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A mixed microbial culture (MMC) of poly-hydroxy-alkanoates (PHAs) producers was developed in a draw- fill reactor (DFR) subjected to sequential nitrogen/carbon limitation stress using short chain fatty acids (SCFAs) as carbon source. The distribution of microorganisms was analyzed in the beginning of the process and after six weeks of limitation, in order to verify the domination of PHA producers in the consortium. The potential of the enhanced MMC for production of co-polymers was then evaluated in batch mode using synthetic media. The parameters tested were the C to N ratio (C/N), the propionate to butyric ratio (prop/but) and the initial pH (pHin). It was shown that the type, yields and productivity of PHAs was highly affected and the optimal yield, 40 % PHAs/dry cell weigh (DCW) (w/w), was achieved for a C/N of 200 (w/w), prop/but 10/90 (mol/mol) and pHin, 7.5. The MMC was further assessed for the production of PHAs from acidified sugary wastewater (ASW) containing SCFAs, sugars and lactate at different ratios. PHAs were solvent-extracted from the microbial biomass; they were further analyzed in terms of their chemical composition, via 1H-NMR and 13C-NMR, their structure at molecular level via Attenuated total reflectance – Fourier transform infrared spectroscopy (ATR-FTIR), and their thermal properties, via differential scanning calorimetry (DSC). It was shown that in all cases, P(3HB-co-3HV) was produced with Tm ranging from 170,0 to 164,1 oC. |
