Surface irrigation and pump-out tanks
Low cost wastewater treatment for the world
Constructing surface irrigation
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:
Discharge should only be to soil that does not have a high water table.
Secondary treated effluent can be discharged to the soil surface using drippers, whereas primary treated effluent must be discharged to subsurface effluent fields.
The inlet to the pump-out tank (red arrow) sets the water level for the secondary treatment sumps. Learn about displacement, surge capacity and equilibrium water level.
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.
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 and batteries, to provide a more versatile system that irrigates 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 40 watt panel is sufficient for most domestic pump-out tanks
Cost: Approx. US $70
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
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
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