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Nitrogen Transformations in Aquaponic Systems
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Transcript of Nitrogen Transformations in Aquaponic Systems
Nitrogen Transformations
in Aquaponic SystemsSamir Kumar Khanal, University of Hawaii at ManoaKartik Chandran, Columbia UniversityClyde Tamaru, University of Hawaii at ManoaHye-Ji Kim, Purdue University
USDA-AFRI PD Meeting, Washington, D.C., October 12-13, 2016
What is aquaponics?Aquaponics is a soilless system in which recirculating aquaculture is integrated with a hydroponic system.
N2O
3
Research objectives
1. Quantify the impact of physical and chemical variables on nitrogen transformations in an aquaponic system.
2. Evaluate the transformations of different forms of nitrogen in an aquaponic system under different conditions.
3. Examine the ecology of functionally important living species and assess microbial contributions to nitrogen transformations in an aquaponic system.
4. Investigate the greenhouse gases emissions from an aquaponic system, with particular emphasis on nitrous oxide (N2O) emission.
4
Pak choi Lettuce
Tilapia
5
Tomato Chive
2-stage biofilter (20 L)
Aquaponic system
pH was controlled in a range of 6.8-7.2 by adding Ca(OH)2 and KOH solution.
Two -stage biofilterGrow bed
Fish tankAir
supply
Feed
Down-flow with partial
aeration
Up-flow
Sediment
Fish tank (330 L)
Grow bed (300 L)
DO in fish tank was about 6-7 mg/L.
7
0.004.00
8.0012.00
16.0021.00
25.0029.00
33.0037.00
2
4
6
8HLR 1.0 m/d
Fish tankBiofilters (outlet)Grow bed (outlet)
Day
DO (m
g/L)
0.004.00
8.0012.00
16.0021.00
25.0029.00
33.0037.00
2
4
6
8HLR 1.5 m/d
Fish tankBiofilters (outlet)Grow bed (outlet)
Day
DO (m
g/L)
0 7 14 21 28 352
4
6
8HLR 2.0 m/d
Fish tankBiofilters (outlet)Grow bed (outlet)
Days
DO (m
g/L)
0 7 14 21 28 352
4
6
8HLR 2.5m/d
Fish tankBiofilters (outlet)Grow bed (outlet)
DaysDO
(mg/
L)
DO dropped significantly in biofilters, due to sediment accumulations
0 7 14 21 28 352345678
HLR 2.0 m/d
Fish tankBiofilters (outlet)Grow bed (outlet)
Days
DO (m
g/L)
0 7 14 21 28 352
4
6
8
HLR 1.5 m/d
Fish tankBiofilters (outlet)Grow bed (outlet)
Days
DO (m
g/L)
Significantly different (Growbed outlet)
Not significantly different
Not significantly different
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Feed Fish
Fece
s
Sedi
men
t
NO3-
Wat
er
Root
s
NO3-
Root
s
Stem
s
NO3-
Stem
s
Leav
es
NO3-
Leav
es
Frui
ts
NO3-
Frui
ts0.05.0
10.015.020.025.030.035.0
Pak choiLettuceChiveTomato
δ15N
(‰)
Natural abundance δ15N of bulk nitrogen and NO3-
Σ (N x δ15N)before = Σ (N x δ15N)after
- Assimilation and redox pathways were identified by the isotopic fractionations. However, The results were isotopically impossible. There should be at least one output that has δ15N below the δ15N value of the feed (< 5.2 ‰) (Robinson, 2001).
- Gaseous nitrogen loss via denitrification caused the δ15N of gas loss below 5.2 ‰.
fN.Mf = (CTAN + CNO2-N + CNO3-N + Corg-N)V + Nveg/T + Nfish/T + Nsed/T + Nloss/TMass balance:
Isotopic mass balance:
0 3 6 9 1217.017.518.018.519.019.520.020.5
Days
δ15N
(‰)
DO affected denitrification and nitrogen loss via denitrification
Low DO
High DO
0 3 6 9 1215.016.017.018.019.020.021.022.023.0
Days
δ15N
(‰)
Actual
No feeding
No denitrification
Note:1. Denitrification caused the enrichment in 15N and increase in δ15N of nitrate.2. Feed lowered δ15N of nitrate during denitrification , but denitrification was identified.
ParametersConditions
Feed 25g/d Feed 20 g/d Feed 15 g/d1.5 m/d 1.0 m/d 1.5 m/d 0.25 m/d 1.5 m/d 0.5 m/d
TKN (mgN/L) 8.2 (2.9)* 10.6 (2.7) 9.4 (0.8) 8.9 (0.9) 10.3 (1.4) 11.5 (0.9)
TAN (mgN/L) 0.69 (0.37)
1.10 (0.29)
0.52 (0.16)
0.59 (0.15)
0.69 (0.09)
0.89 (0.10)
NO2- (mgN/L) 0.155
(0.061)0.255
(0.087)0.303
(0.052)+0.616
(0.161)+0.227
(0.062)0.284
(0.054)NO3
-
accumulation rate
(mgN/L/d)
0.723 (0.129)
0.534 (0.074)
0.814 (0.011)
0.996 (0.173)
0.905 (0.080)
0.897 (0.056)
COD (mg/L) 89.0 (8.5) 91.3 (6.4) 58.6 (4.0) 65.2 (4.5) 61.6 (4.3) 64.2 (4.2)
This is mean value of 15 samples; *represents standard deviation and + represents significant difference. Statistical analyses of the collected data were carried out using an analysis of variance (one-way ANOVA) at a confidence level of α = 0.05
Nitrite oxidation rate dropped at low HLR (below 0.25 m/d), but ammonia oxidation was still active
HLR (< 0.1 m/d) decreased TAN oxidation rates
HLR (< 0.25 m/d) decreased nitrite oxidation rates
0 7 14 21 280.0
0.1
0.2
0.3
0.1 m/d1.5 m/d
Days
NO
2- (m
g N
/L)
0 7 14 21 280.0
0.2
0.4
0.6
0.25 m/d1.5 m/d
Days
NO
2- (m
g N
/L)
0 7 14 21 280.00.20.40.60.81.01.21.41.61.8
0.1 m/d1.5 m/d
Days
TAN
(mg
N/L
)
0 7 14 21 280.00.20.40.60.81.01.21.41.61.8
0.25 m/d1.5 m/d
Days
TAN
(mg
N/L
)
Not significant differentSignificant different
Significant different Significant different
pH (<6.0) decreased TAN oxidation rates. pH 5.2 inhibited TAN oxidation
At low pH (<6.0), decrease in TAN oxidation rate caused the accumulation of TAN and lowered nitrite substrate in nitrite oxidation. This does not mean nitrite oxidation was improved at low pH.
0 7 14 21 28 350
1
1
pH 5.2pH 6.8
Days
TAN
(mg
N/L
)
0 7 14 21 28 350123456
pH 6.0pH 6.8
Days
TAN
(mg
N/L
)
0 7 14 21 28 350.0
0.1
0.2
0.3
0.4
pH 5.2pH 6.8
Days
NO
2- (m
g N
/L)
0 7 14 21 28 350.0
0.1
0.2
0.3
0.4
pH 6.0pH 6.8
Days
NO
2- (m
g N
/L)
Significant different
Significant differentSignificant different
Significant different
0 5 10 15 20 25 30 35 40130
140
150
160
170
180
Days
NO
3- (m
g N
/L)
weekly drained
monthly drained
Sediment draining improved NO3- accumulation and reduced N loss in aquaponics
0 15 30 45 60 75 900
50
100
150
200
ChiveLettucePak choiTomato
Days
Nitr
ate
conc
entr
ation
(m
gN/L
)
Nitrate accumulation/consumption for different plant species in aquaponicsTwo -stage biofilterGrow bed
Fish tankAir
supply
Feed
Down-flow with partial
aeration
Up-flow
Sediment
Root system
Root surface area Pak choi Lettuce Chive Tomato
cm2/plant 724(251)
474(109)
227(104)
6.01 x 104
(1.71 x 104)
This is mean value of 24 samples; *represents standard deviation
Pak choi Lettuce Chive Tomato
15
First month (NO3- accumulation)
16
Third month (NO3- depletion)
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Nitrite Oxidation
Nitrogen loss (denitrification)
Nitrate accumulation& depletion rate
DO
Plant NUE
Feed consumption
Feed Feed DO
DO ≤ 3.5 mg/L
Balance input and output
HLR ≤ 0.25 m/d
DO ≤ 3 mg/L
TANOxidation
TANAccumulation
pH ≤ 6.0pH ≤ 5.2
Redu
ced
N lo
ss
HLR ≤0.1 m/d
Balance between input and outputs
Plant species
Tomato > Lettuce & Pak choi > Chive
pH DrainingHLR
Objective #1: Impact of physical and chemical variables
Increase nitrate
accumulation
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Pak choi Lettuce Chive Tomato Input Input20%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Nitrate inputFish feedN lossPlant biomassNitrate accumulatedSedimentFish biomass
Contribution of nitrogen products by mass balance in aquaponic systems, operated at HLR of 1.5 m/d, feeding rate of 35 g/d and high DO (~7 mg/L).
- NO3- accumulation served as nitrogen output (NO3
- uptake rate < NO3- generation rate) and
nitrogen input (NO3- uptake rate > NO3
- generation rate).- Nitrogen loss was found in aquaponic systems.
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TAN Nitrite
NitrateN2O & N2
(N loss)
Org N in fish
Org N in sediment
Org N in plants
Fish
Nitrate accumulation
Feed
DO
Plant species
pH
HLR
Objective #2 Transformations of different forms of nitrogen
Output
Parameters affecting N transformations
Other N forms
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Feed Fish
Fece
s
Sedi
men
t
NO3-
Wat
er
Root
s
NO3-
Root
s
Stem
s
NO3-
Stem
s
Leav
es
NO3-
Leav
es
Frui
ts
NO3-
Frui
ts0.05.0
10.015.020.025.030.035.0
Pak choiLettuceChiveTomato
δ15N
(‰)
3. Ecology of functionally important living species
• Nitrate reductase could occur in the plant organs and the nitrate reduction occurs after the translocation from recirculating water to leaves (Black et al., 2002).
• High efflux of NO3- occurred in the root zone of plants, and NO3
- concentration exceeded the plant requirements (Evans, 2001); resulting to the accumulation of NO3
-.
• This nitrate in recirculating water could subsequently cause the high nitrogen loss via denitrification by nitrifiers (Ryabenko, 2013).
• Microbial results are still required to support the ecology and microbial contributions to nitrogen transformations.
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Nitrifying bacteria
Types of rootPak choi Lettuce Chive Tomato
EU bacteria 7.57 x 109 2.91 x 1011 1.96 x 1010 2.32 x 1010
Nitrobacter spp. 7.02 x 106 4.09 x 106 6.88 x 106 8.84 x 106
Nitrospira spp. 1.16 x 109 7.74 x 108 9.70 x 108 3.22 x 109
Abundances of bacteria in different root systems(Condition: HLR 1.5 m/d and pH 6.8)
(unit: copies).
High relative abundances of EU bacteria over Nitrobacter spp. and Nitrospira spp. suggested the high abundance of denitrifiers, which contributed to nitrogen loss in aquaponic systems.
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Nitrifying bacteria
Tomato-based aquaponics Pak choi-based aquaponicsRoot surface Water Root surface Water
AOB 3.97 ± 1.18x 1011
6.85 ± 0.85x 108
8.67 ± 0.71x 1010
3.26 ± 0.79x 109
NOBNitrobacter spp.
4.13 ± 0.27x 1012
4.49 ± 1.57x 108
7.39 ± 0.26x 1011
2.47 ± 0.05x 1011
Nitrospira spp. 1.31 ± 0.06x 1011
3.66 ± 0.65x 108
3.59 ± 0.15x 1010
4.55 ± 0.08x 109
Abundance of nitrifying bacteria in different aquaponics
(unit: copies)
Higher NUE were obtained in tomato-based aquaponics, due to higher abundance of nitrifying bacteria on root surface.
(Hu et al., 2015)
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4. Nitrous oxide (N2O) emission from fish tanks
Aquaponic types N2O emission (mgN/d)
N2O conversion (%) References
Tomato-based aquaponics 58.3 (14.9) 1.5 (Hu et al., 2015)
Pak choi-based aquaponics 72.5 (13.2) 1.9 (Hu et al., 2015)
Chive-based aquaponics 29.6 (0.4) 1.2 Our study
Tomato-based aquaponics 17.2 (7.7) 0.7 Our study
Aquaponics without plants 11.9 (10.2) 0.5 Our study
We found that higher N2O emission from biofilters than that in the fish tanks.
* denotes standard deviation
24
Summary• The NO3
- accumulation in recirculating water occurred when NO3- exceeded
the amount that the plants could utilize. NO3- depletion suggested the
insufficient nitrogen input.
• When the NO3- accumulation occurs, reducing the feeding rate can increase
NUE and decrease the denitrification in the systems.
• The growth of plants was dependent on HLR of 0.25 to 2.5 m/d; however, NO2
- and TAN oxidizing rates were significantly dropped at HLR of 0.25 m/d and 0.10 m/d, respectively.
• Low pH (< 5.2) inhibited ammonia oxidation, leading to TAN accumulation.
• The nitrogen mass balance and the isotopic mass balance suggested that denitrification, affected by DO at the inlet of biofilters, was the major factor of nitrogen loss in the floating-raft aquaponic systems.
• To reduce the nitrogen loss in aquaponic systems, higher rate of sediment draining and higher plant-to-fish ratio are recommended.
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On-going research
3. Examine the ecology of functionally important living species and assess microbial contributions to nitrogen transformations in an aquaponic system
4. Investigate the greenhouse gases emissions from an aquaponic system, with particular emphasis on nitrous oxide (N2O) emission
• Quantitative polymerase chain reaction (qPCR) targeting:
• Eubacteria, ammonia monooxygenase subunit A (amoA), Anaerobic ammonia oxidizing bacteria (AMX), Nitrospira spp., Nitrospira spp. and Nitrobacter spp.
• 16S rRNA
• Measurement of N2O emissions from aquaponic systems
• Development of strategies to minimize N2O emission
2. Evaluate the transformations of different forms of nitrogen in an aquaponic system under different conditions
• Labeling isotope study using ammonium 15N sulfate
Student training/Extension/Dissemination activities • One Ph.D., one undergraduate and three high school students
have been trained.• Aquaponic facility tour for farmers, students from Environ.
Science, Nagasaki University (Japan) and staffs from Kapiolani Community College (Hawaii).
Symposium:Wongkiew, S. and Khanal. S.K. “Nitrogen transformations in floating-raft aquaponic systems”, Poster presentation, 28th Annual CTAHR Symposium, University of Hawaii at Manoa, April 8th, 2016. BEST POSTER AWARD.Publications: • Wongkiew, S., Hu, Z., Chandran, K., Lee, J.W., and Khanal, S.K.
Nitrogen transformations in aquaponic systems: A review. Aquacultural Engineering (submitted).
• Wongkiew, S., Popp, B.N., Kim, H.J., and Khanal, S.K. Nitrogen transformations in aquaponics: evaluation of physical and chemical factors (ready for submission).
27
Acknowledgments
• Ryan Kurasaki• Bradley Kai Fox, Mari’s Gardens
• This project is being supported by Agriculture and Food Research Initiative Competitive Grant no. 2013-67019-21376 from the USDA National Institute of Food and Agriculture.