United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
Research and Development
EPA-600/S2-83-067 Oct. 1983
v>ERA Project Summary
Wastewater Treatment with
Plants in Nutrient Films
W. J. Jewell, J. J. Madras, W. W. Clarkson. H. DeLancey-Pompe, and R. M.
Kabrick
The nutrient film technique (NFT) is
a unique modification of a hydroponic
plant growth system which utilizes
plants growing on an impermeable
surface. A thin film of water flowing
through the extensive root system
provides nutrients for plants and
associated microbial growth. Root
masses up to 15 cm thick or more have
been obtained. This self-generating
plant system could be used as a fitter to
immobilize and use the gross and trace
organics in wastewater. The goal of this
study was to determine the economic.
technical, and practical feasibility of
using plants grown in the NFT system
as pollution control systems.
NFT systems appear capable of
providing secondary quality treatment
with some nutrient removal on a
relatively small area compared to
overland flow systems. At loading rates
of 10 cm per day the effluent quality
with primary settled sewage was often
less than 10 mg/l for suspended solids
and biochemical oxygen demand. The
influent sewage temperature was 9°C.
Estimated area needs of an NFT system
designed for BOD and SS removal
appear to be approximately 3 hectares
for a community of 10,000 people,
whereas up to 10 times this amount
may be needed to provide nutrient
control.
' This EPA-sponsored study was par-
tially supported by the Office of Water
Resources and Technology. U.S. De-
partment of the Interior.
This Project Summary was developed
for 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
The use of plants in wastewater
treatment has most often been limited to
slow rate land treatment and the use of
nuisance plants of limited value in
hydroponic systems. A simple advanced
hydroponic system referred to as the
"Nutrient Film Technique" (NFT) enables
all species of plants to be considered for
use in water pollution control systems.
There is increasing interest in the use
of low-cost natural systems that have
existing or built-in pollution control
mechanisms. This project focuses on a
new plant production system that could
lead to new ways of treating wastewater
and water supplies with a solar-powered
pollution control system that could have a
number of useful and valuable by-
products. The main goal of this study was
to:
determine the feasibility of using plants
as pollutant-concentrating, pollutant
assimilating, and nutrient-recycling
facilities in a unique hydroponic system
utilizing the Nutrient Film Technique.
The five specific objectives were to:
1. define advantages of using plants
in the Nutrient Film Technique
system over conventional systems
to collect, concentrate, and assimi-
late pollutants;
2. identify research and development
needs to support a long-term
program to define the full potential
of the Nutrient Film Technique
system as a pollutant management/
resource recovery system;
3. define the engineering require-
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ments to establish a total plant-
based pollutant control system.
This will include area requirements,
hardware, plants and plant produc-
tion system;
4. gather baseline data on system
performance using energy and
mass balance to support econo-
metric data; and
5. determine the feasibility of re-
covering energy, food, and nu-
trients from the plant material.
Design parameters were developed
based on hydraulics and removal of
nutrients, organics, trace organics and
cadmium. Plant selection and manage-
ment methods were investigated and are
described. Finally, the potential evapo-
transpiration (ET) and actual ET and
recovery of ET are discussed.
NFT Basic Concept
The NFT version of hydroponics utilizes
plants grown directly on an impermeable
surface to which a thin film of water is
continuously applied (see Figure 1). The
root production on this impermeable
surface will result in a large mass of roots
and accumulated matter with a large
surface area. Root masses have been
observed to accumulate up to 30 cm deep,
separate from the stalk and fruit. Virtually
all plants tested have been found to grow
well in this system. The hypothesis here
is that these large masses of self-
generating root systems can be used as
living filters. Plant top growth also
provides nutrient uptake, shade for
Plant
Grow Block
protection from algae, and water removal
in the form of transpiration. Sludge that
would settle in the root filter would be
held in place by the roots, and the filter
itself would gradually expand as the
sludge accumulated and occupied more
space. After removal of organics and
suspended solids, the remaining refrac-
tory soluble organics, nutrients, and
remaining toxic elements would continue
to pass through the fine root filter. Since
high flow rates are possible in the
absence of large amounts of suspended
and organic matter, subsequent loading
rates would be related to the sorption
rates of critical wastewater constituents
such as nutrients. This general interaction
of pollutants, plants and water lead to the
following hypothesized wastewater treat-
ment system.
The hypothesized system would be
composed of three distinct sections, with
plant characteristics dependent upon the
pollutant removals required:
1. Roughing or preliminary treatment:
plant species with large root
systems capable of surviving and
growing in a grossly polluted
condition. Large sludge accumula-
tions, anaerobic conditions, and
trace metal precipitation and en-
trapment would characterize this
section. A large portion of the
BOD5 and SS would be removed in
this section.
2. Nutrient conversion and recovery: an
active nutrient uptake, high bio-
mass and/or food production
Nutrient
Solution
Nutrient System
(Continuous Flow)
Roots
~ s _-<£ f S "*^y^^ f f *^
r I * / f /"~J^ Capillary Pad
Purified * Water \ T
Figure 1. The nutrient film technique variation of hydroponic plant production systems.
2
section would follow the first
section. The major interaction here
would be nutrient conversions, but
suspended solids and trace organic
removals would improve.
3. Water polishing: the third section
would be a polishing section that
would necessarily have nutrient-
limited plant production, depending
on the required effluent water
quality.
A schematic of the three-plant series
wastewater treatment system, showing
the major pollution control functions and
the by-products produced in each section,
is presented in Figure 2.
Obviously, the three modules in the
NFT treatment system can also be used
separately for different levels of treatment
of varying input water quality.
Conclusions and
Recommendations
The Nutrient Film Technique (NFT) has
been shown to be a viable alternative for
domestic sewage treatment in this 3-year
multidisciplinary effort. Pilot scale units
up to 36 meters long have been operated
continuously with domestic sewage at
flow rates of up to 11,000 l/d (3000 gpd)
in New York and New Hampshire. Data
presented here should be considered
conservative since most experiments
were conducted under "worst case"
climate and temperature conditions. No
attempt was made to control the plant
environments during most of the testing.
The general approach of this study was
to choose one plant species to demon-
strate the concept, and then to test a wide
range of species under conditions that
would lead to the definition of process
controlling parameters. Reed canary
grass was selected as the main test
species that could accomplish all phases
of treatment (i.e., roughing treatment
through nutrient polishing). Wetland
plants and commercially valuable plants,
such as ornamental roses, were ultimately
tested. Reed canary grass grown in the
NFT system from seed and from trans-
planted sod resulted in the production of
better than secondary effluent quality at
an application of 10 cm/day of settled
domestic sewage and synthetic waste-
water applications throughout the year.
Application rates at 20 cm/day were
found to result in the destruction of the
reed canary grass. Attempts to optimize
multiple species systems that could exist
in low dissolved oxygen environments
eliminated the 20 cm/d limitation.
Example data for a 36-meter long unit
for synthetic wastewater are shown in
Figure 3. Note that the higher loading
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Waste-1
Water
Lagoon Preapplication Treatment
or
Equalization &
Emergency Storage
Preliminary Treatment
i
• Functions:
Screenings
Outputs
Plant Series 1
P
Plant
roducts
Plant Products
Stable ^
X Sludge &
Root
Material \
Plant Series II
Suspended Solids Nitrogen and
and Organic Phosphorus and
Removal Potassium Removal
Plant Products
\
Plant Series III
Polishing of
Soluble Organics
Suspended Solids.
Nutrients and
Toxic Elements
Discharge
Water Rec.
Figure 2. Schematic diagram showing three-stage hypothesized NFTtreatment system for domestic wastewater with functions for each stage and
fate of all materials.
rates tested are equivalent to a system
area required to treat sewage generated by
10,000 people to secondary level of less
than 2 ha.
The suspended solids removal capability
was one of the most efficient character-
istics of the NFT. Even at high loading
rates the turbidity of the effluents were
low and the suspended solids less than
10mg/l.
After some of the removal mechanisms
were defined, a small optimized unit was
constructed and operated for a short time
on raw domestic sewage (unsettled
sewage). Optimized operation included
rapid batch addition of the sewage
followed by slow withdrawal and a brief
resting phase to encourage aeration. The
following represents typical results
obtained at a loading rate of 30 cm/d
(equivalent to a land area requirement of
1.3 ha to treat the sewage from 10,000
people):
Influent
Quality
Total COD, mg/l
TSS, mg/l
TKN. mg/l
320
140
40
Effluent
Quality
92
15
17
Removal Mechanisms
This study was able to define some of
the general pollutant removal mechan-
isms. By accumulating large quantities
of biomass in the form of fine roots, the
possibility of removing pollutants is
greatly enhanced. The solids entrapped in
the roots provide the largest capability of
§'
400 -
300 -
200 -
700 -
Condition 3 Condition 4
Figure 3. Influent and effluent chemical oxygen demand for the Cornell NFT treating
synthetic wastewater in spring, 1981. Conditions correspond to areal loadings of
6.9. 10.2, 20.3. and 40.6 centimeters per day, respectively, for a 36 m long unit.
this treatment system. Measurements of
the solids within the roots indicated that
over 1,000 gm/m2 of entrapped solids
were accumulated. These solids represent
significant potential for manipulation of
pollutant cycles. If, for example, this
biological organic material can be utilized
for pollutant removal, then the solids
retention time becomes important. In
such operations, reasonably high loading
rates result in solids retention times of
greater than 100 days. This indicates that
the process could be stable and provides
an efficient treatment system.
Organic removals are limited by the
level of aeration. The capillary mat of
dense root systems may significantly
increase aeration. The use of plants such
as cattails that translocate air to their
roots could also be a significant factor.
Additional studies are needed in this
area.
The fine suspended solids were found
to biocoagulate in the system, and high
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clarity effluent was achieved under high
loading rates.
A major goal of this study was to
manipulate the nitrogen cycle using both
plants and microbial interactions via
nitrrfication-denitrification. Nitrification
was rarely observed during the study and
produced only 2 or 3 mg/l of nitrate-
nitrogen under the lowest loading
condition during the warmer time periods.
This lack of nitrification resulted in
limited capability for control of the
nitrogen cycle with the NFT.
Phosphorous removal appeared to be
limited by the plant nutrition requirements.
Due to the stress condition of most of the
testing that occurred, phosphorous
removal rates were low in the NFT
system.
The energy that is contained in domestic
sewage is likely to provide enough heat to
maintain plant cultures in the NFT in most
areas of the U.S. where low cost solar
greenhouses can be utilized. In some
locations the greenhouse cover of the
NFT system may be minimized due to this
available energy.
The kinetics of pollutant removal was
examined using several different ap-
proaches. Due to the large number of
variables, no comprehensive model was
established that would predict the
process efficiency. The following rates
indicate the range of observed nutrient
and organic removals that were obtained
in the system:
Removal Rate
Parameter kg/ha-d
BOD
TOO
COD
SS
N
P
44-166
26-97
99-247
17-164
2.8-12.7
0.4-1.8
Both heavy metal and organic toxic
materials were examined in this system.
Cadmium was added to the synthetic
wastewater tested. Trace organics were
added to the domestic sewage in the New
Hampshire test facility. It is proposed that
the removal mechanisms for the metals
and the organics were the extensive root
surface area and the large accumulated
biomass. Between 91 and 98 percent of
the following trace organics were removed:
chloroform, tetrachlorethylene, benzene,
toluene, trichloroethylene, xylene, bro-
moform, M-nitrotoluene, PCB 1248.
Kinetic Analysis
An attempt was made to define the
relationship of hydraulic loading rates
and hydraulic retention time within the
root zone. Due to the large number of
factors that affected the plants and the
flow through the system, only general
comments can be made.
The most promising empirical approach
provided by the kinetic analysis of data
indicated that the loading rate/effluent
quality relationships would hold over a
limited range for domestic sewage. These
relationships will be of limited value in
designing the NFT system for other
wastewaters.
This study attempted to conduct
parallel testing with actual domestic
sewage and a synthetic sewage. Parallel
comparison of these systems indicated
that it was possible to simulate the
domestic sewage systems with the syn-
thetic wastewaters. Since the synthetic
sewage contained soluble substrates
only, it was not possible tosimulate solids
behavior or interactions with the syn-
thetic sewage.
Evapotranspiration Water
Recovery
The water balance was established for
a number of bench scale and pilot tests.
Although in many circumstances the
expected loss of water through evapo-
transpiration was equal to literature
values of approximately 50,000 l/ha-day,
several test conditions resulted in water
losses up to 100,000 l/ha-day. These
exceptionally high values of evapotrans-
piration represent a potential source of
high quality water.
The energy and process requirements to
recover evapotranspired water from the
greenhouse were examined. Energy
costs of ET recovery are extremely high
and prohibit this alternative unless a low
cost energy source is available. The
potential alternative that was identified
was the use of the temperature differen-
tial between the influent wastewater and
the greenhouse air.
NFT Plants for Sewage
Treatment
Although reed canary grass was
examined in the majority of tests in this
study, a wide range of plants was
cultured and propagated to examine their
viability in the NFT system when applied
to wastewater treatment. The following
summarizes those plants that grew well
and those that were less acceptable
under adverse conditions:
Plants
that Flourished
Plants
with Marginal Growth
Cattails
Bulrush
Strawflowers
Japanese millet
Roses
Napier grass
Marigolds
Wheat
Phragmites
Bristly sedge
Chrysanthemums
Carnations
Tomatoes
Comfrey
Reed canary grass
Soft rush
Cucumbers
The above list of plants includes some
that have high monetary value. Reed
canary grass, when grown under relatively
low nutrient conditions, resulted in
biomass with a total nitrogen content of 5
percent with most values greater than 4
percent. This indicates a total protein
content of greater than 30 percent of the
total dry weight in many cases and a plant
that would have a significant animal food
value. Plants with ornamental value such
as shrubs, trees, and roses would
represent plants with significant com-
mercial value. Other plants that showed
promise in this study were several food
plants that would be useful for propagation
purposes. Certain plants with a high
value, such as berry plants, could be
cultured in this system. The potential
carry-over of toxic materials would be a
concern with food products.
The growth of plants in sewage, where
the organic and suspended solids loading
rates are high, results in an optimum
condition for inhibition of plant yield and
pest invasions. The application of hearty
plants such as cattails in the roughing
sections of the NFT eliminated most of the
plant pathogen problems that were
observed; however, fungus invasions,
insect attack on many of the plants, and
other problems of greenhouse plant
production were common. All the prob-
lems were controlled when advice from
specialists was sought and implemented.
The destruction of a total treatment
system by pests or by contaminants in
wastewater is a concern that needs
careful evaluation prior to full scale
implementation.
Feasibility Considerations
This study outlines a new approach to
the use of plants as solar-powered water
and wastewater treatment devices.
The area requirements and necessity
for a greenhouse cover will vary depending
on the location of the system. An NFT
secondary treatment system is shown in
Figure 4. The area needs appear to be
approximately 2.7 ha (6.6 acres) for a
wastewater flow from a population of
10,000 people. This would be divided into
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two sections. The first section would be a
roughing section of approximately one
hectare. It would be subdivided into
relatively small sections so that the
wastewater could be rapidly introduced,
allowed to remain in a quiescent state for
approximately 1 hour, and then removed
slowly so that laminar flow conditions
would occur. The second section would
be a polishing and nutrient removal
section of about 2 ha. The capital
investment of such a system appears to
be attractive, and energy requirements
would be low since only low head
pumping would be required in such a
system. Although a detailed economic
analysis was not completed in this study,
it appears that the capital investment
would be less than conventional sec-
ondary treatment alternatives.
The application of the NFT for nutrient
removal is subject to the limitations of all
plant systems. Even with maximum
growth rates the nutrient removal rates
are relatively low in comparison to high
rate nutrient manipulation processes
such as microbial nitrification-denitri-
fication. However, partial nutrient polishing
could be achieved in NFT units of 10 ha or
larger for flow rates produced by 10,000
people.
The estimates for tertiary treatment or
water reclamation with the NFT indicate
area requirements that may not be
competitive with a conventional unit
process unless the plant products have a
commercial value. If plant management
techniques are achieved that allow plant
products to enter commercial markets,
the use of the NFT as a water reclamation
facility shows significant promise.
Preliminary
Treatment
Waste
Prim
.,
'
Solids
arv
* * t
1
» *
Roughing NFT «1
1 i i
,*,*,
0 ha') '
: : i
I
Sludge to
Treatment
* t t t J
Low Quality Biomass
Effluent Air
Scrubbed for
Odor Removal
• Aeration
NFT for
Treatment and
Nutrient Conversion
2 ha
(Area Available for
Commercial Plant Production
Approximately 1 ha)
-^ Useful Plant
Material
{Ornamental, Chemical,
or Animal Feed)
Solids
Disinfection
Effluent
Figure 4. Schematic of NFT treatment facility capable of treating domestic sewage from
10,000 people.
W. J. Jewell, J. J. Madras, W. W. Clarkson, H. DeLancey-Pompe, and P. M. Kabrick
are with Cornell University, Ithaca, NY 14853.
William R. Duffer andJ. L. Wltherow are the EPA Project Officers (see below).
The complete report, entitled "Wastewater Treatment with Plants in Nutrient
Films," (Order No. PB 83-247 494; Cost: $44.50, 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 Officers can be contacted at:
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
Ada. OK 74820
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
* U.S. GOVERNMENT PRINTING OFFICE: 1983-759-102/0770
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