United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-80-199 Mar. 1981
Project Summary
Production of Non-Food-Chain
Crops with Sewage Sludge
Lilia A. Abron-Robinson, Cecil Lue-Hing, Edward J. Martin, and David W. Lake
A beneficial use for sewage sludge?
This study investigated the feasibility
of using sewage sludge in cultivating
three non-food-chain crops currently
sold on the open market or with good
potential for marketability. A cost
analysis determined how cultivation
costs using sewage sludge compared
with costs using commercial fertilizer.
Cotton, sod, and energy biomass
trees were determined to have the
best potential for cultivation using
sewage sludge, based on the market
values and nutrient requirements for
each crop and on the hectares pres-
ently under cultivation for production
of these crops.
Results indicate that large quanti-
ties of sewage sludge can be used,
based solely on the nitrogen and
phosphorus requirements for the cul-
tivation of these crops. In addition,
although the total costs for fertiliza-
tion using commercial fertilizer are
less than the costs for using sewage
sludge, the latter would be viewed
more favorably if the municipality
generating the sludge bore the costs.
This Project Summary was devel-
oped by EPA's Municipal Environ-
mental Research Laboratory, Cincin-
nati. OH 45268. 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 sludge has historically been
viewed as a spent by-product of sewage
treatment. Recognition of the valuable
properties of sludge, including its high
concentrations of plant nutrients and
organic matter, has led to increasing
emphasis on its beneficial uses for re-
claiming disturbed lands and fertilizing
agricultural soils. The prospect of wide-
spread application on agricultural land
has, however, been accompanied by
concern over possible accumulations of
toxic substances in soils and potential
translocation of toxics throughout the
human food chain.
The purpose of this study was to
evaluate the feasibility and market
potential of land application of munic-
ipal sewage sludge in the cultivation of
non-food-chain crops (NFCC). Using
sludge in this manner would realize the
advantages of its beneficial properties
while circumventing the potential prob-
lems associated with the unknown
impacts of toxic materials on the human
food chain. This study entailed three
broad activities: (1) assessing the fertil-
izer value of sludge, (2) selecting NFCC
amenable to cultivation using sewage
sludge, and (3) determining land re-
quirements and costs associated with
producing NFCC using sludge and com-
paring these costs to the costs of pro-
ducing the same crops using commer-
cial fertilizer. The analyses were based
on data available in the literature or
obtained through personal interviews.
Fertilizer Value of Sludge
The nutrient content of municipal
sewage sludge was found to vary with
the composition of the influent waste-
water and the sewage and sludge treat-
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ment processes employed. Municipal
sludges were found to have a total
nitrogen (N) content of 1 % to 6%, a phos-
phorus (P) content of 1% to 6%, and a
potassium (K) content of 0.04% to 6.1 %.
Because of its low potassium levels,
sludge is generally not considered to be
a good source of this nutrient.
Based on mean sludge N, P, and K
values of 3.2%, 1.8%, and 0.3%, respec-
tively; on inorganic, N, P, and K prices of
$0.253/kg ($0.115/lb), $1.37/kg
($0.621/lb), and $0.259/kg
($0.1176/lb); and on a projected 1985
U.S. sludge production rate of 16,012
dry metric tons/day (17,650 dry
tons/day), the total daily sludge
produced in the United States has an
estimated chemical fertilizer equivalent
market value of $537,000 per day for
the year 1985 (based on 1980 dollars).
Other benefits of using sewage sludge,
such as improvements in tilth and water
holding capacity of soils, are difficult to
quantify. It is crucial also to consider
that using sewage sludge in place of or
as a supplement to chemical fertilizer
avoids or reduces the high energy costs
associated with both commercial fertil-
izer production and sludge incineration.
NFCC Amenable to Sewage-
Sludge Cultivation
The next step was to identify NFCC
and determine which of these are
amenable to cultivation using sewage
sludge. Food-chain crops are defined as
(1) tobacco; (2) crops grown for human
consumption; and (3) pasture, forage,
and feed grain for animals whose prod-
ucts are consumed by humans. NFCC
are, therefore, the crops that remain.
These crops were first identified using
the Standard Industrial Code (SIC), to
which were added research crops such
as jojoba, euphorbia, guayule, and bio-
mass crops. Cotton and soybeans were
also included because these crops have
significant inedible uses, both respond
favorably to commercial fertilization,
and cotton clearly has a high N demand.
The selection of NFCC feasible for
cultivation using sewage sludge was
based on a developed set of criteria. The
most important of these criteria were:
(1) the crop must not produce edible
matter that could easily become a part of
man's food chain; (2) the crop must have
a demonstrated or a high probability of
future market potential; (3) the land
used to raise the crop must have a high
probability of being continuously used
exclusively for production of that crop;
and (4) data must be available giving the
response of the crop to sludge, or suffi-
cient data must be available for similar
crops, to enable a probable response
determination using data extrapolation
and inference.
Six crop categories composed of 20
crops were studied in relation to the
above criteria: timber tracts (five hard-
wood and three softwood varieties);
forest nurseries; flax; horticultural
specialties (greenhouse varieties,
shrubs, sod and turf grasses, lawn
grasses); research crops (jojoba,
guayule, euphorbia, energy biomass
crops); and oil crops (cotton, soybeans).
Using sludge for cultivating hardwood
forests was deemed unacceptable
because hardwoods are best grown in
the open forest environment. These
sites are generally remote from sludge
generating centers and are only inter-
mittently accessible; also, the impacts
of sludge on the open forest
environment are poorly understood.
Furthermore, hardwoods have a slow
rotation period and low N and P
requirements. Flax was deleted
because the market for this crop is
declining and a reasonable possibility
exists that land used to raise this crop
could be used to grow food-chain-crops.
Of the research crops, all were rejected
except biomass crops because not
enough data were available to deter-
mine feasibility.
Based on the above criteria, crops
retained for further study included
monoculture timber tract operations
using softwood, forest nurseries, sod,
and energy biomass trees, and cotton
and soybeans. Of these, cotton, sod, and
biomass trees were selected for detailed
case study analysis. These three crops
are currently sold on the open market or,
in the case of biomass crops, are being
actively researched. Thus, information
was readily available describing the
preferential climatic condition for the
crop, nutrient requirements of the crop,
land required, and minimum size of a
city that could generate enough sludge
to support crop production.
Land Requirements and Costs
Given both the sludge quantities
generated and the land currently under
harvest for each crop in each state, the
following were determined: (1) the
maximum amount of land that could be
fertilized for each crop in each state,
constrained by either the amount of
sludge generated in that state or by the|
land currently harvested; (2) the unitf
costs (excluding land costs) of using
sludge to fertilize this land (by three
application modes—injection, surface
irrigation, truck spreading); and (3) the
unit costs of fertilizing this land using
custom application of commercial fertil-
izer. Application rates of sludge and
commercial fertilizer were calculated in
two different ways: rates needed to
satisfy crop nitrogen requirements and
rates needed to satisfy crop phosphorus
requirements. Aqueous ammonia
containing 30% NHa was used as the
basic source of commercial N; phos-
phorus pentoxide containing 40% P was
used as the basic source of commercial
P. The current cost of commercial fertil-
izer was determined from the chemical
marketing literature, and the costs of
transport and custom application were
based on information from companies
providing these services. The cost of the
sludge itself was taken as zero, and the
sludge transportation costs from the
centers of sludge generation to the
application sites were considered
separately.
Conclusions and
Recommendations |
The cost comparisons for sludge and
commercial fertilizer are compared in
Table 1 . Of the three sludge application
modes, injection is the most expensive
and truck spreading appears to be the
cheapest. Using sludge in lieu of com-
mercial fertilizer appears to be most cost
effective when applying sludge to
biomass crops via truck spreading and
surface irrigation at rates sufficient to
satisfy nitrogen requirements.
Research on the use of sewage as a
substitute for commercial fertilizers for
the production of biomass crops should
be encouraged.
Using sludge for sod production is the
most feasible beneficial sludge use
option at this time. Sod production
would conservatively use 5% to 10% of
the total sludge generated in the sod
producing states. As stated previously,
biomass crops are still in the research
stage. Although most of the cotton
being produced is used in part for food-
chain products, the possibility does exist
whereby a portion of this crop could be
grown for non-food-chain purposes
only.
It became evident from the case study
analysis of the three crops that all of the *
sewage sludge generated cannot be|
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Table 1. Cost Comparisons for Sludge Versus Commercial Fertilizer (Fertilizer Costs Include Both N and P)
Cotton
Average Total Annual Cost ($/ha)
Sod
Biomass
Application Mode
N(S)
P(S) Fertilizer' NfSJ P(S) Fertilizer' NfS)
P(SJ Fertilizer"
Injection
Surface
Irrigation
Truck Spreading
1,229 1,034 290 1,364 1,156
709 1,127 290 660 1,048
296 290 290 704 336
350 1,197
350
350
255
417
746
361
338
432
432
432
'All fertilizer costs are custom application.
used to produce NFCC. Based only on
the crops analyzed in this study, how-
ever, at least 20% of the sludge gener-
ated could be used for NFCC production.
This is significant. The problem of
generating more sludge than that
required for application raises other
concerns such as the need for storage
facilities and the need for other benefi-
cial sludge use options. These needs
should be addressed if the eventual
objective is to use and recycle sludge to
the greatest extent possible.
Transportation costs from the centers
of sludge generation to the application
site will have a significant impact on
cost. When transport costs are added to
the costs presented in Table 1, the dif-
ference between costs for sludge and
commercial fertilizer become even more
pronounced. Clearly, if sewage sludge is
to compete with commercial products,
the costs for the operation will have to
be borne by the municipality generating
the sludge. If the municipality were to
transport the sludge to the application
site and provide the application equip-
ment, the sludge would be a sought-
after commodity.
Lilia A. Abron-Ftobinson and Cecil Lue-Hing are with PEER Consultants, Inc.,
Rockville. MD 20852; Edward J. Martin and David W. Lake are with Environ-
mental Quality Systems, Inc., Rockville, MD 20852.
Gerald Stern is the EPA Project Officer (see below).
The complete report, entitled "Production of Non-Food-Chain Crops with
Sewage Sludge," (Order No. PB 81-125296; Cost$11.OO, 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:
Municipal Environmental Research Laboratory
U. S. Environmental Protection Agency
Cincinnati, OH 45268
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