Innovative strategy for polyhydroxyalkanoates recovery from mixed microbial cultures. Effects of aqueous phase and solvent extraction on polymer properties

This work aimed to investigate various methods of polyhydroxyalkanoates (PHA) extraction and to optimize the recovery in the view of reducing solvents’ use and waste. The extraction tests were applied on PHA-rich biomass collected at the end of the accumulation step, conducted both at pilot and lab scale. PHA-rich biomass obtained from the lab scale process was produced from synthetic feedstock (mixture of acetic and propionic acids), while fermented organic waste was used for PHA production at pilot scale. In the extraction tests, different solutions of NaOH, also in combination with a surfactant (sodium dodecyl sulfate, SDS), were used to recover the polymer from the non-polymeric cellular material (NPCM). Different times (3, 6 and 24 h) and concentrations (0.05 – 1 M) were tested, evaluating also the effect of adding SDS (0.1 % w/v). As a benchmark, solvent extraction with chloroform and oxidation with NaClO were also conducted. Finally, extracted samples were characterized through several techniques: DSC, TGA, GC-FID, capillary viscosimetry. Alkaline treatment at short times and low concentrations resulted to be more efficient in terms of purity (85 – 99 % w/w PHA) and recovery (higher than 80 % w/w), than higher concentration. On the other hand, the presence of SDS had dramatic effects on the recovery (lower than 50 % w/w) and also on the molecular weight, which was two folds lower than that obtained from alkaline extraction. Overall, extraction with aqueous phase reagents had no effects on thermal properties, which resulted to be in the range of those reported in literature

Microalgae cultivation by uncoupled nutrient supply in sequencing batch reactor (SBR) integrated with olive mill wastewater treatment

The growth of bacteria contaminants can be controlled in heterotrophic microalgae cultures by using an uncoupled supply of glucose and nitrate. However, till now this strategy was only described for fed-batch cultivation. The cultivation in a sequencing batch reactor (SBR) could be more promising for the industrial scale. Here in this work, we tested the uncoupled supply of substrates on microalgae cultivated in SBR (feast/famine ratio = 1.33), with an optimized culture medium (based on the microalgae elemental formula), and the integration of this strategy with olive mill wastewater (OMW) treatment. SBR allowed to attain biomass productivities (PX) proportional to the initial biomass concentration (PX = 0.13·X0), showing the possibility to reach the same productivities as conventional axenic cultures, by maintaining bacteria contamination at negligible values (<5%, as CFU/algae). The SBR system showed a stable biomass production (1.54 folds X0) throughout 8 consecutive cycles (53 days), uncoupling biomass production and cell duplication. However, relevant grazer contamination reduced the growth of microalgae cells between the 4th and 7th cycle and the biomass yield on glucose (from 0.31 to 0.17 g g−1). The integration with OMW treatment proved the possibility to remove 52% of phenols, but the loss of fermentable substrates during OMW storage and preliminary processing (by membrane filtration) hindered the exploitation of OMW as a relevant alternative source for organic substrates