This paper presents a comprehensive study on polyhydroxyalkanoate (PHA) production from sewage sludge. Greenhouse gas (GHG) emissions were monitored for the first time to assess the impact of climate change and environmental sustainability. The pilot plant was composed of a fermenter with a membrane and two biological reactors (namely, selection and accumulation). Results showed that despite a low organic loading rate (namely, 0.06 kg BOD kg SS^-1 day^-1), a good PHA yield was obtained (namely, 0.37 g PHA/g volatile fatty acids), confirming that sewage sludge can be a suitable feedstock. GHG emissions were 3.85E-04 g CO₂eq/g and 32.40 g CO₂eq/g, direct and indirect, respectively. Results provided valuable insights in view of finding a trade-off between PHA production and GHG emissions to prove the PHA production process as an effective solution for biosolids disposal at a low carbon footprint.

Conversion of wastewater treatment plants into biorefineries is a sustainable alternative for obtaining valuable compounds, thus reducing pollutants and costs and protecting the environment and human health. Under specific operating conditions, microbial fermentative products of sewage sludge are volatile fatty acids (VFA) that can be precursors of polyhydroxyalkanoate thermoplastic polyesters. The role of various operating parameters in VFA production has yet to be elucidated. This study aimed to correlate the levels of VFA yields with prokaryotic microbiota structures of sewage sludge in two sets of batch fermentations with an initial pH of 8 and 10. The sewage sludge used to inoculate the batch fermentations was collected from a Sicilian WWTP located in Marineo (Italy) as a case study. Gas chromatography analysis revealed that initial pH 10 stimulated chemical oxygen demands (sCOD) and VFA yields (2020 mg COD/L) in comparison with initial pH 8. Characterization of the sewage sludge prokaryotic community structures—analyzed by next-generation sequencing of 16S rRNA gene amplicons—demonstrated that the improved yield of VFA paralleled the increased abundance of fermenting bacteria belonging to Proteobacteria, Bacteroidetes, Chloroflexi, and Firmicutes phyla and, conversely, the reduced abundance of VFA-degrading strains, such as archaeal methanogens.

The wastewater treatment plants (WWTPs) must be transformed into Water Resource Recovery Facilities (WRRFs) in view of a more sustainable approach focusing on the circular economy concept. Different to WWTPs, the WRRFs have as a major goal not only the wastewater treatment to meet the legislation limits but also the recovery of resources such as: treated water for water reuse, carbon, nutrients, biopolymers etc. In view of boosting the WRRFs application in the real WWTs, a WRRF at Palermo University (UNIPA) has been built within the EU project: Achieving Wider-Uptake of Water Smart Solutions. This study is aimed to demonstrate the feasibility of resource recovery from wastewater treatment at UNIPA WRRF. Specifically, the effects of treated wastewater (TWW) and recovered nutrients from wastewater on faba bean were assessed. Results showed that treated water aligned with EU legislation. Further, TWW increased soil electrical conductivity and adversely impacted plant growth. However, the application of biochar and zeolite effectively mitigated these adverse effects. Microbiological investigation revealed that both broad bean pods and seeds analysed did not host pathogenic bacteria.