Evaluation of Sludge Palm Oil as Feedstock and Development of Efficient Method for its Utilization to Produce Polyhydroxyalkanoate

Abstract

Sludge palm oil (SPO), a difficult-to-be-used solid byproduct of the palm oil milling industry, was evaluated as potential carbon source for poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] production using recombinant Cupriavidus necator Re2058/pCB113. The biosynthesis of polyhydroxyalkanoate (PHA) was conducted using single stage shake flask growth to study different parameters affecting the bacterial growth. Fed-batch fermentations were conducted using SPO to increase the PHA productivity and to reach high density culture which is deemed necessary for large scale production. Initial shake flask studies showed that SPO can be utilized by the bacteria for growth and PHA accumulation. However, the yield of SPO conversion into cell biomass and PHA was low due to the difficulty in using the solid oil in liquid medium. With the aid of surfactant and mixing strategy, SPO which consisted mainly of free fatty acids was successfully emulsified in the mineral medium and was used for cell growth and PHA accumulation whereby 10 g/L of SPO supplied as emulsion solution produced 9.7 g/L of CDW containing 74 wt% P(3HB-co-22 mol% 3HHx). The high yield of biomass obtained indicates that SPO is an excellent feedstock for this strain. Fed-batch fermentation was conducted to increase the yield and productivity whereby a biomass productivity of 1.9 g/L/h and PHA productivity of 1.1 g/L/h were achieved. These results suggest that SPO, an inexpensive waste material, can be used to produce PHA in large scale for commercialization purpose with reduced production cost.