11th International Drainage Symposium August 30-September 2, 2022 Des Moines, Iowa

1. The Danish concept for a targeted
differentiated and cost-effective
mitigation of nutrients in drainage
discharge
Charlotte Kjærgaard, PhD Environmental Engineering, NovaDraiN
ApS
11th International Drainage
Symposium August 30 – September 2,
2022
Des Moines, Iowa
2021 NovaDraiN ApS, Chief Scientist
2017 SEGES Innovation, Chief Scientist
2003 Aarhus University, Scientist/Senior Scientist
1999 Aalborg University, PhD Environmental Engineering
MSc. Environmental Chemistry, BSc Agricultural Science

2. © 2021 NovaDraiN Aps. All rights reserved
Take home message
A targeted drainage mitigation strategy can be the most cost-effective
solution for agricultural nutrient mitigation – allowing to balance water quality
protection with economically sustainable agriculture, but it requires:
(I) a systematic targeted mitigation approach and
(II) effective drainage filter technologies
This is a presentation of the Danish Concept

3. © 2021 NovaDraiN Aps. All rights reserved
Nutrient pollution – planetary boundaries exceeded
1
A nitrogen-fueled algae bloom in China's eastern Jiangsu province. LIU JIN/AFP/Getty Images
The planetary boundaries framework. Licenced under CC BY 4.0
(Credit: J. Lokrantz/Azote based on Steffen et al. 2015.)
…..focus on agriculture, which is responsible for about two-
thirds of global nitrogen pollution and main input of P.
Climate Change Will Worsen Algae and Dead Zones.
Scientists expect a 19% increase in the U.S.
Solutions to ensure food
production with simultaneous
protection of water quality is
urgently requested.

4. Agricultural nutrient
pollution – the Danish
challenge

5. © 2021 NovaDraiN Aps. All rights reserved
The Danish Challenge
• Large percentage of arable land (59%)
• >50% tile-drained
• Agriculture: 90% of the coastal N load and 29% of P load
• Drainage losses: >60% of N and 30% of P
Jung-Madsen et al. 2021. NOVANA. Tilstand og udvikling - faglig sammenfatning. Aarhus Universitet, DCE – Nationalt
Center for Miljø og Energi, 70 s. - Videnskabelig rapport nr. 478 http://dce2.au.dk/pub/SR478.pd
Water plans 2021-2027 (published by end of 2022)
• EU-WFD requires “Good ecological status” by 2027
• N reduction of minimum 6.900+13.100 ton/yr by 2027 (national
33% but >50% in some catchments)
• Significant P reductions
The challenge
• No changes in N and P load the last 12-20 years – despite
considerable effort
Phosphorus
(ton)
TN-loss
(kg
N/ha)
TN-load
(10
3
ton
N)

6. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
Houston, we have a problem…………
• 5 out of 109 coastal
waters
• 5 out of 985 lakes (P)
EU WFD requires “Good ecological status” by
2027

7. © 2021 NovaDraiN Aps. All rights reserved
Eriksen, Thomsen, Hoffmann, Hasler, Jacobsen (eds). 2020. Aarhus
Universitet. DCA rapport nr. 174
https://dcapub.au.dk/djfpdf/DCArapport174.pd
Danish mitigation measure catalogue 2020
Field/farm-based
measures
(existing measures)
Marine measures
(not approved
yet)
Drainage- and
riparian
measures
(some approved)

8. © 2021 NovaDraiN Aps. All rights reserved
Coastal N load (kg-N pr ha)
Total
cost
(DKK
pr.
ha)
Field-mitigation Field+ DFT
+40% Set-a-Side
+20% SS
+60% Set-a-Side
Ørum, J.E., Kjærgaard, C., Thomsen, I.K. 2017. IFRO Rapport nr.
258.
Danish economic consequences – 2027 target
• Costs increases to 3.500 DKK (470
USD)/ha/yr
• Set-a-side agricultural land >50%
• Economic loss for the secondary industry
• Critical for the Danish economy
2027 Target
There is a strong motivation to develop
and implement new cost-effective
drainage filter technologies
cost-effective
DFTs

9. A paradigm-shift in Danish
agro-environmental
regulation
From a uniform regulation towards a differentiated targeted and
cost-efficient regulation at catchment scale (<15 km2)
Agricultural Package,
2016

10. © 2021 NovaDraiN Aps. All rights reserved
I. Rootzone leaching (60 kg/ha)
N/
33 kg N/ha
60 kg N/ha
6 kg N/ha
Princip of a differentiated targeted cost-efficient N-mitigation
GW-red 90%
P-targets
II. Drainage N-fraction
N/
Surface water N-reduction
(10 or 90%)
Coastal N-load
0,6-54 kg-N/ha/yr
III. Groundwater N-reduction (<10-
100%) N/
IV. Surface water N-reduction (<10-
100%) N/

11. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
Cost-effective implementation of drainage filter technologies
1. Rootzone N-leaching (NLES) 3. Surface-water N-retention
Subsidy maps SF-CWs
2. Drainage fraction (soil maps)
Requirements for subsidy -> coastal N-effect of ≥300 kg-N/ha DFT/yr
DFT-effect -> local N-effect at field-scale
Kjaergaard & Børgesen. 2017. AU- DCA. J. nr. 2017-760-000042 Kjaergaard, Bach, Greve, Iversen, Børgesen. 2017. AU - DCA.

12. Drainage filter technologies
First generation of drainage filters (surface-flow constructed
wetlands) was approved in 2016 and implemented by farmers from
2017
Danish research in Drainage Filter Technologies was suggested in 2004 but not
initiated untill 2010 with the SupremeTech and iDRAIN projects (Kjaergaard et
al.).

13. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
Visions for the drainage mitigation strategy – keep it simple (cost-
effective)
II. Bufferzones
III. Drainage filters: Upland fields
I. Riparian lowlands
All rely on the same mechanisms for microbial NO3-N reduction and P-retention

14. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
I. Riparian lowlands: Disconnecting tile-drains at the hill-slope
Yearly mean N-removal: 45 ± 22 %
Yearly mean P-retention: -51 ± 49 %
Freshwater wetlands: 569 (7.460) km2

15. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
I. Riparian lowlands: Disconnecting tile-drains at the hill-slope
NO3-N 71%
TN 39%
NO3-N 25%
TN 1%
NO3-N 94% TN
56%
NO3-N 92%
TN 40%
Predicting N-effects is challenged by the local flow-pathway
• Type of flow determines NO3-N removal efficiency
• Hydraulic loading rate vs. infiltration capacity control parameter
• Export of org-N+NH4-N from peat counterbalance TN-effect
• A net in situ P-release from this area (66% of catchment P-loss)
Catchment 194 ha clay till
Riparian lowland: 26 ha peat
Petersen, Prinds, Jessen, Iversen, & Kjaergaard. 2020. Part
II. Water Resources Research, 56
Petersen, Prinds, Iversen, Engesgaard, Jessen, & Kjaergaard, C.
2020. Part I. Water Resources Research, 56

16. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
II. Bufferzone: Measures in test phase (not approved)
1% of drainage catchment
Surface-flow CW (SF-CW)
1% of drainage catchment (<25 ha), sloping terrain
Integrated bufferzones
Yearly mean N-removal: 45 ± 12 %
Yearly mean P-retention: 29 ± 60 %
Yearly N-removal: >50% NO3-N
Yearly P-retention: <0 to 87 %
Saturated bufferzone
ND% of drainage catchment (<25 ha), sloping terrain
HLR vs soil infiltration capacity critical for flow-path and efficiency
Hoffmann, Zak, Kronvang, Kjaergaard, Carstensen, Audet. 2020. Ecol. Eng. 155

17. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
III. Drainage filters: Constructed wetlands (approved measures)
Kjaergaard & Hoffmann,
2017.
Sedimentation
pond
Inlet
Inlet
Outle
t
Outlet
Principal sketch from Kjaergaard & Hoffmann,
2013
Surface-flow CWs (approved 2016)
1-1,5% of drainage catchment
Hoffmann, Larsen & Kjaergaard, 2019. J. Env. Quality 29
Subsurface-flow CWs /woodchips biofilters
(2018)
0,2-0,25% of drainage catchment

18. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
Surface-flow constructed wetlands (SF-CW)
0,78% of drainage catchment
38 ha field, 0,298 ha SF-CW
Photo: SEGES
N-effect: 1.007 kg N/ha/yr (28%)
P-effect: 31 kg p/ha/yr (47%)

19. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
III. Surface-flow CWs – importance of the shallow zone
The shallow zones are the primary drivers for the water mixing in the deep zones and the higher hydraulic
efficiency (λ)
Pugliese, Kusk, Iversen, Kjaergaard, 2020. Ecol. Eng. 144

20. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
Photo: Charlotte Kjaergaard
Surface-flow constructed wetlands (SF-CW)
1,1% of drainage catchment
75 ha field, 0,845 ha SF-CW
N-effect: 295 kg N/ha/yr (25%)
P-effect: 14 kg p/ha/yr (46%)

21. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
Surface-flow CWs - the major controlling parameters
• Large seasonal variations in HLR and temp.
• High HLR at low water temp. during the major
drainage season (winter months)
• Significant yearly variations

22. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
Surface-flow CWs – N-reduction efficiency
Red dotted line is the yearly flow-weighed average in the four years
• Large seasonal variations in N-
removal efficiency explained by temp.
and HLR
• Significant yearly variations in N-
removal efficiency explained by the
yearly drainage discharge distribution

23. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
Surface-flow CWs – seasonal N and P-effects
• Yearly mean N-removal efficiency for 17 Danish SF-CWs are 23± 10% (Kjaergaard, Pugliese, Hoffmann,
Iversen. 2022).
Average of four
year
Average of four year
• P-retention is controlled by P-loading rate and ratio between soluble and particulate P (Mendes et al., 2018a,
b).

24. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
Hoffmann, Larsen & Kjaergaard, 2019. J. Env. Quality 29
First experimental site
• First DK biofilters constructed in 2012
• 6 filterbeds 100 m2 and 1 m depth
• Willow woodchips:seashell ratios 25:70; 50:50
• 3 hydrological designs
Annual N effects (2013-2018)
• 45-64% N-removal
• Water temp. and HRT explained 84-90% of variation
in N-removal efficiency (bioreactor models)
Hoffmann, Larsen & Kjaergaard, 2019. JEQ
Annual P effects (2013-2018)
• Increasing <0 to 48% P-retention
• Net retention of PP
Carstensen, Larsen, Kjaergaard, Hoffmann, 2019. J. Env.
Manag.
III. Drainage filters: Subsurface-flow (SSF-CW) /biofilters

25. • Bioreactor N-models: NO3-N = c + aWT +bHRT
WT: water temp.; HRT: Hydraulic Residence
Time)
• Existing drainage discharge data from
representative catchmentsregions
Kjaergaard & Hoffmann, 2017
• Bioreactors temporary approved* in 2018
• National design guidelines, Hoffmann &
Kjaergaard, 2018
III. Subsurface-flow CWs – dimensions of woodchips based
biofilters
• Average N-removal efficiency vs.
biofilter:drainage catchment ratio
• A 50% N-removal efficiency requires a biofilter
of 0.2-0.25% of the drainage catchmentregions

26. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
Photo: SEGES
Bioreactor type approved* 2018
• Size: 0.2-0.25% (1 m deep) of
drainage catchment
• Storage pond optional
• Aerobic top layer (reduces CH4-gas
emissions)
• Re-oxygenation of effluent required
• By-pass during summer-flow to avid
sulphide and CH4 (effluent)
• Guidelines (Hoffmann & Kjaergaard,
2018)
IDraiN project (2011-2017)
Bioreactor constructed 2015
Drainage catchment ~25 ha
Bioreactor 220 m2 and 1 m deep
50-70% N-reduction
Drone photo: SEGES
Inlet
Outlet
III. Subsurface-flow CWs – biofilter with storage pond

27. © 2021 NovaDraiN Aps. All rights reserved
Full-scale woodchipsbased biofilter – implemented by a farmer
Drone photo: SEGES

28. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
Drainage filter technologies - summarizing
Area (%
of dw)
Yearly N-
red (%)
Yearly P-ret
(%)
N/P-removal rates
(kg/ha/yr)*
Potential negative
side-effects
Status
Disconnect
tile-drains
3-5 45±22 -51±49 N: 225-375
P: Risk
P-release, GHG,
DO-depl.
Approved
SF-CW 1-1.5 23±10 45±20 N: 575
P: 23
Effluent temp.,
GHG
Approved
SSF-CW
(biofilters)
0.2-0.25 50±13 12±4 N: 6.250
P: 30
GHG, DO-depl.,
”DOC-leaching”
Approved*
Integrated
buffers
~1 45±12 29±60 N: 1125
P: 15
Effluent temp.
GHG, DO-depl.
Test phase
Saturated
buffers
ND ND ND -
-
Test phase
* N/P removal rates are calculated from drainage loads of 25 kg-N/ha/yr and P loads of 0.5 kg-P/ha/yr for direct
comparison

29. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
Phosphorus drainage filters (on-going R&D)
I. Physical particle (PP) filters (suspended
particles)
• Lamella filters (30-50% particle removal)
• Dual porosity physical filters (on-going)
• Porous filter media (>60% removal new
project)
DK: Sediment concentrations of 0.05-0.5 g/L
II. Permeable porous soluble reactive P filters
• P-sorbing media (Fe, Al, Ca) in variable
constructions
• Focus P-affinity (rate) and P-capacity (life-time),
hydraulic properties
Clogging challenges hydraulic capacity and life-time
of porous filters -> require prior removal of
suspended particles
3 m3 crushed seashells (2-4 mm) with HLR at 5 L/s

30. Catchment scale mitigation
approach
Comparison of the effect and cost-efficiency of field-based
measures versus drainage filter technologies

31. Mitigation stategy and cost-efficiency
What is required to reach a N-reduction target of 2.594 kg/yr for a ID15 subcatchment?
Mitigation
measure
N-reduction
target
(kg N/yr)
N-effect
rootzone
(kg N/ha/yr)
N-effect on
coastal load
(kg N/ha/yr)
Required area
of measure
(ha)
Cost of
measure
(€/ha/yr)
Cost of mitigation
strategy (ID15)
€/yr
Catch crops 2.594 30 11.4 228 94 21.319
Set-aside 2.594 50 19.0 137 535 73.092
SF-CW 2.594 14 6.75 3.84 87* 33.433*
Biofilter 2.594 27 13.5 0.38 51** 9.773**
*Construction cost depreciation in 10 years (very low maintenace cost)
** Constuction cost depreciation in 5 years (not including new supply of woodchips every 5 years)
• Calculations conducted for a ID15 subcatchment (1.500 ha) with 70% agricultural area (1.050 ha)
• Average N-leaching from rootzone ~60 kg N/ha and average N-reduction is 62%
Kjærgaard et al., 2018. http://idraen.dk

32. © 2021 NovaDraiN Aps. All rights reserved
33 kg N/ha
6 kg N/ha
60 kg N/ha
33 kg N/ha
6 kg N/ha
60 kg N/ha
Conclusions and future perspectives
• Drainage filter technologies (DFTs) are cost-effective solutions that enable to balance water quality and
economic sustainable agricultural production in drained catchments, but a cost-effective mitigation
requires:
• I. A target differentiated implementation strategy accounting for rootzone leaching, drainage
fraction and surface-water retention
• II. Effective and robust drainage filter technologies with no/insignificant negative side-effects
• We need continued R&D in developing and
optimizing cost-effective DFTs and minimize
negative side-effects
• Revolutionary changes -> NovaDraiN drainage
N-filter technologies -> potential game-
changers?!?