Using Denitrifying Bioreactors to Treat Subsurface Drainage

DischargesLarry Geohring, Will Pluer, Todd Walter

Cornell UniversityBiological & Environmental Engineering

Denitrifying Bioreactors

• DNBRs treat excess nitrogen in field runoff

• Designed to provide ideal conditions for denitrifiers– Anaerobic– Carbon source– Excess NO3-

INTRODUCTION

• 3 Farm Sites– Freeville Veggie– Vance Dairy– Burns Dairy

• Susquehanna basin– Upstate NY

• Tile drain systems• Woodchip/biochar fills• Sealed/open designs• Field/control inflow

Field DBNRs

INTRODUCTION

Lab DNBRs

• 6 Lab reactors– 3 Woodchip– 3 Woodchip/biochar

• Control variables:– Inflow NO3-

– pH– Residence time– Temperature– Microbial community

INTRODUCTION

Continuous: NOx

FIELD RESULTS

Continuous: PO4

FIELD RESULTS

Continuous: DOC

FIELD RESULTS

Field Runs: N2O

FIELD RESULTS

Field Runs: CH4

FIELD RESULTS

Lab Runs: NOx

LAB RESULTS

Lab Runs: N2O

LAB RESULTS

Lab Runs: CH4

LAB RESULTS

General Efficacy

CONCLUSIONS

• Effectively remove NO3-

– 45-60% NOx-N reduction• Initial flush periods of P, DOC• No indication of P treatment

– Other media may target PO43- better

• Storm flows reduce treatment time– Missing highest loading period

Control Variables

CONCLUSIONS

• High variability among reactors• Low inflow NO3- results in low reduction and high methane

• High flow results in low reduction and high N2O

• High pH sensitivity• Biochar shifting microbe community?

Gas Emissions

CONCLUSIONS

• Emissions of N2O and CH4– N2O decrease with residence time

• Total GHG footprint could be significant

• No control discouraged N2O + CH4– New designs or controls

• Water quality probably outweighs trace gas emissions

Acknowledgements

PIs: Dr. Todd Walter & Larry Geohring& Dr. Tammo Steenhuis

Partner: Upper Susquehanna CoalitionHelp: Siobhan Powers, Shane DeGaetano,

Sarah Levine, Anne Elise CreamerFunds: USDA NIFA, NRCS-CIG, NSF IGERT

Any Questions?