Trapping Phosphorus in Runoff with a Phosphorus Removal Structure

Abstract

Reduction of phosphorus (P) inputs to surface waters may decrease eutrophication. Some researchers have proposed filtering dissolved P in runoff with P‐sorptive byproducts in structures placed in hydrologically active areas with high soil P concentrations. The objectives of this study were to construct and monitor a P removal structure in a suburban watershed and test the ability of empirically developed flow‐through equations to predict structure performance. Steel slag was used as the P sorption material in the P removal structure. Water samples were collected before and after the structure using automatic samples and analyzed for total dissolved P. During the first 5 mo of structure operation, 25% of all dissolved P was removed from rainfall and irrigation events. Phosphorus was removed more efficiently during low flow rate irrigation events with a high retention time than during high flow rate rainfall events with a low retention time. The six largest flow events occurred during storm flow and accounted for 75% of the P entering the structure and 54% of the P removed by the structure. Flow‐through equations developed for predicting structure performance produced reasonable estimates of structure “lifetime” (16.8 mo). However, the equations overpredicted cumulative P removal. This was likely due to differences in pH, total Ca and Fe, and alkalinity between the slag used in the structure and the slag used for model development. This suggests the need for an overall model that can predict structure performance based on individual material properties.

Appropriate technology for domestic wastewater management in under-resourced regions of the world

“…In addition, long-term field testing of the ditch filter demonstrated a need to regularly till the surface of the gypsum filter bed to maintain satisfactory flow rates for adequate P removal. Penn et al (2012) reported on the development, installation, and monitoring of a P removal structure to treat golf course runoff from a 320-ha catchment near Stillwater, OK (USA). The P removal structure was filled with steel slag, a by-product of the steel industry, and was located in a drainage ditch at the outlet of the catchment.…”

“…The P removal structure was filled with steel slag, a by-product of the steel industry, and was located in a drainage ditch at the outlet of the catchment. Penn et al (2012) monitored a total of 54 runoff events over a period of 5 months in 2010, including 20 resulting from natural rainfall and 34 resulting from irrigation of the golf greens located 130 to 150 m up gradient of the P removal structure. The structure removed about 25% of the total dissolved (TDP) load and the P removal efficiencies were higher for irrigation runoff (62%) than for natural runoff (21%), owing to lower retention times during large flow events produced by heavy rainfall.…”

Potential and limitations of phosphate retention media in water protection: A process-based review of laboratory and field-scale tests

“…Thus, a clear discrepancy was evident between the laboratory batch tests and the practical-scale application. Penn et al (2012) studied the performance of a P removal filter containing electric arc furnace slag sieved to about 6-11 mm in a 320 ha watershed consisting of residential, golf course and undeveloped areas. The volume of the slag material was about 1.5 m 3 , and the performance of the structure was monitored for five months.…”

“…contact time of water inside the structure) such that as the flow increased, retention efficiency decreased. According to the calculations of Penn et al (2012), the amount of P delivered to the structure corresponded to 102.8 µg P g -1 of slag, and the P mass removed by the structure was 26 µg g -1…”

“…The authors argued that the discrepancy stemmed from the different chemical characteristics of the slag used in the field and the slag sample from the same steel mill they had studied in the laboratory (e.g., the pH of the slag used in the field was clearly lower than the pH of the slag tested in the laboratory). The coarse size of the slag also clearly affected P retention though its influence on the reactive surface area, but Penn et al (2012) made the trade-off in favour of high permeability in order to allow conducting peak flows (carrying the majority of the P mass) through the slag. …”