Bioplastic Production with Nitrogen Removal via Polyhydroxyalkanoate-Driven Denitrification under Aerobic Feast/Anoxic Famine Conditions: A Comparison with Conventional Aerobic Feast/Aerobic Famine and Microbial Community Analysis

Integrating polyhydroxyalkanoate (PHA) bioplastic production into wastewater treatment supports a circular economy. However, conventional aerobic feast/aerobic famine conditions do not facilitate nitrogen removal. This study investigated PHA production with organic matter and nitrogen removal using a sequencing batch reactor (SBR) under aerobic feast/anoxic famine (SBRaf/anf), compared with a conventional aerobic feast/aerobic famine system (SBRaf/af). SBRaf/anf and SBRaf/af achieved chemical oxygen demand (COD) removal of 87.6 ± 1.7% and 88.1 ± 1.3%, respectively. Nitrification occurred in both reactors. Total nitrogen removal (78.0 ± 1.9%) was achieved only in SBRaf/anf through PHA-driven denitrification, while no nitrogen removal was observed in SBRaf/af. The excess sludge enriched in both reactors can be used for PHA production in the fed-batch reactors (FBRs). Sludge from SBRaf/af demonstrated a higher maximum PHA content (26.0 ± 1.8%w/w) in an FBR compared to sludge from SBRaf/anf (21.4 ± 1.9%w/w). 16S rRNA gene amplicon sequencing (MiSeq) revealed high relative abundances of Thauera─a facultative aerobic denitrifier and PHA-accumulating microorganism─in both reactors. For nitrifying populations, quantitative polymerase chain reaction (qPCR) analyses revealed that ammonia-oxidizing bacteria (AOB) and comammox were dominant in SBRaf/af, with increasing ammonia-oxidizing archaea (AOA) over time, whereas comammox remained dominant in SBRaf/anf throughout.