Using Phosphorus Removal Structures to Treat Tile Drainage Water in the Midwest - Dr. Chad Penn, USDA-ARS, from the 2020 Conservation Tillage and Technology Conference, held March 3-4, 2020, Ada, OH, USA.

1. Phosphorus Removal
Structures as a Tool for
Reducing Dissolved
Phosphorus Losses
Chad Penn
USDA Agricultural Research Service
National Soil Erosion Research
Laboratory

2. Target Form: Dissolved P
Target Source: Legacy P Soils
(at least 100 mg/kg M3-P)

3. Dissolved P is a more potent
eutrophication agent than
particulate P
• Aquatic organisms can
immediately uptake dissolved P
from water
• Particulate P
– Degree of bioavailability depends
on the conditions
• Some sediment that contains P may
not release any P
• Some may actually adsorb dissolved
P

4. “Legacy Phosphorus”
Cease P application and
begin P drawdown with
crops in 1998
Safe soil P level
SoiltestP(mg/kg)
Fiorellino et al., 2017

5. Cease P applications
P
P
P
P
P
PP
Uptake P
from soil
via crops
Harvest crop/soil P
Export crop
from high P
areas

6. During That Long Time Period
of Drawdown, You are Still
Losing P

7. PO4
3-Fe
PO4
3-Fe
PO4
3-Al
PO4
3-Al
OH-Fe
OH-Fe
OH-Al
OH-Al
+
P Removal Structure Theory
Retained P in PSM
Dissolved P
from flow
P-free water

8. 3 Necessary Components
• Effective PSM in
sufficient quantity
• Sufficient flow
rate and contact
time
• Ability to retain
and replace PSM

9. Many Types of Structures

10. Phosphorus Sorption Materials
Metal filings
Steel slag
Drinking
water
treatment
residuals
Fly ash
Waste
recycled
gypsum
Photo Credit: K.D. Chamberlain
Manufactured
PSMs

11. Manufactured PSMs
• Tend to be efficient
• Most are extremely expensive
• Examples
– “Fe Osorb®”
• (Bio-Max: ABS Materials)
– “Imbrium”
– “Acti-guard”: Axens Solutions

12. Discrete P removed = 83.8e-0.004 * CPadd
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400 500 600 700
DiscretePremoved(%)
CPadd (mg kg-1)
Example “Design Curve”
• Varies with inflow P concentration and retention time

13. P removal & lifetime
1. Target P removal (%)
2. Target lifetime
+
Model
+
PSM characterization
1. P sorption
2. Safety
3. Physical properties
Design parameters
1. Area
2. Mass of PSM
3. Depth of PSM
4. Pipe reqmt
Input Output
Site hydrology
1. Peak flow rate
2. Annual flow volume
3. Dissolved P level
4. Max footprint
Design Software

14. If a site is worth treating, it
is going to require a large
mass of PSMs

15. Cartridge Filters
and small
modular boxes?
§ Portable, easy to
install
§ Only works in
limited situations
§ Is it worth using
them?
§ Limited amount
of PSM
§ Poor flow rate

16. Inflow water
Flow over the PSM: 6% P removal
Inflow water
Flow through the PSM: 32% P removal
Filter Sock?
Limited mass, contact, and
contact time

17. Current State
• The technology is effective but can be
improved
– Many structures constructed and monitored
throughout the world
• Penn et al., 2017; Water (review paper)
• The current challenge is economics and
site locations

18. NRCS Standard 782

19. Completed Confined Bed
Structure
• Removed 7.5 lbs dissolved P in 2.5 years
• 23% of the 2.5 year load: still effective at that point
• 40 tons treated slag
• Handled ~ 1000 gpm flow
• $5 K
Penn et al., 2014; JSWC

20. Confined Bed
• Small proto-type
– Only 3 tons sieved
slag
– 8 month 25%
removal with ¼
minus
– 16 month 33%
removal with 0.5 mm
minus
• $2.5 K
Overflow weir
Penn et al., 2012; Journal of Env. Qual.

21. Ditch Filter
• Allows large amount
of material to be
used
• Easy to build
• Use flow control to
build head
• Low cost (< $4K)
• Probably best option
for ditches

22. MD Ditch Filters
Site PSM
Cumulative
inflow P
load
Flow-
weighted
inflow P
concentration
PSM
mass
Average P
removal
per event
Cumulative
P removed
Measured P load
removed
kg mg L-1 Mg g % kg
Barclay
FGD
gypsum
3.8 0.48 58 75.9 28 1.06
Marion
FGD
gypsum
0.86 1.58 46 16.4 36 0.31
Westover
FGD
gypsum
7.2 1.3 49 132.4 15 1.06
Barclay Slag 3.4 0.57 80 25.5 25 0.84
Marion Slag 4.6 1.49 62 29.8 11 0.51
Westover Slag 7.1 0.88 67 133.2 24 1.73
Centreville Slag 0.53 1.04 15 12.9 26 0.14
Penn et al., 2016; Chemosphere
Mediocre PSMs: removal ~ 25%
over 2 years

23. Example Greenhouse P Filter
• Inflow P concentration ~ 20 mg/L
• 190 pounds of mine drainage residual
(MDR)
• Still removing over 90% P after 2 years
• $500

24. Bio-retention cell
• 147 tons of sand-fly ash mixture
• Suburban area: 0.3 kg P/yr
• 76 to 93% reduction over one year
Kandel et al. 2017; Water

25. Removed 55% dissolved P load over 1.5 years
- 36 tons normal slag
- 43 lbs dissolved P removal
- Short lived (little removal after 6 mo.)
- $ 11K
- Penn et al., 2020: Water
- Do not recommend normal slag for tile
drains, only surface runoff
Subsurface Tile Filter: Waterloo, IN

26. Tile drain outlet into ditch
structure: Mercer county
• 50 tons Al coated slag
• 30% cumulative dissolved P load removal
in 14 months (~ 6 lbs removed)
• Poorly constructed
• $15K
• Shedekar et al., 2020; in process

27. Subsurface Tile Drain Filter:
30 tons Al-Coated slag: still
removing 40 to 95% of DP per
event, even after two years. No
data on loads yet ($13K)

28. Blind inlet; Waterloo, IN
- Traditional blind inlet: limestone
sand/gravel ($2K)
- 40% particulate P removal of 12 yr load
- Negligible dissolved P removal
- Some herbicide removal
- Penn et al., 2019, Critical Reviews in
Environmental Technology:
https://doi.org./10.1080/10643389.2019.1
642836

29. Blind inlet: Auburn, IN
- Alternative to limestone: 12 inches of sieved steel slag over
railroad ballast
- Installed 2016; 15 tons slag. Treats surface water only.
- Inflow monitoring not established until late 2017. Currently
only have 2018 data analyzed.
- 2018: 1 lb dissolved P removal (46% of the 2018 load)
- 2018: removed 80% of glyphosate, 94% dicamba
- Since it is a filter, we can assume 2016 and 2017 removal
efficiency was equal to or greater than 2018
- Currently being written for publication

30. Re-generatable tile drain filter
- Manufactured PSM (2.5 tons Fe-coated
alumina)
- Designed to remove 40% of 10 yr-load: then
re-generate PSM media in-situ
- Currently monitored
- ~ $12K

31. 1. P is retained by
ligand exchange
PO4
3-
PO4
3-
PO4
3-Fe
PO4
3-Fe
PO4
3-Fe
PO4
3-Fe
KOH
OH-Fe
OH-Fe
OH-Fe
OH-Fe
2. P is stripped by
hydroxide treatment
and collected. PSM is
recharged

32. Metal shavings mix
(sand or gravel)
- Pilot box: 200 lbs metal/sand or metal/gravel mix (12% metal)
- Received 100K gallons for overall 77% cumulative DP load
reduction
- Cheap: $200/ton for metal

33. Economics
• Wastewater treatment cost of P removal is
50 to 800 dollars/lb P removed
• P removal structures are within that range,
but consider that dissolved P removal and
non-point sources are more difficult to treat.
• Cost of P removal using rechargeable media
is nearly cut in half at each
regeneration.
• Metal shavings shows
promise to be most
economical

34. Conclusions and Future
• Use normal slag only for surface water such as
blind inlets, not for tile drains. Be sure it is sieved
to remove fines
• Al-treated slag so far appears to be suitable for tile
drainage
• Other slag to be evaluated: brown slag and metal-
gravel
• Less expensive manufactured media shows great
promise
• Other PSMs to evaluate in lab
– People are sending us new potential materials all the
time

35. Current Research and Improvements
• Regeneration of PSMs in-situ
• Bottom-up flow design in flat landscapes
– How do we do that for Fe-rich PSMs?
• Metal shavings show great promise: needs
field testing
• Start training contractors
– Creating a series of training modules with
ASA, ASABE, and NRCS

36. Lots more details…
Penn, C.J., and J.M. Bowen. 2017. Design
and construction of P removal structures
for improving water quality. Springer
Publishing. ISBN 978-3-319-58657-1

37. Questions?
Chad.penn@ars.usda.gov
Twitter Handle: House of Phos
• Kevin King et al.; Larry Brown; Margaret
Kalcic; Nathan Stoltzfus et. al; TNC; Justin
McBride; OH NRCS; Aaron Heilers; Josh
McGrath