Utilization of steel slag in blind inlets for dissolved phosphorus removal

Authors: Gonzalez, Javier; Penn, Chad; Livingston, Stanley

Submitted to: Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2020
Publication Date: 6/3/2020
Citation: Gonzalez, J.M., Penn, C.J., Livingston, S.J. 2020. Utilization of steel slag in blind inlets for dissolved phosphorus removal. Water. 12(6):1593. https://doi.org/10.3390/w12061593.
DOI: https://doi.org/10.3390/w12061593

Interpretive Summary: Blind inlet, which filters surface runoff, has been proposed as an alternative to tile riser for draining farmed potholes in the Midwest. Traditionally, limestone aggregates are used as the blind inlet bed material. However, limestone does not remove dissolved phosphorus (P), and excessive P has caused harmful algal blooms. Steel slag, a byproduct from steel manufacturing, may be used as an alternative to limestone in blind inlets to remove dissolved P. In this study, we constructed a blind inlet with steel slag and evaluated its efficiency to remove dissolved P, nitrogen (N), and herbicides. The blind inlet with steel slag was constructed in late 2015, but only data from 2018 are reported due to sampling issues. The blind inlet removed at least 45% of the dissolved P and was still effective after three years. Organic N and ammonium were significantly reduced, but nitrate was increased. More than 70% of glyphosate, its byproducts, and dicamba were removed. Greater amounts of atrazine and organic carbon were measured in the outlet than inlet, likely due to sediment deposition in the blind inlet, and then dissolved into solution with time. At a cost similar to local aggregates, steel slag in blind inlets represents a simple update for improving dissolved P removal.

Technical Abstract: Blind inlets are implemented to promote obstruction-free surface drainage of field depressions as an alternative to tile risers for removal of sediment and particulate phosphorus (P) through an aggregate bed. However, conventional limestone used in blind inlets does not remove dissolved P, which is a stronger eutrophication agent than particulate P. Steel slag has been suggested as an alternative to limestone in blind inlets for removing dissolved P. The objectives of this study were to construct a blind inlet with steel slag and evaluate its ability to remove dissolved P, nitrogen (N), and herbicides. A blind inlet was constructed with steel slag in late 2015; data from 2018 is reported due to inflow sampling issues. The blind inlet removed at least 45% of the dissolved P load and was still effective after three years. The dissolved P removal efficiency was greater with higher inflow P concentrations. More than 70% of glyphosate and its metabolite, and dicamba were removed. Total N was removed in the form of organic N and ammonium, although N cycling processes within the blind inlet appeared to produce nitrate. Higher dissolved atrazine and organic carbon loads were measured in outflow than inflow, likely due to deposition of sediment-bound particulate forms not measured in inflow, which then solubilized with time. At a cost similar to local aggregate, steel slag in blind inlets represents a simple update for improving dissolved P removal.