Long-term validation of polyhydroxyalkanoates production potential from the sidestream of municipal wastewater treatment plant at pilot scale

In this study, polyhydroxyalkanoates (PHAs) production integrated with the via-nitrite nitrogen removal from anaerobic reject water was investigated at pilot scale under long-term period. The pilot plant was located in Carbonera wastewater treatment plant (WWTP) (Treviso, Italy) and comprised the following units: i) rotating belt dynamic filter (RBDF) for the recovery of cellulosic primary sludge (CPS); ii) fermentation unit for the production of volatile fatty acids (VFAs); iii) ultrafiltration unit (UF) for solid/liquid separation of the fermented sludge; iv) nitritation sequencing batch reactor (N-SBR) for the oxidation of ammonia to nitrite; v) selection SBR (S-SBR) where aerobic-feast and anoxic-famine conditions were established to select PHA-accumulating biomass and vi) an accumulation SBR (A-SBR) were intracellular PHA content was maximized through the feed-on-demand strategy. Results showed that around 80% of the influent ammonia was efficiently removed by the system when both N-SBR and S-SBR operated with volumetric nitrogen loading rate (vNLR) of 1.64–1.72 kgN/m3 d and 0.60–0.63 kgN/m3 d, respectively. Accumulation tests showed PHA yields ranging between 0.58 and 0.61 g CODPHA/g CODVFA, indicating an effective selection strategy. The overall mass balance assessment demonstrated that around 0.32 g of COD per gram of COD treated can be recovered as bio-based products. The integration of nitrogen removal and PHA production in the sidestream resulted in a methane recovery up to 4.0 m3CH4/PE y and a maximal PHA production of 1.2 kgPHA/PE y with a potential revenue for the WWTP up to 6.5 €/PE y.