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Anaerobic Digestion

Anaerobic digestion is a biological process used to treat the biosolids that are a by-product of wastewater treatment.  In the process, bacteria capable of living in the absence of oxygen utilize biodegradable matter in biosolids as a food source, reducing the organic matter to more stable end products.

Anaerobic digestion accomplishes the following:

  1. Breaks down organic matter into simpler more stable compounds.
  2. Minimizes further biological activity in the sludge.
  3. Transforms a portion of the sludge solids into liquid and gas.
  4. Reduces the sludge volume to be dewatered.
  5. Produces usable methane gas (CH4) for fuel.
  6. Eliminates (or greatly reduces) pathogenic bacteria and odors

LAWPCA has two fixed cover mesophilic anaerobic digesters, each with a capacity of 690,000 gallons, which provide detention and mixing of wastewater biosolids and high organic strength feedstocks. Each digester has a gas collection pipe that ties into the gas system and the storage membrane of the digested sludge and biogas storage tank.

In 2022, LAWPCA utilized the biogas in co-generation units to produce 1,753,771 kW’s. This was enough to power the equivalent of approximately 267 Maine households. These same units also produced enough waste heat to provide heating to the equivalent of 78 Maine households.