Anaerobic Digestion
Authors:
Contents
Introduction
Anaerobic digestion is the conversion of organic matter to biogas which is flammable if the methane content of the biogas is high enough. Digestion
Principles of Operation
Bacteria and Archea that perform the individual stages of anaerobic digestion are naturally present in the feces and organic matter that enter the digester or can be introduced from an already functioning digester. The conditions within the digester can select for which organisms will perform best.
Alkalinity
(Needs work)
Versions on Market
Home Biogas 2.0is a market ready version marketed for use in digested food waste to produce biogas.
Regulations
(Needs work)
Operating Requirements
Site Requirements
Temperature
Three different temperature ranges are ideal for anaerobic digestion, (but successful operation can be achieved outside these ranges); phsycrophilic (insert temp), 30-38°C (85-100°F) for Mesophilic Digestion, 50 to 57°C (122-135°F) for thermophilic digestion. Of these psyochrophilic and mesophilic digestion is more commonly used at the building scale level.
Troubleshooting Common Failures
Lack of Methane Production
Methanogens are typically the most sensitive organisms in the process but are the most crucial because they perform the final step of converting acids to methane. Methanogen can be sensitive to high amounts of acid or high amounts ammonia. A low pH indicates high amounts of acid which can occur by putting too much organic matter in the digester. This is especially the case with carbohydrates (e.g. from food waste) which break down quickly to acids causing acid build up. A high pH could The quickest indicator of conditions that are hostile to methanogens is pH, which should be near 7.
Non-flammable Gas
Non-flammable gas could be due to too much moisture in the gas or not enough methane in the gas. In order to ignite, biogas must be at least X% methane. This is common for some time during digester startup. It may indicate too much oxygen is being introduced which drives a higher portion of CO2 in the final gas.
