lipolytica on pyrolyzed plastic waste-derived n-hexadecane.

## Key findings

- A Yarrowia lipolytica strain was selected and optimized for growth on n-hexadecane with no inhibitory effects.
- High cell density fermentation achieved 145.6 g·L−1 biomass with 22.0% triacylglycerols.
- Lowering pH to 2.5 significantly reduced citrate formation without affecting biomass or TAG production.

## Abstract

The recycling of fossil-based plastic waste remains a key challenge in reducing environmental pollution and greenhouse gas emissions. An innovative approach is the biotechnological conversion of the n-alkane mixture obtained from thermal pyrolysis of plastic waste. This study focuses on the use of the oleaginous yeast Yarrowia lipolytica for the valorization of polyethylene (PE)-derived pyrolysis oil. From a screening of 50 Y. lipolytica strains, the most promising candidate was selected, and its single-cell phenotype was stabilized by MHY1 deletion. In shake flask experiments, this strain grew similarly on 5–20 vol% of n-hexadecane, revealing no inhibitory effects. Subsequently, a high cell density fermentation was established in a 4 L bioreactor using a pulsed fed-batch approach, resulting in biomass concentrations of up to 145.6 g·L−1, which contained 22.0% triacylglycerols. In addition, cultivation at pH 2.5, compared to pH 4.0, reduced citrate formation from 95.6 to 0.8 g·L−1, while biomass and TAG titers remained similar. Overall, these results highlight the potential of integrating plastic waste-derived pyrolysis oil into future bioprocesses using Y. lipolytica as an effective platform for high cell density production.