The precipitate from chemical phosphorus removal systems typically becomes a component of the total biosolids produced by a wastewater facility. Biosolids containing ferric and alum sludge are often used as a soil amendment to add phosphorus as well as other nutrients.
But if your plant is considering switching to rare earth coagulant to achieve an ultra-low phosphorus target or other operational benefits, how effective will the biosolids be as a soil amendment and how will the rare earth metals impact the plants that will grow in that soil?
To find out, a study was conducted in Wisconsin to compare the availability of phosphorus to corn crops from rare earth biosolids, ferric biosolids and commercial fertilizer. Small plot studies were conducted at four different locations in the state and each one included plots with an untreated control and those that were treated with a commercial P fertilizer, ferric biosolids and rare earth biosolids.
The results showed that the commercial fertilizer increased phosphorus in the soil the most, followed by rare earth biosolids, then ferric biosolids, suggesting that rare earth biosolids provide more available phosphorus than ferric biosolids.
Measurements of corn whole-plant dry matter showed that the yield either increased or was unaffected by the rare earth biosolids. This indicates that soil amendment with rare earth biosolids is not expected to negatively impact the growth and yield of corn.
Since rare earth metals were also found in plants from the untreated control plots, researchers concluded that the application of rare earth biosolids is not adding foreign metals to the soil. The study also suggests that since rare earth concentration in the plant material is not significantly higher than the control, the rare earths are not bioavailable. As a result, the application of rare earth biosolids is not expected to increase the concentration of rare earths in corn beyond what would be found naturally.
Learn about ClariPhos™, a game-changing rare earth coagulant that outperforms aluminum- and iron-based alternatives for phosphorus removal.
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