• MMC and DMC from top-down and bottom-up engineering were compared for PO wax bioupcycling. • DMC of Sn and H16 showed the highest PHA accumulation under nitrogen-limiting condition. • MMC was robust and highly adaptable toward process operational and environmental changes. • Fed-batch with optimized hybrid feeding increased PHA production by 5.6-fold. • Highest PHA titer and productivity were achieved solely from non-oxidized PO wax. The linear plastic value chain and the inefficient end-of-life management raise significant environmental concerns. As closed-loop recycling alone cannot effectively handle mixed post-consumer plastics, with polyolefins (PO) representing 40% of it, innovative strategies are needed to complement recycling and avoid mismanagement of plastic waste. Currently, there is no “one-fits all” solution to solve the plastic waste challenge, but a proper integration of different technologies could provide a substantial contribution. Here, we demonstrate a tandem process combining pyrolysis and microbial consortia-based biotechnological conversion to upcycle PO waste into the biodegradable polymer polyhydroxyalkanoate (PHA). Using a top-down and bottom-up eco-engineering approach, we developed efficient PO pyrolysis wax-utilizing mixed microbial consortia (MMC) and defined mixed consortia (DMC). Under nitrogen-limiting conditions in shake-flask experiment, DMC of Serratia nematodiphila and Cupriavidus necator H16 produced 193.0 ± 4.3 mg/L PHA, comparable to enriched MMC (138.6 ± 51.5 mg/L). Employing batch fermentation with pulse-feeding of PO wax increased PHA titer of the MMC process by 4.4-fold in shake-flask, while no change or even decrease in titer was observed in DMC, likely due to inhibition and altered interspecies interactions. Consequently, 1.5 L-fed-batch fermentation with hybrid feeding strategy (exponential feeding, followed by pulse feeding) was further developed to increase PHA titer, yield, and productivity from the MMC process. The final titer at 96 h was 772.1 ± 93.3 mg/L, or 5.6-fold improved from unoptimized shake-flask process. PHA yield and productivity peaked at 50 h, achieving 0.049 ± 0.005 gPHA/gPOwax-added, and 13.2 ± 1.4 mg/L/h, representing 2-fold and 1.5-fold increases, respectively, compared with the unoptimized feeding scheme. The results represent the highest reported PHA titer from non-oxidized PO pyrolysis wax, achieved solely through optimization of fed-batch feeding strategy relying solely on PO wax.
Lomwongsopon et al. (Wed,) studied this question.