TUESDAY, JAN 17, 2023: NOTE TO FILE
Module 2-12
Biogas digesters
A BIOGAS DIGESTER is similar to a septic tank, except that the main chamber is domed to capture and siphon off the methane gas. Furthermore, all green waste can be loaded into a biogas digester, namely, kitchen scraps, garden cuttings, (Hu)manure, etc., thereby minimizing solid waste disposal off site. As the solid waste settles and is treated through natural anaerobic digestion, the more viscous slurry, or “black water”, flows out of the biogas digester and needs to be treated through a natural aerobic process via a constructed wetland (SSFCW or SFCW) or Wetland Ecological Treatment (WET) system. Through the second treatment, “black water” is thus cleansed into “grey water” fit for use in recycling water for flushing toilets or irrigation of trees and landscape but should not be directly applied onto crops. The more solid slurry that is emptied from the biogas digester is effectively bio-fertilizer.
Source: slide 21. https://www.slideshare.net/muttukhavi/biogas-production-from-waste
The biogas digester has some advantages over a septic tank when we apply a holistic approach to wastewater treatment. In combination with a wetland treatment, the system is highly productive, turning waste into useful biogas (for cooking or heating), slurry for biofertilizer, grey water for irrigation and the wetland plants that can also be harvested for use as mulch and composting system. Some wetland plants also provide food and attractive flowers.
In permaculture, there are some excellent, small-scale examples of the combination of biogas digesters running on animal and human excrement combined with constructed wetlands that provide gas for cooking, biofertiliser for trees and grey water irrigation, the constructed wetland can also provide biomass for mulch. This system closes the loop: cows feed on grass, which is cannot be digested by humans, and add their own internal anaerobic biogester to the process, humans feed on home-grown vegetables, the manure from both passes through the wastewater treatment system, the nutrients and organic matter are returned to the soil, the water and energy is retained in the loop and there is milk and more fresh food: a perfect whole-systems’ approach.
These are all good examples of ways we can combine mapping with ecological knowledge to make the most productive and regenerative choices for our communities and projects.
Module 2, lesson 13
