Introduction

1
Q
Use of a Pilot Plant Sequencing Batch Reactor for
the Treatment of Shrimp Aquaculture Wastewater
C. Lyles, Q. Fontenot, M. Kilgen, and R. Boopathy
Nicholls State University, Thibodaux, LA 70310,
USA.
Introduction  One of the main issues for
intensive inland recirculating culture systems is
the accumulation and disposal of sludge. Besides
the cost of sludge disposal, usable water and
salt is lost through sludge disposal. Previous
work has shown that sequencing batch reactor
(SBR) is effective at removing nitrogen and
carbon from sludge, so that water and salt can be
safely returned to the culture system (Boopathy
et al. 2005, Boopathy et al. 2007, Fontenot et
al. 2007). Sequencing batch reactor (SBR)
incorporates alternating aerobic and anaerobic
periods to achieve nitrification and
denitrification in a single container (Figure 1).
Naturally occurring microbes associated with the
sludge are responsible for the nitrification and
denitirification process (Figure 2). Time is
needed at the end of the sequence to allow the
sludge to settle so that surface water can be
decanted. The carbon and nitrogen composition
of sludge from shrimp aquaculture operations
depends largely on the feed used. Microbial
degradation of any waste depends on the amount of
carbon, nitrogen, and phosphorus available for
their activity. If there is too little nitrogen
present, the bacteria will be unable to produce
necessary enzymes to utilize the carbon. If
there is too much nitrogen, particularly in the
form of ammonia, it can inhibit the growth of the
bacteria. Previous work involving treatment of
wastewater consisted of multiple bench top
studies (Boopathy et al. 2005, Boopathy et al.
2007, Fontenot et al. 2007). This study evaluated
a pilot scale SBR at the Waddell Mariculture
Center (WMC), SC, and the Gulf Coast Research
Laboratory (GCRL), MS. Nitrogen removal by SBR
was compare to a control tank that remained
unaerated for the study duration.
Discussion SBR appears to be a viable option for
treating wastewater produced by intensive
recirculating shrimp culture systems. Results of
this study are not as obvious as previous studies
(Boopathy et al. 2005 Boopathy et al. 2007
Fontenot et al. 2007). Initial ammonia, nitrite,
and nitrate concentrations were lower than
previous treatment studies (Boopathy et al. 2005
Boopathy et al. 2007 Fontenot et al. 2007).
Both the WMC and GCRL has just started their
culture system for the season and the necessary
microbes may not have been established. High
levels of nitrite may have been caused by partial
denitrification. Because the culture system had
just been started for the season, the microbial
community responsible for denitrification may
have been limited. The most promising results
occurred when the SBR was operated anaerobic
first (Figure 6). This may have allowed the
denitrifying bacteria to become more established
and reduce some of the initial nitrite before
ammonia denitrification. More work needs to be
conducted at the pilot scale. Future studies
will include work with a more mature sludge
source. Microbial isolates from an active SBR
will be identified to determine the more
important species.
Figure 2. Illustration of the aerobic - anaerobic
sequence used for a sequencing batch reactor
during the react stage
Acknowledgements This work was supported by the
funds from the U.S. Department of Agriculture,
Cooperative State Research Service United States
Marine Shrimp Farming Program. Heidi Atwood
(WMC) and John Ogle (GCRL) provided assistance
for this project.
Methods Experiments were conducted at the Waddell
Mariculture Center (WMC), SC, and and the Gulf
Coast Research Laboratory (GCRL), MS. The WMC
operates a 228,000 L intensive recirculating
shrimp culture raceway. Solids are removed via
backflushing a bead filter approximately 227 L
per backwash. Backwash was pumped into two
12,545 L round fiberglass holding tanks (Figure
3). One tank was left unaerated and the other
was operated as a SBR. The SBR sequence was
aerobic 2 days, anaerobic 3 days, and aerobic 2
days for a 7 day cycle. Aeration was provided by
forcing air through submerged airstones. The
purpose of this experiment was to compare SBR
treatment to an unaerated treatment. This
experiment was conducted twice, however only one
replicate was obtained for days 7 and 8. GCRL
operates 12 raceways within a single greenhouse
for intensive shrimp culture and solids are
removed via individual settling cones. Solids
are gravity fed to one of two central round 500 L
fiberglass collection tanks. Each collection
tank is located within a separate greenhouse (SG1
and SG2). Within each greenhouse are 4
additional 300 L fiberglass round tanks that can
be operated as a SBR. Two experiments involving
different aeration sequences were conducted at
GCRL. For the first experiment, the wastewater
in the SG1 collection tank was continuously
aerated before transfer to SBR and control tanks.
The wastewater in the SG2 greenhouse was not
aerated prior to transfer to the SBR and control
tanks. This design resulted in four treatments
SBRPreaerated, SBRNotpreaerated,
ControlPreaerated, ControlNotpreaerated. The
SBR sequence was aerobic 2 days, anaerobic 3
days, aerobic 2 days, and settle one day for an 8
day cycle. Each treatment was duplicated. A
third experiment involved manipulating the
aerobic-anaerobic sequence at GCRL. SBR tanks
were run anaerobically the first three days and
then aerobically for the last four days of a
seven day sequence. The control tank was run
anaerobiclly for the duration of the experiment.
As with the second experiment, one holding tank
was pre-aerated prior to transfer to experimental
tanks and the other holding tank was not
pre-aerated. However, data from samples taken
from the pre-aerated and not pre-aerated holding
tank was pooled within the SBR (N2) and control
(N2) treatments. To determine ammonia, nitrite,
and nitrate concentrations (mg/L), 30 mL of
sample was taken from each tank, centrifuged at
5,000 rpm for 10 min and the supernatant was
analyzed colorimetrically with a Hach water
analysis kit and spectrophotometer. Data were
subject to analysis of variance (alpha 0.05)
followed by Tukeys post hoc analysis if necessary.
References Boopathy, R., C. Bonvillain, Q.
Fontenot, and M. Kilgen. 2007. Biological
Treatment Of Low-Salinity Shrimp Aquaculture
Wastewater using Sequencing Batch Reactor.
International Journal of Biodeterioration and
Biodegradation 5916-19. Fontenot, Q.C., C.P.
Bonvillain, M.B. Kilgen, and R. Boopathy. 2007.
Effects of Temperature, Salinity, and
CarbonNitrogen Ratio on Sequencing Batch Reactor
Treatment of Recirculating Intensive Aquaculture
Wastewater. Bioresource Technology
981700-1703. Boopathy, R., Q. C. Fontenot, and
M. B. Kilgen. 2005. Biological Treatment of
Shrimp Wastewater with Sequencing Batch Reactor.
Journal of the World Aquaculture Society
36542-545.
Results Initial nitrogen levels were relatively
low for the WMC experiment. By day 6 of the WMC
experiments, ammonia and nitrate were lower in
the SBR than the control tank however, there was
no difference between the two treatments for
nitrite (Figure 4). Nitrite levels increased for
the SBR and control treatment for the duration of
the experiment (Figure 4). Aeration of the
wastewater at the GCRL previous to SBR treatment
reduced ammonia and nitrite levels (Figure 5).
Although ammonia and nitrate levels were
generally lower in the SBR than the control tanks
by the end of the experiment, there was no
difference between the treatments for nitrite
(Figure 5). Ammonia, nitrite, and nitrate were
lower in the SBR than the control tanks by the
end of the third experiment (Figure 6). Variance
was greater for the control tank than for the
SBR.