Anaerobic digestion

**Process Overview**:
– Anaerobic digestion involves microorganisms breaking down biodegradable material without oxygen.
– Process stages include hydrolysis, acidogenesis, acetogenesis, and methanogenesis.
– Marsh gas methane was discovered through anaerobic digestion in 1776.
– Occurs naturally in soils, lake sediments, and oceanic basins.

**Configuration and Operation**:
– Anaerobic digesters can operate in batch or continuous process mode.
– Different configurations include mesophilic vs. thermophilic temperature conditions.
– High vs. low portion of solids affect the design and operation.
– Single-stage vs. multistage process setups.

**Benefits and Applications**:
– Used in waste and sewage treatment to reduce landfill gas emissions.
– Produces biogas containing methane, carbon dioxide, and traces of other gases.
– Biogas can be used as fuel or upgraded to biomethane.
– Digestate produced can be used as fertilizer.
– Widely used as a source of renewable energy in various countries.

**Digestion Methods**:
– Batch digestion vs. continuous digestion.
– Temperature control: mesophilic vs. thermophilic.
– Solids content: high vs. low solids digesters.
– Complexity: single-stage vs. two-stage digestion systems.

**Process Parameters**:
– Residence time variations based on feed material and system configuration.
– Pressure’s impact on biogas production.
– Inhibition factors like ammonia, sulfide, heavy metals, and organics.
– Feedstocks suitability and putrescibility for biogas production.
– Factors affecting anaerobic digestion efficiency: moisture content, temperature control, nutrient balance, retention time, and pH level.