United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
'/I
vxEPA
Research and Development
EPA-600/S2-82-080 Sept. 1982
Project Summary
Rapid-Infiltration System for
Wastewater Renovation and
Beneficial Reuse
Herman Bouwer, R. C. Rice, J. C. Lance, and R. G. Gilbert
A 1 6-ha rapid infiltration waste-
water treatment system at Phoenix,
AZ, was used to treat 90 m/yr of
conventionally treated effluent. The
reclaimed water was suitable for
unrestricted irrigation and aquatic
recreation. The renovated water
typically contained 7 mg/l nitrogen, 1
to 20 fecal coliforms per 100 ml, 1
virus unit per 100 ml and less than 0.1
mg/l trihalomethanes.
This Project Summary was developed
by EPA's Robert S. Kerr Environmental
Research Laboratory, Ada, OK, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information
at back).
Introduction
Sewage effluent can be an important
source of water, particularly in water-
short areas. Conventionally treated
effluent can be used for restricted
irrigation (fiber and seed_ crops, for
example). With additional treatment,
the effluent can also be used for
unrestricted irrigation and aquatic
recreation. This study shows how the
necessary additional treatment can be
obtained with soil-aquifer treatment
systems using rapid-infiltration basins to
get the effluent into the ground and the
wells to pump the renovated water
from the aquifer.
Following successful renovation of
secondary (activated sludge) sewage
effluent by soil-aquifer treatment using
small, experimental infiltration basins
(the Flushing Meadows Project) in the
Salt River bed west of Phoenix, Arizona,
a larger system was installed in 1975 to
study operational aspects and perform-
ance of a full size project, including
recovery of the renovated water by
wells for irrigation. The system, called
the 23rd Avenue Project, was constructed
by splitting an existing 16-ha rectangular
oxidation pond into four intermittently
flooded infiltration basins averaging 89
x 465 m in size. The surface soil in the
basins consisted of loamy sand, coarse
sand, and coarse sand plus gravel and
boulders. Gravel and coarse-sand
strata prevailed below 0.5 m depth and
continued to a depth of at least 60 m
(the depth of the deepest well in the
area). A large capacity well was installed
in the center of the project as the first of
three production wells on the center
dike necessary for complete recovery of
the renovated water from the aquifer.
The well casing was perforated from 30
to 55 m. Groundwater table depths
varied from 3 to 20 m. Monitoring wells
were installed in the center of the
project and on the north and south sides
(Figure 1). Their depths ranged from 18
to 30 m.
Initially, the infiltration basins received
effluent that had passed through a 32-
ha lagoon. High algae concentrations in
this effluent produced hydraulic loading
rates of only 22 m/yr. This value was
increased to 90 m/yr after the effluent
was bypassed around the lagoon with a
newly constructed channel and after
the surface crust of the soil in the
infiltration basins was ripped. Flooding
-------
North Well
•^
Basin 1 Inflow
Outflow ^D'- -
30 24 18 -ML Well
^ Basin2 ^ Xg
CV_ Center Well ^-°
Basin 3
cf*"~ Basin 4 ^D" "
South Well
•N^
!A
/
/
/
/
/
/
', 32-HA Pond
/
/
^ By Pass
'/ 1 Channel
/ /Is / / ////////
(
>
/////////
ff
/
/
/
/
/
/
/
£
^- Secondary Effluent
0 WO 200 300-M
Figure 1. Schematic of 23rd Avenue Rapid Infiltration Project.
and drying periods were about two
weeks each.
The renovated water typically con-
tained 750 mg/l dissolved solids, 0.9
mg/l suspended solids, 7 mg/l nitrogen
(mostly nitrate), 0.25 mg/l phosphate-
phosphorus, 1 to 20 fecal coliforms per
100 ml (average yearly values), about
one virus unit per 100 I, and 1.8 mg/l
total organic carbon. Except for the
dissolved solids, these values were
much lower than those for the secondary
effluent entering the ground. Total
organic carbon in the renovated water
included a wide variety of organic
compounds, including trihalomethanes
(total concentration less than the
interim maximum EPA limit of 0.1 mg/l
for drinking water), chlorinated aliphatic
and aromatic hydrocarbons, pesticides,
plasticizers, and others (concentrations
generally on the order of nanograms to
micrograms per liter). Significant losses
of volatile organic compounds occurred
in the infiltration basins. Some com-
pounds were also significantly attenuated
in the soil-aquifer system.
The renovated water is suitable for
unrestricted irrigation and for lakes
with primary contact recreation. Reuse
for drinking water will require additional
treatment (ozonation, activated carbon
adsorption, and possibly reverse osmo-
sis).
System Performance
Hydraulic Capacity
The main problem encountered when
the system started operation was the
low infiltration rates in the basins. This
was caused by a high algae content of
the effluent after it had first gone
through the 32-ha lagoon (Figure 1).
The main algal bloom organism was
Carter/a klebsii Dillworth which is a
suspended algae that clogged the
surface soil in the basins so severely
that infiltration rates often dropped from
about 0.5 m/day to less than 0.1 m/day
in the first two or three days of a flooding
period. The relatively large water depth
(1 m) in the basins was not sufficient to
overcome the hydraulic impedance of
the algal "filter cake." Since large water
depths decreased the turnover rate of
the water in the basins, they actually
contributed to the problem by allowing
additional algae growth in the infiltration
basins. Drying periods of more than two
weeks were required to get some
recovery in infiltration capacity. Clogging
very likely was not only by formation of
an algal filter cake on the soil surface,
but also by precipitation of calcium
carbonate due to the high pH of the
effluent as the algae absorbed carbon
dioxide for photosynthesis. Thus, hydrau-
lic loading rates initially were a dis-
appointing 22 m/yr.
After it was established that the high
algae content was the sole cause of the
low infiltration rate (and not, for
example, air-pressure buildup in the
vadose zone below advancing wet
fronts), a levee was constructed on the
east, south, and west sides of the 32-ha
lagoon to create a bypass channel
(Figure 1). This allowed the effluent
from the treatment plant to flow directly
into the infiltration basins. Use of the
bypass channel reduced the suspended
solids content of the effluent entering
the basins from a range of 50 to 100
mg/l (mostly as algae) to a range of 10
to 15 mg/l. The basins were also ripped
to remove residual crusts on the soil.
The water depth in the basins was
reduced to about 25 cm to increase the
turnover rate of the water in the basins
and, hence, to decrease the time for
suspended algae to develop. As a result,
the hydraulic loading rate increased to
90 m/yr. The basins were operated in
symmetric pairs using flooding and
drying periods of two weeks each.
These periods were selected on the
basis of previous experimental results
from the Flushing Meadows Project,
which showed that 2-week rotations
yielded high hydraulic loading rates and
also maximized nitrogen removal by
denitrification in the soil
The flooding depth of 1 m initially
used for the basins prevented the
development of vegetation. However,
when the depth was reduced to about
25 cm, a lush vegetation developed.
Main plant species were barnyard grass
(Echinochloa Crusgalli) and willow leaf
(Polygonum Lapathifolium). The plants
were about 0.5 to 1.5 m tall and since
they grew well above the water, they
provided ideal circumstances for mos-
quitoes to breed. To minimize mosquito
breeding, the vegetation should be
periodically mowed and water depths
should be large enough to completely
submerge the plants during flooding
The hydraulic loading rate of 90 m/yr
was 14 percent of the average vertical
hydraulic conductivity of the basin soil.
At 90 m/yr, the capacity of the 16-ha
system thus was 14.4 million mVyr or
40,000 mVday (11 million gal./day).
Since irrigation wells in the area
typically have a capacity of about
13,500 mVday (2,500 gal./minute),
three wells evenly spaced on the center
dike will be sufficient to pump renovated
water out df the aquifer at the same rate
that it arrives from the infiltration
basins. This would minimize movement
of renovated water into the aquifer
around the system. Plans for discharging
the renovated water into an irrigation
canal for unrestricted irrigation have
been discussed with officials from the
City of Phoenix and of the Roosevelt
Irrigation District.
Groundwater and Aquifer
Depths to the groundwater table
varied from 3 to 20 m, depending on
time of year (irrigation pumping) and
recharge from the nearby Salt River.
Groundwater tables in the center
typically rose about 1 m in response to
infiltration from the two center, basins,
and declined when the two center
basins were dried and the two outer
basins were flooded. Small diurnal
-------
fluctuations of water levels in monitoring
wells were observed in response to
daily patterns of barometric pressure.
Hydraulic properties of the aquifer
beneath the basins were determined
with the slug test, step-drawdown test,
and Theis pumping test on the production
well in the center. They were also
calculated from the rise of the ground-
water mound in the center of the basin
area in response to infiltration from the
two adjacent basins. Different values
were obtained. However, a transmissivity
of 50,000 mVday and a specific yield or
fillable porosity of 0.05 seemed reason-
able for predicting groundwater mounds
and underground flow systems.
Quality of Effluent and
Renovated Water
Typical quality parameters of the
secondary unchlorinated effluent from
the treatment plant entering the infil-
tration basins and of the renovated
water pumped from the production well
in the center of the project are shown in
Table 1. The slight increase in TDS
content may have been due to evapora-
tion in the basins (about 1.8 m/yr or
2% of the hydraulic loading rate)and/or
dissolution of calcium carbonate in the
soil -and vadose zone. Nitrogen was
almost all in the ammonium form for the
secondary effluent and in the nitrate
form for the renovated water. The data
showed that the soil-aquifer treatment
system removed about 60 percent of the
nitrogen. This agreed with results from
previous field and column studies,
which showed that denitrification was
maximized when using flooding periods
of 9 to 14 days. Most of the denitrification
occurred in the top layer of the soil. The
nitrogen concentration in the renovated
water was close to the Oto 5 mg/l range
where nitrogen in irrigation water will
have no adverse effects on crops. It is
also below the maximum limit of 10
mg/l for nitrate nitrogen for drinking
water. Phosphate removal was about
95 percent. The phosphate phosphorus
content in the renovated water was still
above threshold values for algae growth
but low enough to be used in recreational
lakes. The fecal coliform concentration
of the renovated water was well below
the upper limit of 200/100 ml for
unrestricted irrigation in Arizona. In the
future, this upper limit probably will be
reduced to a mean of 2.2/100 ml with
no single sample exceeding a count of
25/100 ml. At the end of 1980,
however, the sewage treatment plant
started to chlorinate its effluent,
Tablet.
Typical Quality Parameters of Secondary Effluent from Treatment Plant
and of Renovated Water from a Production Well in Center of Project.
Secondary
Effluent
Renovated
Water
Total dissolved solids, mg/l
Suspended solids, mg/l
Total nitrogen, mg/l
Phosphate phosphorus, mg/l
Total organic carbon, mg/l
Fecal coliforms per 100 ml
Viruses, PFU per 100 I
700
13
18
6
10
106
2100
740
1
7
0.25
2
22
1
resulting in fecal coliform concentrations
of a few thousand per 100 ml for the
effluent and 0 to 4 per 100 ml for the
renovated water with a mean of less
than 2.2/100 ml. Thus, the fecal
coliform concentrations will be low
enough to meet the new requirements
for unrestricted irrigation. The virus
concentration in the sewage effluent
shown in Table 1 was taken from
previous studies at the Flushing Mea-
dows Project. The virus level in the
renovated water from the 23rd Avenue
Project averaged about 1 plaque forming
unit (PFU) per 100 I, when samples of
800 to 2,000 I were used. The total
organic carbon concentration in the
renovated water indicates the trace or
refractory organics remaining in the
water after the readily degradable
organic carbon has been removed.
Identification of the residual organic
carbon showed a wide variety of
compounds, including trihalomethanes,
numerous other organohalides, aromatic
compounds, anisoles, phthalates, and
pesticides. Concentrations often were
on the order of nanograms and micro-
grams per liter. The total concentration
of trihalomethanes in the renovated
water was below the EPA interim
maximum limit of 0.1 mg/l for drinking
water. Significant losses of volatile
organics took place in the basins
themselves. Some compounds were
significantly attenuated in the soil-
aquifer system whereas others were
not. More systematic studies of the
organics are planned for the future,
including the effect that chlorination of
the effluent in the treatment plant will
have on the trace organics in the
effluent and their fate in the soil-aquifer
system.
Conclusions
The results of the 23rd Avenue
Project showed that large-scale renova-
tion of conventionally treated sewage
effluent by rapid-infiltration systems
and recovery of renovated water from
wells within the project are feasible.
Since most of the cost of renovating the
effluent with such a system is in
pumping the water from the wells,
renovating municipal wastewater by
soil-aquifer treatment also is cost
effective. The renovated water is
suitable for unrestricted irrigation and
for recreational lakes with primary-
contact activities. The renovated water
could also be used for drinking after
further treatment, including activated
carbon adsorption, ozonation and/or
reverse osmosis. Advanced treatment
of sewage effluent after it has gone first
through a soil-aquifer system could be
much cheaper and effective than
advanced treatment of the plant effl uent
directly.
U5 SOVEnNMENTPRINTINBOFFICE 18K-559-017/0836
-------
Herman Bouwer, R. C. Rice, J. C. Lance, and R. G. Gilbert are with the U.S.
Department of Agriculture, SEA, Phoenix, AZ 85040.
Carl G. Enfield is the EPA Project Officer (see below).
The complete report, entitled "Rapid-Infiltration System for Wastewater Renova-
tion and Beneficial Reuse." (Order No. PB 82-252 941; Cost: $13.50, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
P. 0. Box 1198
Ada, OK 74820
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
Pb 0000329
U S ENVJK PRuTtCIIUN
RtCaON 5 LIBRAKY
230 S DEAKttuRN STREEi
CHICAGO IL t.0604
------- |