Recovery and characterization of polyhydroxyalkanoates produced from fermented sewage sludge at pilot scale

The interest for a biobased economy spread wide in the last decades, indeed the application of biotechnological processes for the exploitation of renewable resources can contribute to the development and recovery of new sustainable products. Among them, polyhydroxyalkanoates (PHAs) are biopolyesters synthesized and stored by microorganisms inside the cells. PHA production from mixed microbial cultures (MMC) in combination with fermented organic waste as feedstock allows to reduce costs of the process. However, the optimization of an extraction method for PHA recovery may enhance the market competitivity, indeed an alternative to traditional chlorinated solvent extraction should be developed. The present study shows various strategies for PHA recovery from biomass produced at pilot scale through a three-step process, exploiting MMC and fermented sewage sludge (SS) from the municipal wastewater treatment plant in Treviso (Italy). The biomass was taken at the end of the typical accumulation step and stabilized with acidic treatment for a complete preservation of PHA content and properties, as reported in a previous study (Lorini et al. 2020). Conventional extraction procedures, including chloroform extraction (CHCl3) and oxidation by sodium hypochlorite (NaClO), were compared with other oxidative chlorine-free treatments. The recovery performance was evaluated in terms of PHA purity and viscosity average molecular weight (Mv). The traditional methods, , allowed to obtain a polymer characterized by purity higher than 99 % w/w and relatively high Mv (around 400 kDa). The alternative PHA recovery was carried out by chemical digestion using NaOH and also coupling NaOH and H2O2. The digestion with only NaOH did not allow to achieve the optimal results, on the contrary coupled treatment showed high purity values (92.3 ± 0.5 PHA %w/w) and high Mv (571 ± 25 kDa).. Treating the wet biomass brings several advantages, since in this way neither drying and neutralization steps are required and consequently time and cost of polymer extraction can be reduced. In parallel recovery by using non-toxic solvents such as dimethyl carbonate and ethyl acetate is being investigated and most recent results will be also presented at the workshop