Gone with the Wind: Effects on Nitrogen Removal in Soil Receiving Wastewater
Laboratory of Soil Ecology and Microbiology, University of Rhode Island
Faith Anderson
• Jen Cooper, PhD
• Jose Amador, PhD – Principal Investigator
• Costal Fellows Program
• URI Honors Program
• RI Agricultural Experiment Station
• NE Onsite Wastewater Training Center
Acknowledgments
Outline
1. The Nitrogen (N) problem • Environmental effects
2. N removal in septic systems • Types and mechanisms
3. Linn & Doran (1984) revisited • Accounting for wastewater
4. Experiment #1 • N2O production from wastewater
5. Experiment #2 • 15N tracer
6. Experiment #3 • Factors limiting N2O production
Why Linn & Doran (1984)? • Study cited frequently • Many regulations have been based
on this study • Have we been applying their results
wrongly?
• N is not well removed from septic systems
• 9 kg per household per year is released into the groundwater
The Nitrogen Problem
Environmental Health
Human Health
The Resulting Problems
Last Chance to Remove N…
…In the soil
…In the drainfield…
1. Primary Treatment 2. Drainfield
WATER TABLE
Conventional System
1. Primary treatment
2. Secondary treatment
4. Controls - timers 3. Shallow Drainfield Advanced System
Septic tank effluent (STE) Sand-filtered effluent (SFE)
Septic tank effluent (STE)
NH4
+NO3- (N2O) N2O N2
Nitrification Denitrification (aerobic) (anaerobic)
- Requirements for Denitrification:
- Nitrate - Low or no oxygen - Organic C source
- Anaerobic conditions can be created by a low dissolved oxygen (DO) water (i.e. wastewater) and/or high soil moisture
Nitrification and Denitrification
- Requirements for Nitrification: - Ammonium - High oxygen
Water Table
Nitrogen (N)
Denitrification
NH4+
NO3-
Nitrification
Nitrifying bacteria O2
Denitrifying bacteria
O2 C
N2O N2
NO3-
Controls on N Removal
Type of water Type of soil Level of soil saturation
High
Low
Fine
Coarse Carbon-Poor
Carbon-Rich
Water-Filled Pore Space (WFPS)
• WFPS = percentage of soil pore space filled with water • More water less space for O2 • More water less diffusion of O2 (not easily diffusible in water)
• Linn and Doran (1984) has informed current understanding of WFPS and how it affects N removal.
Here’s What We Know…
• Linn and Doran (1984) used clean water and agricultural/surface soil horizon.
• Wastewater has organic C and varying amounts of N and O2.
• Wastewater is not dispersed in soil surface.
How Does This Apply to Wastewater?
Water Type
DO (mg/L)
BOD (mg/L)
Total N (mg/L)
NH4+
(mg/L)
NO3-
(mg/L) Septic Tank Effluent 0 200 84 47 0
Sand-Filtered Effluent 2 2 53 6 51
Deionized Water 8 0 0 0 0
How does N removal respond to changes in WFPS when we use wastewater?
The Question
Experiment #1: N2O production from wastewater
1. Optimum WFPS for denitrification will be lower for STE and even lower for SFE relative to deionized water. 2. The optimum WFPS for denitrification will be different in fine versus coarse soil.
Hypotheses:
Microcosms
Two Kinds of Soil: Fine and Coarse Three Kinds of Water: 1. Septic Tank Effluent (STE) (0 mg DO/L) 2. Sand-Filtered Effluent (SFE) (3 mg DO/L) 3. Deionized (DI) water (8 mg DO/L) Ten WFPS: 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%
SFE + Soil DI + Soil STE + Soil
Experiment #1: N2O production from wastewater
Step 2: Add preliminary amount of DI water to all microcosms and incubate for 1 week
B or C B or C B or C
Step 1: Fill microcosms with 1 cm of soil done for both the B and C horizon
B or C + DI B or C + DI B or C + DI
Step 3: Add STE, SFE, or DI in varying amounts to produce 10 different WFPS ranging from 10-100%
Step 4: Fit with a septa and allow to incubate for 1 hour. Sample gases after incubation period.
SFE + Soil DI + Soil STE + Soil
N2O N2O N2O
Effects of Water Type and Soil Texture
0.0 0.2 0.4 0.6 0.8 1.0
N 2O (
L/L)
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
B horizonC horizon
DI
0.0 0.2 0.4 0.6 0.8 1.0
N 2O (
L/L)
0
5
10
15
20
25
30
B horizonC horizon
SFE
0.0 0.2 0.4 0.6 0.8 1.0
N 2O (
L/L)
-0.20
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
B horizonC horizon
STE
WFPS
N2O
(μL/
L)
N2O
(μL/
L)
N2O
(μL/
L)
WFPS WFPS
Normalized Values
WFPS
0.0 0.2 0.4 0.6 0.8 1.0
N2O
(L/
L/m
L)
-1.6-1.4-1.2-1.0-0.8-0.6-0.4-0.20.00.2
B horizonC horizon
DI
WFPS
0.0 0.2 0.4 0.6 0.8 1.0
N2O
(L/
L/m
L)0
2
4
6
8
10
12
14
16B horizonC horizon
SFE
WFPS
0.0 0.2 0.4 0.6 0.8 1.0
N 2O (
L/L/
mL)
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
B horizonC horizon
STE
N2O
(μL/
L/m
L)
N2O
(μL/
L/m
L)
N2O
(μL/
L/m
L)
1. Optimum WFPS for denitrification will be lower for STE and even lower for SFE relative to deionized water.
2. The optimum WFPS for denitrification will be different in fine versus coarse soil.
Take Home from 1st Experiment
REJECT
SUPPORT
• Why we used it: - Most of N not lost to N2O,
instead it’s lost as N2 Cooper et al. (2016)
- Since N2 is the main
product of denitrification – we decided to measure it using an 15N tracer.
Experiment #2: 15N Tracer
Experiment #2 : 15N Tracer
B or C
Water + 15NH4Cl
B or C B or C O2
15NH415NO3 15NO3
15N2O
Sample Gases
15N2O 15N2
15N Results B vs. C Horizon
WFPS
0.0 0.2 0.4 0.6 0.8 1.0
15N
2 (
g/vi
al/m
L)
0
2
4
6
8
10
12
14
16
15N
2O (p
g/vi
al/m
L)
0
50
100
150
200
250
300
350
15N215N2O
DI waterC horizon
WFPS
0.0 0.2 0.4 0.6 0.8 1.0
15N
2 ( g
/via
l/mL)
0
2
4
6
8
10
12
15N
2O (p
g/vi
al/m
L)
0
50
100
150
200
250
300
15N215N2O
SFEC horizon
WFPS
0.0 0.2 0.4 0.6 0.8 1.0
15N
2 ( g
/via
l/mL)
0
10
20
30
40
50
15N
2O (p
g/vi
al/m
L)
0
50
100
150
200
250
300
350
400
15N215N2O
SFEC horizon
WFPS
0.0 0.2 0.4 0.6 0.8 1.0
15N
2 (
g/vi
al/m
L)
0
2
4
6
8
10
15N
2O (p
g/vi
al/m
L)
0
20
40
60
80
100
120
140
160
15N215N2O
DI waterB horizon
WFPS
0.0 0.2 0.4 0.6 0.8 1.0
15N
2 ( g
/via
l/mL)
0
2
4
6
8
10
12
14
16
15N
2O (p
g/vi
al/m
L)
0
50
100
150
200
250
300
15N215N2O
SFEB horizon
WFPS
0.0 0.2 0.4 0.6 0.8 1.0
15N
2 ( g
/via
l/mL)
02468
101214161820
15N
2O (p
g/vi
al/m
L)
0
200
400
600
800
1000
15N215N2O
STEB horizon
15N
2(μg/vial/m
L)
15N
2(μg/vial/m
L)
15N
2(μg/vial/m
L)
15N
2(μg/vial/m
L)
15N
2(μg/vial/m
L)
15N
2(μg/vial/m
L)
NH4+NO3
- (N2O) N2O N2 Nitrification Denitrification
(aerobic) (anaerobic)
• If just denitrification, should see linear relationship between N2O and N2.
• If other processes are occurring, relationship will not be linear.
Nitrification and Denitrification
Relationship Between Nitrification and Denitrification
15N2O
0 50 100 150 200 250 300 350
15N
2
0
2
4
6
8
10
12
14
16DI waterC horizon
15N2O
0 50 100 150 200 250 300
15N
2
0
2
4
6
8
10
12SFEC horizon
15N2O
0 50 100150200250300350400
15N
2
0
10
20
30
40
50STEC horizon
15N2O
0 20 40 60 80 100120140160
15N
2
0
2
4
6
8
10DI waterB horizon
15N2O
0 50 100 150 200 250 300
15N
2
0
2
4
6
8
10
12
14
16SFEB horizon
15N2O
0 200 400 600 800 1000
15N
2
02468
10121416182022 STE
B horizon
• N2 gas production appears to be related to WFPS but it’s not as simple as Linn and Doran’s model.
• N2 gas production occurs even when the soil is very dry. • Both denitrification and other processes seem to contribute to N gas
production – depending on water and texture.
• Aerobic denitrification? • Robertson, L. A., T. Dalsgaard, N.-P. Revsbech, and J.G. Kuenen. 1995. Confirmation of 'aerobic denitrification' in batch
cultures, using gas chromatography and 15N mass spectrometry. FEMS Microbiol. Ecol. 18: 113-120.
Take Home from 2nd Experiment
Hypotheses:
1. The availability of organic C limits N2O production in soil amended with SFE.
2. Nitrate availability limits N2O production in soil amended with STE.
Experiment #3: Factors Limiting N2O Production
Water Type
DO (mg/L)
BOD (mg/L)
Total N (mg/L)
NH4+
(mg/L)
NO3-
(mg/L) Septic Tank Effluent 0 200 84 47 0
Sand-Filtered Effluent 2 2 53 6 51
Deionized Water 8 0 0 0 0
SFE + Acetate Addition
WFPS
0.0 0.2 0.4 0.6 0.8 1.0
N 2O (
L/L/
mL)
-2
0
2
4
6
8
10
12+ AcetateNo additions
N2O
(μL/
L/m
L)
STE + Nitrate Addition
WFPS
0.0 0.2 0.4 0.6 0.8 1.0
N2O
(L/
L/m
L)
-0.2
0.0
0.2
0.4
0.6
0.8
+NO3
No additionsN
2O (μ
L/L/
mL)
Take Home from 3rd Experiment
1. The availability of organic C limits N2O production
in soil amended with SFE. 1. Nitrate availability limits N2O production in soil
amended with STE.
REJECT
REJECT
• Does wastewater behave like Linn and Doran’s theory?
• Nitrogen gases produced at all WFPS?
• Do NO3- and C limit N2O production?
• Should we rethink the relationship between soil moisture
and N removal?
YES
Conclusion
NO
NO
YES