National Academies Press: OpenBook

Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas (2014)

Chapter: Chapter 4 - Treatment of Metals in Highway Runoff

« Previous: Chapter 3 - Environmental Chemistry of Metals in Surface Waters
Page 45
Suggested Citation:"Chapter 4 - Treatment of Metals in Highway Runoff." National Academies of Sciences, Engineering, and Medicine. 2014. Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. Washington, DC: The National Academies Press. doi: 10.17226/22389.
×
Page 45
Page 46
Suggested Citation:"Chapter 4 - Treatment of Metals in Highway Runoff." National Academies of Sciences, Engineering, and Medicine. 2014. Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. Washington, DC: The National Academies Press. doi: 10.17226/22389.
×
Page 46
Page 47
Suggested Citation:"Chapter 4 - Treatment of Metals in Highway Runoff." National Academies of Sciences, Engineering, and Medicine. 2014. Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. Washington, DC: The National Academies Press. doi: 10.17226/22389.
×
Page 47
Page 48
Suggested Citation:"Chapter 4 - Treatment of Metals in Highway Runoff." National Academies of Sciences, Engineering, and Medicine. 2014. Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. Washington, DC: The National Academies Press. doi: 10.17226/22389.
×
Page 48
Page 49
Suggested Citation:"Chapter 4 - Treatment of Metals in Highway Runoff." National Academies of Sciences, Engineering, and Medicine. 2014. Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. Washington, DC: The National Academies Press. doi: 10.17226/22389.
×
Page 49
Page 50
Suggested Citation:"Chapter 4 - Treatment of Metals in Highway Runoff." National Academies of Sciences, Engineering, and Medicine. 2014. Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. Washington, DC: The National Academies Press. doi: 10.17226/22389.
×
Page 50
Page 51
Suggested Citation:"Chapter 4 - Treatment of Metals in Highway Runoff." National Academies of Sciences, Engineering, and Medicine. 2014. Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas. Washington, DC: The National Academies Press. doi: 10.17226/22389.
×
Page 51

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

45 Highway runoff can contain dissolved and particle-bound metals at concentrations that require treatment, nominally with a unit process such as adsorption and unit operation such as sedimentation or filtration, respectively. The sources, mag- nitude, as well as the partitioning and distribution of these metals with particles have been reviewed. This review provides the basis for assessing the potential viability of a unit process such as adsorption for removing dissolved metals. It is noted that the term “adsorption” as used herein can represent a range of mass transfer phenomena including surface complexation, ion exchange, chemical precipitation, diffusion, and hydrolysis. Treatment of highway runoff continues to pose unique chal- lenges due to the unsteady nature of processes including rain- fall runoff, mobilization, partitioning, and delivery of metals. There are no simple solutions for the removal of a metal or particle once released in stormwater, and there are BMPs that can be misapplied for the intended purpose, unfortunately at a significant cost. BMPs for metals and particles are essentially garbage cans and as such they must be emptied and cleaned occasionally. The purpose of effective design is to provide constituent capture given the complexities of runoff hydrau- lics and chemistry, reasonable time between media backwash- ing and replacement, and a preferred design life cost/benefit ratio among treatment alternatives. The strategies for remov- ing dissolved metals in runoff have traditionally focused on infiltration and adsorption. 4.1 Infiltration A variety of structural BMPs that are designed for infiltrating runoff into surrounding soils have been implemented. These include facilities where infiltration is the primary mechanism for stormwater treatment, such as infiltration trenches and basins. In addition, infiltration occurs as a secondary process in controls such as vegetated buffer strips and swales. Infiltration is adaptable and potentially can remove dissolved and particle-bound constituents. There have been applications of infiltration concepts adopted in many parts of the world because of the potential benefits for stormwater chemistry and hydrologic control (Fujita 1993; Krejci et al. 1993; Jahangir- Issa 1998; Yu 1993; Sansalone 1999; Li et al. 1999; Teng and Sansalone 2004; Sansalone and Teng 2004). For example, infiltration systems along the edge of a pave- ment have been used to attenuate stormwater runoff peak flow and to reduce the runoff volume to natural, predevelop- ment conditions. Swedish infiltration systems are utilized to promote shallow groundwater recharge and reduce surface drainage infrastructure in transportation systems (Hogland and Niemczynowicz 1986; Niemczynowicz and Hogland 1987). Investigation of long-term hydraulic behavior of linear stormwater infiltration systems has demonstrated that infiltra- tion is feasible even when the field saturated hydraulic conduc- tivity of surrounding soils was as low as 10-6 m/s (0.14 in/hr) (Warnaars et al. 1999; Li et al. 1999). Li et al. (1999) used a numerical two-dimensional variably saturated flow model to evaluate transport and residence time distribution for a long linear trench. These studies indicate that infiltration systems offer the potential for infiltrating stormwater runoff from paved and urban areas. Benefits of these infiltration BMPs are increased mean resi- dence times relative to pre-BMP conditions, and promotion of discharges to surrounding soils, even for soils with low saturated hydraulic conductivity. Infiltration BMPs in soils of lower hydraulic conductivity (typically clayey materials of higher SA and surface charge) have a reduced risk for soil and groundwater contamination from increased loadings of pol- lution in urban and highway runoff, especially heavy metals (Li et al. 1999). Water chemistry results for metals indicate that accumula- tion of metals occurs at the geotextile layer between the granular subgrade and surrounding soil. (Hogland and Niemczynowicz 1986). Long-term examination of such systems in clean granu- lar soils is required to quantify any risk of elevated water chem- istry constituents such as metals beyond the infiltration system (Hogland and Niemczynowicz 1986). C H A P T E R 4 Treatment of Metals in Highway Runoff

46 There are a variety of infiltration BMP systems that range from permeable pavement to sand filter inlets (Urbonas 1993). A common type of infiltration-exfiltration system is the com- bination of asphaltic permeable pavement and a granular- backfilled subgrade (clean, non-engineered gradation of sand and gravel) in a linear trench such as the Swedish Unit Super- structure. In comparison, a linear infiltration system imple- mented along an interstate catchment in Cincinnati, combined cementitious permeable pavement (CPP) and adsorptive- filtration media that had been tested in breakthrough studies. The two major differences in these systems is the use of asphaltic as compared to CPP and the use of clean non- engineered granular backfill as compared to media engineered for adsorptive-filtration capacity as well as structural capac- ity. Both systems promote infiltration using permeable pave- ment and granular subgrade systems for hydrologic and water chemistry control. Another common type of infiltration BMP that has been widely used is a vegetated or grassed swale infiltration system. Studies in Europe and the United States indicate that these vegetated swale infiltration systems can be effective at inter- cepting, conveying, and infiltrating stormwater runoff (Sieker 1998). For example the German “Mulden-Rigolen-System” (MR-System) provides in situ hydrologic and water chemistry control for stormwater. Swale infiltration trenches such as the MR-System are typically comprised of an upper layer of highly porous material such as gravel, with finer gradations of sand and soil in lower layers of the trench. The vegetated or grassed surface of the swale provides effective separation of the coarser sediment particles (>75 µm) trapping these particles at the sur- face of the swale. Infiltration treatment results from these sys- tems indicate that water chemistry parameters such as metals can be attenuated by mechanisms of filtration and adsorption with resulting reductions in effluent concentration of greater than 90% by designs such as the MR-System (Sieker 1998). Two long-term monitoring studies in the Washington, D.C., area on partial infiltration systems in suburban Maryland and Virginia (Schueler 1987) demonstrate the potential of such sys- tems as in situ treatment for stormwater constituents. Both sites exhibited similar removal capability of TSS, with mass removal ranging from 85% to 95%. Approximately 65% of total phos- phorus and 75–85% of the total nitrogen load were removed through partial infiltration, mainly volumetric reduction. Passive infiltration systems, in particular those systems designed for dissolved metal treatment, cannot be consid- ered sustainable if such systems are used to provide signifi- cant removal of particles and particles-bound constituents through mechanisms such as deep-bed filtration due to the potential for clogging and inability to backwash such in situ systems (Sansalone et al. 2009). Some form of particle sepa- ration is usually employed as pretreatment before storm- water is infiltrated. For example, an infiltration system under a highway shoulder or adjacent to the edge of pavement may be configured with an upper permeable pavement surface, which functions as both an infiltrating surface and provides surfi- cial straining of particles transported from the traveled lanes. These surficially strained particles accumulate in a layer on the surface (commonly referred to as a “schmutzdecke”) promot- ing further surficial straining. Legret and Colandini (1999) investigated an asphalt perme- able pavement with a lower reservoir structure for filtration of suspended particles and metals in runoff. The accumulation of particle-bound metals in the permeable asphalt and the absence of soil contaminant under the reservoir were demonstrated for a period of 8 years. Similar structures but with different sub-base stone were also constructed in the United Kingdom and initially reduced particles from 1000 mg/L to 50 mg/L although con- cerns over clogging and sustainability were recognized for such high particles loadings (Pratt et al. 1995). Beyond costs and structural considerations, there are four primary design considerations (and failure modes) for pas- sive infiltration systems: (1) hydrologic and hydraulic design, (2) filtration and filter ripening design, (3) dissolved constitu- ent capacity and breakthrough design (in this case for metals), and (4) design for operation and maintenance (O & M) as well as constituent management. 4.2 Adsorption Recent developments in stormwater treatment indicate that removal of dissolved metals through adsorption on engineered media is an effective strategy. Metal adsorption onto natural and engineered media, such as sand, soils, granular activated carbon (GAC), and oxide-coated media, has been studied (Stumm 1992). Specific media have been proposed for adsorp- tion of metals transported in stormwater. While most of these media are inherently able to provide some level of particle- bound metals treatment depending on physical quantities such as surface loading rate, geometry of the media system, and the granulometry (size and gradation) of the media, there is a much greater variability with respect to adsorption of dis- solved metals, and in many cases the adsorption by the media is only nominal. Assuming that adequate hydrologic, hydraulic, filtration, and O&M design has been facilitated, the primary component of systems that adsorb dissolved metals is the media onto which the dissolved metal mass is transferred. The types of media that have been suggested for treatment of dissolved metals range from non-engineered media such as sand, gravel, limestone, perlite, or zeolite to organic/biogenic media that requires pro- cessing such as peat, litter pellets, or chitin/chitosan (from shells of crustaceans, insects and fungi); recycled or reclaimed infrastructure materials such as brick (clay), masonry, or con- crete; or engineered media such as oxide-coated substrates.

47 In selecting a media the potential viability in an adsorptive- filtration system will be dependent upon the following factors: 1. Structural (required shear, compressive, and stability/ degradation properties subject to cyclic wetting/drying and anaerobic/aerobic conditions), 2. Hydraulic (required hydraulic conductivity and internal/ external pore distribution properties), 3. Filtration (particle separation, filter ripening properties), 4. Adsorptive (required equilibrium, kinetics, breakthrough and leaching properties), 5. Operation and maintenance properties for systems includ- ing the regeneration or replacement and ultimately the long-term management of material enriched with metals. There are a plethora of media that are promoted in the mar- ketplace for removal of metals in stormwater, media that may be well-intentioned from either a business point of view or from an intuitive point of view but simply cannot achieve dis- solved metals removal efficiency (Liu et al. 2005a, 2005b). To meet current and expected water quality standards, in situ met- als treatment technologies and materials require development and implementation based on knowledge of the loadings and chemistry of runoff combined with a quantitative knowledge of media behavior. These media-based technologies represent the combination of engineered media, an engineered system, and quantitative O&M practices that synthesize influent chem- istry and loadings, effluent requirements, and the quantitative behavior of the engineered media and system. Sand and fine gravel are the most common conventional media because of their initial economy, inertness, increased strength when subject to confining stresses, and availability. However, results from previous work (Sansalone 1999) dem- onstrated that plain sand or gravel media has insignificant SA (< 0.1 m2/g) and is ineffective for removal of dissolved metals. Johnson et al. (2004) initially screened a suite of 12 media, after which the three best performing media for metals removal were further tested based on equilibrium and kinetics experi- ments. Results illustrated that a peat-sand mix had the highest metal capture capacity yet had the most detrimental impact on pH, the greatest headloss, and the highest potential for clogging. Organic compost had an intermediate metal capture capacity, colored the filter effluent, and had a lower impact on pH, headloss, and clogging. Zeolite had the lowest metal cap- ture capacity, low impact on pH, lower headloss as a granular material, and less potential for clogging. Similar ineffectiveness was also shown for perlite with the additional weaknesses of friability and inadequate compressive strength. Any dissolved metal removal occurred by metal adsorption onto particles filtered by these plain substrates yet was subject to sloughing from the filter under changing hydrodynamic conditions (Liu et al. 2005b). Because of poor performance of sand, perlite, and gravel for metal adsorption and filtration, other substrates are needed for stormwater treatment (Sansalone 1999; Sansalone and Ma 2009). After a decade of testing and evaluation of conventional media that demonstrated negligible to nominal adsorption capacity for dissolved metals in stormwater, research has con- centrated on identifying more effective media. Within this same period, engineered media that combined oxides (Al, Fe, Mn, and Si) either singly or in combination have been applied to economical, stable, and competent substrates that provided sufficient SA and adhesion, including permeable clayey or cementitious substrates. Oxide-coated metals have long been used for dissolved metal adsorption. In the presence of water, oxide surfaces such as Mn and Fe are covered with surface hydroxyl groups, protons, and coordinated water molecules. These mineral surfaces are amphoteric (net surface charge is a function of pH) with protons and hydroxyl ions co-existing at the sur- face in relative populations determined by solution pH. Con- sequently, the sorption of a metal ion to the hydrous oxide surface (manganese and iron) is strongly pH dependent. This amphoteric behavior leads to the point of zero charge (PZC) definition. The PZC in its most simple definition is the pH at which the net surface charge is zero (net positive and negative charges sum to zero). Since many iron oxides have a PZC typically above 7 (in contrast, most manganese oxides have a PZC between 3 and 6), a stormwater solution pH greater than 7.0 can result in a predominance of negatively charged surface sites. Conversely, a solution pH less than 7.0 would result in an increasing amount of positively charged surface sites at least for Fe oxides. Engineered amphoteric oxide-coated surfaces on filter media can have large SAs for adsorption in a chosen pH range. Amphoteric materials can be utilized for metal species adsorp- tion because of their relatively high SA and their surface charge characteristics, which are generally negative at higher pH val- ues. Having the opposite charge of the dissolved metal ions promotes adsorption. Therefore engineered media such as the oxide-coated filter substrates or cementitious media with high SA and amphoteric surface charge can be utilized to carry out the combined unit operations of filtration and processes of surface complexation for a range of treatment configurations for either decentralized treatment or centralized treatment. Such treatment can be designed as a passive and integral part of existing infrastructure, for example transportation infrastruc- ture, or can be designed as a centralized stormwater treatment component. To facilitate surface complexation of metals in stormwater by engineered amphoteric oxide-coated media, the pH of the stormwater must be considered in respect to the PZC of the media’s surface coating. Utilizing pH, synthesizing mineral coatings of the appropriate PZC, or both will enhance removal capability and efficiency of the stormwater treatment device.

48 For example, an oxide-coated media surface with a net nega- tive charge is preferred to remove the dissolved metals that exist as cations in stormwater. Despite the high affinity of iron oxide for metal ions, iron oxide has not been widely used as a surface complexation media for stormwater because its physical properties are not conducive to this process. For example, it is bulky, hydrated, amorphous, flocculent material with extremely low hydraulic conductivity. However, iron oxide coated media was devel- oped to overcome these physical limitations. Previous research with respect to performance of iron oxide-coated media for sorptive-filtration of stormwater has demonstrated proof- of-concept for oxide-coated media in systems such as partial exfiltration as applied as a full-scale passive treatment system in the highway environment (Sansalone 1999, Liu et al. 2005a, 2005b). Iron oxide can also remove dissolved metals to a lower level than that achieved by precipitation. Granulated iron oxide media has also been used in a 1:1 combination with calcite (Steiner and Boller 2006) to treat roof runoff. The iron oxide provided the main copper and zinc adsorption capacity while the calcite controlled the pH and increased the mechanical and hydraulic stability of the system. This system has not been fully explored for applica- tions in stormwater treatment, but the results from treatment of roof runoff suggest that this may be a good candidate for an adsorption system. Negatively charged filtration media with a PZC sufficiently below the pH of stormwater could simplify the design for in situ stormwater treatment by eliminating any consideration of pH control. Compared to the iron oxide, manganese oxides have a very high negative surface charge in the range of typi- cal stormwater pH values (usually pH 6–8). For example, at a pH of 7, a synthetic goethite (a–FeOOH) has a positive charge of approximately 0.2-µmol/m2, while cryptomelane (a–MnO2) has negative charge of 4.0-µmol/m2, and birnessite (d–MnO2) has a negative charge of 18-µmol/m2 (McKenzie 1981; 1989). Therefore, coating manganese oxide onto stormwater treatment media surfaces offers high potential for cationic metal removal. Manganese oxide media, including manganese coated poly- meric media (MOPM) and manganese oxide-coated cementi- tious media (MOCM) were evaluated by Liu and Sansalone (2004a, 2004b, 2005a, 2005b) in sorptive-filtration system as a rainfall-runoff or snowmelt unit operation and process media for treatment metal species. Birnessite-coated and cryptomelane-coated forms of manganese, as well as iron oxide coated media were tested by Liu et al. (2001a, 2001b), Sansalone (1999a, 1999b), Li et al. (1999). Sansalone and Buchberger (1995) utilized filtration and exfiltration systems for treatment of metals urban rainfall-runoff that included iron oxide coated media. Results indicate a significant capacity for metal species, with the surface chemistry favoring the adsorp- tion of metal species as opposed to phosphorus. Engineered media also include manganese oxide-coated polymeric media (MOPM) for adsorption of metals (Liu et al. 2001). Manganese oxides (MO) have a PZC below the typical pH range of 6 to 8 for runoff resulting in a negatively charged surface, allowing their use as adsorbents without pH control (Liu et al. 2001). MO has a high negative charge at higher pH levels and their cation adsorption capabilities increase with increasing pH. Metal adsorption at or below the PZC illustrates that a number of adsorption forces, in addition to electrostatic forces, are involved in the adsorption process (Murray 1974). Spectroscopic analyses of metal coordination by MO minerals utilizing extended X-ray absorption fine structure indicates that uptake of cationic metals at the pH lower than PZC is through the mechanism of ion exchange (Randall et al. 1998). MOPM capacity has been shown to be significantly higher than polymeric media under the same set of loading condi- tions. MOCM provided the highest capacity of all media examined. Although manganese coated media offers poten- tial for metal removal, little stormwater related research has been carried out (Liu et al. 2001a, 2001b). Compared to plain filter sand, cementitious media, or polymeric media the cost of oxide coating increases media costs by a factor of approxi- mately five (approximately three for admixture MOCM). This cost increase is more than offset by greater breakthrough- exhaustion capacities, and breakthrough stability, in particular for MOCM. Results based on Cincinnati hydrologic and met- als loadings (Sansalone and Buchberger 1997; Sansalone and Teng 2004) indicate breakthrough in an in situ system for filter sand or polymeric media are a fraction of a year, at least 5 years for an engineered Fe oxide-coated media configuration, and can exceed 10 years for MOCM. Cementitious media such as graded concrete, masonry, rub- ble or brick, when coated, sprayed, or synthesized with oxides or oxide-admixture can also be an effective media for metal removal. Cementitious media has been generated from eco- nomical concrete rubble, recycled concrete, or crushed con- crete with an oxide-admixture (Liu et al. 2005a, 2005b) and clay-based substrates effectively utilized for oxide-coated media (Sansalone and Ma 2009). The idea of using cementitious infra- structure material or recycled cementitious material is based on three advantages beyond the inherent economy of the substrate. First, after carbonation in the ambient environment, cementi- tious media creates a slightly alkaline aqueous environment since calcite (CaCO3), portlandite [Ca(OH)2], and calcium silicate hydrate (3CaO • 2SiO2 • 3H2O) are major components of the concrete, and all contribute alkalinity to the aqueous solu- tion. This alkaline environment will not only improve the metal removal efficiency by precipitation of dissolved metals, but also benefit from the electrostatic interaction between the oxide and dissolved cationic metal, because MO have larger negative surface charge in higher pH solutions. Another advantage is the rough surface of higher SA created by the coating.

49 While concrete media alone without an oxide coating or admixture is temporarily effective, the mass transfer is that of precipitation resulting in an unstable buildup of metals on the media surface with such physical precipitate buildup being sloughed off periodically into the effluent. This result is also observed for metal precipitates on concrete media (Liu et al. 2005a, 2005b). The use of dilute aqueous admixtures to the initial water-cement-sand mixture offer promise for cementi- tious materials from which such sorptive-filtration media can be produced. A mix of admixtures such as iron and manga- nese or coatings/admixtures combined with aluminum oxide can be effective for removal of cations (positively charged) and anions (negatively charged) such as phosphate. Table 4-1 presents axial flow breakthrough experiments that were conducted to assess media capacity for metals utilized in snow or rainfall-runoff unit operation/processes. Results indicated that sand or polymeric media exhibited rapid break- through with little capacity and served as control to compare other media. While an improvement over control media, GAC’s low capacity and low compressive strength limit applicability. Uncoated cementitious media had high capacity but break- through instability. Iron oxide coated sand (IOCS) had greater capacity compared to sand, and a combination of uncoated cementitious media and IOCS had improved capacity com- pared to IOCS. Sansalone (1999) also illustrated media breakthrough behav- ior (equilibria and kinetics), comparing plain media substrates such as sand, perlite, or GAC to engineered media such as Fe oxide coated sand or in situ systems that combine Mn-oxide as either an admixture or coating to the portland cement concrete (PCC) or onto polymeric media. Specific media and combina- tions were based in an in situ partial exfiltration reactor (PER) design implemented along an interstate in Cincinnati (Teng and Sansalone 2004; Sansalone and Teng 2004; Sansalone and Teng 2005; Li et al. 1999). Based on annual hydrologic and water chemistry loads from the Cincinnati catchment as described earlier, results are summarized in Table 4-2. Natural organic or biogenic-based media were avoided in these tests due to dete- rioration of such media in a cyclically wet and dry environment, and the commensurate leaching of metals as well as nutrients from the biogenically-based media. Sansalone and Ma (2009) examined batch equilibrium for oxide-coated clay-based media in a parametric study that included media and water chemistry parameters. In this study they demonstrated that leaching from oxide-coated media was negligible. In addition to oxide minerals, a number of recent studies have evaluated low cost adsorbents for metal ion removal from stormwater. While many of these have little potential for widespread application due to impacts on pH, headloss, and clogging, one particular material that has demonstrated potential for application to stormwater treatment is crab- shell waste. Crabshells contain two important components, chitin and proteins (Lee et al. 2004). Chitin is a linear poly- meric molecule containing the repeating unit 2-acetamido- 2-deoxy-D-glucose-_Nacetylglucosamine. The combination of chitin and calcium carbonate has been proposed as an ideal media combination because the calcium carbonate promotes the formation of metal carbonate microprecipitates and chitin is a good adsorbent for these microprecipitates (Vijayaraghavan et al. 2010). In their recent study evaluating the potential of seven different sorbents including Amberlite XAD7, chitosan, crab shell, peat, Sargassum biomass, sawdust, and sugarcane bagasse to remove 11 different metals from simulated storm- water, Vijayaraghavan et al. (2010) found that crab shell media achieved capacities of 7.96, 7.94, 4.84, and 1.55 mg/g for Zn, Cu, Cd, and Pb, respectively. Based on these numbers, this media warrants further study. Applications of oxide-coated media configurations for dis- solved metal removal have applications in snow and rainfall- runoff control. In situ examples include partial exfiltration, infiltration systems, permeable pavement, filtration, and clar- ification systems. Ex-situ applications include deformable or tubular filters, upflow clarifiers, and many forms of in situ low impact development (LID) systems including permeable pavement. Media also provides filtration mechanisms; there- fore, ex-situ systems require design, operation, and backwash- ing or replacement based on metal/particulate breakthrough and head loss considerations. In situ systems have similar considerations, and many such systems are passive and not amenable to backwashing. As a result, some form of primary treatment, protection, or source control to reduce particulate loadings to passive systems is required. Examples include CPP or asphaltic permeable pave- ment functioning as surficial pretreatment for media in a PER and for upstream primary clarification/particle separation (Teng and Sansalone 2004). While there have been many evaluations of BMPs containing media, for example, monitoring for total metal percent reduc- tion; to date there has been little quantitative and mechanistic evaluations of adsorptive-filter media for dissolved stormwater metal (or other solutes) adsorption. Exceptions are the refer- ences identified herein. Media applications that do exist with reported information are still challenged due to the limited quantitative information of the mechanistic behavior of the media. Furthermore, many regulatory requirements require percent removal for total metal and thereby do not differenti- ate between dissolved metal adsorption and particles-bound metal filtration. With respect to the economics of media, there is little exami- nation of media lifetime and replacement costs; all too often the lowest initial cost media (which typically correlates to lowest capacity and lifetime) drives commercial applications. Some materials have abundant sources and relative low costs, such as those made from different types of waste; an examination of the

Zn Cu Cd Pb X/Mb mg/g (mg/ml) X/Mexh mg/g (mg/ml) Vb (BV) X/Mb mg/g (mg/ml) X/Mexh mg/g (mg/ml) Vb (BV) X/Mb mg/g (mg/ml) X/Mexh mg/g (mg/ml) Vb (BV) X/Mb mg/g (mg/ml) X/Mexh mg/g (mg/ml) Vb (BV) Conventional mono-medium uncoated filter media Sand* < 0.001 (< 0.001) < 0.001 (<0.001) < 10 < 0.001 (< 0.001) 0.0016 (0.003) < 10 < 0.001 (< 0.001) < 0.001 (< 0.001) < 10 < 0.001 (< 0.001) 0.0015 (0.003) < 10 GAC 0.40 (0.19) 1.63 (0.80) 45 3.51 (1.71) 4.10 (2.00) 300 0.02 (0.01) 1.11 (0.54) 15 1.63 (0.79) 3.33 (1.62) 120 Uncoated cementitious media 0.57 (0.66) 0.66 (0.77) 1300 0.60 (0.70) 0.67 (0.79) 1300 0.19 (0.23) 0.66 (0.77) 400 0.59 (0.69) 0.67 (0.78) 1300 Mono-medium iron oxide-coated sorptive media or dual-medium iron oxide coated media and cementitious media (BSPER) IOCS (iron oxide- coated sand) 0.013 (0.022) 0.019 (0.032) < 10 0.006 (0.011) 0.122 (0.210) < 10 0.013 (0.022) 0.017 (0.029) < 10 0.19 (0.34) 0.36 (0.63) 80 BSPER (porous pavm over IOCS) 0.059 (0.10) 0.49 (0.86) 80 1.64 (2.83) 1.64 (2.83) > 600 0.06 (0.10) 0.39 (0.67) 70 1.05 (1.81) 1.53 (2.64) 420 Manganese oxide-coated sorptive media MOCS (Mn-oxide- coated sand) < 0.001 (< 0.001) < 0.001 (<0.001) < 10 0.028 (0.048) 0.15 (0.25) 100 < 0.001 (<0.001) < 0.001 (<0.001) < 10 0.084 (0.15) 0.11 (0.18) 100 MOPM (Mn-oxide polymeric media) 0.40 (0.46) 0.48 (0.55) 500 0.56 (0.64) 1.14 (1.30) 800 0.35 (0.40) 0.44 (0.50) 350 0.84 (0.96) 1.33 (1.51) 1000 MOCM Run #1 2.18 (2.54) > 4.57 (> 5.33) 2500 3.97 (4.64) > 4.97 (5.80) 4000 2.33 (2.72) > 4.64 (>5.41) 2500 3.69 (4.31) > 4.83 (>5.63) 4000 Run #2 1.04 (1.21) 1.50 (1.75) 900 1.08 (1.26) 1.78 (2.08) 1200 0.88 (1.02) 1.33 (1.55) 900 1.04 (1.21) 1.51 (1.76) 1200 X/Mb : Breakthrough capacity as C/C0 = 0.1; X/Mexh: Exhaustion capacity as C/C0 = 0.9; Vb: Number of bed volumes (BV) treated at an effluent breakthrough level of C/C0 = 0.1; The values in parentheses are the breakthrough or exhaustion capacities as the ratio of mass of metal per unit bed volumes. > means breakthrough capacity are larger than the followed values (the experiment terminated before C/C0 = 0.9). Run #1: EBCT = 1.1 minutes, 1 mg/L each of Pb, Cu, Zn, and Cu, influent pH = 6.0; Run #2: EBCT = 0.5 minutes, 1 mg/L each of Pb, Cu, Zn, and Cu, influent pH = 6.0; * Uncoated polymeric media performance results very similar to sand performance, and had little metal adsorption capacity MOCM: manganese oxide-coated cementitious media Table 4-1. Illustration of media breakthrough bed volumes, breakthrough, and exhaustion capacity for metal adsorption.

51 adsorptive performance for dissolved metal (or other solutes) removal is unknown and may present environmental/ecological challenges through the leaching or desorption of metals or in the case of biogenic pelletized materials, nutrients. Therefore media need to be tested and compared under both controlled surro- gate loadings yet also subject to actual stormwater uncontrolled loadings to illustrate the performance difference. 4.3 Recommendation for Media Selections The preferred matrix of choices, after a decade of work, includes crabshells and oxides of Fe, Mn, Al, and Si. The com- bination of chitin and calcium carbonate is a potential ideal media combination because the calcium carbonate promotes the formation of metal carbonate microprecipitates and chitin is a good adsorbent for these microprecipitates. The metal oxides can be implemented as either coatings or admixtures, either singly or in combination onto or into rough, robust, inert, and porous substrates of concrete, clay, volcanic materials such as pumice, masonry rubble, and porous calcium- based materials. Each of these substrates have sufficient adhe- sive and SA to further support a higher SA of reactive oxide. It is also recognized that substrates such as fired clay or con- crete retain their adsorptive and complexation properties to provide parallel mechanisms for dissolved metal treatment. Biogenic or natural organically based substrates are not preferred as such media or media combinations (for example GAC, perlite, zeolite) have low capacity, leach constituents, desorb metals or do not have sufficient structural capacity. While it is well-known that organic and biogenic substrates can bind metals; such substrates are degradable in situ or in the conditions of a BMP. In addition, the presence of organics in the effluent from these systems can impact the speciation of metals and make them more mobile and less adsorptive. Non-engineered media such as sand, gravel, and perlite can be designed to physically separate metals in the particulate phase, but this process is reversible through leaching processes or specific deposit sloughing, requiring frequent O&M. The fol- lowing are the media recommended for testing in this study. • Iron and MO have demonstrated the highest potential for adsorbing the range of metals observed in highway runoff. Therefore, commercially available forms of these oxide met- als will be evaluated as well as mixtures containing both types of media. The pH of the PZC is different for these two oxides. Therefore, both types of media will be tested over a range of pH values for a variety of metals that exhibit varying affin- ity for the oxides. Concentration ranges to be tested will be consistent with the concentrations observed in stormwater. • Concrete materials and calcite offer the possibility of provid- ing adsorptive capacity as well as pH buffering. Both of these materials will be assessed for their potential for adsorption of metal ions. While calcite represents a well characterized and less variable material, concrete provides the opportunity to recycle waste materials. • Crab shell has also been shown to have potential for removal of metal ions from stormwater due to the presence of chi- tin and calcium carbonate. Thus, this sorbent will also be evaluated for its potential to synergistically promote adsorp- tion of metal ions. These five materials: iron oxide, manganese oxide, chitin, calcite, and concrete will be tested independently and in combination (as admixtures and dual media) to provide the maximum adsorption capacity for metal ions. Since maximum adsorption capacity will be pH dependent, the assessment will include evaluation of various combinations of the materials for pH control as well as adsorptivity. Selection of the particu- lar source, size, and porosity of each of these materials will be based on optimizing SA while minimizing head loss. For all media, desorption potential will also be assessed as a function of pH (within expected pH ranges). Media Time to breakthrough (years) Media capacity at breakthrough [mg/g] Plain silica sand or perlite 0.0015 0.0001 to 0.00015 CPP + Fe oxide coated sand 2.2 0.13 Granular activated carbon 2.8 0.19 Mn-oxide polymer media 6.9 0.46 Plain crushed concrete media 9.9 0.66 Mn-oxide concrete media 10+ 2.54 Table 4-2. Comparative breakthrough times from a PER utilized as a replacement for conventional paved shoulder underdrain design and utilizing specific media tested to breakthrough. (Sansalone and Buchberger 1997; Sansalone et al. 1998; Glenn and Sansalone 2002).

Next: Chapter 5 - Laboratory Testing and Modeling Methods »
Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

TRB’s National Cooperative Highway Research Program (NCHRP) Report 767: Measuring and Removing Dissolved Metals from Stormwater in Highly Urbanized Areas presents prototype best management practices (BMPs) for the removal of dissolved metals in stormwater runoff.

The report presents three conceptual configurations in detail: two vault system configurations for urban and rural settings, and an inlet scupper with media for bridge deck drainage systems.

The report also includes standard protocols to accurately measure the levels of dissolved metals in stormwater. Practical guidance on the use of these protocols is provided in an appendix to the final report. The report is accompanied by an Excel spreadsheet on CD designed to assist in sizing the filter bed in the vaults and the bridge deck inlet scupper.

The CD is also available for download from TRB’s website as an ISO image. Links to the ISO image and instructions for burning a CD from an ISO image are provided below.

Help on Burning an .ISO CD Image

Download the .ISO CD Image

CD Disclaimer - This software is offered as is, without warranty or promise of support of any kind either expressed or implied. Under no circumstance will the National Academy of Sciences or the Transportation Research Board (collectively "TRB") be liable for any loss or damage caused by the installation or operation of this product. TRB makes no representation or warranty of any kind, expressed or implied, in fact or in law, including without limitation, the warranty of merchantability or the warranty of fitness for a particular purpose, and shall not in any case be liable for any consequential or special damages.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!