Feast-famine selection of microbial mixed-cultures for PHA production based on carbon removal from municipal wastewater without previous fermentation

Polyhydroxyalkanoates (PHA) have attracted interest since they are biodegradable polyesters with comparable properties to petroleum-based polyolefins. The PHA production by mixed microbial cultures (MMC) has been largely investigated in sequencing batch reactors (SBRs) under dynamic feeding conditions (feast-famine, FF). Streams rich in volatile fatty acids (VFAs), obtained from the acidogenic fermentation of wastewaters, have been used for MMC selection in SBR, and for subsequent PHA accumulation/production with the pre-selected MMC. In the proposed novel approach, the MMC selection is achieved in SBR treating municipal notfermented wastewater, and PHA accumulation/production is conducted with VFA-rich streams in subsequent step. The MMC selection was conducted at pilot-scale with real wastewater and confirmed at lab-scale with a synthetic one. The storage capacity of the selected MMCs was evaluated in batch accumulation tests using synthetic VFAs stream. In both SBRs, the feasibility of selecting a MMC with enhanced PHA storage capacity was demonstrated and a stable FF regime was established, as evidenced by respirometric profiles. In the lab-scale SBR, the treatment efficiency of the influent soluble COD (SCOD) was more than 90%, whereas in the pilot-scale, around 70-80%. In batch tests, the lab-scale biomass achieved up to 20% (gPHA/gVSS) PHA content whereas the pilot-scale biomass achieved up to 34% (gPHA/gVSS), even if the initial storage kinetics was lower than the lab-scale biomass. Differences in performance between SBRs are possibly derived from differences in feed characteristics and operating conditions. Both SBRs demonstrated the possibility to combine PHA production with municipal wastewater treatment. This approach opens the possibility to profit from the C content of municipal wastewaters for MMC selection without the need to utilize fermented VFA-rich feedstocks, which can then be fully utilized for PHA accumulation/production.