Phosphorus Removal Structure
A new best management practice to help improve water quality
What is the cause of eutrophication?
While eutrophication is a natural process, it is accelerated by increased inputs of phosphorus (P) and nitrogen (N) to surface waters. Of these nutrients, P tends to be the most damaging. The source of P to surface waters can be from point sources, such as wastewater treatment plants, and also from non-point sources such as urban and agricultural runoff and subsurface drainage. Non-point P sources can occur from soils that possess excessive P concentrations, or soils recently amended with chemical fertilizer or animal manure.
Phosphorus is transported to surface waters as both “particulate” and dissolved P (DP). Particulate P (PP) is P that is adsorbed onto transported sediments, while DP is already “free” in solution. Dissolved P is immediately 100% biologically available to aquatic life, its transport is sustained for many years in soils with excessive P concentrations, and conventional BMPs are only able to limit PP transport, not DP. For these reasons, the P removal structure was developed to trap DP in runoff.
The P removal structure is a large, landscape scale filter for DP, intended to intercept and trap dissolved P from “hot spots” before reaching a surface water body. The P removal structure has four basic principles:
- Contains solid media with high affinity for P, commonly known as a “P sorption material”, or PSM.
- PSM is contained and placed in a hydrologically active area with high dissolved P concentrations.
- High DP water is able to flow through the contained PSM.
- The PSM is able to be removed and replaced after it is no longer effective.
Phosphorus Sorption Materials:
Many PSMs are by-products from different industries, and therefore can be obtained for low or no cost. However, all PSMs must first be screened for safety before use in a P removal structure. Some examples include steel slag and acid mine drainage treatment residuals.
Types of Phosphorus Removal Structures
A P removal structure can be constructed in many different ways and be effective, as long as they contain the four basic principles listed previously. Some options include a box structure, confined bed, and tile drain structure.
Phrog software package
The Phrog software is a tool for designing a P removal structure for a specific site. It requires a series of inputs that includes information about the flow of water, P concentrations, area available for the structure, as well as the P sorbing material (PSM) that is to be used in the structure.
The cost of a P removal structure will vary depending on site characteristics, target removal, and PSM characteristics and location. However, we have found that after several years of use, the total cost of P removal can be 30-100 dollars per lb of P removed, which partly included profit from a company to provide the service. This cost is low compared to waste water treatment which usually requires 50-200 dollars per lb P removed. A nutrient credit trading program, combined with enforced non-point total maximum daily load limits, could potentially result in profit for those who build P removal structures.
Spent PSMs are poor P sources since the P is usually tied up tightly. However, some materials such as slag, make excellent road construction materials. Other material may provide some or neutral benefit through disposal by land application to a suitable location.
EQIP Cost Share Program
The NRCS is currently developing a national standard for this new BMP so that construction of P removal structures may be cost-shared.
A P removal structure was constructed on a poultry farm in Eastern Oklahoma. Runoff originating from around the poultry barns contained elevated DP and drained into a tributary of the Illinois River. A P removal structure was constructed by intercepting runoff before it reached the creek, and channeling it into a single point where it could flow into the structure. This confined bed filter contained 40 tons of sieved and treated steel slag. The structure was designed to remove 45% of the estimated annual DP load (20 lbs) and handle flow rates from a 2 yr-24 hr storm (1.6 cfs)
Information about Dr. Penn’s research program: http://soilchemistry.okstate.edu
P removal structure introductory powerpoint presentation (pdf)
Blog chronicling the installation of a structure: http://p-structure.blogspot.com/
P removal structure brochure (pdf)
Extension publication: http://usgatero.msu.edu/v11/n02.pdf
SUNUP Video: http://www.youtube.com/watch?v=KAIXmFEQY1k
OK Gardening Video: http://www.oklahomagardening.okstate.edu/category/es/2013/112313-scrubbing
More detailed information can be found in the following publications:
Penn, C.J., J.M. McGrath, J. Bowen, and S.M. Wilson. 2014. Phosphorus removal structures: A management option for legacy phosphorus. Journal of Soil and Water Conservation. 69(2):51A-56A.
Penn, C.J., J.M. McGrath, E. Rounds, G. Fox, and D. Heeren. 2012. Trapping phosphorus in runoff with a phosphorus removal structure. J. Environ. Qual. 41:672-679.
Penn, C.J., R.B. Bryant, M.A. Callahan, and J.M. McGrath. 2011. Use of industrial byproducts to sorb and retain phosphorus. Commun. Soil. Sci. Plant Anal. 42:633-644.
Penn, C.J., R.B. Bryant, P.A. Kleinman, and A. Allen. 2007. Removing dissolved phosphorus from drainage ditch water with phosphorus sorbing materials. J. Soil Water Cons. 62:269-276.
Penn, C.J., J.M. McGrath, and R.B. Bryant. 2010. Ditch drainage management for water quality improvement. In “Agricultural drainage ditches: mitigation wetlands for the 21rst century”. Ed. M.T. Moore. 151-173.
Similar work by other researchers:
Active wetlands – the use of chemical amendments to intercept phosphate runoffs in agricultural catchments. http://wwf.fi/mediabank/4368.pdf
Klimeski, A., Chardon, W.J., Turtola, E. and Uusitalo, R. 2012. Potential and limitations of phosphate
retention media in water protection: A process-based review of laboratory and field-scale tests.
Agricultural and Food Science 21: 206–223.
Vohla, C.; Koiv, M.; Bavor, H. J.; Chazarenc, F.; Mander, Ü. Filter materials for phosphorus removal from wastewater in treatment wetlands-A review Ecol. Eng. 2010, 10.1016/j.ecoleng.2009.08.003
Mining waste byproduct capable of helping clean water: http://www.usgs.gov/newsroom/article.asp?ID=3482&from=rss
Wastewater treatment with by-products: http://publications.polymtl.ca/860/
Removal of nutrients from tile drainage in The Netherlands: Dr. Stefan Jansen