Understanding Anaerobic Digestion

Anaerobic digestion consists of a series of processes through which microorganisms break down biodegradable materials in an environment which lacks oxygen. Anaerobic digestion is widely used as a means of producing renewable bioenergy.

Anaerobic digestion consists of four phases. It begins with bacterial hydrolysis of the input materials, which in Opus’ case is our purpose-grown energy crop, opuntia cactus. Insoluble organic polymers such as carbohydrates are broken down by hydrolytic bacteria into soluble derivatives that become available for other bacteria.

The second phase, acidogenesis, refers to the process through which acidogenic bacteria convert sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids.

Next, acetogenesis takes place, whereby acetogenic bacteria convert these resulting organic acids into acetic acid, along with additional ammonia, hydrogen, and carbon dioxide amongst other compounds.

Finally, methanogenesis occurs as methanogenic (methane-producing) bacteria convert these products to methane and carbon dioxide. This raw biogas can be used directly as fuel in combined heat and power (CHP) applications, or it can be upgraded to biomethane.

One reason anaerobic digestion is widely regarded as a viable means of producing renewable energy is because its only waste/byproduct is digestate (a nutrient rich sludge consisting of the solids and water left over after digestion).  In optimized operations where a closed nutrient loop is present, the nutrient-rich digestate can be used as fertilizer to produce more biomass or crops.

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