Similar to a septic tank, a digester treats waste with anaerobic bacteria but includes a methane gas collection system.
Treatment Level: Primary
Relative Cost: high
Amount of Maintenance Interaction: high
Beneficial Byproduct: some – lots (gas and nutrient rich slurry)
Advantages
- Generate gas to supplement energy needs
- “Digestate” slurry can be used as fertilizer (preferably fruit trees) or fish food
- Ease strain on local natural fuel resources
Disadvantages
- 1 family may not generate enough without animal waste as well
- Needs daily interaction to ‘feed’ the system
- If animal waste is needed, must either co-locate toilet, sty & digester or manually collect & load the waste
- Needs regular supply of water
- Need training & time to maintain temperature, fermentation times & feedstock material
Operation & Maintenance
- Add manure every 1 – 2 days
- Assuming digester is kept active, clean out digester every 2 years. Otherwise, clean it out when digester has been inactive
- Replace tubing between digester & storage/use every 2 years
Blackwater vs Graywater?
- The process begins with a slurry, so it’s best for combined wastewater; otherwise, liquid must be added
Secondary Treatment Options
- Slurry: Aquaculture, treatment wetlands, drying beds, or land application
Additional Notes:
- Need to locate in an area with easy access for inspection & maintenance
- Watch what you flush! Minimize bleaches & chlorine, don’t use caustic products or drain cleaners as these things can kill the beneficial bacteria in the digester
- Typical uses are methane cook stoves, burners, and lamps.
Farm Scale Example (www.diclatraining.com)