Agency Agriculture Dept

Contractor U of M, Dr. Jeff Strock

SWIFT Contract Number 63906

Project Name Nutrient removal in agricultural drainage ditches

Project Number (if applicable) {Empty}

Summarize purpose of the contract, including why it was necessary: Ditches convey surface runoff water and subsurface tile drainage from artificially drained agricultural lands and are important to the agricultural economy of Minnesota and other Midwestern states. However, traditional methods of surface and subsurface drainage often result in degraded water quality. There has been increased interest in developing Best Management Practices (BMPs) for mitigating the effects of subsurface drainage. Ideally, a successful BMP would mitigate the negative impact of subsurface drainage while limiting its negative consequences on crop production practices and crops. A potentially successful BMP would be the design of a bioreactor which can mitigate both nitrogen (N) and phosphorus (P) efficiently under a wide range of flow and environmental conditions. Additionally, the bioreactor would be easily accessible for replacing and recycling the P sorbing and N denitrifying constituents. The effectiveness of a novel bioreactor design that could be placed into or adjacent to agricultural drainage ditches for the removal of N and P was the primary focus of this study. This research key tasks were to 1) evaluate the physical and chemical characteristics of selected P sorbing and N denitrifying media that have potential for use in a bioreactor, 2) select promising P sorbing and N denitrifying media and test the efficiency of P and N removal in laboratory flow columns under a range of temperatures and flow conditions, 3) construct a novel two phase bioreactor and evaluate N and P removal from agricultural runoff under field conditions.

The proper design of bioreactors and assessments of their performance require information on the materials used to construct the bioreactor. Laboratory characterization experiments were carried out to determine the most promising materials for denitrification and P sorption based on their physical and chemical characteristics. Various materials were assessed under laboratory conditions for their ability to remove nitrate from solution. The forms of nitrogen used in this experiment were dissolved ammonium (NH4+) and nitrate (NO3-). The materials investigated include 21 biochars, four Minnesota top soils, 12 biochar and soil (1:10, w/w) mixtures, and 3 other materials. The results of this study show that approximately 86% of biochars statistically removed NH4+ and 77% removed NO3- from aqueous solution. On the other hand, once mixed with soils, only 18% of biochars possessed increased NH4+ adsorption over unamended soil. It is noteworthy that no biochar addition increased soil NO3- removal or adsorption capacities once mixed with soil.

Laboratory column experiments were conducted to identify best combinations of materials for N and P removal in a denitrifying bioreactor at short hydraulic residence times (HRT). The denitrifying materials were corn cobs and wood chips and a supplemental C source, to enhance/stimulate denitrification, was potassium acetate. The P sorbing materials used were crushed concrete, limestone and steel slag. Because several materials for N and for P removal were identified, testing all combinations was deemed to be too complicated for one experiment. So, six materials or material combinations were tested in columns with a focus on nitrate removal performance. The experiment was operated at 15°C for 14 weeks, 5°C for 13 weeks, and again at 15°C for 7 weeks. Flow simulated a typical drainage hydrograph throughout each week, with water sampling occurring after HRTs of 1.5, 8, 12, and 24 hours. Nitrate-N load reductions ranged from 24 to 96% in the two runs at 15°C and from 4 to 80% during the cold run. The addition of acetate, a readily available carbon source, to wood chips resulted in the highest removal of nitrate-N. The three treatments with corn cobs – corn cobs, corn cobs + modified coconut coir, corn cobs + MCC + biochar – performed better than wood chips and wood chips + biochar. A separate, preliminary experiment identified P-sorbing candidate materials for the field experiment: crushed concrete, steel slag, and limestone.

Field experiments were conducted at the University of Minnesota Southwest Research and Outreach Center (SWROC) in Lamberton, Minnesota to experimentally assess the impact of a novel two phase bioreactor design for removing N and P from agricultural subsurface drainage water. Modular bioreactors were constructed using mixed woodchips plus corn cobs for facilitating denitrification plus either crushed concrete, steel slag or limestone fragments for P sorption. Experimental bioreactors were installed adjacent to an existing drainage ditch/waterway. Flows from the bioreactors were directed to flow gauges and water sampling equipment. The response of the different bioreactors was assessed using a calibration and a treatment period. During the calibration period only subsurface drainage water was delivered to the bioreactors. During the treatment period subsurface drainage water spiked with potassium acetate was delivered to the bioreactors. Data were collected and analyzed to determined the performance and efficiency of the modular bioreactors under various temperature regimes.

Nitrate removal was tied to the retention time in the bioreactor coupled with the addition of acetate. Longer retention time resulted in a greater removal of nutrients however, acetate improved nitrogen removal efficiency. Results also indicate that reduced conditions within the bioreactors but only consistently when acetate was added to the subsurface drainage water. All three P sorbing materials performed adequately for removing P from drainage water. Toward the end of the field experiment, as temperatures decreased, the P removal efficiency of the materials declined. During this time some of the materials acted as a source of P rather than a sink for P removal. Additional research is necessary to determine the longevity of the N and P removal materials.

Project Duration

Start Date Tue, 07/09/2013 - 00:00

Original end date Wed, 06/01/2016 - 00:00

Actual end date Sat, 12/31/2016 - 00:00

Did project finish on time? Yes

Total billable hours utilized (if applicable) {Empty}

Contract Amounts

Original contract: $404112.00

Amendments $-25000

Contract total $379112

Did project finish within budget? Yes

What was the funding source? Clean Water funds

Is this a sole source contract? No

If this was a single source contract, explain why the agency determined there was only a single source for the services (if applicable) {Empty}

Evaluator Name Heather Johnson

Evaluator Email Address heather.johnson@state.mn.us

Evaluate the contractor's timeliness Overall, Dr. Strock provided materials when asked and quarterly submitted reports about project details. We talked several times a year about progress and if there were any problems he was encountering. He made time for several MDA staff to visit him on-site to get a tour of the project and learn further details.

Evaluate the contractor's quality Dr. Strock provided well written quarterly reports that summarized the progress on the different components of the project. When applicable, he put in tables, figures and or maps to describe the work more fully. I felt he provided very nice quality work to us and if I had any question or needed further detail, he provided that information back in a timely manner.

Evaluate the contractor's cost Considering all the aspects of this project, the cost for the work was reasonable.

Evaluate the contractor's overall performance Dr. Strock and his team did a great job on this research project. It can be quite difficult to take an idea, come up with a budget and then actually do the research and implement it. MDA is quite happy with his work and the products that he has produced from it. The final report they submitted is quite thorough and addressed the initial project question quite well.

Would you engage the contractor's services again? Yes

Describe any negative action taken during the duration of this contract (i.e., termination, pursuit of suspension, etc.): {Empty}

Please rate the overall experience with the contractor 5 - very satisfied