Evaluation of Woodchip Bioreactors and Nutrient reduction. 
There is a critical need to develop additional practices for reducing nitratenitrogen
load deposition through tile drainage systems in the Mississippi River Basin and ultimately achieving the target of reducing the hypoxic zone in the Gulf of Mexico. Denitrifying woodchip bioreactors are one example of a method to remove nitratenitrogen from the drainage water. 

A bench top experiment was conducted to develop the following flow equation for the V-notch weir used in the study to estimate flow rates: Q=1.7406 H 1.9531, where Q is flow rate (l/min), and H is thickness in cm of the nappe flowing over the V notch. An economic analysis showed that the annualized installation costs for the three bioreactors were between $60 and $76 per hectare of effective drained area. The cost to remove one unit mass of nitrate-nitrogen was calculated for one of the bioreactors only due to monitoring equipment failure or lack of flow at the two others. It was approximately $8.68 per Kg N removal. 
The average concentration-based nitrate removal at both the Baltic and Montrose bioreactors were 81% and 51%, respectively during 2013. At the Montrose bioreactor, the average removal rate of nitrate nitrogen in calculated for the entire volume of woodchips (wetted and unwetted) was 0.98 g N /m3 per day. The nitrate-nitrogen removal rate calculated for the volume of wetted woodchips for the Montrose bioreactor was estimated as 12.58 g N/m3/d.

The performance of three bioreactors was determined by the nitrate-nitrogen removal rate and cost per pound of nitrate-nitrogen removed by the bioreactors. The average concentration-based nitrate removal at both the Baltic and Montrose bioreactors were 81% and 51%, respectively during 2013. At the Montrose bioreactor, the average removal rate of nitrate-nitrogen in calculated for the entire volume of woodchips (wetted and unwetted) was 0.98 g N /m3 per day. The nitrate-nitrogen removal rate calculated for the volume of wetted woodchips for the Montrose bioreactor was estimated as 12.58 g N/m3/d.

The objectives of this study and evaluate the effectiveness of woodchip bioreactors in removing nitrate-N from subsurface drainage water. Four woodchip bioreactors were installed and monitored between 2012 and 2016 near Arlington, Baltic, Hartford and Montrose in eastern South Dakota. One P adsorption structure was designed, installed and monitored for 2016 near Baltic, South Dakota downstream of the Baltic bioreactor. Results showed that nitrate-N reductions ranged from 7% to 100% for the four bioreactors, based on upstream concentrations of 0.79 to 60.9 mg/L during 2014-2016 study period. Nitrate-N load removal rates varied between 0.01 to 14.6 gm N/m3/day, with upstream and downstream loads of 0.03 to 116 kg/ha/year and 0.0 to 91 kg/ha/year, respectively. The average cost of nitrate removed were estimated to be $11, $20, $13, and $61 kg/N per year for the Arlington, Baltic, Hartford, and Montrose.




Location and Design data 
GPS location 
Montrose: 43.77240 N, 97.13139 W
Arlington: 44.24642 N, 97.12808 W
Hartford: inlet 43,53116 N, 96.97514 W, outlet 43.53142 N, 96.97472 W
Baltic: inlet 42.73099 N, 96.68113 W


Location Installation
Month-year
Dimension (m)
Catchment Name
Area Drained (ha)
Arlington (Brookings County)
Jul-13
38.1 L x 3.6 W x 1.52 D
Lake Sinai 6.9
6.9
Baltic (Minnehaha County)
Jul-12
35 L x 5.4 W x 1.52 D
Silver Creek
16.2
Hartford (Minnehaha County)
Nov-14
38.1 L x 3 W x 1.52 D
Wall Lake
8.09
Montrose (McCook County)
Dec-12
39.6 L x 6.4 W x 1.52 D
Skunk Creek
15.4

Four woodchip bioreactors were installed in eastern South Dakota with different dimensions and treatment areas (Table 3.2). The bioreactors are located near Arlington, Baltic, Hartford, and Montrose, South Dakota. The contributing area of the Baltic bioreactor has silty clay loam soil in a corn-soybean-wheat rotation during the study period (2013-2016). A theoretical HRT of 5.4 hours was used to design the bioreactor to handle up to 25% of the peak flow from the contributing area.
The Montrose bioreactor receives drainage from approximately 15.4 ha of silty clay loam soil in a corn-soybean rotation during four years of study period (2013-2016). This bioreactor was designed with an estimated HRT of 4.9 hours and designed to handle up to 25% of peak flow from a 20 cm main drain line. 
The drainage area for the Arlington bioreactor is approximately 6.9 ha of silty clay loam soil. This site was in a corn-soybean rotation during the study period (2014-2016), and the bioreactor was designed to handle 18% of peak flow from a 15 cm main drain line with 6.3 hours HRT.
The Hartford bioreactor was designed with 6.3 hours HRT to handle 18% of peak flow from a 15 cm main drain line that drains approximately 8.1 ha. This site was in a corn-soybean rotation during the study period (2015-2016). Common for all sites was the installation of 3-chamber or 4-chamber control structures on the main subsurface drainage line upstream of the bioreactor to divert water through the bioreactor. During high flow conditions, excess water is directed through a bypass and directly into the outlet of the drainage system. A 2-chamber control structure was installed downstream of all bioreactors to measure the outflow before the open ditch, except at the Arlington site, which has a 4-chamber control structure. The retention time is controlled by adjusting the elevation difference between the inlet and outlet of the bioreactor. The particle size of the woodchips ranged from 0.6 to 5.1 cm.
Decagon CTD-10 sensors (Decagon Devices, Pullman, WA) were used to measure water depth, temperature, and electrical conductivity in the control structures. The Baltic site used Campbell Scientific sensors (Campbell Scientific, Inc., Logan, UT) while the other three sites were outfitted with Decagon sensors. These sensors utilize pressure transducers to obtain water level measurements. Tipping bucket rain gauges were also installed near upstream of the bioreactors to measure precipitation every 10 minutes. Campbell Scientific TE525 and Decagon ECRN-100 double spoon gauges were installed, respectively, at the Baltic and Arlington sites, and Montrose and Hartford sites. Each transducer was suspended between 0.63 to 1.27 cm above the bottom of the control structure, and flow depth readings were relative to the pressure transducer location. A standard 45? V-notch weir (AgriDrain Corp, Adair, Iowa) was installed in the control structures and the drainage flow rate was estimated based on the thickness (i.e. depth) of the sheet of water flowing over the weir. All the sensors, including pressure transducers and rain gauges were connected to data loggers that record and store the data every 10 minutes. During drain flow events, grab water samples were collected directly within the upstream and downstream control structures. Samples were collected using a water bottle attached to a steel rod placed in each control structure. Collected water samples were immediately stored in a cooler with packed ice until transported to the analysis laboratory.

What methodology did you use (tools, experimental protocol, lab notes)?

Bioreactor installation,
Baltic
The first bioreactor was installed near Baltic, SD in July 2012. The bioreactor was installed in the NE ¼, NW ¼, sec 14, T103N, R49W in Minnehaha County in the Silver Creek watershed (Figure 2.7). The Baltic bioreactor was installed to treat water from a drainage area of 16.2 ha. The contributing area has silty clay loam soil. Using the Iowa State bioreactor design spreadsheet, bioreactor dimensions of 115 ft. long and 18 ft. wide were chosen (Table 2.1). The outlet was a 6-inch drainpipe. Based on the design tool estimates, the hydraulic retention time is 5.4 hours and 24.5% of peak flow can be passed through the bioreactor. The presence of E. coli was studied from 2017 on Baltic and Hartford bioreactors. Samples were collected from the inlet as well as the outlet, using sterile bottles and analyzed using membrane filters and mTEC agar.

Installation of monitoring equipment at Baltic bioreactor
At the Baltic bioreactor, monitoring equipment was installed in the upstream and downstream control structures (Table 2.5). The sensors were connected to a CR 1000 data logger storing the data every 10 minutes (Figure 2.11). Data were downloaded from the data logger onto a laptop computer during the field visits and screened for outliers and spurious values. Two separate pressure transducers were installed to measure the flow rate from both upstream and downstream control structures. Logger net software was used to create a program for the data logger to diagnose the sensors. For the tipping bucket rain gauge, leveling was checked during every field visit. Because the upper part of the rain gauge is removable and due to the external
disturbances such as bird sitting on the gauge may be brought out of level

Installation of the bioreactor near Montrose
The second bioreactor was installed on December 5-6, 2012. The location where the bioreactor was installed is Sec 36, T104 N, R53W in McCook County in the Skunk Creek watershed (Figure 2.8). The design outlet was an eight-inch tile. Based on the design tool, the hydraulic retention is be 4.9 hours and 24.8% of the peak flow can be passed through the bioreactor. The Montrose bioreactor was designed to treat water from a drainage area of 15.4 ha. The drainage area has silty clay loam soil.

Installation of monitoring equipment at the Montrose bioreactor
At the Montrose bioreactor we used sensors and data loggers from Decagon Devices to measure the meteorological and water quality data. Two data loggers (Em50) were installed near both upstream and downstream control structures (Figure 2.12). An instrument combining a thermometer, an electrical conductivity sensor and a pressure transducer (Decagon CTD) was installed in both the upstream and downstream control structures. A rain gauge (ECRN-100) was installed near the upstream control structure to measure the precipitation received near the bioreactor site. A temperature and relative humidity sensor (VP-3) with radiation shield was installed near the upstream control structure. ECH2O Utility software was used to program the data logger to receive and store the data from each sensor.

Installation of the bioreactor near Arlington
The third bioreactor was installed on July 23-24, 2013. The location where the bioreactor was installed is Sec 18, T109N, R52W, SW ¼, in Brookings County within the Lake Sinai watershed (Figure 2.9). A portion of the Wenk Waterfowl Protection Area (WPA), where the US Fish and Wildlife Service holds an easement, is located immediately north of the field, and the discharge from the bioreactor drains onto the WPA. Using the ISU design tool, the chosen length and width of the bioreactor were 125ft. and 12 ft., respectively (Table 2.3). Based on the design tool, hydraulic retention time will be 6.33 hours, and 18.38 % of peak flow can be passed through the bioreactor. The Arlington bioreactor was designed to treat water from a drainage area of 6.9 ha. The drainage area has clay silt loam soil.

Installation of monitoring equipment at the Arlington bioreactor
At the Arlington site bioreactor, sensors were connected to a Campbell Scientific CR 1000 data logger. We used the SDI-12 protocol to program the data logger to conserve channels on the data logger. Based on the SDI-12 commands, each sensor was given its own unique address. Logger net software was used to program the data logger to communicate with the sensors. The rain gauge (Campbell Scientific TE525) and the humidity and temperature probe (Vaisala HMPO 60) which measures temperature and relative humidity with radiation shield were installed near the bioreactor site. In addition, three soil moisture sensors (Decagon 5TM) were installed cross-sectional in the woodchips approximately 25 ft from the upstream end of the bioreactor (Figure 2.10). Two sensors were inserted into the woodchips vertically one foot from the side wall and one foot from the bottom of the trench. The third sensor was inserted approximately in the middle of the two other sensors.

Data tables 
2017 
Hartford



Date
Upstream
Downstream
%removal
4/13/2017
15.67
14.97
4
5/16/2017
17.50
15.18
13
5/25/2017
21.42
18.09
16
6/7/2017
17.21
14.36
17
6/13/2017
14.03
12.92
8
6/29/2017
18.55
13.87
25
7/12/2017
10.45
7.58
28
 
 
 
 
 
16.40
13.85
15.77
 
3.49
3.20
8.41

Montrose



Date
Upstream
Downstream
% removal
4/13/2017
21.00
17.34
17
5/25/2017
24.67
21.48
13
6/7/2017
23.85
17.39
27
6/13/2017
18.05
12.72
30
6/29/2017
17.27
11.58
33
7/7/2017
17.87
7.39
59
7/12/2017
16.06
2.60
84
 
 
 
 
 
19.82
12.93
37.48
 
3.38
6.48
25.14

Arlington



Date
Upstream(mg/L)
Downstream(mg/L)
%removal
4/13/2017
24.99
21.55
14
5/16/2017
25.42
17.07
33
5/25/2017
26.29
0.26
99
6/7/2017
20.71
1.02
95
6/13/2017
19.82
0.30
99
6/29/2017
19.43
12.54
35
7/7/2017
17.03
5.43
68
 
 
 
 
Average
21.96
8.31
63.25
Stnd
3.57
8.76
35.83

NOTE: NO ANY SAMPLES WERE COLLECTED FROM BALTIC SITE THIS YEAR

Hartford



Date
Upstream
Downstream
% removal
5/15/2015
11.50
1.72
85.04
5/20/2015
13.06
3.43
73.74
6/1/2015
11.90
1.55
86.97
6/5/2015
11.55
7.60
34.20
6/12/2015
12.10
3.67
69.67
6/26/2015
12.30
1.16
90.57
7/2/2015
6.06
0.56
90.71
7/7/2015
7.44
1.27
82.93
7/17/2015
12.30
0.18
98.58
7/28/2015
15.70
0.25
98.39
10/26/2015
12.50
7.86
37.12
5/4/2016
10.65
7.00
35.09
5/16/2016
30.70
22.86
25.97
5/26/2016
6.63
6.08
8.96
6/17/2016
17.50
11.06
36.79
6/30/2016
9.81
6.53
33.47
7/14/2016
7.41
3.74
50.25
7/25/2016
6.59
4.35
34.92
8/1/2016
5.92
2.35
61.07
Max
30.70
22.86
98.58
Min
5.92
0.18
8.96
Average
11.67
4.91
59.71

Arlington


% removal
Date
Upstream
Downstream

3/18/2014
9.71
0.82
91.56
3/23/2014
13.2
1.18
91.06
4/11/2014
6.96
0.85
87.79
4/14/2014
2.96
0.39
86.82
4/23/2014
1.07
0.38
64.49
5/18/2014
7.03
0.44
93.74
5/21/2014
6.8
0.51
92.50
5/23/2014
7.42
0.53
92.86
5/28/2014
7.29
0.31
95.75
6/27/2014
8.42
0.85
89.90
6/30/2014
13.05
0.61
95.33
7/3/2014
8.62
0.31
96.40
7/7/2014
7.53
0.42
94.42
7/11/2014
17.83
0.49
97.25
7/17/2014
25
1.19
95.24
5/8/2015
13.50
0.00
99.96
5/15/2015
15.70
0.01
99.94
5/22/2015
14.20
2.34
83.52
6/1/2015
18.72
1.92
89.74
6/5/2015
7.43
3.31
55.45
6/12/2015
17.20
5.13
70.17
6/26/2015
20.07
0.45
97.76
7/2/2015
6.83
1.52
77.75
7/7/2015
8.55
0.49
94.28
7/17/2015
12.80
0.23
98.20
7/28/2015
6.95
0.00
99.93
8/7/2015
0.79
0.00
99.40
10/26/2015
17.10
0.00
99.97
3/7/2016
18.79
13.94
25.82
4/12/2016
19.23
7.23
62.40
4/14/2016
17.18
11.84
31.12
4/26/2016
8.86
5.33
39.88
5/4/2016
10.71
3.83
64.24
5/16/2016
21.39
9.12
57.34
5/19/2016
17.01
2.58
84.82
5/26/2016
14.35
8.42
41.31
6/2/2016
19.10
11.87
37.83
6/9/2016
14.13
2.36
83.29
6/17/2016
23.81
8.77
63.17
Max
25.00
13.94
99.97
Min
0.79
0.00
25.82
Avearge
12.49
2.82
80.06

Montrose



Date
Upstream
Downstream
%removal
3/18/2014
11.4
2.97
73.95
3/23/2014
12.3
4.35
64.63
4/11/2014
12.05
0.91
92.45
5/2/2014
13.35
0.2
98.50
5/5/2014
13
0.26
98.00
5/18/2014
13.3
1.54
88.42
5/21/2014
13.55
0.32
97.64
5/23/2014
13.75
0.27
98.04
5/28/2014
5.73
0.13
97.73
6/5/2014
19.8
10.35
47.73
6/10/2014
16.3
15.05
7.67
6/13/2014
10.8
9.48
12.22
6/17/2014
15.9
14.85
6.60
6/21/2014
13.3
12.25
7.89
6/24/2014
20.05
16.05
19.95
6/27/2014
9.1
8.31
8.68
6/30/2014
18.8
15.3
18.62
7/7/2014
14.66
9.47
35.40
7/11/2014
18.64
0.24
98.71
7/17/2014
14.65
0.53
96.38
5/8/2015
10.90
0.01
99.91
5/15/2015
14.78
1.69
88.59
5/22/2015
9.07
5.24
42.23
6/1/2015
14.78
2.11
85.72
6/12/2015
14.1
4.74
66.31
7/2/2015
14.3
0.0095
99.93
7/7/2015
6.89
0.00475
99.93
7/17/2015
10.1
4.91
51.39
7/28/2015
20.4
0.0095
99.95
7/28/2015
7.37
0.0045
99.94
3/7/2016
13.82
10.76
22.14
4/12/2016
15.80
9.64
38.98
4/14/2016
15.41
8.26
46.43
4/26/2016
9.51
6.81
28.38
5/4/2016
10.85
8.93
17.66
5/19/2016
13.89
11.25
19.02
5/26/2016
13.94
10.57
24.14
6/2/2016
23.16
9.93
57.13
6/9/2016
7.92
6.74
14.91
Max
23.16
16.05
99.95
Min
5.73
0.00
6.60
Average
13.52
5.75
58.25

Baltic



Date
Upstream
Downstream
% removal
6/2/2014
40.7
30.2
25.80
6/5/2014
17.9
3.835
78.58
6/10/2014
28.65
4.68
83.66
6/13/2014
31.55
9.445
70.06
6/17/2014
33.9
20.45
39.68
6/21/2014
27.3
21.55
21.06
6/24/2014
40.5
33.6
17.04
6/27/2014
22.8
18.15
20.39
6/30/2014
36.1
26.35
27.01
7/3/2014
28
19.37
30.82
7/7/2014
25.7
12.89
49.84
7/11/2014
29.1
11.79
59.48
7/17/2014
24.25
0.234
99.04
5/15/2015
43.78
17.4
60.26
5/22/2015
35.1
25.6
27.07
6/1/2015
55.1
40.2
27.04
6/5/2015
36.1
19.74
45.32
6/12/2015
42.05
17.6
58.15
6/26/2015
60.95
18.8
69.16
7/2/2015
7.77
0.01
99.87
7/7/2015
26.00
2.72
89.54
7/10/2015
59.60
18.3
69.30
7/17/2015
9.33
0.58
93.78
7/28/2015
55.40
4.32
92.20
8/7/2015
29.90
11.8
60.54
10/26/2015
54.8
8.54
84.42
3/7/2016
44.48
10.24
76.97
3/22/2016
50.55
21.88
56.72
4/12/2016
52.71
17.61
66.60
4/14/2016
33.32
16.92
49.23
4/26/2016
26.02
22.54
13.36
5/4/2016
20.94
9.32
55.52
5/16/2016
40.34
19.16
52.52
5/19/2016
33.31
30.84
7.40
5/26/2016
23.55
21.15
10.22
6/2/2016
36.69
23.41
36.20
6/9/2016
16.11
7.24
55.07
6/17/2016
38.87
22.81
41.32
6/30/2016
37.63
15.10
59.88
7/8/2016
38.07
5.37
85.91
7/14/2016
31.48
10.56
66.44
Max
60.95
40.20
99.87
Min
7.77
0.01
7.40
Average
34.79
15.91
54.45

5