The whole system
Low cost wastewater treatment for the world
Construction:
The whole system
Vermidigester for primary treatment
This system produces treated wastewater suitable for surface irrigation. This is a high level of treatment and achievable only with primary + secondary treatment.
The system operates off-grid and utilises solar panels and batteries to operate the pumps required to function.
If you only want a simple system (primary treatment, subsurface discharge) then build just the vermidigester and a soak pit.
Full tertiary treatment system
This system incorporates a twin vermidigester and sump, a secondary vermifilter, a tertiary vermifilter, and a pump-out tank for surface irrigation of the treated effluent.
Lets break the system down into its components:
1. Primary treatment vermidigester and sump
Surge capacity is the volume between the floor of the digester and the equilibrium water level in the sump (see the red arrows on this page). The whole system works via "displacement". When wastewater enters the system faster than it exits, that water level temporarily rises, thus requiring capacity for that "surge" of water.
The recirculation pump (see above) operates once every couple of days for about 20 seconds, to pump fine settling solids from the sump back into the digester. The recirculation pump is not essential, but without it fine solids that are suspended in the wastewater slowly settle and build up in the bottom of the sump as sludge, which would require periodic removal (e.g. annually).
2. Secondary treatment vermifilters
Secondary and tertiary treatment vermifilters can be added in series. More vermifilters increase level of treatment.
In this example the vermifilter sits on top of a sump . Two plastic 40 gallon drums are required to construct the vermifilter and sump.
Wastewater is recirculated from the sump through the vermifilter and back into the sump using a small pump and timer.
Note that in this example the inlet into the sump discharges to the bottom of the sump and the outlet discharges from near the top of the sump. The outlet from the vermifilter also discharges to the bottom of the sump. This ensures all of the wastewater is treated before it exits the sump.
As more wastewater enters the sump, displacement drives an equal volume to exit the sump.
The red arrow again shows the equilibrium water level. This level is set by the level of the inlet to the pump-out tank (see below). Note also that the water level in the sump should provide for some surge capacity (the cavity above the water).
Learn more about constructing secondary treatment vermifilters »
3. Pump-out tank and surface irrigation
The inlet to the pump-out tank (see red arrow to the left) sets the equilibrium water level for the preceding secondary treatment sumps (see red arrow above).
The pump has a float switch which turns the pump on before the water level reaches the inlet.
The float switch also switches the pump off before the water level gets too low, so the pump doesn't run dry.
Alternatively a bell siphon could be used instead of a pump and float switch if there is fall to the irrigation field. The irrigation field must be lower than the pump-out tank for gravity to discharge the water to it.
Learn more about constructing the pump-out tank and surface irrigation »
See the video below for how these components can be put together in a working recirculation system: