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Low cost wastewater treatment for the world
Low cost wastewater treatment for the world
System types
System types
System design requires an understanding of the site, the location of the dwelling, and where the treated effluent will be irrigated.
Three system types are described below:
Gravity-flow vermifilter: This requires no energy to operate and can only irrigate crops below the effluent source (passive treatment).
Single-pass vermifilter: This uses a single pump (active treatment) followed by gravity flow (passive treatment).
Recirculating vermifilter: This uses recirculation pumps to pass wastewater through a vermifilter multiple times (active treatment).
Gravity flow vermifilter
Gravity flow vermifilter
Gravity flow vermifilters offer a simple method for high levels of treatment where there is fall between one reactor and the next reactor and the effluent field being irrigated. Gravity flow vermifilters achieve a lower level of treatment than recirculating vermifilters, but are simpler to construct and maintain. Pumps are required for recirculating vermifilters but no fall is required between vermifilters.
The example below shows a gravity flow vermifilter system with primary and secondary treatment:
This is the simplest system, which can gravity feed treated effluent to land or crops, so no pump is required. Multiple secondary vermifilter reactors can be employed in series. This design suits land with fall between the wastewater entry and treated water exit. Additional fall would be required for sufficient pressure to operate a bell siphon and irrigation lines.
However, an elevated site with sufficient fall is not always available, for example where the land is flat or the wastewater flow is at (or below) ground level.
Where the effluent needs to be raised into the inlet of the vermifilter (or to the soakage field), a pump is required. The wastewater should go through a primary digester first to remove the solids from the flow.
The following systems treat wastewater to the secondary level suitable for surface irrigation. If soakage trenches or soak pits are used, the primary digester is all that is required for primary treatment, followed by disposal to sub-surface soakage field.
Single pass vermifilter
Single pass vermifilter
This uses a single pump, followed by gravity flow. The example below shows a single-pass vermifilter with primary and secondary treatment:
This system uses a pump to raise the primary-treated wastewater up into an elevated vermifilter, with the outlet elevated sufficiently to gravity discharge the treated wastewater to surface irrigation. The outlet should have sufficient head for a bell siphon to generate pressure on the irrigation lines for even distribution of water through the drippers.
Recirculating vermifilter
Recirculating vermifilter
The recirculating vermifilter is perhaps the simplest design to produce a high level of treatment required for surface irrigation. A recirculation pump passes wastewater through a vermifilter reactor multiple times. The example below shows a primary vermidigester followed by a secondary recirculating vermifilter:
The primary treated wastewater is pumped from the sump into the top of a secondary vermifilter and returns via gravity back to the sump. The sump overflows via displacement into a tank with a pressure pump and float switch, or alternatively gravity feeds using a bell siphon to surface irrigation.
Construction
Construction
Vermifilter.com have put together a section focussed on constructing off-grid solar vermifilter systems that treat wastewater to a standard suitable for surface irrigation of crops, pasture or trees:
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