Valorization of organic wastes using bioreactors for polyhydroxyalkanoate production: Recent advancement, sustainable approaches, challenges, and future perspectives

Spatial separation of nitrifiers and denitrifiers promotes selection and enrichment of polyhydroxyalkanoates storing mixed cultures fed by crude glycerol and propionate wastewater

Polyhydroxyalkanoates (PHA) recovery from industrial wastewater has been highlighted as a promising strategy for a circular bioeconomy. However, the high and varying level of nitrogen in wastewater makes enrichment of mixed microbial culture (MMC) low efficiency. In this study, spatial separation of nitrifiers and denitrifiers was adopted by adding biocarriers in MMC and decreasing the sludge retention time (SRT) to accelerate the enrichment of PHA-storing MMC fed by mixed wastewater containing glycerol and propionate. Nitrifiers and denitrifiers were sustained on biocarriers, obtaining a high total inorganic nitrogen removal and allowing a more efficient selective pressure of a high carbon and nitrogen ratio (C/N) under low SRT conditions. The maximum PHA cell content and relative abundance of PHA-storing bacteria were increased to 60.51 % (SRT 6 d) and 49.62 % (SRT 6 d) with the decrease of SRT, respectively. This study demonstrates an efficient way to highly enrich PHA-storing MMC from crude glycerol, which provide a relevant technical support for high-efficiency enrichment of PHA-storing bacteria in low C/N wastewater.

An efficient and eco-friendly approach for the sustainable recovery and properties characterization of polyhydroxyalkanoates produced by methanotrophs

Synthetic biodegradable and bio-based polymers have emerged as sustainable alternatives to nonrenewable petroleum-derived polymers which cause serious environmental issues. In particular, polyhydroxyalkanoates (PHA) are promising biopolymers owing to their outstanding biodegradability and biocompatibility. The production of the homopolymer poly(3-hydroxybutyrate) (PHB) and copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) from type II methanotrophs via microbial fermentation was presented. For the efficient extraction and recovery of intracellular PHA from methanotrophs, different extraction approaches were investigated including solvent extraction using 1,3-dioxolane as a green solvent, integrated cell lysis and solvent extraction, and cell digestion without the use of organic solvents. Among various extraction approaches, the integrated method exhibited the highest extraction performance, with PHA recovery and purity exceeding 91 % and 93 %, respectively, even when the PHA content of the cells was low. Furthermore, the molecular weight, thermal stability, and mechanical properties of the recovered PHA were comprehensively analyzed to suggest its suitable practical applications. The obtained properties were comparable to that of the commercial PHA products and PHA produced from other microbial species, indicating an efficient recovery of high-quality PHA produced from methanotrophs.