Woodchip Bioreactors: Multi-Contaminant Removal from Agricultural Drainage

Natasha Hoover and Michelle SoupirDepartment of Agricultural and Biosystems Engineering - ISU

Thomas Moorman USDA ARS National Lab for Agriculture and the Environment

Illustration by Laura Christianson

How is Iowa addressing nutrient removal goals? The Iowa Nutrient Reduction Strategy was released in May of 2013 as a

science and technology-based approach to assess and reduce nutrients delivered to Iowa waterways and the Gulf of Mexico.

The collaborative effort between ISU, Iowa Department of Natural Resources, and the Iowa Department of Agriculture and Land Stewardship outlined the potential of multiple technologies and BMPs for both nitrogen and phosphorus reduction.

The ‘Strategy’ emphasizes the need to adopt multiple practices to achieve the 41% N and P non-point source reduction goals.

What is the role of woodchip bioreactors in the Iowa Nutrient Reduction Strategy?

Bioreactors alone have an estimated potential to reduce18% nitrate-N per year if treating all tile drained land in Iowa.

Two detailed scenarios incorporate heavy adoption of bioreactors to achieve 42% overall NPS reduction when combined with other practices.

NCS1: Cover crops, wetlands, and bioreactors to treat 60% of drained land. (76,000- 114,000 bioreactors!)

NCS8: Controlled drainage, buffers, multiple BMPs, and bioreactors to treat 70% of drained land. (88,000-133,000 bioreactors!)

With approximately 9.5 million acres of drained land, that’s a lot of bioreactors.

We are currently working at three scales to improve understanding of contaminant removal from woodchip bioreactors

Column studies to evaluate the potential of woodchip bioreactors to treat multiple contaminants: nitrate, phosphorous, and fecal indicator bacteria

Field scale monitoring to evaluate the performance of one installed bioreactors, also evaluating removal of multiple contaminants

Pilot scale bioreactors installed at the Ag Engineering Research Farm near Boone, Iowa

Can woodchip bioreactors also remove other contaminants from tile drainage?

There is evidence to support the potential of bioreactors to remove pathogens.

Tanner et al., 2012 report potential for E. coli reduction of 1.2 to 1.9 log10 reductions.

50% reduction in E. coli levels observed in a single season of field sampling in Minnesota.

What about phosphorus?

Tanner et al., 2012 reported TP removals of 36-65%

Source: Keegan Kult, Iowa Soybean Association, Greene County bioreactor installation

Denitrification woodchip bioreactor installation is outpacing necessary research

Predict nitrate removal under varying conditions Precipitation patterns

Expected flow volumes

Temperature

Nitrate concentrations

Address potential unintended consequences Support pathogen growth

Eutrophication in carbon limited environments

Sulfate reduction, mercury methylation

Determine the impact of achievable HRTs on nitrate removal as well as other pollutants (phosphorous, pathogens)

Quantify nitrate removal at 12-hour and 24-hour HRTs, at 10°C and Room Temperature.

Evaluate the fate of phosphorus with limestone addition

Study the impact of temperature on bacteria survival

Figure 1. Photographs of PVC (top) , & acrylic (lower) column bioreactors.

Column studies were designed to answer these questions.

Nitrate removal was double at room temperature.

Room Temperature(RT), 22°C24 h HRT

Controlled Temperature (CT), 10°C24 h HRT

0%

25%

50%

75%

100%

0

10

20

30

40

50

NO

3-N

redu

ctio

n (%

)

NO

3-N

(mg

L-1)

influent removal reduction

0%

25%

50%

75%

100%

0

10

20

30

40

50

NO

3-N

redu

ctio

n (%

)

NO

3-N

(mg

L-1)

influent removal reduction

96% average reduction

48% average reduction

Greater nitrate removal was also observed in the RT columns during the 12 h HRT

Room Temperature (RT), 22°C12 h HRT

Controlled Temperature (CT), 10°C12 h HRT

0%

25%

50%

75%

100%

0

10

20

30

40

50

NO

3-N

redu

ctio

n (%

)

NO

3-N

(mg

L-1)

influent removal reduction

0%

25%

50%

75%

100%

0

10

20

30

40

50

NO

3-N

redu

ctio

n (%

)

NO

3-N

(mg

L-1)

influent removal reduction

66% average reduction

36% average reduction

0

0.25

0.5

0.75

1

-0.50

0.00

0.50

DR

P re

duct

ion

(%)

DR

P re

mov

al (m

g L-1

)

RT removal CT removal CT reduction RT reduction

After an initial flush, P was removed in the bioreactor columns.

Target influent concentration: 0.1 mg/LAverage influent concentrations:

RT= 0.06 mg/L(0.09 mg/L with high/low points omitted)CT= 0.07 mg/L (0.09 mg/L with high/low points omitted)

RT = 20C CT = 10C

0

0.25

0.5

0.75

1

-0.50

0.00

0.50

DR

P re

duct

ion

(%)

DR

P re

mov

al (m

g L-1

)

RT removal CT removal CT reduction RT reduction

After an initial flush, P was removed in the bioreactor columns.

Limestone addition at RT

on 11/21Release of P at start of CT

Higher percent reduction at 22°RT: 93%

CT: 76% (excluding the P flush)

Relatively even P removal after initial P flush in the CT columns.

Limestone had no impact on P removal.

The columns were effective at potential pathogen removal.

HRT did not appear to impact bacteria reduction

Reduction was lower at 10°C Room temperature

reductionSalmonella: 92%

E.coli: 94%

Controlled temperature (10°C)Salmonella: 76%

E.coli: 75%

0%

25%

50%

75%

100%

0

20000

40000

60000

80000

RT CT RT CT

Salmonella E.coli

Bac

teria

redu

ctio

n (%

)

Bac

teria

con

cent

ratio

n (C

FU/1

00 m

L)

influent effluent reduction

The columns were effective at potential pathogens removal.

HRT did not appear to impact bacteria reduction

Reduction was lower at 10°C Room temperature

reductionSalmonella: 92%

E.coli: 94%

Controlled temperature (10°C)Salmonella: 76%

E.coli: 75%

0%

25%

50%

75%

100%

0

20000

40000

60000

80000

RT CT RT CT

Salmonella E.coli

Bac

teria

redu

ctio

n (%

)

Bac

teria

con

cent

ratio

n (C

FU/1

00 m

L)

influent effluent reduction

51,227

33,086

57,676 64,210

Summary: The column reactors did what they are designed to do…remove

nitrate.

Nitrate removal functioned as expected, with higher removal at the higher temperature and at the longer HRT.

In general, the columns removed phosphorus.

HRT did not appear to impact P removal.

Phosphorus reduction was greater at RT than CT, with 93% and 76% respectively.

Addition of limestone did not affect P removal.

Bacteria removal was similar at 12-h and 24-h HRTs.

Bacteria removal was greater at room temperature than controlled temperature.

Field bioreactors had mixed results.

• Story County Bioreactor had excellent nitrate removal

• Greene County and Dyersville bioreactor N removals were relatively low.

• Greene is being excavated and refilled this fall

• Hydraulic conditions are being evaluated on both reactors.

• P results were highly variable.

• Field bioreactor bacteria concentrations were very low.

Contaminant Greene Dyersville Story

Nitrate-N (mg/L)

IN 30.67 30.36 9.20OUT 21.80 22.49 0.345

Reduction 8.87 7.87 8.85%-reduction 29% 26% 96%

Dissolved Reactive Phosphate (mg/L)

IN 0.050 0.075 0.034OUT 0.047 0.003 0.194

Reduction 0.003 0.072 -0.160

%-reduction 6% 96% -466%

E. coli (cfu/100mL)

IN 28 26 15OUT 2 28 30

Reduction 26 -2 -15

%-reduction 93% -8% -100%

Acknowledgements

Research Assistants: Ji Yeow Law, Jordan Muell, Rene Schmidt, Ben

MorrisonWater Quality Research Lab:Leigh Ann Long

Funding: Iowa Soybean Association

Questions….

References

Tanner, CC, Sukias, JPS, Headley, TR, Yates, CR, Scott, R. 2012. Constructed wetlands and denitrifying bioreactors for on-site and decentralisedwastewater treatment: Comparison of five alternative configurations. Ecological Engineering. (42) 112-123.