Nitritation membrane-based process for enhancing nitrogen removal and PHA production from waste-activated sludge

Abstract

This work explores the combined application of biological nitrogen removal and polyhydroxyalkanoate (PHA) synthesis within the operational framework of a wastewater treatment plant (WWTP), employing waste-activated sludge as both the microbial inoculum and carbon source. Consistent and high-yield PHA production was achieved through a membrane-assisted microbial enrichment strategy, carried out in alternating aerobic and anoxic conditions, comprising a nitritation sequencing batch reactor (N-SBR), a membrane-based selection reactor (S-SBR), and a continuously operated PHA accumulation unit (A-SBR). The A-SBR reached 40–44 % w/w of PHA for about 70 days, while the storage yield was within 0.32–0.53 g CODPHA g−1 CODVFA. The system maintained high efficiency despite the C/N variation around 2 and 6 g COD g−1 N. Nitrous oxide (N2O) was monitored to assess the direct greenhouse gas (GHG) emissions. The N-SBR achieved the peak concentration of 0.62 ± 0.08 mg N2O-N L−1 during period I (C/N 2), while the highest emission factor of 0.49 ± 0.08 % was reached during period IV (C/N 6). This research highlights the benefits of integrating PHA production into WWTP operations, which involves recovering resources while meeting stricter nutrient removal and environmental impact standards. Future work should focus on optimizing nutrient removal and mitigating GHG emissions to fully meet the requirements of evolving urban wastewater treatment regulations.