Products of Anaerobic Digestion

 Anaerobic digestion

- in this process, bacteria breaks down organic matter such as animal manure, wastewater biosolids, and food wastes while in the absence of oxygen.

- in the reactors, complex microbial communities which digest the waste can be found:

The products of this reaction include Biogas and digestate (the solid and liquid material end-products of the AD process) which is discharged from the digester.

As previously discussed, the biogas itself is composed of a mixture of different gases which include:

  • methane (CH4) - relatively high percentage (50 to 75 percent)
  • carbon dioxide (CO2)
  • hydrogen sulfide (H2S)
  • water vapor 
  • trace amounts of other gases.


Digestate

- this is the residual material remained after the digestion process is completed.

- It is composed of liquid and solid portions which are normally dealt with separately since each have value that can be realized with varying degrees of post processing.

USES:
With appropriate treatment, both the solid and liquid portions of digestate can be used in many beneficial applications :
  • animal bedding (solids)
  • nutrient-rich fertilizer (liquids and solids)
  • a foundation material for bio-based products (e.g., bioplastics), organic-rich compost (solids)
  • soil amendment (solids), the latter of which may include the farm spreading the digestate on the field as fertilizer. 




Diagram showing the process of Anaerobic Digestion and the uses of its Products

 

https://www.eesi.org/papers/view/fact-sheet-biogasconverting-waste-to-energy 
https://www.epa.gov/agstar/how-does-anaerobic-digestion-work

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