Giving credit to residual bioresources: From municipal solid waste hydrolysate and waste plum juice to poly (3-hydroxybutyrate)

Municipal solid waste (MSW) is massively generated all over the world. Its organic fraction (OFMSW), which represents a high percentage of MSW, mainly contains biodegradable materials, namely food waste, paper and garden waste. The social cost of OFMSW treatment and/or disposal is a serious and widespread problem, particularly in highly populated areas. Thus, effective and innovative solutions, which include the upgrading of OFMSW, are being currently sought. In fact, the OFMSW abundance, availability and average composition suggest its considerable potential within the circular economy desideratum, paving the way to valorisation approaches. In this context, an OFMSW sugar-rich hydrolysate and its validation as a substrate for the production of the polyester poly(3-hydroxybutyrate) (P(3HB)), to date the only bioplastic easily biodegradable in marine environment, were successfully obtained in a previous study. Based on those results, this work addresses the upscaling of the fermentative production, in fed-batch mode, of P(3HB) by Burkholderia sacchari. The OFMSW hydrolysate was used as cultivation medium due to its balanced nutrient composition, while a plum waste juice, also rich in sugars, was applied as feed to the bioreactor. By implementing this strategy, a maximum P(3HB) production of 30 g·L⁻¹ with an accumulation of 43% g (P(3HB))/g cell dry weight (CDW) after 51 h, was achieved. The use of the hydrolysate as initial medium resulted in higher CDW (71 g·L⁻¹) than that of the simulated hydrolysate (62 g·L⁻¹ in average), probably because the OFMSW hydrolysate favours biomass growth in detriment of P(3HB) production.