Abstract:Reducing dissolved phosphorus (P) losses from legacy P soils to surface waters is necessary for preventing algal blooms. Phosphorus removal structures containing steel slag have shown success in treating surface runoff for dissolved P, but little is known about treating subsurface (tile) drainage. A ditch-style and subsurface P removal structure were constructed using steel slag in a bottom-up flow design for treating tile drainage. Nearly 97% of P was delivered during precipitation-induced flow events (as opp… Show more
“…The slag used in this study did not clog up, continues to remove dissolved P after three years, and performed as expected based on laboratory flow-through experiments, unlike the slag P removal structure reported by Penn et al [31]. The main difference in those studies is the source water; this study treated surface runoff water instead of tile drainage water, which contains appreciable bicarbonate and dissolved forms of CO 2 compared to surface runoff [31]. The under-performance of slag in their study was attributed to the formation of Ca carbonate instead of Ca phosphate through bicarbonate input, which additionally clogged the structure, besides consuming soluble Ca that would usually precipitate Ca phosphate for P removal.…”
Section: Summary and Implicationssupporting
confidence: 61%
“…While limestone-based blind inlets have been shown to remove little to no dissolved P [4,5], this study demonstrated that a simple update to slag would permit blind inlets to remove dissolved P in addition to sediment, particulate P, and provide obstruction-free drainage of depressions. The slag used in this study did not clog up, continues to remove dissolved P after three years, and performed as expected based on laboratory flow-through experiments, unlike the slag P removal structure reported by Penn et al [31]. The main difference in those studies is the source water; this study treated surface runoff water instead of tile drainage water, which contains appreciable bicarbonate and dissolved forms of CO 2 compared to surface runoff [31].…”
Section: Summary and Implicationsmentioning
confidence: 58%
“…This is expected since it has been suggested that for Ca-phosphate precipitation to occur at pH 8, Ca concentrations between 30 and 100 mg L −1 are necessary; at least 50 mg Ca L −1 is required for complete dissolved P removal [29]. For a tile-drain P removal structure utilizing EAF slag, dissolved P removal dramatically decreased when the pH of treated water dropped to 8.5 or less [31]. In addition, Ca phosphate precipitation is also subject to kinetics, and therefore favored by a greater retention time [7].…”
Blind inlets are implemented to promote obstruction-free surface drainage of field depressions as an alternative to tile risers for the 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 only 2018 are 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 the 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.
“…The slag used in this study did not clog up, continues to remove dissolved P after three years, and performed as expected based on laboratory flow-through experiments, unlike the slag P removal structure reported by Penn et al [31]. The main difference in those studies is the source water; this study treated surface runoff water instead of tile drainage water, which contains appreciable bicarbonate and dissolved forms of CO 2 compared to surface runoff [31]. The under-performance of slag in their study was attributed to the formation of Ca carbonate instead of Ca phosphate through bicarbonate input, which additionally clogged the structure, besides consuming soluble Ca that would usually precipitate Ca phosphate for P removal.…”
Section: Summary and Implicationssupporting
confidence: 61%
“…While limestone-based blind inlets have been shown to remove little to no dissolved P [4,5], this study demonstrated that a simple update to slag would permit blind inlets to remove dissolved P in addition to sediment, particulate P, and provide obstruction-free drainage of depressions. The slag used in this study did not clog up, continues to remove dissolved P after three years, and performed as expected based on laboratory flow-through experiments, unlike the slag P removal structure reported by Penn et al [31]. The main difference in those studies is the source water; this study treated surface runoff water instead of tile drainage water, which contains appreciable bicarbonate and dissolved forms of CO 2 compared to surface runoff [31].…”
Section: Summary and Implicationsmentioning
confidence: 58%
“…This is expected since it has been suggested that for Ca-phosphate precipitation to occur at pH 8, Ca concentrations between 30 and 100 mg L −1 are necessary; at least 50 mg Ca L −1 is required for complete dissolved P removal [29]. For a tile-drain P removal structure utilizing EAF slag, dissolved P removal dramatically decreased when the pH of treated water dropped to 8.5 or less [31]. In addition, Ca phosphate precipitation is also subject to kinetics, and therefore favored by a greater retention time [7].…”
Blind inlets are implemented to promote obstruction-free surface drainage of field depressions as an alternative to tile risers for the 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 only 2018 are 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 the 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.
“…29 The efficiency of steel slag in removing P from different types of water, surface water as well as wastewater, has been confirmed in the literature. [30][31][32] However, the present study contributes to the literature by explaining the role of aeration at different pH values in enhancing the removal mechanisms.…”
BACKGROUND: The discharge of wastewater with heavy loads of phosphorus (P) leads to eutrophication in natural water systems. The current work investigated the removal of P from synthetic wastewater via a slag filtration system with a high content calcium oxide (CaO) filter media (HCa) followed by treatment in an electric arc furnace (EAF). The pH, point of zero charge (PZC) and X-ray fluorescence (XRF) of the HCa filter medium was studied. The removal of phosphorus was investigated in a designed vertical column filters in aerated HCa (AEF) and unaerated HCa (UEF) systems. Fourier transform infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray (SEM-EDX) analyses was implemented for studying the microstructure of HCa. RESULTS: The results of XRF revealed that CaO ranged from 20.2 to 49.5%. The PZC for the HCa filter was recorded at pH 17.75. The highest efficiencies recorded were 94.65 ± 3.46% and 96.13 ± 2.75% at pH 3, and 93.70 ± 2.59% and 97.15 ± 1.59% at pH 5 for AEF and UEF, respectively. These findings indicated that AEF performed greater removal than UEF systems, possibly resulting from the presence of high Ca concentration in AEF, which plays an important role in the process of phosphorus removal. The main elements on the surface of HCa included oxygen, carbon, magnesium, Ca, aluminium and silicon. XRD analysis indicated that the precipitation of orthophosphate as Ca and Ca-phosphates was the removal mechanism, which was confirmed by FTIR analysis. CONCLUSION: These findings demonstrated the efficiency of HCa in removing P from wastewater.
“…Calcium carbonates precipitate on the slag instead of calcium phosphate when bicarbonate and dissolved forms of CO 2 are present in the subsurface drainage, which results from water infiltrating through calcareous soils and microbial respiration [ 41 , 42 ]. This decrease in capacity is due to (1) the bicarbonate and phosphate ions competing to adsorb to the calcium minerals and (2) the decrease in pH due to the formation of calcium carbonate and soluble calcium concentration, which negatively impacts the SFS’s ability to precipitate phosphate ions as calcium phosphate [ 41 , 42 ]. Specifically, the SFS has a decrease in P removal via calcium phosphate precipitation when the pH of the solution is below 8.5 [ 41 , 42 ].…”
Phosphorus (P) is a valuable, nonrenewable resource in agriculture promoting crop growth. P losses through surface runoff and subsurface drainage discharge beneath the root zone is a loss of investment. P entering surface water contributes to eutrophication of freshwater environments, impacting tourism, human health, environmental safety, and property values. Soluble P (SP) from subsurface drainage is nearly all bioavailable and is a significant contributor to freshwater eutrophication. The research objective was to select phosphorus sorbing media (PSM) best suited for removing SP from subsurface drainage discharge. From the preliminary research and literature, PSM with this potential were steel furnace slag (SFS) and a nano-engineered media (NEM). The PSM were evaluated using typical subsurface drainage P concentrations in column experiments, then with an economic analysis for a study site in Michigan. Both the SFS and generalized NEM (GNEM) removed soluble reactive phosphorus from 0.50 to below 0.05 mg/L in laboratory column experiments. The most cost-effective option from the study site was the use of the SFS, then disposing it each year, costing $906/hectare/year for the case study. GNEM that was regenerated onsite had a very similar cost. The most expensive option was the use of GNEM to remove P, including regeneration at the manufacturer, costing $1641/hectare/year. This study suggests that both SFS and NEM are both suited for treating drainage discharge. The use of SFS was more economical for the study site, but each site needs to be individually considered.
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