SUBSURFACE DRIP DISPERSAL OF PRIMARY TREATED EFFLUENT
2/27/98
The use of WASTEFLOW® for subsurface drip
irrigation dispersal of secondary treated effluent is well known
and well proven in more than 1,000 systems both large and small.
Ayers and Associates under a grant funded by the EPA, have been
conducting experiments in the Florida Keys by taking septic tank
effluent from a prison and passing it through two Geoflow
VORTEX™ filters and then into a WASTEFLOW subsurface drip
system in sand and two artificial mediums. These experiments have
been very successful both from the point of view of the excellent
performance of the filters and the WASTEFLOW but also from the
point of view of absorption of nitrates and phosphates. Caution
should be exercised in extrapolating the experience gained in
sand to heavier soils. The purpose of this paper is to combine
the knowledge that we have at this time to establish guidelines
which are conservative enough to ensure safe reliable dispersal of
primary treated effluent at an economic cost.
Figs. 1 shows the layout of a typical system. We recommend using the WASTEFLOW Manager™ for control, monitoring with auto-dialer, and data logging, but lower cost simple controllers can be used.
Referring to Figure 1:
1. Ensure that the septic tank is adequate in size and design for the designed flow.
2. Use an in–tank filter in the septic tank.
3. The VORTEX filter operates alternatively
either supplying effluent to the drip irrigation field or being
forward washed through the centrifuge. Ensure that the flow
through the filter is within the optimal design flow for the size
of filter selected – see figure 2: VORTEX filter design
parameters.
A critical factor is the sizing and design of the drip dispersal field.
Drip dispersal is a point source application and
failure comes about by overloading the point with BOD and forming
an anaerobic bacterial mat (schmutzdekke). Therefor we need to
reduce the bacterial load per emitter down to the levels which we
have found by experience to be failure proof when applying
secondary treated effluent. If we use 12" x 12" spacing
of drippers and driplines we have immediately increased the
number of drippers by four-fold over the known configuration of
24" by 24" spacing. If we then increase the area by
doubling it we are up to 8 times the number of drippers as
compared with the number of emitters we are experienced in using
when applying secondary treated effluent. Table 2 below sets out
these standards.
Dripper selection: To give the aerobic soil
bacteria maximum time to absorb the anaerobic bacteria in the
effluent it is useful to use the 1Ž2 gallon per hour emitter. For
effluent the 1Ž2 gph flow rate is only available in pressure
compensating WASTEFLOW.
To summarize the above arguments for this
application we recommend WFPC16–2–12.
Control and Monitoring:
The use of septic tank effluent obviously
carries considerably higher risk to both health and environment
than the use of secondary treated effluent. Geoflow offers a
WASTEFLOW Manager which will control and continuously monitor the
septic tank, the pump chamber, the filters and the subsurface
drip dispersal fields. The Manager will automatically dial to up
to six 'phone numbers in the event of any failure. The Manager
can be accessed and both operated and re-programmed over a
telephone line. The Manager will hold one year's data in the data
log. We strongly urge that larger systems using septic effluent
should consider the technology of the WASTEFLOW Manager to ensure
safe and effective operation.

WASTEFLOW MANAGER is the preferred controller and monitor for larger systems using a flowmeter to continuously monitor flows.
For small systems which are not monitored the preferred controller is the GEO-1 or GEO-2
Typical Program:
24 cycles each hour per day. Each cycle 4 minutes.
At the end of each cycle flush the filter (open valve B) for one minute.
Flush the system (open valve A) every 100 cycles.
Design Information:
Minimum | Maximum | |
Length of WASTEFLOW | 250' | 10,000' |
Flow at each valve | 4 gpm | 21 gpm |
Dripline length per valve | ||
Classic 24" x 1 gph | 400' | 2,250' |
Classic 12" x 1 gph | 200' | 1,000' |
P/C 24" x 1 gph | 500' | 2,500' |
P/C 12" x 1/2 gph | 500' | 2,500' |
Cleaning the VORTEX filter
Scrubbing very fine particles with a brush does no good, and filters "cleaned" in this way tend to plug very quickly.
Clean with a pressure hose from the outside of the mesh cartridge inwards to the middle. Also because we are dealing with high strength effluent a soaking in chlorine will help. The screen is stainless steel and this will not have any adverse effects. Use 50% Chlorox with 50% water. Chlorox is 7% chlorine.
SUGGESTED | APPLICATION | RATES | |||||||
---|---|---|---|---|---|---|---|---|---|
Typical treatment: | Secondary | Lagoon
| |||||||
Maximum | >Minimum | BOD < 30 mg/l | BOD < 60 mg/l | BOD < 90 mg/l | BOD < 150 mg/l | BOD < 180 mg/l | |||
Texture | Approx. | Application | Area in sq. ft | Min. # | Min. # | Min. # | Min. # | Min. # | |
Group | Perc rate | GPD/Sq.Ft. | / 100 gpd | drippers/sq.ft. | drippers/sq.ft. | drippers/sq.ft. | drippers/sq.ft. | drippers/sq.ft. | |
I Coarse sand | >5 | 1.00 | 100 | 1.00 |
1.00 |
1.00 |
1.25 |
1.50 |
|
I Fine sand
|
5 - 10 | 0.80 | 125 | 0.50 | 0.50 | 0.75 | 1.25 | 1.50 | |
II Sandy loam | 10 - 20 | 0.60 |
167 |
0.25 |
0.50 |
0.75 |
1.25 |
1.50 |
|
II Loam |
<20 - 30 |
0.50 |
200 |
0.25 |
0.50 |
0.75 |
1.25 |
1.50 |
|
III Clay loan |
30 - 45
|
0.40 |
250 |
0.25 |
0.50 |
0.75 |
1.25 |
1.50 |
|
III Silty clay loam |
45 - 60 |
0.30 |
333 |
0.25 |
0.50 |
0.75 |
1.25 |
1.50 |
|
IV Sandy clay |
60 - 90 |
0.15 |
667 |
0.25 |
0.50 |
0.75 |
1.25 |
1.50 |
|
IV Silty clay |
90 - 120 |
0.10 |
1000 |
0.50 |
1.00 |
1.00 |
1.25 |
1.50 |
|
IV Clay |
>120
|
0.05
|
2000 | 1.00 | 1.00 | 1.00 | 1.25 |
1.50 |
|
Typical
treatment: |
Filtered
Septic tank |
||||||||
Maximum
|
Minimum
|
BOD < 120
mg/l |
BOD < 150
mg/l |
BOD < 180
mg/l |
|||||
Texture
|
Approx.
|
Application
|
Area in sq. ft
|
Min. #
|
Min. #
|
< Min. #
|
|||
Group
|
Perc rate
|
GPD/Sq.Ft.
|
/ 100 gpd
|
drippers/sq.ft.
|
drippers/sq.ft.
|
drippers/sq.ft.
|
|||
I Coarse sand | >5 |
1.00 |
100 |
1.00 |
1.25 |
1.50 |
|||
I Fine sand
|
5 - 10 |
0.80 |
125 |
1.00 |
1.25 |
1.50 |
|||
II Sandy loam
|
10 - 20
|
0.60 |
167 |
1.00 |
1.25 |
1.50 |
|||
II Loam |
20 - 30
|
0.50 |
200 |
1.00 |
1.25 |
1.50 |
|||
III Clay loam
|
30 - 45
|
0.40 |
250 |
1.00 |
1.25 |
1.50 |
|||
III Silty
clay loam |
45 - 60
|
0.30 |
333 |
1.00 |
1.25 |
1.50 |
|||
IV Sandy clay
|
60 - 90
|
0.15 |
667 |
1.00 |
1.25 |
1.50 | |||
>IV Silty clay
|
90 - 120
|
0.10 |
1000 |
1.00 |
1.25 |
1.50 |
|||
u>IV Clay |
>120
|
0.05
|
2000
|
1.00
|
1.25
|
1.50
|
Table 2: SUGGESTED APPLICATION RATES OF EFFLUENT |