Two-stage microbial conversion of crude glycerol to 1,3-propanediol and polyhydroxyalkanoates after pretreatment

Anaerobic fermentation of organic solid waste: Recent updates in substrates, products, and the process with multiple products co-production

The effective conversion and recycling of organic solid waste contribute to the resolution of widespread issues such as global environmental pollution, energy scarcity and resource depletion. The anaerobic fermentation technology provides for the effective treatment of organic solid waste and the generation of various products. The analysis, which is based on bibliometrics, concentrates on the valorisation of affordable and easily accessible raw materials with high organic matter content as well as the production of clean energy substances and high value-added platform products. The processing and application status of fermentation raw materials such as waste activated sludge, food waste, microalgae and crude glycerol are investigated. To analyse the status of the preparation and engineering applications of the products, the fermentation products biohydrogen, VFAs, biogas, ethanol, succinic acid, lactic acid, and butanol are employed as representatives. Simultaneously, the anaerobic biorefinery process with multiple product co-production is sorted out. Product co-production can reduce waste discharge, enhance resource recovery efficiency, and serve as a model for improving anaerobic fermentation economics.

Strategies and tools for the biotechnological valorization of glycerol to 1, 3-propanediol: Challenges, recent advancements and future outlook

Global efforts towards decarbonization, environmental sustainability, and a growing impetus for exploiting renewable resources such as biomass have spurred the growth and usage of bio-based chemicals and fuels. In light of such developments, the biodiesel industry will likely flourish, as the transport sector is taking several initiatives to attain carbon-neutral mobility. However, this industry would inevitably generate glycerol as an abundant waste by-product. Despite being a renewable organic carbon source and assimilated by several prokaryotes, presently realizing glycerol-based biorefinery is a distant reality. Among several platform chemicals such as ethanol, lactic acid, succinic acid, 2, 3-butanediol etc. 1, 3-propanediol (1, 3-PDO) is the only chemical naturally produced by fermentation with glycerol as a native substrate. The recent commercialization of glycerol-based 1, 3-PDO by Metabolic Explorer, France, has revived research interests in developing alternate cost-competitive, scalable and marketable bioprocesses. The current review outlines natural glycerol assimilating and 1, 3-PDO-producing microbes, their metabolic pathways, and associated genes. Later, technical barriers are carefully examined, such as the direct use of industrial glycerol as input material and genetic and metabolic issues related to microbes alleviating their industrial use. Biotechnological interventions exploited in the past five years, which can substantially circumvent these challenges, such as microbial bioprospecting, mutagenesis, metabolic, evolutionary and bioprocess engineering, including their combinations, are discussed in detail. The concluding section sheds light on some of the emerging and most promising breakthroughs which have resulted in evolving new, efficient, and robust microbial cell factories and/or bioprocesses for glycerol-based 1, 3-PDO production.

Revealing the Phenotypic and Genomic Background for PHA Production from Rapeseed-Biodiesel Crude Glycerol Using Photobacterium ganghwense C2.2

Polyhydroxyalkanoates (PHA) are promising biodegradable and biocompatible bioplastics, and extensive knowledge of the employed bacterial strain's metabolic capabilities is necessary in choosing economically feasible production conditions. This study aimed to create an in-depth view of the utilization of Photobacterium ganghwense C2.2 for PHA production by linking a wide array of characterization methods: metabolic pathway annotation from the strain's complete genome, high-throughput phenotypic tests, and biomass analyses through plate-based assays and flask and bioreactor cultivations. We confirmed, in PHA production conditions, urea catabolization, fatty acid degradation and synthesis, and high pH variation and osmotic stress tolerance. With urea as a nitrogen source, pure and rapeseed-biodiesel crude glycerol were analyzed comparatively as carbon sources for fermentation at 20 °C. Flask cultivations yielded 2.2 g/L and 2 g/L PHA at 120 h, respectively, with molecular weights of 428,629 g/mol and 81,515 g/mol. Bioreactor batch cultivation doubled biomass accumulation (10 g/L and 13.2 g/L) in 48 h, with a PHA productivity of 0.133 g/(L·h) and 0.05 g/(L·h). Thus, phenotypic and genomic analyses determined the successful use of Photobacterium ganghwense C2.2 for PHA production using urea and crude glycerol and 20 g/L NaCl, without pH adjustment, providing the basis for a viable fermentation process.

Production of polyhydroxyalkanoates by three novel species of Marinobacterium

Several species of novel marine bacteria from the genus Marinobacterium, including M. nitratireducens, M. sediminicola, and M. zhoushanense were found to be capable of producing polyhydroxyalkanoates (PHA) using sugars and volatile fatty acids (VFAs) as the carbon source. M. zhoushanense produced poly-3-hydroxybutytate (PHB) from sucrose, achieving a product titer and PHB content of 2.89 g/L and 64.05 wt%, respectively. By contrast, M. nitratireducens accumulated 3.38 g/L PHB and 66.80 wt% polymer content using butyrate as the substrate. A third species, M. sediminicola showed favorable tolerance to propionate, butyrate, and valerate. The use of 10 g/L valerate yielded 3.37 g/L poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), with a 3-hydroxyvalerate (3 HV) monomer content of 94.75 mol%. Moreover, M. sediminicola could be manipulated to produce PHBV with changeable polymer compositions by feeding different mixtures of VFAs. Our results indicate that M. sediminicola is a promising halophilic bacterium for the production of PHA.

Progress in Production of 1, 3-propanediol From Selective Hydrogenolysis of Glycerol

1,3-propanediol (1,3-PDO) is an important bulk chemical widely used in the polyester and polyurethane industry. The selective hydrogenolysis of glycerol to value-added 1,3-PDO is extremely attractive. However, the formation of 1,3-PDO is less thermodynamically stable than 1,2-PDO, and the steric hindrance effect in the reaction process makes the highly selective production of 1,3-PDO a great challenge. In this mini review, the recent research progress on the selective catalytic hydrogenolysis of glycerol to 1,3-PDO is overviewed and the catalytic mechanism of the reaction is summarized. We mainly focus on the different performances of each type of catalyst (Pt-W-based catalysts, Ir-Re based-catalysts, and other types) as well as the interactions between metals and supports. Finally, several personal perspectives on the opportunities and challenges within this promising field are discussed.

Production of polyhydroxyalkanoates by halotolerant bacteria with volatile fatty acids from food waste as carbon source

In this study, a halotolerant strain was isolated from high salinity leachate and identified as Bacillus cereus NT-3. It can produce a high concentration of polyhydroxyalkanoates (PHAs) with no significant changes when NaCl concentration is up to 50 g/L. FTIR and NMR spectra of PHAs synthesized by Bacillus cereus NT-3 were similar to the standard or previous results. Effluent from acidogenic fermentation of food waste and pure volatile fatty acids (VFAs) mixture was used as carbon source to check the effect of non-VFAs compounds of the effluent on PHAs production. The maximum PHAs production was 0.42 g/L for effluent fermentation, whereas it was 0.34 g/L for pure VFAs fermentation, indicating that bacteria could use actual effluent in a better way. Furthermore, a mathematical model was established for describing kinetic behavior of bacteria using different carbon sources. These results provided a promising approach for PHAs biosynthesis with a low-cost carbon source.