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

Abstract

Transformation of wastewater streams into commodity chemicals could potentially shift the energy-intensive wastewater treatment plants (WWTPs) into sustainable biorefineries. Nevertheless, the available microbial chassis is still very scarce. Herein, we isolated an alkali-tolerant Paracoccus sp. ZQW-2 and developed a “one-stone-for-two-birds” strategy that simultaneously realized pyridine wastewater upcycling and poly(3-hydroxybutyrate) (PHB, a typical bioplastic) recovery. Specifically, Paracoccus sp. ZQW-2 was able 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 intermediates identification and transcriptome analysis. For the first time, the 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 the ecological niche and guaranteed the dominant role of Paracoccus sp. ZQW-2 throughout the open fermentation process. Life-cycle assessment revealed that the proposed PHB-oriented wastewater valorization route significantly reduced the carbon-footprint by 24.4%. Overall, this strategy brings the paradigm shift from pollution control to resource recovery one step forward, and paves the way to circular economy.