Community Succession and Carbon Footprint Accounting of a Pilot-Scale Anaerobic Filter During Recovery After Long-Term Shutdown Under Low-Temperature Stress

• • After 234-day starvation, the pilot AF recovered within 63 days by extending HRT from 8 to 12 h, achieving TCOD and SCOD removal of 58.6 mg/L and 21.5 mg/L, respectively; this demonstrates a practical recovery protocol for anaerobic systems after prolonged shutdowns. • • Under 100-day low-temperature stress (influent as low as 11.7 °C), TCOD and SCOD removal remained at 54.6 mg/L and 28.6 mg/L, and specific methane yield was maintained at 0.244 L CH4/g TCODre (vs. 0.276 L during recovery), indicating stable energy conversion efficiency despite reduced absolute methane production. • • EPS protein secretion increased significantly under low temperature and showed a negative correlation with temperature along the filter height, playing a key role in maintaining reactor stability; this highlights a protective mechanism that can be targeted for process optimization. • • Microbial community succession followed a distinct order: hydrolytic acidogens, hydrogen-producing acetogens, then methanogens; Methanobacterium dominated after starvation, while Methanosaeta became dominant under low temperature, reflecting adaptive shifts that affect reactor performance and stability.