Construction

Low cost wastewater treatment for the world

Use the system design page to guide how your system should be constructed. This page is dedicated to domestic systems that utilise a twin vermidigester for primary treatment, a recirculating secondary treatment vermifilter, an optional recirculating tertiary treatment vermifilter and pumped surface irrigation distribution.

The whole system

Lets start with diagrams of the whole system ...

Primary + secondary system

This system incorporates a twin vermidigester, a single secondary vermifilter and a series of settling tanks, followed by a pump-out tank to surface irrigation

Primary + secondary + tertiary system

This system incorporates a twin vermidigester, a secondary vermifilter, a tertiary vermifilter and a series of settling tanks, followed by a pump-out tank to surface irrigation.

Now, lets break it down into the components:

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 sump

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 pallet

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.

The substrate

The substrate is usually coarse organic material that is slow to decompose, such as coarse pine bark that is contained in a coarse textile cloth lining such as shade cloth or windbreak cloth. The substrate must be thick enough (e.g. 10-20cm) to retain the solids influent on the surface, filter larger suspended solids out of the wastewater flow and provide habitat for the worms.

Although woodchips have good porosity, they decompose over time and may require replenishing. Composted sawdust, wood shavings, coir fibre and peat may work, but a coarser media with good porosity is recommended.

If a suitable organic material is not available for substrate, inorganic materials such as coarse gravel can be used. Soil doesn't have sufficient porosity - the water needs to filter through the substrate relatively unimpeded.

Constructing vermifilters (for secondary treatment)

Constructing vermifilter from 250 litre plastic drum

Plastic oyster mesh. This is available as tubes, perfect diameter for 200-250 litre plastic drums

Textile cloth stitched to the inside of the oyster mesh.

Plastic drainage coil and windbreak attached to the bottom with cable ties

Inserted into drum

Bark media added

Plastic drainage coil spacers added

Recirculating secondary vermifilter powered by a solar panel:

This example shows secondary domestic wastewater treatment using a recirculating vermifilter. The pump is powered by a solar panel.

Setting up solar-powered recirculating vermifilters

Solar vermifilters are designed to run intermittently, for example ten seconds every minute, twenty four hours per day. Four components are required: the pump, the solar panel, the battery and the timer.

  1. Pumps

Recirculating pumps suitable for solar vermifilter systems:

Recommended: Whale gulper 220

The secondary vermifilter requires a pump suitable for recirculating water with high levels of suspended solids.

12 volt DC, no clog, no filter waste pump, large single diaphragm, 12.6 litres per minute with current draw of 4 amps at 1m head. 19mm hose connections. Max discharge head of 3m.

Recommended: 19 watt brushless centrifugal water pump

The tertiary vermifilter requires a pump suitable for recirculating water with low levels of suspended solids.

12 volt DC, 800 litres per hour, maximum discharge head of 5m, 1/2" male threads, 1.6 amps

2. Battery and timer

A single battery is required, along with separate timer controls for each recirculation pump. The timer operates the recirculation pumps intermittently.

Recommended: 12.8V 21Ah Lifepo4 battery pack (4S3P, with 12x 32700 cells)

Overvoltage and undervoltage protection are required. The Small Den battery available on Ali Express has Discharge Cutoff Voltage: 10 +/- 1V and Charge Cutoff Voltage: 14.6V, with a 40 amp balance BMS suitable for direct solar charging

Cost approx. US $100

Recommended: JZ-801 or XY-J02 Cycle Delay Automation Timer Control

12 volt, low power consumption, provides a separate "on" time and "off" time.

Cost approx. US $4

3. Solar panel

A single 50 watt solar panel is sufficient for intermittently running a secondary recirculation pump and a tertiary recirculation pump.

Make sure to use a nominal 12 volt solar panel for a 12 volt system.

Cost approx. US $100 for a 50 watt solar panel.

4. Assemble the components

*Under construction*

Constructing the settling tanks

Why settling tanks?

A series of settling tanks provides a buffer between the vermifilter and the irrigation drippers. Without settling tanks, worms and detritus can exit the vermifilter and block irrigation lines. Instead of settling tanks, inline filters could be used but these would require regular maintenance. Settling tanks not only settle out any remaining solids, but they also provide additional treatment to the wastewater. They are simple to construct, virtually maintenance free and are required for recirculation.

Constructing a series of settling tanks or "baffled reactors" is very simple using 200 litre drums and tank fittings. The drums are joined together, one tank fitting joins two drums.

Plastic tank fitting. Two drums can be joined together with one tank fitting

Water exits from inside one drum through here...

...and enters the next drum through here.

Black HDPE (alkathene) pipe fitted into the tank fitting. Water travels down the pipe to enter the bottom of the next tank.


Two drums joined together with tank fitting. Once the tank fitting is screwed up the tanks will be tight against each other and waterproof.

Note that the final settling tank that discharges to the pumpout drum should have an outlet slightly higher than the preceding settling tanks. This ensures the outlets from each settling tank are below the water level in the tank so that scum on the surface does not drain into the next tank.

The final outlet (red arrow) sets the water level in the preceding drums. The outlets for the settling drums (purple arrows) are below the water level set by the final settling drum. This is the equilibrium water level, whereby when more water is added from the primary digester, the same volume exits the settling drums into the pump-out drum.

Make sure this level is not too high, because the first drum requires surge capacity. If a surge of water is added (e.g. emptying a bath), capacity is required until that volume exits the system.

The surge capacity in the diagram above is the volume above the equilibrium water level (red arrows)

Pump-out tank and surface irrigation

Although in some circumstances a bell siphon could provide sufficient water pressure to irrigate drip lines, this section will focus on solar systems incorporating water pumps, solar panels and batteries, to provide a more versatile system that irrigates uphill or downhill of the site.

A solar pump-out tank requires a DC pump, a battery, a solar panel and a controller to switch the pump on and off:


  1. Solar panel

A nominal 12 volt 40 watt panel is sufficient for most domestic pump-out tanks

Cost: Approx. US $70

2. Battery

Recommended: 12.8V 14Ah Lifepo4 battery with overvoltage and undervoltage protection

The Small Den battery available on Ali Express has:

Output voltage range: 10V-14.6V

Discharge cut-off voltage (V): 10 +/- 1V

Charge cut-off voltage (V): 14.6V

30A BMS, 4S2P (8x 32700 cells)

Cost: Approx. US $70

3. Controller

XH-M203/HCW-M203 Water Level Controller Pump Switch Module

A single water level controller is required, with a relay output capacity of 10 amps

Cost: Approx US $5

2x Water Level Sensor Right Angle Float Switches

Two switches are required, an upper water level switch and an under water level switch

Cost: US $5

4. Pump

The pump should not draw more than 10 amps (the capacity of the controller relay) and should exceed the head required for the irrigation lines.

Recommended: Seaflo 01 series 1100GPH Bilge pump

SFBP1-G1100-01

Flow rate 1130 GPH, Voltage 12v, Max draw 6.0 A , Head 4.5m, Outlet diameter 1-1/8"

Cost: Approx. US $25

5. Assemble the components

*Under construction*