Module 4 · Digestion and Stabilization
Anaerobic Digestion
treats solids without supplied oxygen in a closed vessel.
Microorganisms break down part of the organic material and may produce a gas rich in . The process needs suitable feed, temperature, mixing, and time. Most heated anaerobic digesters run in the mesophilic range, near 95 °F (35 °C). It can respond slowly to changes. For Class B, federal rules list anaerobic digestion at 15 days at 35 °C to 55 °C (95 °F to 131 °F) up to 60 days at 20 °C (68 °F). A stable-looking tank does not mean every part is being mixed or heated well. Gas equipment adds fire and asphyxiation hazards.
A heater fails while feed continues. Temperature may decline slowly over many hours. Trend review matters before the change affects gas and solids quality.
Know the feed, withdrawal, gas, heat, and mixing paths. Never open a sealed system casually.
Anaerobic systems do not benefit from adding air. Keep access hatches and gas piping in their designed condition. Watch for slow trends because the biology may not respond immediately to a feed change. Operators should document the timing of changes so later results can be interpreted.
Exam Need to Know
- Anaerobic digestion treats solids without oxygen in a closed tank.
- It can make a gas rich in methane.
- Adding air does not help it.
Exam area: Treatment Process