This document summarizes research on using denitrifying bioreactors to treat subsurface agricultural drainage. Key findings include: 1) Bioreactors successfully removed nitrate from drain discharges, with removal efficiencies between 38-68% and rates of 2-31 mg/L/day. 2) Nitrate removal was influenced by temperature, with bioreactors most effective in summer and fall when soils are warmer. The presence of dissolved organic carbon also helped removal. 3) Hydraulic residence time in bioreactors did not consistently correlate with nitrate removal efficiency. Two bioreactor sites removed between 50-66 kg of nitrate over a summer/fall period. 4

1. Treating Subsurface Drainage
Discharges with Denitrifying
Bioreactors
Larry D. Geohring
70th Annual SWCS
Conference
W. Pluer, B. Hassanpour, S. Giri,
T. Steenhuis, M. Todd Walter

2. What we’re doing:
With Cooperators: USC, Schuyler
& Steuben SWCD’s, farmers
Research, Demonstrate,
Monitor, Technology Transfer
With CIG Grant funding from:

3. What we’re finding:
 Bioreactors were successful in removing
nitrate (NO3
- - N) from drain discharges
 Key operational parameters are
temperature, dissolved organic carbon
(DOC), available NO3
- - N
 Hydraulic Residence Time (HRT) poorly
correlated to NO3
- - N removal efficiency
and hard to control
 Biochar addition helped a little
 Farmers don’t like you messing with
their tile drains

4. The Water Quality Problems - Nitrates
- 1.5 to 10 mg/L
> 10 mg/L

5. The Water Quality Problems

6. Agriculture

7. 0
5
10
15
20
25
0 365 730 1095 1460 1825
Days
FP NT
NO3-Nconcentration,mg/L
1995 1996 1997 1998 1999
<-fertilizer
<-fertilizer
<-manure
<-fertilizer
<-fertilizer
<-manure
<-fertilizer
<-allplotsFP
Nitrate-N in tile discharge
Affects Aquatics
Drinking
water
Represents 10 to 30+
pounds N/acre/yr lost
through tile discharge

8. L
W
d
Q
Bioreactor Design Challenge
(Retention time)(Flowrate)
Area or (WxL) =
(Porosity of Media)(Depth)

9. hWL
Q

 
Q qLW RLW 
h
Q AK
x



1
b
o
S
G
h
L


 
 
Q
Wd
h
K
L

 
 
  1/22
0.1 oh K
L
q

  
 
3 2
o
q
K
G
h
L

 
 

 
 
Denitrifying Bioreactor
Design Flowchart
0.5
1 *
*
s
o
Q A
W
h m K
 
   
Say
what?
??
[Christianson et al., 2011]

11. Monitoring

12. NO3
- - N Removal - Project Sites
Removal Efficiency
(38 - 68%)
Removal Rates
(2 - 31 mg L-1 d-1)
3 farms
6 bioreactors

13. Temperature Effects
So more effective in summer and
fall when ground is still warm

14. DOC Effects
Organic fertilizers may help

15. Between 6/10 to 11/20, 2014
Site 1: 65 kg (143 pounds) IN
15 kg (33 lbs) OUT
for 50 kg (110 lbs) REMOVED;
Site 2: 46 kg (101 lbs) IN
16 kg (35 lbs) OUT
for 30 kg (66 lbs) REMOVED
NO3
- - N Load Removal
Between 7/1 to 11/20, 2014
33 kg (73 lbs) IN
10 kg (22 lbs) OUT
23 kg (51 lbs) REMOVED
Chemung Site
Steuben Site
Inlet
Outlet
3 2NO NO 

2 2( ) ( ) ( )NO g N O g N g   

16. Tompkins Site
Steuben County Site
Seeding denitrifiers
Permeable -
Impermeable
Liners

17. 12/15/2014
Do they work for Phosphorus?

18. 12/15/2014

19. Do they work for
Phosphorus?
P concentration spike
was reduced following
manure application

20. The End - Questions