Letter to the editor of Chemosphere regarding Yang et al. (2021) and techniques for assessing realistic phosphorus removal in the field

Authors: Penn, Chad

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2021
Publication Date: 8/9/2021
Citation: Penn, C.J. 2021. Letter to the editor of Chemosphere regarding Yang et al. (2021) and techniques for assessing realistic phosphorus removal in the field. Chemosphere. 286:131843. https://doi.org/10.1016/j.chemosphere.2021.131843.
DOI: https://doi.org/10.1016/j.chemosphere.2021.131843

Interpretive Summary: In correcting water quality issues, many filter materials are tested in their ability to remove phosphorus (P) from non-point source runoff and tile drainage. This letter provides the rationale for the need for use of flow-through methodology when assessing phosphorus sorption materials (PSMs) to be used in P removal structures. Previously published articles, specifically by Yang et al. (2021) utilized a static batch system to test PSMs; such a method is inappropriate and highly overestimates the degree of P removal by the filter material.

Technical Abstract: Yang et al. (2021) presented results from a laboratory study in which the phosphorus (P) sorption ability of a “designer” biochar was quantified regarding P removal capacity, kinetics, and mechanisms. This was a high-quality study and provided useful information about production of designer biochar, how it is different from regular biochar, and the mechanisms of P removal. The purpose of this letter is to illustrate that while their methodology was sound, the estimate for P removal was extremely high compared to what can be expected in actual use. P sorption maximum determined by the flow-through technique was 0.5 mg/g, only a fraction of the isotherm P sorption max value (25 mg/g). Phosphorus sorption values for filter material obtained from utilization of batch isotherms such as Yang et al. (2021) will provide an extreme overestimation of dissolved P removal compared to what can be expected when those materials are used in P removal structures. The flow-through technique explained here has been shown to accurately estimate P removal performance in field scale units if conducted under similar conditions of P concentration and retention time.