Abstract
BackgroundTo establish bioplastics as a real alternative to conventional plastics, high production costs must be constrained by using different kinds of wastewater streams as organic substrates and novel microbial strains as material-accumulating bacteria with high performance. Volatile fatty acids (VFAs) from the effluent of dairy wastewater biodigestion represent a new and inexpensive feedstock, which was used in this study for biopolymer production through microbial processes.ResultsCupriavidus necator DSM 13513 was particularly able to accumulate PHAs when operating in fed-batch mode by limiting the oxygen level together with intermittent feeding of a carbon source; maximum poly-β-hydroxybutyrate (PHB) accumulation was achieved in 48 h without compromising microbial growth. The complex VFAs mixture from the digestate did not influence PHA homopolymer accumulation. In fact, structural characterization by NMR analysis revealed PHB synthesis by C. necator DSM 13513 grown with different VFAs mixtures. Moreover, the bioplastic disk obtained from C. necator DSM 13513 cells grown on VFAs from digested dairy wastewater effluent presented good thermic properties and low affinity to water.ConclusionsOverall, the results make digested dairy wastewater effluent suitable for PHB production for specific biobased industrial applications.
Highlights
To establish bioplastics as a real alternative to conventional plastics, high production costs must be constrained by using different kinds of wastewater streams as organic substrates and novel microbial strains as material-accumulating bacteria with high performance
Ability of C. necator strains to grow in media containing Volatile fatty acids (VFAs) A preliminary screening of the strains C. necator DSM 13513, DSM 531 and DSM 428 was performed on the basis of their capacity to grow in the presence of a mixture of VFAs
C. necator DSM 13513 showed the highest growth, achieving 1.97 O.D.600 nm at 40 h in the presence of VFAsynthetic (Fig. 1a), in contrast to the control assay (0.90 O.D.600 nm; Fig. 1c). These results demonstrated that these bacterial strains were well adapted to the acidogenic nutritional conditions due to the addition of the VFAs mixture
Summary
To establish bioplastics as a real alternative to conventional plastics, high production costs must be constrained by using different kinds of wastewater streams as organic substrates and novel microbial strains as material-accumulating bacteria with high performance. Volatile fatty acids (VFAs) from the effluent of dairy wastewater biodigestion represent a new and inexpensive feedstock, which was used in this study for biopolymer production through microbial processes. Effluent from dark fermentation H 2 processes, containing large quantities of VFAs, represents an interesting feedstock for the PHA production process and an opportunity to enhance the treatment of such effluents [9] In this context, in recent decades, many studies have focused on energy sources, such as hydrogen produced from dairy wastes [6, 10], showing options to valorize this effluent in the chemicals industry or by other biological systems for energy recovery (e.g., methane). An interesting integrated system can be designed to combine an energy source (mainly hydrogen) and biopolymer production (PHA) utilizing an acid-rich wastewater stream [4]. The resulting VFAs with lower carbon numbers are the main precursors for PHA production by many microbial species
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