Influence of inoculum variation and nutrient availability on polyhydroxybutyrate production from activated sludge

Effect of enrichment conditions of secondary feeding on the synthesis of polyhydroxyalkanoates (PHAs) by activated sludge

Polyhydroxyalkanoates (PHAs) are biodegradable plastics with great performance and development prospects. However, their traditional anaerobic/aerobic enrichment process requires a high concentration of dissolved oxygen (DO), resulting in high energy consumption. In this study, an anaerobic/oxygen-limited with secondary feeding enrichment mode was used to enhance the synthesis of PHAs while reducing energy consumption. The enrichment process of PHAs-synthesizing bacteria lasted up to 100 days, and the experiment was conducted to investigate the change of the PHAs synthesizing ability of the system in this mode by detecting the PHAs content and community distribution of the activated sludge under different stages. Under these conditions, the system enriched two major genera of PHAs-synthesizing bacteria, Thauera (30.21%) and Thiothrix (21.30%). The content of PHAs in the sludge increased from 4.51% to 30.87% and was able to achieve a concomitant increase in poly(3-hydroxyvalerate) (PHV) monomer content. After nitrogen limitation (C/N = 150) treatment, the content of PHAs reached 63.05%. The results showed that the enrichment mode of anaerobic/oxygen-limited with secondary feeding could enrich more PHAs-synthesizing bacteria and significantly increase the synthesis amount of PHAs, which revealed the great potential of this mode in solid waste value-added and reduce the production cost of PHAs and could provide a theoretical basis for the production of PHAs from activated sludge.

Biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxvalerate) from volatile fatty acids by Cupriavidus necator

A promising strategy to alleviate the plastic pollution from traditional petroleum-based plastics is the application of biodegradable plastics, in which polyhydroxyalkanoates (PHAs) have received increasing interest owing to their considerable biodegradability. In the PHAs family, poly(3-hydroxybutyrate-co-3-hydroxvalerate) (PHBV) has better mechanical properties, which possesses broader application prospects. With this purpose, the present study adopted Cupriavidus necator to synthesize PHBV utilizing volatile fatty acids (VFAs) as sole carbon sources. Results showed that the concentration and composition of VFAs significantly influenced the production of PHAs. Especially, even carbon VFAs (acetate and butyrate) synthesized only poly(3-hydroxybutyrate) (PHB), while the addition of odd carbon VFAs (propionate and valerate) resulted in PHBV production. The 3-hydroxyvalerate (3HV) contents in PHBV were directly determined by the specific VFAs compositions, in which valerate was the preferred substrate for 3HV accumulation. After optimization by response surface methodology, the highest PHBV accumulation achieved 79.47% in dry cells, and the conversion efficiency of VFAs to PHBV reached 40%, with the PHBV production of 1.20 ± 0.05 g/L. This study revealed the metabolic rule of VFAs converting into PHAs by C. necator and figured out the optimal VFAs condition for PHBV accumulation, which provides a valuable reference for developing downstream strategies of PHBV production in industrial applications in future.

Community Structure of Bacteria and Archaea Associated with Geotextile Filters in Anaerobic Bioreactor Landfills

Landfills are an example of an environment that contains highly complex communities of microorganisms. To evaluate the microbial community structure, four stainless steel pilot-scale bioreactor landfills with single- and double-layered geotextile fabric were used. Two reactors (R-1 and R-2) contained municipal solid waste (MSW) and sewage sludge, while the other two reactors (R-3 and R-4) contained only MSW. A single layer of geotextile fabric (R2GT3 and R3GT3) was inserted in the drainage layers of the two reactors (R-2 and R-3), while a double layer of geotextile fabric (R4GT2 and R4GT1) was inserted in one of the reactors (R-4). Scanning electron microscopy demonstrated that biomass developed on the geotextile fabrics after 540 days of bioreactor operation. The metagenomics analyses of the geotextile samples by 16S rRNA gene sequencing indicated that the geotextile bacterial communities were dominated by the phyla Firmicutes, Bacteroidetes, and Thermotogeae, while Proteobacteria were detected as the rarest bacterial phylum in all the geotextile samples. Treponema, Caldicoprobacter, and Clostridium were the most dominant anaerobic and fermentative bacterial genera associated with the geotextile fabric in the bioreactors. Euryarchaeota was the predominant archaean phylum detected in all the geotextile samples. In the archaeal communities, Methanosarcina, and Vadin CA11 were identified as the predominant genera. The diversity of microorganisms in landfill bioreactors is addressed to reveal opportunities for landfill process modifications and associated operational optimization. Thus, this study provides insights into the population dynamics of microorganisms in geotextile fabrics used in bioreactor landfills.