A combined aquaculture/agriculture system that brings together the three major components of a Controlled Ecological Life Support System (CELSS) - biomass production, biomass processing, and waste recycling - was developed to evaluate ecological processes and hardware requirements necessary to assess the feasibility of and define design criteria for integration into the Kennedy Space Center (KSC) Breadboard Project. The system consists of a 1 square meter plant growth area, a 500 liter fish culture tank, and computerized monitoring and control hardware. Nutrients in the hydrophonic solution were derived from fish metabolites and fish food leachate. In five months of continuous operation, 27.0 kg of lettuce tops, 39.9 kg of roots and biofilm, and 6.6 kg of fish (wet weights) were produced with 12.7 kg of fish food input. Based on dry weights, a biomass conversion index of 0.52 was achieved. A nitrogen budget was derived to determine partitioning of nitrogen within various compartments of the system. Accumulating nitrogen in the hypoponic solution indicated a need to enlarge the plant growth area, potentially increasing the biomass production and improving the biomass conversion index

Hall, C. R.

Owens, L. P.

English

NASA Technical Reports Server

N91"81789
BIOMASS PRODUCTION AND NITROGEN DYNAMICS IN AN
INTEGRATED AQUACULTURE/AGRICULTURE SYSTEM
L.P. Owens and C.R. Hall. The Bionetics Corp.; NASA, Biomedical
Operations and Research Office, Kennedy Space Center, FL.
A combined aquaculture/agriculture system that brings together
the three major components of a Controlled Ecological Life
Support System (CELSS) - biomass production, biomass processing,
and waste recycling, was developed to evaluate ecological
processes and hardware requirements necessary to assess
feasibility of and define design criteria for integration into
the KSC Breadboard Project. The system consists of a 1 m 2 plant
growth area, a 500 liter fish culture tank, and computerized
monitoring and control hardware. Nutrients in the hydroponic
solution were derived from fish metabolites and fish food
leachate. In five months of continuous operation, 27.0 kg of
lettuce (Lactuca sativa cv. Waldmann's Green) tops, 39.9 kg of
roots and biofilm, and 6.6 kg of fish (tilapia, Oreochromis
aureus), wet weights, were produced with 12.7 kg of fish food
input. Based on dry weights, a biomass conversion index of 0.52
was achieved. A nitrogen budget was derived to determine
partitioning of nitrogen within various compartments of the
system. Accumulating nitrogen in the hydroponic solution
indicated a need to enlarge the plant growth area, potentially
increasing biomass production and improving the biomass
conversion index. A computer simulation model is being developed
to project production potentials and define data needs for more
effective management of the system.
INTRODUCTION
One objective of CELSS research is the development of
systems that recycle inedible waste into high quality edible
biomass. The concept of recycling mass for the purpose of
optimizing secondary production of edible food stuffs and
minimizing waste has been the subject of several investigations
utilizing combined aquaculture/hydroponic systems. Zweig(1),
Serfling and Mendola(2), Pierce(3) and Bender(4) reported on
"soft technology" systems suitable for home use, that produced
265
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high quality vegetables and fish protein while effectively
utilizing space, nutrients and water. These systems generally
consisted of a fish culture tank, a vegetable growing area and in
some cases a biological filtration system for the microbial
conversion of ammonia (NH4) to nitrites (NO2) and nitrates (NO3).
The systems were designed primarily for use in greenhouse
environments in temperate climates. The use of hydroponic
systems to prevent the accumulation of nitrate nitrogen and
orthophosphorus in recirculated water in fish culture systems was
evaluated by Lewis et al(5) who found acceptable water quality
could be maintained by allowing plant growth to serve as a sink
for undesirable levels of nutrients. McMurtry et al(6) found
that the integration of fish culture, biological filtration, and
hydroponic vegetable culture was an economical way to
commercially produce bush bean, cucumber, tomato, and tilapia.
Development of secondary production combined aquaculture/
hydroponic systems in CELSS would optimize energy and materials
utilization, provide resiliency and stability, and maximize the
use of available space. Fish were selected as candidates for
secondary producers in CELSS for the following reasons. They
occupy a low position in the food chain, are a good source of
high quality animal protein, and can be cultured in nutrient
solution tanks already in use. Tilapia (Oreochromis aureus) were
chosen because they are tolerant to extremes in water quality,
resistant to disease, and fast growing, reaching a harvestable
266
size in 6 months (7). This species of tilapia is also
omnivorous, easy to handle, and populations are readily
manageable in controlled environments (7).
As part of ongoing CELSS research, system scale-up and
integration, we designed a combined aquaculture/agriculture
system that incorporated the three major components of CELSS -
biomass production, biomass processing, and waste processing. In
this system biomass production included fish, higher plants, and
algae. Biomass processing based on the incorporation of inedible
plant biomass, fish processing waste, biomass conversion
by-products, and table scraps into a fish diet is being
evaluated. This system will potentially allow for waste
management by the use of condensate and gray water, control of
oxygen and carbon dioxide balance, and the recycling of nutrient
solution.
One goal of this research was to quantify the biomass
production potential of fish, lettuce, and biofilm (organic
matter and attached microbial community). Other objectives were
to describe the partitioning of nitrogen between system
compartments, evaluate the response of biological components, and
develop a computer simulation model of nutrient dynamics and
biomass production. A computer monitoring and control system was
designed and system hardware and software were also tested and
evaluated during this study.
267
MATERIALS AND METHODS
The integrated system consisted of a 500 liter conical
bottom fish culture tank and a 1 m 2 plant growing area. Thirty
various sized (27-144g) tilapia were stocked at the beginning of
the study. Twenty additional fish were stocked after 28 days to
give a total fish biomass of 4.9 kg at that time. Plans are to
operate the system at the CELSS Breadboard Project scale of one
person. This stocking density should provide three filets per
week. A commercial fish chow was fed at the rate of 2% body
weight per day divided into three feedings. Every 2 weeks fish
were weighed to monitor growth and adjust feeding rate.
Lettuce (Lactuca sativa, cv. Waldmann's Green) was planted
on six polyvinyl chloride (PVC) pipes which were 2 inches in
diameter and 1.5 m long. Plants were spaced 15 cm apart, 9-10
plants per pipe. The lettuce was planted and harvested
approximately every 7 days.
Water from the fish culture tank was pumped through the PVC
pipe where it served as the nutrient solution for the plants.
Lettuce roots were in direct contact with the solution where they
functioned as a biofilter substrate for bacterial colonization,
allowing for nitrification of ammonia. Free ammonia (NH3) is
toxic to fish (8), therefore the biofilter component is important
in this system. Solution flow through each PVC pipe ranged
between 0.5 and 1.5 L/min. Water samples were collected weekly
from the tank for chemical analyses. Parameters monitored
included pH, conductivity, macronutrients, micronutrients,
268
ammonia, total kjeldahl nitrogen, total suspended solids and
total organic carbon. Light was provided by three high pressure
sodium (HPS) lamps which produced an average photosynthetic
photon flux (PPF) of 245 umol s -I m -2, with an 18 hours on and 6
hours off photoperiod. Air temperature over the plant canopy was
ambient, averaging 29.2 ± 2.1 °C. Relative humidity was
controlled at 65% and tank water temperature was 24.1 ± 1.4 °C.
Solution pH was controlled at a maximum of 6.2 units and averaged
5.8 ± 0.5 units. Dissolved oxygen was measured daily and
remained at 6.6 ± 0.6 ppm.
At the start of the study the nutrient solution was one
quarter strength Hoagland's and was replenished twice during the
next two weeks until the fish food leachate and fish metabolites
provided enough plant nutrients. Total minerals added during the
first two weeks of the study, exclusive of fish feed were as
follows:
Element
N
P
K
Ca
Mg
S
Fe
Mn
Zn
Cu
B
Mo
m__
7.35
1.09
8.19
7.00
1.68
2.24
4 34
0 031
0 0031
0 0012
0 033
0 00062
269
After the second replenishment, the addition of nutrients to the
solution was totally through fish feed wastes and fish
metabolites.
A simulation model was developed to examine biomass
production and nutrient dynamics. The model diagram was drawn
using energy circuit language symbols (9). Programming was
conducted with Lotus 1-2-3 (i0).
RESULTS AND DISCUSSION
After 5 months of continuous operation the system produced
27.0 kg of lettuce tops, 39.9 kg of roots and biofilm, and 6.6 kg
of fish on a wet weight basis. During this 5 month period 12.7
kg of feed was added. This resulted in a biomass conversion
index, based on dry weights, of 0.52. The partitioning of
nitrogen added to the system over the 5 month period is described
in Figure i. Fish tissue incorporated 35.2% of the nitrogen
while lettuce tops contained 7.9%, and the roots and biofilm
accounted for 12.5%. The nutrient solution retained 35.5% of the
nitrogen. Loss of nitrogen gas through denitrification and from
ammonia volatilization, in addition to unquantified biofilm
inside system plumbing was believed to account for the remaining
8.9%.
Figure 2 shows the behavior of NO3, NO2, and NH 4 in the
solution over time. A dramatic increase in NH 4 and NO 3 occurred
after the addition of 20 fish on day 28. The relationship
between ammonium ion (NH4 +) and free ammonia is pH dependent
(Ii). In order to keep the NH 3 below toxic levels we maintained
27O
the solution pH below 7.0. Ammoniumand NO3 increased at equal
rates until about day 84, after which time NH4 levels fell and
NO3 continued to rise, suggesting the development of an adequate
community of nitrifying bacteria. Nitrite, the end product of
the first stage of nitrification, stabilized after a small peak
around day 28 which coincided with the addition of fish.
Preliminary work on a biomass production model of the system
is shown in Figure 3 which depicts the producer module with its
lettuce storage, the consumer module with fish storage, and the
biofilm with attached microbes. Results of the simulation run
depicted in Figure 4a show production in the system over a i00
day period. Lettuce tops and roots were harvested every 7 days
along with the attached biofilm. Fish biomass was shown to
increase steadily at a rate that was similar to the observed
growth. Since the plant area and production rate were held
constant and fish were growing and being fed more, the biofilm
compartment increases rapidly around day 85. Based on
observaton, fish wastes and waste feed which compose the
substrate for the biological film began to accumulate not only on
the roots but also as suspended solids in the tank. Figure 4b
shows a simulation where the lettuce biomass on the system was
doubled which allowed it to run ii0 days before the biofilm began
its rapid increase. The increase in the biofilm component was
slowed by the additional harvest of lettuce roots and biofilm.
The response of fish biomass to biweekly harvest can be seen in
this simulation. Fish production with harvest remains fairly
constant.
271
CONCLUSIONSANDRECOMMENDATIONS
After 5 months of system operation it was concluded that
nitrogen accumulated in the solution, and therefore the plant
growth area needs to be increased. This concept was also
supported in the simulation model runs. A larger plant growth
area should allow for more production and better biofiltration.
Fish growth rates and productivity should also increase with
improved water quality resulting from better filtration, and by
operating the system at a higher temperature. In addition,
system improvements such as oxygen injection and foam
fractionation to remove organics, bioloqical oxygen demand (BOD),
and solids could also improve production. The simulation model
will continue to be developed and tested and used for system
management. The revised model will incorporate not only biomass
but also energy, and nutrient dynamics.
272
LITERATURE CITED
1.
2 •
3o
4.
5.
6.
7 •
8.
9 •
I0.
Ii.
Zweig, R. D. 1986. An integrated fish culture hydroponic
vegetable production system. Aquaculture., May/June,34-40.
Serfling, S. and Mendola, D. 1978.
controlled environment ecosytems.
Farmer., pp. 15-18.
Aquaculture using
The Commercial Fish
Pierce, B. A. 1980. Water reuse aquaculture systems in two
solar greenhouses in northern Vermont. Proc. World Maricul.
S.c., 11,118-127.
Bender, J. 1984. An integrated system of aquaculture,
vegetable production and solar heating in an urban
environment. Aquacultural Engineering., 3,141-152.
Lewis, W. M., Yopp, J. H., Schramm, Jr., H. L., and
Brandenburg, A. M. 1978. Use of hydroponics to maintain
quality of recirculated water in a fish culture system.
Trans. Am. Fish. S,c., 107(1), 92-99.
McMurtry, M. R., Nelson, P. V., and Sanders, D. C. 1987.
Personal communication. North Carolina State university,
Raleigh, N. C.
Pullin, R. S. V. and Lowe-McConnell, R. H., Eds. 1982. The
biology and culture of tilapias. Proceedings of the Inter-
national Conference on the Biology and Culture of Tilapias,
2-5 September 1980. ICLARM, Manila.
Spotte, S. 1979. Fish and invertebrate culture. John
Wiley and Sons, Inc., New York. pp. 112-114.
Odum, H. T. 1983. Systems ecology: An introduction. John
Wiley and Sons, Inc., New York. pp. 7-8.
Lotus Development Corporation.
2.01.
1986. Lotus 1-2-3. Release
Sawyer, C. N. and McCarty, P. L. 1978. Chemistry for
environmental engineering. 3rd Ed. McGraw-Hill, Inc., New
York. p. 445.
273
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277



Biomass production and nitrogen dynamics in an integrated aquaculture/agriculture system

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