Recovery of failed solid-state anaerobic digesters.

Area of Science:

• Biotechnology
• Environmental Science
• Chemical Engineering

Background:

• Solid-state anaerobic digestion (SSAD) systems can fail, leading to significant loss of methane production.
• Corn stover is a common feedstock, but digester failure at a feedstock/inoculum (F/I) ratio of 10 resulted in negligible methane yields in this study.

Purpose of the Study:

• To evaluate three different methods for recovering failed solid-state anaerobic digesters.
• To compare the efficiency and methane yield of top-addition, injection, and well-mixed inoculum strategies.

Main Methods:

• Three 9-L solid-state anaerobic digesters fed with corn stover were intentionally failed at an F/I ratio of 10.
• Recovery was initiated by adding inoculum to achieve an F/I ratio of 4 using three methods: top addition, injection, or well-mixing.
• Methane yields and recovery rates were monitored over time.

Main Results:

• Top-addition and injection methods rapidly resumed digestion, reaching peak methane yields within 10 days.
• The well-mixed method exhibited slower recovery but ultimately achieved 50% higher peak methane yields compared to the other methods.
• All three recovery methods successfully reclaimed 30-40% of the potential methane from the failed digesters.
• The well-mixed method demonstrated the highest overall methane yield, followed by injection and top-addition.

Conclusions:

• Inoculum addition is an effective strategy for recovering failed solid-state anaerobic digesters.
• While faster, top-addition and injection methods were less efficient in terms of peak methane yield compared to the well-mixed approach.
• Slow mass transfer and microbial growth kinetics are likely the primary limitations hindering rapid recovery in failed anaerobic digesters.