Key Takeaways & Executive Findings
- •• • 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.
Abstract
The transition of municipal wastewater treatment from energy-intensive aerobic processes to energy-recovering anaerobic technologies is critical for achieving carbon neutrality. However, anaerobic treatment of low-strength wastewater faces operational challenges, especially after prolonged shutdowns and under low-temperature stress. This study investigated the recovery and performance of a pilot-scale anaerobic filter (AF) packed with volcanic rock media (effective volume 240 L) treating actual municipal wastewater. After a 234-day starvation period, the AF recovered within 63 days by extending hydraulic retention time from 8 to 12 hours, achieving total chemical oxygen demand (TCOD) and soluble chemical oxygen demand (SCOD) removal amounts of 58.6 mg/L and 21.5 mg/L, respectively. Following 100 days of low-temperature operation (influent temperature dropped to 11.7 °C), TCOD and SCOD removal amounts remained at 54.6 mg/L and 28.6 mg/L, respectively. Although methane production volume decreased, the specific methane yield was not significantly affected (0.276 L CH4/g TCODre during recovery vs. 0.244 L CH4/g TCODre under low temperature). Mechanistic analysis revealed that increased protein secretion in extracellular polymeric substances (EPS) was crucial for resistance to low-temperature stress, with protein content negatively correlated with temperature. Microbial community analysis showed that functional populations recovered in the order of hydrolytic acidogens, hydrogen-producing acetogens, and methanogens. Methanobacterium dominated after starvation, while Methanosaeta became dominant after low-temperature exposure due to its high affinity for acetate. Carbon footprint accounting indicated that recovering dissolved methane and coupling with nitrate-dependent methane oxidation is the optimal strategy for carbon reduction.
1. Introduction
Conventional municipal wastewater treatment relies on energy-intensive aerobic processes, which conflict with global carbon neutrality goals. Anaerobic technologies offer a sustainable alternative by recovering energy as methane, yet their application to low-strength wastewater is hindered by operational vulnerabilities, particularly after unexpected shutdowns and during seasonal temperature drops. These stressors can cause significant performance deterioration and microbial community disruption, limiting the reliability of anaerobic systems in real-world settings.
This study addresses these bottlenecks by systematically evaluating a pilot-scale anaerobic filter (AF) that underwent a 234-day starvation period followed by low-temperature operation. By documenting recovery dynamics, microbial succession, and carbon footprint, the research provides actionable insights into operational strategies—such as extending hydraulic retention time—and identifies key microbial players that confer resilience. The findings offer a roadmap for enhancing the robustness of anaerobic wastewater treatment, facilitating its adoption as a carbon-negative alternative.
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ZHANG Shiyong, LIU Xiuhong, CHENG Rong, YANG Qing (2026). Community Succession and Carbon Footprint Accounting of a Pilot-Scale Anaerobic Filter During Recovery After Long-Term Shutdown Under Low-Temperature Stress. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202608003
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Frequently Asked Questions
What is the recommended recovery strategy after a prolonged shutdown of an anaerobic filter, and what performance metrics can be expected?
After a 234-day starvation, extending the hydraulic retention time from 8 to 12 hours facilitated recovery within 63 days. Stable performance was achieved with TCOD and SCOD removal amounts of 58.6 mg/L and 21.5 mg/L, respectively. This indicates that operational adjustments can effectively restore reactor functionality.
How does low-temperature stress affect methane production and microbial community structure in anaerobic filters?
Under continuous low-temperature operation (influent temperature down to 11.7 °C), the overall methane production volume decreased, but the specific methane yield remained relatively stable (0.244 L CH4/g TCODre compared to 0.276 L during recovery). Microbial analysis revealed a shift in dominant methanogens from Methanobacterium to Methanosaeta, which has a higher affinity for acetate, indicating an adaptive response to low temperatures.
What role do extracellular polymeric substances (EPS) play in the resistance of anaerobic filters to low-temperature stress?
EPS protein secretion increased significantly under low-temperature conditions and exhibited a negative correlation with temperature along the filter height. This increased protein secretion is believed to protect the microbial community, enabling stable reactor operation despite the cold stress, although methane production volume was still reduced.
What is the optimal carbon footprint reduction strategy for anaerobic filters treating municipal wastewater?
Carbon footprint accounting indicates that recovering dissolved methane and coupling the anaerobic filter with nitrate-dependent methane oxidation is the most effective approach for carbon reduction. During recovery and low-temperature phase I, the energy recovered from combined heat and power (CHP) was sufficient to meet the energy demands of the peristaltic pumps, demonstrating energy self-sufficiency.
How does the microbial community recover after a long-term starvation period, and what is the succession order?
After starvation, the functional microbial populations recovered in a sequential order: hydrolytic acidogens, hydrogen-producing acetogens, and then methanogens. Initially, Methanobacterium was the dominant methanogen, while Methanosaeta was significantly reduced. This succession pattern is crucial for understanding reactor recovery dynamics and optimizing restart protocols.
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