Phosphorus Sequestration by Chemical Amendments to Reduce Leaching from Wastewater Applications

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Abstract
Phosphorus‐immobilizing amendments can be useful in minimizing P leaching from high P soils that may be irrigated with wastewater. This study tested the P‐binding ability of various amendment materials in a laboratory incubation experiment and then tested the best amendment in a field setup using drainage lysimeters. The laboratory experiment involved incubating 100‐g samples of soil (72 mg kg−1 water‐extractable phosphorus, WEP) with various amendments at different rates for 63 d at field moisture capacity and 25°C. The amendments tested were alum [Al2(SO4)3·14H2O], ferric chloride (FeCl3), calcium carbonate (CaCO3), water treatment residual (WTR), and sugarbeet lime (SBL). Ferric chloride and alum at rates of 1.5 and 3.9 g kg−1, respectively, were the most effective amendments that decreased WEP to 20 mg kg−1, below which leaching has previously been shown to be low. Alum (1.3 kg m−2), which is less sensitive to redox conditions, was subsequently tested under field conditions, where it reduced WEP concentration in the 0‐ to 0.15‐m layer from 119 mg kg−1 on Day 0 to 36.1 mg kg−1 (85% decrease) on Day 41. Lysimeter breakthrough tests using tertiary‐treated potato‐processing wastewater (mean total phosphorus [TP] = 3.4 mg L−1) showed that alum application reduced leachate TP and soluble reactive phosphorus (SRP) concentrations by 27 and 25%, respectively. These results indicate that alum application may be an effective strategy to immobilize P in high P coarse‐textured soils. The relatively smaller decreases in TP and SRP in the leachate compared to WEP suggest some of the P may be coming from depths below 0.2 m. Thus, to achieve higher P sequestration, deeper incorporation of the alum may be necessary.
Funding Information
  • Minnesota Pollution Control Agency

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