Two birds with one stone: pyridine wastewater depuration with the recovery of poly(3-hydroxybutyrate)

Abstract

The transformation of wastewater into commodity chemicals could potentially shift energy-intensive wastewater treatment plants (WWTPs) to become sustainable biorefineries. Nevertheless, there is still a scarcity of available microbial chassis. Herein, we isolated alkali-tolerant Paracoccus sp. ZQW-2 and developed a “two-birds-with-one-stone” strategy that simultaneously realized pyridine wastewater upcycling and poly(3-hydroxybutyrate) (PHB, a typical bioplastic) recovery. Specifically, Paracoccus sp. ZQW-2 could be used to synthesize PHB by using pyridine as the sole carbon and nitrogen source. The metabolic pathways, including pyridine degradation and PHB synthesis, were proposed based on the identification of intermediates and transcriptome analysis. For the first time, selective pressure and alkaline stress synergistically enabled the stable operation of an open fermentation system. Through process optimization, we achieved a high PHB content (75.9%) and titer (5.58 g L⁻¹) from actual pyridine wastewater under non-sterile conditions. The specific nitrogen source (pyridine) reconstructed an ecological niche and guaranteed the dominant role of Paracoccus sp. ZQW-2 throughout the open fermentation process. A life cycle assessment revealed that the proposed PHB-oriented wastewater valorization route significantly reduced the carbon footprint by 24.4%. Overall, this strategy brings a paradigm shift from pollution control to resource recovery one step closer and paves the way to a circular economy.