Polyhydroxyalkanoates from mixed microbial culture: Production and extraction through green methods

Large scale polyhydroxyalkanoates (PHA) production is limited by high production costs compared to that of petroleum-based plastics. Two key factors can be pin down to reduce costs: i) the use of mixed microbial cultures (MMC) instead of pure cultures and ii) the application of cheap and environmental friendly recovery technologies. In this work, the MMC biomass with PHA-accumulating capacity was selected in a sequencing batch reactor fed with a synthetic effluent emulating a fermented oil mill wastewater. The biomass was harvested and transferred to an accumulation reactor, where PHA contents up to 54% of the dry cell weight were obtained, using a mixture of acetic and propionic acids. A copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate with 47% (wt) 3-hydroxyvalerate was obtained. The polymer extraction was done in aqueous phase using chemicals that destroy the non-PHA cellular material releasing the polymer’s granules. The effectiveness of the switchable anionic surfactant NH4-Laurate was investigated and compared with that of sodium dodecyl sulphate and NH4OH by testing them on lyophilized biomass, with and without a NaClO pre-treatment. Further, a purification post-treatment was performed on some of the samples as well. When operating the extraction at 90°C for 3h with a ratio surfactant to biomass of 200:100 w/w, gas chromatography analysis showed that all the tested extraction agents allow obtaining PHA with an excellent purity (≈100%) after a pre-treatment with NaClO at 100°C for 1 h. The highest recovery yield (73 %) was obtained when using NH4-Laurate for which operating conditions of the extraction process such as temperature, concentration and contact time have been optimized. When the extracted polymer was washed with a 0.1 N NH4OH solution and ethanol, purity was improved, but lower recovery yields were obtained. To determine the effect of extraction process on the PHA purity, Nuclear Magnetic Resonance Spectroscopy was used.