Purpose
To illustrate a case study design and construction of a phosphorus removal structure on a poultry farm, and to present the basics of how to properly design a structure.
What did we do?
We constructed a phosphorus (P) removal structure on a poultry farm in Eastern OK; this is a BMP that can remove dissolved P loading in the short term until soil legacy P concentrations decrease below levels of environmental concern. A P removal structure contains P sorbing materials (PSMs) and are placed in a location to intercept runoff or subsurface drainage with high dissolved P concentrations. As high P water flows through the PSMs, dissolved P is sorbed onto the materials by several potential mechanisms, allowing low P water to exit the structure. While they vary in form, P removal structures contain three main elements: 1) use of a filter material that has a high affinity for P, 2) containment of the material, and 3) the ability to remove that material and replace it after it becomes saturated with P and is no longer effective.
A site was identified which met all criteria for justification of construction of a P removal structure: 1) elevated dissolved P concentrations in runoff (>0.2 ppm), 2) hydraulic connectivity between the runoff/drainage produced and a surface water body, and 3) flow convergence: the site possessed potential to channel the runoff water to a single point in order to treat the water. This site was located on a poultry farm in Eastern OK.
The site was surveyed in order to obtain the necessary inputs for properly designing the P removal structure. This involved a basic NRCS survey to estimate watershed size, peak flow rates, and average annual runoff volume. In addition, several runoff grab samples were taken and analyzed for dissolved P. This information was used to determine the average annual dissolved P load, which was 45 lbs.
Knowing flow and P load parameters, we additionally chose P removal targets and desired lifetime of the structure. We chose to design a structure that would remove 20 lbs of dissolved P during the first year and be able to handle 700
gpm flow rate. Several hypothetical designs were made based on the available P sorbing materials (PSMs), such as drinking water treatment residuals, acid mine residuals, and gypsum. We chose to use a treated steel slag material as the PSM in the structure; this required about 35 tons of material.
After construction, the performance of the structure was monitored by measuring flow rates and dissolved P concentrations at the inlet and outlet. In addition, we developed software to aid in proper design of a site specific P removal structure using any PSM, in order to meet desired P removal goals and lifetime. Alternatively, this software can be used to predict the performance and lifetime of a P removal structure that has been already constructed. Licensing of software is available for private industry.
We constructed a P removal structure on a poultry farm in Eastern OK; this is a BMP that can remove dissolved P loading in the short term until soil legacy P concentrations decrease below levels of environmental concern. A P removal structure contains P sorbing materials (PSMs) and are placed in a location to intercept runoff or subsurface drainage with high dissolved P concentrations. As high P water flows through the PSMs, dissolved P is sorbed onto the materials by several potential mechanisms, allowing low P water to exit the structure. While they vary in form, P removal structures contain three main elements: 1) use of a filter material that has a high affinity for P, 2) containment of the material, and 3) the ability to remove that material and replace it after it becomes saturated with P and is no longer effective.
A site was identified which met all criteria for justification of construction of a P removal structure: 1) elevated dissolved P concentrations in runoff (>0.2 ppm), 2) hydraulic connectivity between the runoff/drainage produced and a surface water body, and 3) flow convergence: the site possessed potential to channel the runoff water to a single point in order to treat the water. This site was located on a poultry farm in Eastern OK.
The site was surveyed in order to obtain the necessary inputs for properly designing the P removal structure. This involved a basic NRCS survey to estimate watershed size, peak flow rates, and average annual runoff volume. In addition, several runoff grab samples were taken and analyzed for dissolved P. This information was used to determine the average annual dissolved P load, which was 45 lbs.
Knowing flow and P load parameters, we additionally chose P removal targets and desired lifetime of the structure. We chose to design a structure that would remove 20 lbs of dissolved P during the first year and be able to handle 700 gpm flow rate. Several hypothetical designs were made based on the available P sorbing materials (PSMs), such as drinking water treatment residuals, acid mine residuals, and gypsum. We chose to use a treated steel slag material as the PSM in the structure; this required about 35 tons of material.
After construction, the performance of the structure was monitored by measuring flow rates and dissolved P concentrations at the inlet and outlet. In addition, we developed software to aid in proper design of a site specific P removal structure using any PSM, in order to meet desired P removal goals and lifetime. Alternatively, this software can be used to predict the performance and lifetime of a P removal structure that has been already constructed. Licensing of software is available for private industry.
What have we learned?
The P removal structure has removed approximately 67% of all dissolved P that has flowed into it over a 16-month time period. In addition, it has handled all flow volume from every event, including a runoff event that resulted in 600 gpm. That single event delivered 2/3 lb of dissolved P, in which the structure removed 66%. While the structure is removing P as predicted based on P loading, the structure has greatly outlasted the goal of removing 45% of cumulative dissolved P in one year. This is due to the below average rainfall received over the last two years.
We also learned about the potential positives and negatives of using certain PSMs. For example, although we could have used other PSMs, in much smaller quantities (2-10 tons) that would remove equal amounts of P, we would have had to build a structure that was much larger in surface area, due to the fact that the hydraulic conductivity of these PSMs is relatively low. It is also possible to build these structures with other materials for the frame, such as concrete, earth, or wood. Structures can be constructed in ditches or potentially in the subsurface to treat tile drainage.
Last, we have some sense of economics for P removal structures and the general cost of P removal compared to other BMPs.
Future Plans
We will continue to monitor the structure. In addition, we are cooperating with several people throughout the US in helping to design P removal structures. We are also releasing design software for licensing in an attempt to promote commercialization of this BMP through private industry. A NRCS standard is currently underway and the goal is for this BMP to become cost-shared. Last, we are continuing to investigate the economics of P removal structure over a large scale area.
Authors
Chad Penn, Associate professor of agricultural and environmental chemistry, Oklahoma State University chad.penn@okstate.edu
Josh Payne, Animal waste specialist, Oklahoma State University; James Bowen, graduate assistant; Stuart Wilson, senior research specialist, Oklahoma State University; Josh McGrath, associate professor of nutrient management, University of Kentucky
Additional information
Chad Penn; chad.penn@okstate.edu; 405 744 2746
http://www.jswconline.org/content/69/2/51A.full.pdf
http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-9345/L-447%20Phosphorus%20Removal.pdf
Acknowledgements
NRCS for funding of this demonstration
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