UNIVERSITY OF WISCONSIN SYSTEM SOLID WASTE RESEARCH PROGRAM Student Project Report. Dissolved Phosphorus Removal using Steel Slag By-Products

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1 UNIVERSITY OF WISCONSIN SYSTEM SOLID WASTE RESEARCH PROGRAM Student Project Report Dissolved Phosphorus Removal using Steel Slag By-Products May 2015 Student Investigator: Matt Tlachac Advisor: Dr. Daniel Keymer University of Wisconsin-Stevens Point

2 Introduction The Lower Green Bay and Fox River Valley has been designated an Area of Concern (AOC) in the Great Lakes Region. The watershed has recently come under an Environmental Protection Agency (EPA) approved Total Maximum Daily Limit (TMDL) to reduce discharges of Total Suspended Solids (TSS) and phosphorus. Over half of these discharges are known to be coming from agricultural lands. Means to reduce surface run-off sources of TSS and phosphorus are well understood and local conservation agencies are in the process of working with producers to improve and expand these practices. However, there is currently no means of containing dissolved phosphorus from drain tile lines. Initial United States Department of Agriculture (USDA) Agricultural Research Service work indicates that dissolved phosphorus concentrations in tiled lands testing excessive for phosphorus and/or that have receive heavy applications of manure applications are likely to have phosphorus concentrations in discharge of 1 mg L -1 or greater (Joern et al., 1998). The AOC has a number of areas identified as having high soil P concentrations and there are many large dairy operations in the area. The need for these farm operations to land apply their manure often leads to over saturation of phosphorus in agricultural fields. Phosphorus in the environment binds readily to a handful of very specific elements due to phosphorus most common molecular form in the environment: phosphate. Phosphates consist of one phosphorus atom bonded to four oxygen atoms and carry an inherent 3- charge; often seen as PO 3-4. The negative charge often repels the phosphate molecule away from slightly negative soil particles. But clay particles in particular often have positive trivalent elements at their center, allowing for a strong attraction between the 3- charge of the phosphate and the 3+ charge of the clay particle site. Iron and aluminum are the two most popular trivalent clay components that strongly

3 interact with phosphorus. Calcium and magnesium are also commonly associated with having strong attractive forces with phosphorus. Steel slag is an industrial by-product often used for beneficial uses under Wisconsin Administrative Code NR 538; however there are still many thousands of tons of slag being landfilled each year from operational foundries across the state. Facilities that use electric arc furnaces and have more basic conditions produce slags that tend to have higher phosphorus removal capabilities (Jones, 2015). Basic conditions refer to an environment that have a higher concentration of OH - molecules than H + atoms, which occurs at ph values above 7. The more basic slag, often referred to as electric arc furnace slag (EAF slag), will also provide a similar environment to many soils that have basic parent materials such as limestone. Iron, aluminum, calcium, and magnesium are often common constituents in the composition of EAF slag, which gives the slag its natural tendency to sequester dissolved phosphorus. Being able to utilize EAF slag as an adsorbent for phosphorus could provide multiple benefits: diverting slag waste from landfills and limiting nonpoint phosphorus discharges to surface waters. The objective of this research project was to quantify the effect of contact time on phosphorus adsorption to two separate sources of electric arc furnace (EAF) slag. The hypothesized outcome was if the contact time was increased between the phosphorus solution and the EAF slag, then higher amounts of phosphorus would be removed from the water. We also hypothesized that the slag source with the higher iron concentrations would be the more effective filter media for removing phosphorus. Methods In order to quantify the effectiveness of phosphorus removal due to adsorption onto EAF slag, a phosphorus solution with a known concentration the design of this experiment was testing two different times of contact between and the EAF slag in a

4 laboratory setting. Two different sources of EAF slag were also tested side by side in the experiment for removal effectiveness. The times of contact tested were 10 and 30 minutes, chosen to approximate peak and average tile drain flow rates, respectively. A stock solution containing phosphorus was prepared to a M concentration in the lab by dissolving dibasic potassium phosphate (K 2 HPO 4 ) in distilled water. The phosphorus stock solution was then mixed into 400 liters of tap water to achieve an influent solution with 1.2 mg L -1 phosphorus, contained in two 55 gallon HDPE drums connected in parallel to allow equal draw from each drum. The phosphorus solution was pumped up through the reaction vessels containing the EAF slag using a peristaltic pump. Flow rate was estimated from the vessel volume and slag porosity ( ) using the following equations: V pore = V vessel * HRT = V pore /Q where HRT is the hydraulic residence time and Q represents flow rate. The vessels ranged from L to L in volume. Each trial lasted for a duration of 48 hours, and 10 total effluent samples were taken during each trial. The sample schedule was as follows: 0, 0.5, 1, 1.5, 2, 3, 5, 9, 21, and 48 hours into each trial. The early phase of each trial was sampled more intensively due to the findings of past studies showing decreased removal rates of EAF slag over time. Each slag sample was run in triplicate vessels for each contact time to ensure more reliable data, for a total of twelve trials. Effluent samples were refrigerated at 4 degrees C for no more than two weeks, before being filtered through a 0.45 µm filter. The filtrate from the test trials was run through a Lachat QuikChem Autoanalyzer to measure the soluble reaction phosphorus (SRP) concentration.

5 The two slag sources varied in their particle size distribution. Slag source 1 from Whitesville, IN, had been already crushed, whereas slag source 2, from Wisconsin Rapids, had not been crushed yet. Manual size reduction of slag aggregates was used to try and obtain a more homogenous mixture of particle sizes comprising the adsorbent. In order to measure the distribution of particle sizes, a sieve analysis was performed with mesh opening sizes as follows, from top to bottom, in millimeter measurements: 12.7, 4.75, 2.36, 2.0, 1.18, and 1.0. Performance metrics for the adsorption trials were calculated using formulas derived by McGrath and Penn (2011). The maximum phosphorus (P) added calculation determines what mass of phosphorus could be added to the slag filter before the effluent phosphorus concentrations would rise above 99% of the original influent concentration. Variables B and m were the same as explained in the Cumulative P Removed (%) equation. The equation used to calculate it was: MMMMMMMMMMMMMM PP AAAAAAAAAA = LLLL BB mm mg P kg-1 Cumulative P removed (%) is a calculation that determines what percentage of the maximum phosphorus loaded into the slag filters would be sequestered by the media. The integrated expressions containing variables B and m in the equation below are taken from curves fit for P removal with incremental P addition (Figures 1-4) and x is the maximum P added (calculated above): CCCCCCCCCCCCCCCCCCCC PP RRRRRRRRRRRRRR (%) = xx 0 (BBBB^mmmm)dddd xx mg P Cumulative P removed is also expressed as a mass value with units of mg/kg. The equation does utilize a couple of the previously mentioned calculations. The equation used was:

6 CCCCCCCCCCCCCCCCCCCC PP RRRRRRRRRRRRRR = MMMMMM PP aaaaaaaaaa (CCCCCCCCCCCCCCCCCCCC PP RRRRRRRRRRRRRR (%) 100) The lifespan of each filter was calculated to determine how many days the filter could last until all the phosphorus sequestering ability was spent. The equation used was: LLLLLLLLLLLLLLLL = MMMMMM PP AAAAAAAAAA IIIIIIIIIIIIIIII [PP] FFFFFFFF RRRRRRRR MMMMMMMM oooo SSSSSSSS Results EAF Slag 1 had a more homogenous composition of aggregates according to the particle size distribution experiment % of the material was between 12.7 and 4.75 mm in diameter. EAF Slag 2 had a higher diversity of particle sizes with 28.41%, 58.38%, and 9.89% in the 12.7+, , and mm classes respectively. Slag 2 was expected to have more diversity in its particle sizes due to the manual crushing that was needed in order to obtain the more homogenous aggregate size. However, Slag 1 had a higher proportion of aggregates smaller than 4.75 mm (20.3% versus 13.2% for Slag 2). The results for the particle size distribution can be found in Table 1 for both EAF slags. The chemical composition of EAF Slag 1 revealed a high concentration of phosphorus binding elements that were expected to be present. Iron and calcium were the two largest components with 23.79% and 22.03% respectively. The next three largest components were magnesium, manganese, and aluminum; with 6.04%, 4.09% and 2.29%, respectively. Table 2 gives a complete chemical composition of Slag 1; a composition of Slag 2 was not available at the time of the study. The flow rate was derived from a calculation utilizing the porosity of the slag in use. With an average porosity measurement of 0.467, the average pore space in the

7 reaction vessel came out to be L. When the goal was to have a 10 minute retention time, calculations told us we wanted a flow of ml/s. When our goal was to have a 30 min retention time, the flow calculation came to ml/s. The maximum P added calculation told us that EAF Slag 1 with a 30-minute contact time would be able to handle the highest phosphorus loading rate. The treatment condition that would accept the lowest phosphorus loading rate would be EAF Slag 1 with a 10-minute contact time. The max P added calculation for EAF Slag 2 with a 10-minute contact time seems to have been skewed by some measure within the calculation. After comparing the rest of the data, Slag 2 with a 10-minute contact time would have been expected to have the lowest allowable phosphorus loading rate. The lifespan calculations for the different treatment conditions varied quite a bit. The longest lifespan of 44 days belonged to Slag 1 with a 30-minute contact time, and the shortest lifespan of 2 days belong to Slag 1 with a 10-minute contact time. Slag 2 s lower readiness to remove phosphorus would explain why the filters would have a longer lifespan. The needed mass of phosphorus to saturate every bonding site would require a longer time to reach with Slag 2. Within the same contact time treatment, EAF Slag 1 had a higher Cumulative P Removal (%) in the 10-minute trials. Slag 1 removed approximately 20% of the phosphorus on average, and Slag 2 removed approximately 4% consistently. The 30- minute contact time treatment did not produce significant differences in percent phosphorus removed between the two slag sources. The mass of phosphorus removed per mass of slag had the highest result with EAF Slag 1 with a 30-minute contact time with 117 mg P kg -1. The lowest removal rate was seen using Slag 2 with a 30-minute contact time with a value of 9 mg P kg -1.

8 Even though replicate trials of each treatment condition were carried out, similar results were rarely seen. Attempting to hold all variables constant proved to be more difficult than thought. Water behavior and flow inside the reaction vessel also could have varied from trial to trial, which could explain the variability witnessed in the calculations. In future studies, more replicate trials will need to be completed in order to give a more concise data set. Discussion Slag 1 was more than 3 times higher than Slag 2 in the 10-minute contact time treatment, and also higher in the 30-minute contact time treatment. This conclusion also applies to the cumulative mass of phosphorus removed. The particle size distribution of the two EAF slags would support this conclusion as well due to Slag 1 s higher portion of smaller size aggregates. The prevalence of those smaller size aggregates means there is more surface area within the EAF slag media for the phosphorus to interact and bind to those phosphorus attracting elements such as: calcium, magnesium, aluminum, and iron. C. J. Penn et al. also found the concentrations of those 4 elements in particular to be strong indicators of a filters phosphorus removal capacity (McGrath and Penn, 2011) Table 2 confirms that those 4 elements are present in relatively high concentrations within that slag. The impact of contact time has two different stories when comparing the data within each slag source. For Slag 1, the longer contact time had created a difference in the calculated max P added, lifespan of the filters, and the cumulative mass of P removed. The max P added values for the longer contact time suggest those trials could have accepted over twice as much phosphorus loading than the shorter trial and still produce a clean effluent. Finding that contact time is a significant factor is consistent with what C. J. Penn found in his 2011 study of EAF slag flow through phosphorus

9 removal filters (McGrath and Penn, 2011). Slag 2 on the other hand did not exhibit such predictable results. Although the removal percentage went up, many of the other calculated factors do not follow the same trend. Even within the same treatment, different trials produced varied results. As with any project, a few limitations stood out as the trials were carried out and unfolded. The lack of constant mixing in the 55-gallon drums could have led to uneven loading rates of the dissolved phosphorus to the filters. With slag 2 not being pretreated for homogenous aggregate size, manual crushing of the aggregates was required. I believe this fact heavily influenced the difference in the particle size distribution witnessed between the two slags. While running the trials with 30-minute contact times, periodic observation of the discharge flows would lead one to believe that steady even flows was not being achieved. The construction and design of the equipment was often correct on paper, but would run into issues in reality. In order to avoid these issues, running each trial separately; one bin at a time would be advised. Future studies in the area of dissolved phosphorus removal using EAF slag adsorption could research the ease and availability of phosphorus reclamation out of the slag filters. If possible, the reclaimed phosphorus and nutrients could then be reapplied to the field it came from, or a surrounding area in need of phosphorus, but be applied in a more conservation minded method. Running multiple filters side by side, with some in service, and some out of service in reclaim stages could be a potential layout. From the data generated by this laboratory study, a pilot scale project should be conducted in order to further investigate the feasibility of using EAF slag as a phosphorus removal structure for agricultural tile drainage fluid.

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11 Tables and Figures Table 1. Particle size distribution for both EAF slags 1 and 2. Slag 1 Slag 2 Particle Sizes (mm) % weight Particle Sizes (mm) % weight < < Unaccounted 0.13 Unaccounted 0.01 Total Total Table 2. Elemental composition of EAF slag 1. Results were provided by Whitesville Mill Services. Metal and trace element concentrations were found using a inductively coupled plasma optical emission spectrometer. Material Slag 1 Element Concentration (PPM) Aluminum Antimony <0.278 Aresenic <0.036 Barium Beryllium 0.80 Cadmium 3.33 Calcium Chromium Cobalt 6.51 Copper Iron Lead 8.89 Magnesium Manganese Molybdenum Nickel 5.01 Potassium Selenium <0.037 Silver <0.052 Sodium Sulfur

12 Thallium Titanium Vanadium Zinc Table 3 shows various calculations for the trials with 10 minute residence times. The Maximum P Added calculation determines how much P could have been added to each slag filter before effluent P concentrations rose about 1% of the original concentration. The lifespan calculation determines how many days the slag filter could remain effective before becoming spent. Cumulative P Removal % is a calculation to determine what percentage of the P added to the slag was sequestered by the filter. The mass of P removed during each trial is quantified by the Cumulative P Removed calculation. 10 Minute Contact Time Slag 1 Slag 2 Trial Maximum P Added (mg) Lifespan (days) Cumulative P Removal (%) Cumulative P Removed (mg/kg) Table 4 shows various calculations for the trials with 30 minute residence times. The Maximum P Added calculation determines how much P could have been added to each slag filter before effluent P concentrations rose about 1% of the original concentration. The lifespan calculation determines how many days the slag filter could remain effective before becoming spent. Cumulative P Removal % is a calculation to determine what percentage of the P added to the slag was sequestered by the filter. The mass of P removed during each trial is quantified by the Cumulative P Removed calculation. 30 Minute Contact Time Slag 1 Slag 2 Trial Maximum P Added (mg) Lifespan (days) Cumulative P Removal (%) Cumulative P Removed (mg/kg)

13 P removed (%) y = 96.94e x R² = y = e x R² = P added (mg/kg) y = e x R² = Figure 1 shows slag 1 s ability to remove phosphorus when 10 minutes of contact is allowed. Trial A is depicted with diamonds, has a trendline equation of Y=78.237e x and an R 2 value of Trial B is depicted with squares, has a trendline equation of Y=110.51e -.044x and has an R 2 value of Trial C is depicted with triangles, has a trendline equation of Y=96.94e x and has an R 2 value of P removed (%) y = y e = e x y = x e x R² = R² = R² = P added (mg/kg) Figure 2 shows slag 2 s ability to remove phosphorus when 10 minutes of contact is allowed. Trial D is depicted with diamonds, has a trendline equation of Y=12.157e x and an R 2 value of Trial E is depicted with squares, has a trendline equation of Y=14.055e x and an R 2 value of Trial F is depicted with triangles, has a trendline equation of Y=16.954e x and has an R 2 value of

14 P removed (%) y = e x R² y = e y = e x R² = x R² = P added (mg/kg) Figure 3 shows slag 1 s ability to remove phosphorus when 30 minutes of contact is allowed. Trial A is depicted with diamonds, has a trendline equation of Y=83.524e x and an R 2 value of Trial B is depicted with squares, has a trendline equation of Y=84.826e x and has an R 2 value of Trial C is depicted with triangles, has a trendline equation of Y=82.553e -0.01x and has an R 2 value of P removed (%) y = e x R² = y = e x R² = y = e x R² = P added (mg/kg) Figure 4 shows slag 2 s ability to remove phosphorus when 30 minutes of contact is allowed. Trial D is depicted with diamonds, has a trendline equation of Y=68.995e x and an R 2 value of Trial E is depicted with squares, has a trendline equation of Y=66.749e x and an R 2 value of Trial F is depicted with triangles, has a trendline equation of Y=53.107e x and has an R 2 value of

15 References Fox, Garey, Derek Heeren, Joshua M. McGarth, Chad J. Penn, Elliot Rounds Journal of Environmental Quality. Trapping Phosphorus in Runoff with a Phosphorus Removal Structure. Vol 41: Joern, B. C., R. R. Simard, J. T. Sims Journal of Environmental Quality. Phosphorus Loss in Agricultural Drainage: Historical Perspective and Current Research. Vol 27: Jones, Jeremy A. T American Iron and Steel Institute. Electric Arc Furnace Steelmaking. Webpage. Info/Electric%20Arc%20Furnace%20Steelmaking.aspx McGrath, Joshua. M., Chad J. Penn Journal of Water Resource and Protection. Predicting Phosphorus Sorption onto Steel Slag Using a Flow-through Approach with Application to a Pilot Scale System. Vol 3: