Conversion of waste cooking oil into medium chain polyhydroxyalkanoates in a high cell density fermentation

•Valorisation of waste cooking oil through conversion into polyhydroxyalkanoate PHA.•A high cell density bioprocess with high PHA volumetric productivity was developed.•PHA composition reflects the fatty acid composition of the waste cooking oil used. Biodegradable and biocompatible polymers polyhydroxyalkanoates (PHAs) have a wide range of applications from packaging to medical. For the production of PHA at scale it is necessary to develop a high productivity bioprocess based on the use of a cheap substrate. The objective of the current study was to develop a high cell density bioreactor-based process for the production of medium chain length polyhydroxyalkanoate (mclPHA) with waste cooking oil as the sole carbon and energy source. A number of substrate feeding strategies for bacterial growth and polymer production were investigated. Pseudomonas chlororaphis 555 achieved high biomass of 73 g/l medium and a good biomass yield (including PHA in the cell) of 0.52 g/g substrate. P. chlororaphis 555 accumulated 13.9 g mclPHA/L and achieved polymer productivity of 0.29 g mclPHA/(L h). The mclPHA contained predominantly (R)-3-hydroxyoctanoic acid and (R)-3-hydroxydecanoic acid monomers, with a high fraction of (R)-3-hydroxydodecanoic acid monomers. This polymer is of low molecular weight (18 324 kDa), low polydispersity, it is amorphous, and has a glass transition temperature of −64 °C.