Phosphorus Removal Structure

A new best management practice to help improve water quality

Problem          P Removal Structures           Design           Cost          Example Structures      Links/Information

What is eutrophication?

Eutrophication is a condition that results in poor aquatic ecosystem health through decreased oxygen levels and excessive plant and algae growth.


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 Phosphorus Removal Structure


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:

  1. Contains solid media with high affinity for P, commonly known as a “P sorption material”, or PSM.
  2. PSM is contained and placed in a hydrologically active area with high dissolved P concentrations.
  3. High DP water is able to flow through the contained PSM.
  4. 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.

Design Structures

Types of Phosphorus Removal Structuretri-pic

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.PhROG logo (official tm)


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.

Example Structures

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)



poultry farm aerial

General information about P removal structures can be found at the following websites:

Information about Dr. Penn’s research program:

P removal structure introductory powerpoint presentation (pdf)

Blog chronicling the installation of a structure:

P removal structure brochure (pdf)

Slide show and video:

Extension publication:

SUNUP Video:

OK Gardening Video:

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.

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:

Wastewater treatment with by-products:

Removal of nutrients from tile drainage in The Netherlands: Dr. Stefan Jansen


PhROG logo (official tm)