Lowtech Graph lists low-tech options for every need of a home. Here you can compare them, find tutorials to build them, and link them together into a circular system. Why low-tech?
Constructed wetland blackwater treatment
Passive
One of 4 ways to meet this need. Cost, carbon, footprint and rankings are relative to other solutions for the same need, not absolute.
What your site needs
Land area available for a larger blackwater-rated wetland bed, and enough fall through the treatment train to run on gravity
A larger, longer series of planted gravel beds that cleans toilet water as well as sink and shower water. Bacteria on the gravel and roots break down the waste as the water flows slowly through. It treats all the household’s wastewater on site, without power where the ground slopes enough.
15-25 years before media/gravel bed needs partial renewal, same as the greywater constructed wetland
Embodied carbon
Low
Space / material use
High
Output timing
Continuous process
Skill to repair
Basic
Regulation (FR example)
On-site sanitation (assainissement non collectif): the installation must be declared to and approved by the local SPANC before work starts, and is subject to periodic inspection. Arrete du 7 septembre 2009 modifie.
Levels are relative to the other options for this need, not absolute. Fewer dots is lighter.
Constructed wetland blackwater treatment (This page) Can I use it? Not in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · Skill to build: Intermediate · Upkeep: Light · Change to daily life: Occasional · Works without the grid: Yes Choose it if you want all your wastewater treated on site by planted beds, with no power.
Septic tank + drain field Can I use it? Not in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · Skill to build: Intermediate · Upkeep: Light · Change to daily life: Occasional · Works without the grid: Yes Choose it if you are off the sewer and have a garden for a drain field.
Aerobic treatment unit / micro-station d'epuration (package plant) Can I use it? Not in a flat · No rebuilding needed What does it cost me? Upfront cost: High · Skill to build: Specialist · Upkeep: Heavy · Change to daily life: Occasional · Works without the grid: No Choose it if your plot is small or wet, where a drain field would fail.
Mains sewer Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · Skill to build: Specialist · Upkeep: None · Change to daily life: None · Works without the grid: Yes Choose it if the house is on the public sewer and you want nothing to maintain.
Sources
Constructed-wetland treatment performance literature (NCBI vertical-flow constructed wetland studies)
Limitations of this page
We don’t list sizing or quantities, as the yield of each technique depends on the quality of its build. The catalogue compares options but doesn’t dimension them. Regulatory notes are indicative, with a French example, and need to be confirmed locally.