Variations in phosphorus retention by a solid material while scaling up its application

Abstract

Abstract Significant reductions in phosphorus (P) inputs from point sources into bodies of water have been achieved in many countries, but curbing losses from non-point P sources still poses a challenge. One potential solution is to use solid P-retaining filters. In this study, we scaled up the application of a promising material (Sachtofer PR ® ) and observed the effects of variable flows, influent P concentrations, the presence of organic matter, and material alteration on P retention. The test set-ups included 1) a 6-g filter that received influents with a dissolved P concentration of 50 mg/l, 2) a 20-kg filter that received variable flow rates of tap and river water containing dissolved P amounts of up to 6 mg/l, and 3) a seven-ton filter constructed in a ditch that collected water (P concentration of up to 0.25 mg /l) from 17-ha of cropland. All filters achieved similar initial discrete P removals, but increasing the scale finally reduced cumulative P retention. The laboratory filter retained 19 mg P/g vs. 3.2 mg P/g for the meso-scale filter vs. 0.06 mg P/g for the large-scale filter, a result due largely to the decrease in the influent P concentration and the presence of humic substances. In addition, low retention times due to preferential flows and high-flow conditions greatly compromised the efficiency of the large filter. Filters should target critical sources and, consequently, the loading with significant amounts of P would improve their economic value while facilitating the future recovery and reuse of P.