Primary treatment vermifilter construction
Low cost wastewater treatment for the world
Use the system design page for guidance on design.
The construction pages:
twin vermidigesters for primary treatment
settling tanks; and
treated effluent distribution to surface irrigation using a pump.
Constructing twin vermidigesters (for primary treatment)
Domestic vermidigester with twin vaults. The cladding material is fibre cement board
Twin primary vermidigesters should be constructed so the inlet can be rotated between them. The contents of one side can be rested while the other side is being used.
Construction of twin digesters is easily achieved with a shallow concrete sump (to the height of the false floor) that fits two large fruit crates (see below, the type designed for handling with forklifts). The digester walls are fixed directly to the crates, with an air cavity to allow air circulation around the crate walls and underneath the false floor. Ventilation into the digester is required, which should restrict entry of cockroaches and flies into the digester. Shadecloth, windbreak or similar porous textile cloth is fixed on the inside of each crate and 10-20cm of coarse media substrate is placed in the bottom of the crates. Pine bark is recommended, because this decomposes much more slowly than wood chips, coarse sawdust or wood shavings.
Large fruit crates are ideal for constructing vermidigesters. Note the ventilated walls and "false floor", which allows ventilation underneath the vault.
This vermidigester is made from two fruit crates, with a frame and cladding attached to the outside of the crates. A ventilation cavity is provided so that fresh air flows around the walls and underneath the crate.
The vermidigester retains solids on top of the substrate while the liquid drains through and exits the reactor. The sump provides an outlet below the false floor for water to exit the reactor. This liquid must drain away and exit freely from the sump at all times. If water builds up above the level of the false floor the worms will be killed and the system will become anaerobic and fail.
The sump can be as simple as an earth platform with shallow earth walls and an exit pipe that drains water away. An earth platform is only suitable where there is no risk of wastewater entering the water table or the water table entering the sump. Usually a steel-reinforced concrete platform is constructed, with a floor and shallow walls around the perimeter that are no higher than the false floor. The digester is a composting vault, not a water tank!
If there is fall away from the digester, then gravity can be used for removing water at the outlet. If not, a pump with float switch and alarm is required to keep the water level below the false floor at all times.
If your vermidigester sump must be installed below the soil surface, NEVER depend on effluent percolation into the soil (e.g. soakage trenches) to remove water from the sump. Poor drainage would raise the water level in the sump above the false floor with catastrophic results.
The 10cm walls of this concrete sump were made slightly wider than the plastic crates. The two crates were positioned up against each other on the sump floor, the corrugated plastic walls fixed to them, then the cavity between the crate walls and the sump walls were filled with concrete.
Plastic fruit crate
Plastic fruit crates provide a durable "false floor" between the media substrate and the sump, where liquid drains away. These fruit crates also provide a structure to which walls and roof are attached to and are well ventilated.
Plastic pallets provide a durable "false floor" between the media substrate and the digester sump, where liquid drains away.
Vermidigester walls and roof
The vault must be enclosed with walls and roof that are vermin-proof. Rats, dogs, flies and cockroaches should not be able to access the contents.
The vault must also be well ventilated. Vermin-proof vents are usually installed at the top of the vault, and must provide adequate air circulation.
Walls should allow ventilation around the outside of the crates. This can be achieved with corrugated plastic or by using spacers between the crate and plasterboard.
A pervious textile cloth such as windbreak or shadecloth is fixed to the inside walls of the basket and must fully cover the walls and floor. The substrate is then added.