Comparing two advanced selection strategies for polyhydroxyalkanoate production from domestic waste activated sludge

• Two MBR-based enrichment strategies to produce PHAs were compared. • Waste-activated sludge’s fermentation produced VFAs used to produce PHA. • PHA accounted for 38 % w/w with storage yields of 0.4 ± 0.1 gCOD PHA /gCOD VFA . • The anoxic famine enrichment resulted in higher N 2 O emissions (0.7 ± 0.2 mg N 2 O-N/L). • The anoxic famine enrichment emitted 10.2 kg CO 2eq /day. This study compares two membrane bioreactor-based enrichment strategies to produce polyhydroxyalkanoates (PHAs) from domestic waste-activated sludge. The aerobic dynamic feeding was implemented in layout 1 while layout 2 employs an aerobic/anoxic enrichment adopting an additional nitritation reactor. Both systems achieved around 38 % w/w of PHA with storage yields of 0.28–0.42 and 0.35–0.53 gCOD PHA /gCOD VFA for layouts 1 and 2, respectively. Layout 2 demonstrated an average N removal efficiency of 88.8 ± 3.9 %, slightly higher than layout 1 (82.7 ± 9.9 %). However, layout 2 showed greater nitrous oxide (N 2 O) emissions, averaging 0.7 ± 0.2 mg N 2 O-N/L almost doubling layout 1 (0.4 ± 0.1 mg N 2 O-N/L). Additionally, layout 2 exhibited a 42 % increase in carbon footprint compared to layout 1, reaching 10.2 kg CO 2 /day. This research highlights the high potential and drawbacks of the AE/AN enrichment strategy for integrating PHA production into wastewater treatment plant operations.