Revalorization of adsorbed residual oil in spent bleaching clay as a sole carbon source for polyhydroxyalkanoate (PHA) accumulation in Cupriavidus necator Re2058/pCB113

Spent bleaching clay (SBC) containing ~33 wt% adsorbed residual oil from the refining of palm oil in the milling industry was evaluated for use as a sole carbon source for poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] production by the recombinant strain Cupriavidus necator Re2058/pCB113. The biosynthesis of polyhydroxyalkanoate (PHA) was conducted in a one-stage cultivation process using shaken flasks. Palm olein and the extracted oil from SBC were used for comparison with the adsorbed residual oil (ARO) in SBC to evaluate the efficiency of the latter as a carbon source. The ARO in SBC can be utilized by the bacterium for the growth and accumulation of PHA. Cell growth and PHA accumulation were observed to be the best when 20 g/L ARO was supplied as a carbon source, resulting in the production of 11.8 g/L dry cell weight containing 39.8 wt% P(3HB-co-15 mol% 3HHx). The biomass yield showed that ARO in SBC is a suitable carbon feedstock for this strain. Thus, these results suggest that ARO in SBC, an inexpensive carbon source, can be used to produce low-cost commercialized PHA in bulk. Polyhydroxyalkanoate (PHA) is a biopolyester similar to some commodity plastics. The production cost of PHA is high partly due to the cost of feedstock. Spent bleaching clay (SBC) is a byproduct of the palm oil refining process. Adsorbed residual oil in SBC was successfully utilized by Cupriavidus necator Re2058/pCB113 in shaken flask culture for PHA production. Both the SBC and the resulting PHA were characterized by SEM, rheometer, TGA, DSC, GC and 1H-NMR to demonstrate the production of a PHA copolymer containing 3-hydroxyhexanoate.