Utilization of Steel Slag in Blind Inlets for Dissolved Phosphorus Removal

Techno-Economic Analysis of Phosphorus Removal Structures

Excess phosphorus (P) is a major pollutant in aquatic systems. Phosphorus removal structures, landscape-scale filters designed to capture dissolved P from runoff, drainage, and wastewater offer promise in curbing P pollution. While the environmental benefits of various P removal structures are well documented, the cost-effectiveness of each structure's ability to sequester P is lacking. In this study, we compare the cost-effectiveness of P removal of the most prominent P removal structures. Specifically, we calculate the average cost per kilogram (kg) of P removed by eight different P removal structures across a range of parameter assumptions. Absent constraints, we found that (1) larger structures that use (2) regionally available phosphorus sorption materials that are (3) byproducts of industrial production (e.g., metal shavings and steel slag) rather than manufactured are more cost-effective. The average cost of P removal for most structures varies from $100 to 1300 per kg in our baseline estimations, which is comparable to the average cost for wastewater treatment. This work provides further information to guide the optimal implementation of P removal structures for conservationists.

Techno-economic and life cycle analysis of circular phosphorus systems in agriculture

Fertilizer runoff is a global nuisance that disrupts biogeochemical cycles of nitrogen and phosphorus. We perform techno-economic and life cycle analyses of selected approaches for enabling a circular economy of phosphorus. We consider four schemes: capturing P with ion-exchange resins followed by precipitation, interception by wetland and recovery in char after biomass pyrolysis, removal by bioreactor and recovery in char after bioreactor substrate pyrolysis, and using legacy phosphorus accumulated in a saturated wetland to grow crops by wetlaculture. For each system, we analyze the mass flow, calculate the degree of circularity, and examine the feasibility by techno-economic and life cycle analyses. We find that although ion exchange outperforms the others, the associated economic and emissions burden are too high. Approaches that rely on wetlands are most economically attractive and can have lower impact. However, without policy interventions, the linear economy of phosphorus is likely to remain economically most attractive.

Field Application of Spent Lime Water Treatment Residual for the Removal of Phosphorus and other Pollutants in Urban Stormwater Runoff

The threat of anthropogenic eutrophication and harmful algal blooms in lakes requires the development of innovative stormwater best management practices (BMPs) to reduce the external loading of phosphorus (P). This paper presents the findings of a 5-year study of a full-scale P removal structure constructed in Minnesota, USA with spent lime drinking water treatment residual (DWTR), a by-product of water softening at a local water treatment plant. Influent and effluent water samples were collected by auto-samplers during 43 storm events during the growing season. Samples were analyzed for P constituents, heavy metals, total suspended solids (TSS), and pH. Toxicity of the effluent was assessed using Ceriodaphnia dubia. Flow-weighted removal effectiveness was calculated for each storm event. Overall, the spent lime DWTR reduced total P loading by 70.9%, dissolved reactive P by 78.5%, dissolved P by 74.7%, and TSS by 58.5%. A significant reduction in heavy metals was also observed. Toxicity tests indicated the aquatic toxicity of the effluent treated with spent lime DWTR was not different from untreated stormwater. This study provided long-term real-world data that demonstrated that a full-scale P removal structure with spent lime DWTR significantly reduced P and other pollutants in stormwater discharging to an urban lake. Therefore, spent lime DWTR, which is currently treated as a waste product, is a promising filter material for stormwater treatment.

Estimating the variability of steel slag properties and their influence in phosphorus removal ability

Steel slag has been proven to be an effective phosphorus (P) removal media, and a potential aid to mitigate point and nonpoint P pollution in freshwater systems. However, the behavior of steel slag as a P sorption material (PSM) is often oversimplified through the generalization of its chemical and physical properties, preventing proper design of P removal structures. In this work, we tested eighteen steel slag samples from different batches, production processes, and steel-making plants, for the purpose of relating slag origin and chemical and physical properties to P removal ability, under two different flow regimes. Slag samples were also coated with aluminum (Al) and tested for P removal. Characterization included elemental composition, particle density, buffer capacity, and P removal ability. There was great variability in the evaluated properties across slag sources and origin, compelling the individual characterization of steel slag samples, since their intrinsic characteristics were key variables in determining their potential P removal capacity. Specifically, electrical conductivity (EC), bulk density, particle density and magnesium (Mg) content could explain around 70% of the variability of P removal by uncoated steel slags. Increasing residence time (RT) always increased P removal for uncoated slags. Steel slags showed a high variability in their P removal ability, but such variability was considerably decreased by coating the slags with Al. Additionally, the Al-coating process significantly improved P removal performance under more rapid flows (lower RT).

Less Agricultural Phosphorus Applied in 2019 Led to Less Dissolved Phosphorus Transported to Lake Erie

Extreme precipitation events affect water quantity and quality in various regions of the world. Heavy precipitation in 2019 resulted in a record high area of unplanted agricultural fields in the U.S. and especially in the Maumee River Watershed (MRW). March-July phosphorus (P) loads from the MRW drive harmful algal bloom (HAB) severity in Lake Erie; hence changes in management that influence P export can ultimately affect HAB severity. In this study, we found that the 2019 dissolved reactive P (DRP) load from March-July was 29% lower than predicted, while the particulate P (PP) load was similar to the predicted value. Furthermore, the reduced DRP load resulted in a less severe HAB than predicted based on discharge volume. The 29% reduction in DRP loss in the MRW occurred with a 62% reduction in applied P, emphasizing the strong influence of recently applied P and subsequent incidental P losses on watershed P loading. Other possible contributing factors to this reduced load include lower precipitation intensity, altered tillage practices, and effects of fallow soils, but more data is needed to assess their importance. We recommend conservation practices focusing on P application techniques and timing and improving resiliency against extreme precipitation events.

Adsorption Media for the Removal of Soluble Phosphorus from Subsurface Drainage Water

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.