Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas (2014) / Chapter Skim
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52 5.1 Introduction This chapter describes the laboratory testing and modeling methods used to reduce the dissolved metals concentration in stormwater. The first objective of this work was to develop a standard protocol for evaluating effectiveness of various processes for treating highway runoff.
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53 Figure 5-1. Adsorption data for single solute Cu(II)
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54 ter to sorb to the media. Indeed, Grassi et al.
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55 Binding constants for metal-ligand complexes are frequently an order of magnitude smaller for both inorganic species and one to three orders of magnitude smaller for organic species. Thus, the presence of organic matter may have little effect on sorption of zinc, unless the organic matter sorbs to the media and changes the affinity of zinc for the surface.
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56 course of experimentation to ensure that the protocol could handle different media and solution compositions. Prefiltering and pH control were key modifications to the design to ensure that the tests could be conducted over suitable time frames and still capture the contaminant breakthrough profiles.
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57 Most in-line filters have a maximum operating pressure of about 100 psi and a maximum differential pressure of about 35 psi. Due to the variation in particle size in stormwater, a step-wise filtration process is justified.
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58 For this application, a brackish water membrane provides the tightness and pressure rating required to concentrate the DOM. Having a greater membrane SA enables higher flow rates at lower osmotic pressures (Pressman et al.
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59 removed from the system. Because sulfate is an anion, it is not removed during the cation ion exchange process and is concentrated through reverse osmosis proportionally to the DOM (Serkiz and Perdue 1990; Pressman et al.
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60 Table 5-3. The ionic strength of the water was calculated to be 0.009 M
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61 SA of the crab-shell waste was determined to be 13.3 m2/g and the XRD spectra verified the presence of calcite. All media must be sized to meet the hydrodynamic considerations of the experimental column system.
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62 design was appropriate and that experimental runs would be conducted within a reasonable time frame. A preliminary rate study was performed to verify that 48 hours of equilibration time was sufficient.
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63 into a peristaltic pump. The three separate lines were fed to the bottoms of each of the column series (A,B,C)
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64 tops of the tanks were covered with Parafilm® to minimize gas exchange between the tanks and the atmosphere. Solution Refill Setup A filling tank (Tank 2)
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65 5.6 Experimental Results 5.6.1 Batch Reactor Studies of Cu Adsorption Capacity and Equilibration Times The evaluation of zinc and copper adsorption to GFO suggests that equilibration is achieved within several hours at pH 6 as shown in Figure 5-11. The data also suggests that adsorption of copper is significantly greater than zinc as nearly all of the copper is removed from solution and only approximately 20% of the zinc added to the system is removed from the solution.
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66 5.6.2 Column Protocol Verification Selected results from column experiments conducted in this research are presented to highlight several different key issues including the ability to distinguish performance of different media for different metal ions, sensitivity of removal to changes in pH, the role of organic matter, the role of ionic strength, and the potential benefits of dual media systems. A summary of the results from all of the experiments is presented in Table 5-5.
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Experimental Conditions Experimental Results Trial Influent Conc. Media pH Ionic Strength Matrix Flow Rate (mL/min)
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68 Figure 5-15. Relationship between pH and log KD for sorption of copper onto GFO (Trials 2, 3, and 11)
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69 5.6.4 Impact of Highway Organic Matter In a separate experiment (Trial 9) , reconstituted organic matter was added to the synthetic stormwater solution containing salts and adjusted to a pH of approximately 6.
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70 Figure 5-18. Comparison of FBR breakthrough profiles for Cu from synthetic stormwater solution with and without reconstituted NOM.
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71 for the isolation and study of mechanisms affecting adsorptive behavior (i.e., pH, ionic strength, alkalinity) , to accurately capture the performance of the media systems under real conditions organic matter is indispensable.
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72 the influent concentration highlights the need to control pH in metal ion sorption treatment systems. In order to assess the effect of high ionic strength, an additional test was conducted with synthetic stormwater of ionic strength on an order of magnitude higher (0.1M)
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74 Figure 5-24. FBR pH data for Cu and Zn sorption onto granular iron hydroxide in two tests varying in the ionic strength of the synthetic stormwater solution.
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75 Figure 5-26.
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76 Figure 5-28. pH profile in FBR breakthrough profiles for removal of Cu in a series of columns packed with crushed crab shell (C1 and C2)
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77 Figure 5-29. FBR breakthrough profiles for Cu from a synthetic stormwater solution onto granular iron hydroxide (Columns A1–A3 in series)
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78 5.6.9 Experiments Conducted at Alkalinity Representative of Stormwater Experiments were conducted with a synthetic runoff solution formulated to have an alkalinity similar to that observed in real stormwater in order to understand the breakthrough behavior observed with real stormwater. The alkalinity of the solution was raised to 2.15 meq/L by addition of NaHCO3 so to be comparable to the alkalinity of the real stormwater (2.4 meq/L)
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79 even enter the columns. Indeed, precipitates were visually observable in the feed tank.
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80 Figure 5-32. FBR breakthrough profiles for copper and zinc from a synthetic stormwater solution high in carbonate concentration (Trial 14)
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81 and carbonate were observed to affect copper sorption onto GFO (as in Trial 13) follows from the demonstrated linearity of the individual relationships.
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82 model was developed for tracer experimental data analysis to investigate transport of solutes in the groundwater systems. The model optimizes parameters for equilibrium or non-equilibrium advection-dispersion-reaction models.
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