Application of Immersed Membrane Bioreactor for Semi-Continuous Production of Polyhydroxyalkanoates from Organic Waste-Based Volatile Fatty Acids

Abstract

Volatile fatty acids (VFAs) appear to be an economical carbon feedstock for the cost-effective production of polyhydroxyalkanoates (PHAs). The use of VFAs, however, could impose a drawback of substrate inhibition at high concentrations, resulting in low microbial PHA productivity in batch cultivations. In this regard, retaining high cell density using immersed membrane bioreactor (iMBR) in a (semi-) continuous process could enhance production yields. In this study, an iMBR with a flat-sheet membrane was applied for semi-continuous cultivation and recovery of Cupriavidus necator in a bench-scale bioreactor using VFAs as the sole carbon source. The cultivation was prolonged up to 128 h under an interval feed of 5 g/L VFAs at a dilution rate of 0.15 (d−1), yielding a maximum biomass and PHA production of 6.6 and 2.8 g/L, respectively. Potato liquor and apple pomace-based VFAs with a total concentration of 8.8 g/L were also successfully used in the iMBR, rendering the highest PHA content of 1.3 g/L after 128 h of cultivation. The PHAs obtained from both synthetic and real VFA effluents were affirmed to be poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a crystallinity degree of 23.8 and 9.6%, respectively. The application of iMBR could open an opportunity for semi-continuous production of PHA, increasing the feasibility of upscaling PHA production using waste-based VFAs.

Development and Characterisation of Composites Prepared from PHBV Compounded with Organic Waste Reinforcements, and Their Soil Biodegradation

“…Biodegradation does not appear to significantly change the morphology of the pure polymer according to the solid-state NMR spectrum. Due to time restrictions, it was not possible to run all samples using the direct excitation experiment (which is quantitative for the PHBV methyl peak [36]). To estimate the ordered/disordered amounts of PHBV polymer quantitatively, a comparison was made of the ordered/disordered methyl peak amounts around 20 ppm from the direct excitation and CPMAS NMR spectra of three of the samples.…”

Development of a hybrid bio-purification process of lactic acid solutions employing an engineered E. coli strain in a membrane bioreactor

“…Both UF and NF membranes were used to separate the LA solution from the fermentation broth achieving a maximum productivity of 17.1 g L -1 h -1 . MBR process has been also used for the production of bioethanol [21] and polyhydroxyalkanoates (PHA) [22] employing organic wastes or by-products as substrate. Bioethanol production through fermentation of wheat straw hydrolysate was studied using an immersed MBR and a recombinant, xylose-utilizing Saccharomyces cerevisiae strain achieving continuous fermentation operation and process intensi cation [21].…”

“…Bioethanol production through fermentation of wheat straw hydrolysate was studied using an immersed MBR and a recombinant, xylose-utilizing Saccharomyces cerevisiae strain achieving continuous fermentation operation and process intensi cation [21]. An immersed MBR was also used for the production of PHA through a semicontinuous cultivation and recovery of Cupriavidus necator bacteria grown on food-derived Volatile Fatty Acids (VFA) [22]. The semi-continuous mode resulted in increased bacterial tolerance to VFA concentration and maximum PHA production.…”