Software Release: PhROG

The design software for P removal structures has been completed, and is available for licensing from Oklahoma State University.  PhROG: "Phosphorus Removal Online Guidance".

This software can serve two purposes:

1. Design a site-specific P removal structure using any suitable PSM, in order to meet the desired dissolve P load removal goal and  lifetime
2. Estimate the P removal and lifetime of a previously constructed P removal structure.

Again, the structure can be built in a variety of settings, as long as the following principles are maintained:

1. Contains sufficient mass of solid media with high affinity for P, commonly known as a “P sorption material”, or PSM.  A PSM is not simply a typical gravel material, although it may be the same particle size as gravel, since the material must have a strong capacity to adsorb P.  PSMs are usually industrial by-products or manufactured.  However, there are some PSMs that occur naturally.
2. PSM is contained and placed in a hydrologically active area with high dissolved P concentrations. 
3. High dissolved P water is able to flow through the contained PSM at a suitable rate.
4. The PSM is able to be removed and replaced after it is no longer effective.

The most suitable placement for a P removal structure includes drainage ditches, tile drain outlets, and areas where surface flow naturally converges.  For each site, the following information must be obtained in order to make a proper design:

1. Average annual dissolved P load, which can be calculated from average annual flow volume and typical flow-weighted concentration
2. Peak flow rates desired for the structure to be able to handle
3. Chemical and physical characteristics of the PSM to be used
4. Available area
5. Hydraulic head, which is a result of both the landscape slope and the depth of the ditch
6. Desired P cumulative P removal goal and lifetime

 Three examples of different settings for a P removal structure are diagrammed below.

P removal structure designed to treat all ditch-flow:

An in-field subsurface P removal structure designed to treat a tile drain:

An in-ditch P removal structure that only treats the tile drain outlet:

Example Design Using PhROG Software

Conditions: Ditch drainage system with average annual flow of 2.35 million gallons and flow-weighted dissolved P concentration of 0.25 mg/L.  Also total P concentrations of 2 mg/L and sediment of 4 mg/L.  Assume certain ditch dimensions as shown below.  PSM is a flue-gas gypsum.  Desired removal goal of 35% cumulative, over 3 years.

The output below provides all the information necessary to construct the ditch structure and meet the desired goals, include flow rate, in addition to not exceeding the current ditch flow capacity more than 20%

1. Mass and detph of flue-gas gypsum required
2. Length of structure
3. Number of subsurface drainage pipes needed (pipe diameter specified by user, in this case, 4 inches).
4. Actual retention time and flow rate
5. % decrease in ditch flow capacity as a result of the structure
6. A table of output, year by year, for dissolved and total P removal presented as both a % and a mass.

Here is another example design, except in this case we will design a "bed" structure for a below-ground tile treatment.  

Conditions:  Flow weighted P concentration of dissolved P = 1 mg/L, Annual flow volume of 1.4 million gallons and peak flow rate of 468 gpm.  Hydraulic head of 24 inches and maximum area of 20 x 20 ft.  PSM is a treated steel slag material and removal goal is 35% over 3 years.  See input below:

The output below specifies the requirements for the target goals to be met for this subsurface bed structure, using the specified material:

1. Required treated slag mass of 38.4 tons at 24 inches deep
2. Bed is 20 x 17.4 ft 
3. 7 subsurface drainage pipes at a diameter specified by user (in this case, 4 inches)
4. Actual flow rate through the material is 517 gpm.
5. Material is not sensitive to retention time (RT)
6. A table of yearly performance for the hypothetical structure.  

Please contact Chad Penn at Oklahoma State University if you are interested in obtaining a license for the software.