Surface irrigation and pump-out tanks

Low cost wastewater treatment for the world


The whole system

Vermidigester for primary treatment

Secondary treatment vermifilter

Surface irrigation

The whole system produces treated wastewater suitable for surface irrigation. This high level of treatment is 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 go back to Primary vermidigester.

Treated effluent disposal

Discharge of treated wastewater should never be into or near water bodies. The golden rule is "dispersal is always better than concentration". The advantage of small scale and domestic vermifiltration is that households can irrigate their own land (plants and trees) at low cost. Once the vermifilter removes pathogens and biological oxygen demand (BOD), the nutrient-rich water has value for irrigating and feeding valuable plants.

Important considerations include:

The inlet to the pump-out tank (red arrow) sets the water level for the preceding secondary treatment sumps (learn about displacement, surge capacity and equilibrium water level here »).

The float switch turns the pump on before the water level in the tank reaches the inlet; and switches the pump off before the water level gets too low, ensuring the pump doesn't run dry.

Alternatively a bell siphon could be used instead of a pump and float switch if the irrigation field is sufficiently lower than the pump-out tank. 

Pump-out tank

Where there is sufficient fall to the irrigation field, a bell siphon could provide sufficient water pressure to irrigate drip lines. However this section will focus on solar systems that incorporate water pumps and batteries, to provide a more versatile irrigation options (uphill OR downhill of the treatment plant).

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 50 watt panel is sufficient for smaller domestic pump-out tanks (e.g. 3 users). Use a 100 watt panel for larger domestic systems.

Cost: Approx. US $70 (50 watt panel).

2. Battery

Recommended: 12.8V 21Ah LiFePO4 (lithium iron phosphate) battery with overvoltage and undervoltage protection.

The Small Den 12.8V 21 AH battery (4S3P, with 12 x 32700 cells) 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

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.

Low head applications

Recommended: Seaflo 01 series 1100GPH Bilge pump


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

Cost: Approx. US $25

High head applications

Recommended: 12 volt helical rotor pump (often referred to as a "submersible solar pump"). These are available on Ali Express for approx. $130, have a 30m head and draw approx. 180 watts

5. Assemble the components

Setting the Water Level Controller Pump Switch Module:


Barbed dripper nozzles are fitted into holes drilled in polythene pipe. These provide better water distribution than simply drilling holes in the pipe. Irrigation lines can either be moved to new locations at regular intervals, or multiple irrigation lines are attached to a main line with taps and rotated into and out of service. Number of nozzles is limited by the flow and pressure provided by the pump to those nozzles. 

This system avoids using filters, because these require regular maintenance and are not necessary. However, 3mm barbed nozzles are much less likely to block with solids than 2mm nozzles. As nozzle diameter increases, the maximum number to maintain an even pressure between all the nozzles decreases. An even pressure between nozzles is required for even water distribution in the irrigation field.

For the system described here, treated effluent is pumped through 10-30 barbed irrigation nozzles at a time. Trial and error will be required to determine number of nozzles used, which will depend on head, irrigation line length and irrigation line diameter. 

3mm internal diameter barbed irrigation nozzles

See the video below for how these components can be put together for a full system.