Effects of a temporary increase in OLR and a simultaneous decrease in HRT on dry anaerobic digestion of OFMSW

Area of Science:

• Environmental Engineering
• Waste Management
• Biotechnology

Background:

• Dry anaerobic digestion is a key technology for treating municipal solid waste.
• Process stability is crucial for efficient biogas production.
• Understanding operational limits is vital for optimizing digester performance.

Purpose of the Study:

• To assess the impact of temporary increases in organic loading rate (OLR) and decreases in hydraulic retention time (HRT) on pilot-scale dry anaerobic digester stability.
• To determine if short-term overloading is feasible without long-term process failure.
• To evaluate the recovery potential after process disturbances.

Main Methods:

• Investigated a pilot-scale dry anaerobic digester treating the organic fraction of municipal solid waste at 40°C.
• Implemented temporary increases in OLR (10.8, 11.7, and 12.5 kg TVS m⁻³ d⁻¹) with corresponding HRT decreases (21, 19, and 18 d).
• Monitored digester stability and recovery after stress periods.

Main Results:

• Stable operation was maintained at OLRs of 10.8 and 11.7 kg TVS m⁻³ d⁻¹ for three weeks, with rapid recovery to baseline conditions.
• An OLR of 12.5 kg TVS m⁻³ d⁻¹ led to significant process imbalance and failure.
• Full recovery of the digester was achieved within two months even after the severe imbalance.

Conclusions:

• Dry anaerobic digesters can tolerate short-term increases in OLR and decreases in HRT up to 11.7 kg TVS m⁻³ d⁻¹.
• Exceeding this threshold (e.g., 12.5 kg TVS m⁻³ d⁻¹) can cause failure but does not preclude eventual process recovery.
• Careful management of OLR and HRT is essential for robust and resilient anaerobic digestion systems.