Transcript Document

418 Durham Hall
Virginia Tech
Blacksburg, VA 24061
David Kuhn, Ph.D. Student
Dr. Gregory D. Boardman
Recycle of Nutrients in Wastewater Effluent to Sustain Fish Polyculture
Department of Civil & Environmental
Engineering
Background
email: [email protected]
Discussion
Methods/Analysis
ve 1Overfishing
methods: Twelve
37fisheries
liter (L)isaquaria
used to test tilapia effluent supplemented with various salts/ions versus a seawater control. Shrimp survival/growth were monitored.
Four independent
42 day trials
were used
Fish effluent
can be responsible
for negative
cashto colle
of natural
a globalwith
issueRAS
that were
is
flowsspecific
for producers,
using
shrimp
a “cash
crop” ra
moreflocs
urgent
the humansupplemental
population increases
tobecoming
test biomass
asasa potential
feed for shrimp culture. Biomass flocs were produced in 37 liter aerobic bioreactors as tilapia effluent was treated. Shrimp survival rates,
growth but
rates
(SGRs),
andasfood
conversion
exponentially. According to the FAO, over 70% of the
in the effluent is potentially an option that might
encing batch reactors (SBRs) are currently being used to determine the treatability of the tilapia effluent and how to best recycle nutrients into biomass (microbial floc) proteins. Kinetic modeling, substrate supplementation, and microbial flo
world’s seafood species are fully exploited or depleted.
enable the operation to be environmentally sustainable.
5 L aquaria systems
This high demand for seafood protein is not going away.
Results from objective 1 are encouraging because
In fact, an astonishing one out of five people depend on
Findings/Results
marine shrimp can be cultured in freshwater tilapia
this source of protein. To meet the growing demand for
Water
quality during
this study
was within
safe levels
between
treatmentsion
for supplementation
objectives 1 andand
2.
effluent
with minimum
seafood,
aquaculture
(the farming
of aquatic
organisms)
is and no differences (P > 0.05) between shrimp treatments were observed for dissolved oxygen, nitrite, pH, ammonia, and temperature
compromising
survival
growth
compared
on1the
rise andResults
reportedly
the fastest
growing
sector ofthat marine shrimp can be cultured in freshwater tilapia effluent with sufficient ion supplementation; 0.6 g/L synthetic without
tive
results:
from
this study
indicated
sea salt,
50 mg/L Ca2+
(CaO),orand
30 mg/L
Mg2+to(Mg
shrimp reared in sea water. The requirement of Ca2+
agriculture worldwide. Traditional aquacultural practices
and Mg2+ supplementation are not surprising, given
use pond and flow-through systems which are often
responsible for discharging pollutants (e.g. nutrients and
that shrimp exoskeletons are largely composed of these
solids) into the environment. Furthermore, aquacultural
cations. Culturing shrimp in fish effluent maximizes
feeds often contain high levels of fish or seafood protein,
the reuse of a waste stream that would have been
so the demand on wild fisheries is not completely eased.
normally discharged to the environment.
Even though traditional aquaculture has these drawbacks,
Evidence that shrimp can utilize microbial flocs
there is a significant movement towards more sustainable
generated in bioreactors used to treat the tilapia
practices, especially in developed countries. For example,
effluent (objective 2) is extremely encouraging. This
recirculating aquaculture systems (RAS) are being used to
alternative source of nutrition could reduce the demand
maximize the reuse of water; and, alternative proteins
(e.g., soy bean) are replacing fish and seafood proteins in
for commercial shrimp feed. Consequently, less
aquaculture diets.
fishmeal would be required, thereby easing the
pressures on wild fisheries.
Objective 1: Determine ion supplementation
requirements to sustain marine shrimp culture in
freshwater tilapia effluent.
Objective 2: Determine if shrimp can utilize
microbial flocs generated in bioreactors as a
supplemental feed (e.g., alternative source of
protein). Microbial flocs are generated through
the biological treatment of the tilapia effluent.
Objective 3: Characterize the biological
treatability of fish effluent and the capacity of
the treatment system to recycle nutrients in the
effluent for shrimp feed.
This table presents correlation values (P-values in parenthesis) between shrimp survival/growth and ion concentrations. Correlation values range from no
correlation 0 to perfectly correlated 1.0 or -1.0. Lower P-values denotes more significance, * denotes P < 0.05 and ** denotes P < 0.01.
Objective 2 results: Results from this study
demonstrated that microbial flocs generated
in bioreactors, and offered as a supplemental
feed, significantly (P < 0.05) improved shrimp
growth and SGRs in shrimp fed a restricted
ration of commercial shrimp feed.
Implications
Culturing marine shrimp in fish effluent could
potentially reduce water use, reduce the discharge
volume of aquacultural wastewaters to receiving
streams, serve as a model for the treatment of fish
farm effluent, help a fish farm expand into
polyculture while creating job opportunities, and offer
a sustainable option for the culture of shrimp.
Objective 3 results: This project is currently
underway. The following kinetic coefficients are
reported for treating the effluent with carbon
supplementation (sugar): operating biomass
concentration 1,380±150 (mg biomass)/(L),
observed yield 0.71±0.05 (g biomass)/(g soluble
COD), soluble COD uptake rate 9.1±0.8 (mg
soluble carbon/L)/(min), and biomass generation
rate 6.3±0.9 (mg biomass/L)/(min). Organic
content of the microbial flocs generated include,
organic matter 89±1% and Kjeldahl protein
content 54±1% on a dry weight basis.
Results from objective 3 are promising. Even though
carbon input (to increase C:N ratios) is required to
generate a healthy population of biomass, nitrogenous
constituents in the effluent are recycled into bacterial
protein which will be offered a supplemental feed to
shrimp. Carbon is relatively inexpensive compared to
protein. High values for observed yield, carbon uptake
rate, biomass generation rate, organic matter content,
and Kjeldahl protein content are being noted and are a
reflection of high efficiencies in terms of nutrient
recycling. For example, microbial flocs contain > 50%
protein and shrimp feeds typically contain 35-40%
protein.
Doctoral student, David
Kuhn, examining the health
of an adult shrimp.
Objectives
Acknowledgements
We would like to thank Dr. George Flick, Dr. Steven Craig, Dr. Ewen
McLean, Dr. Lori Marsh, and Peter Van Wyk for their research
advisement and support.
This figure demonstrates the growth of shrimp fed various diets over 35 days. Shrimp fed diet three
(6% body weight of shrimp feed per day with microbial flocs significantly outperformed other diets
(P < 0.05), even diet one in which shrimp were fed higher rates of shrimp feed but without flocs.
Three 4 L sequencing batch reactors in a water bath
maintained at 28±0.3 oC outfitted with a programmable
electronic controller, power head pumps, control valves,
float switches, air flow meters, air manifolds, solenoid
valves, and peristaltic pumps.
We would also like to thank Blue Ridge Aquaculture (Martinsville,
VA) for providing logistical support.
This project is funded by USDA-CSREES.