Production of poly (3-hydroxybutyrate) from a dairy industry wastewater using Bacillus subtilis EPAH18: Bioprocess development and simulation

Abstract

The production of biopolymers such as poly (3-hydroxybutyrate) (PHB) from renewable resources has gained revived attention; although, fermenting media cost affects the production price. Whilst cheese whey (CW) is an alternative source of nutrients it is managed as wastewater in rural dairy factories. Thus, this can serve as a low-cost fermenting media improving the economics of PHB production. The aim of this work is to develop the fermentation conditions for enhanced Bacillus subtilis EPAH18 PHB biosynthesis and evaluate the economics of the bioprocess by process simulation. Shake flask fermentations performed in order to identify improved PHB biosynthesis conditions were obtained at 37 °C, 24 h of fermentation, 200 rpm, 0.5% (w/v) ammonium sulphate and an inoculum of 5% (v/v). PHB biosynthesis was scaled-up to a batch bioreactor where the optimized fermentation conditions were an agitation of 500 rpm, carbon to nitrogen ratio (C/N) of 17.5/1 and pH of 7.6. The highest values of PHB production and yield (YP/S) were 0.54 g/L and 0.057 g/g respectively. The bioprocess was competitive at 1000 ton/h CW feed achieving a PHB production cost of 10.2 US$/kg. It can be concluded that CW could be exploited as a platform for a PHB biorefinery.