Environmental Characterization of Ash from the Combustion of Wood and Tires for Beneficial Use in Florida

11th North American Waste to Energy Conference Copyright C 23 by AS ME NAWTEC11-168 Environmental Characterization of Ash from the Combustion of Wood and Tires for Beneficial Use in Florida Thabet Tolaymat and Timothy Townsend Department of Environmental Engineering Sciences University of Florida Gainesville, Florida INTRODUCTION Non-hazardous industrial solid wastes are frequently proposed for beneficial use rather than being disposed in MSW landfills. An example of such an industrial waste is waste-to-energy (WTE) ash. Proposed beneficial use projects for WTE ash often involve some form of land application. Prior to the land application of any solid waste, the possible risk to human health and the environment should be assessed. The Florida Department of Environmental Protection (FDEP) has developed a beneficial use guidance document that provides WTE ash generators with the testing requirements that must be demonstrated before a particular beneficial use scenario is determined appropriate (FDEP 21). For WTE ash to be deemed safe for land application, the risk associated with two separate pathways should be assessed: direct human exposure and the contamination of groundwater via leaching. While organic pollutants (e.g. dioxins) might be a concern, heavy metals are typically the pollutants that most limit the potential for reuse; heavy metals are the focus of the discussion in this paper. Direct human exposure is typically addressed by measuring the total concentration of various heavy metals of concern (mg/kg) and comparing the results to risk-based target concentrations. In Florida, the risk-based target concentrations used are FDEP's soil cleanup target levels (SCTLs; units mg/kg). The direct exposure SCTLs are based on assumed exposure scenarios, toxicological information and acceptable risk. The potential risk of ground water contamination as a result of leaching is evaluated in one of several methods. The first method is to compare the total concentration (mg/kg) and to a SCTL derived specifically for leaching (units mg/kg). The leaching SCTL is derived from an assumed value for "leachability" of the metal from a solid matrix (partition coefficient or ; typically derived for a soil). It represents the theoretical amount of metal that would have to be present (mg/kg) to result in a pore water concentration equal to the groundwater standard or target level (mgil). A dilution factor is often incorporated into the leaching SCTL to account for potential dilution and attenuation that might occur between the contaminated media (soil, ash) and the point of interest in the groundwater. The second method for evaluating the potential risk to groundwater from a land applied ash is to produce a leachate from the ash and to compare the concentration of metals in the leachate (mgil) to a risk-based groundwater target concentration. The FDEP has developed a set of groundwater cleanup target levels (GWCTL; unit mgil). The most common procedure is to produce the ash leachate is to conduct a batch leaching test. The US EPA's synthetic precipitation leaching procedure (SPLP) is one that would commonly be used as it simulates the leaching that results from an acid rainfall. Other batch leaching tests that professionals in the WTE community might be more familiar with are the Toxicity Characteristic Leaching Procedure (TCLP) and California's Waste Extraction Test (WET). Both of these tests are designed to simulate leaching within a municipal solid waste landfill. This paper reports the results of research conducted to characterize WTE ash from the combustion of wood waste and tires. Analyses that would typically be required for a beneficial use demonstration in Florida were conducted. This work was not intended to be an actual beneficial demonstration, so the required number for samples needed for such a characterization was not analyzed. The results were compared to Florida's risk-based target levels. In addition to characterizing this particular ash for reuse potential, a special focus was paid to evaluate the best method for simulating ash leachate and its potential impact 145

on groundwater. A leaching colunm (lysimeter) study was performed to simulate ash leachate concentrations, and the results were compared to those obtained using the more standardized batch leaching tests (TCLP, SPLP and WET). The results presented here are part of a larger study evaluating the use of leaching tests in risk-based decision making for solid waste management (Townsend et al.,23). METHODOLOGY The WTE targeted in this study was from a facility that combusted waste wood (yard trash, pallets, C&D debris wood) and automobile tires for fuel. This waste stream was selected because records indicated that it was not a hazardous waste but it did contain small amount of trace metals. Facility operators had also expressed an interest in finding a beneficial use for the ash. The samples were collected from the neighboring landfill where the ash was disposed. Eight samples of a combination bottom and fly ash were collected during the period of one day. Each sample represented a different truckload of ash hauled to the landfill. Total metal analysis was conducted on the ash following standard analytical procedures. The ash was also subjected to regulatory batch leaching tests SPLP, TCLP, and WET. A colunm leaching experiment was also performed using stainless steel leaching lysimeters containing 1 ft of ash. A detailed description of the methods follows: 1. Total Extractable Metals. EPA method 3SB was used to digest the ash samples. The method calls for weighing out 2 g sample, adding concentrated nitric acid and slowly refluxing the mixture between 2 and 8 hours (U.S.EPA 1996).The acid digestates were analyzed for metals using graphite furnace atomic absorption spectrophotometry (GF AAS) or inductively coupled plasma atomic emission spectroscopy (rcp AES). 2. The TCLP. The TCLP is the method that is used under the Resource Conservation Recovery Act (RCRA) to establish whether a solid waste is hazardous by the toxicity characteristic (TC). In this method, 1 g of a size-reduced waste material are leached in 2 L of a buffered acetic acid solution for 18 hours (EPA SW -846 method 1311; (U.S.EPA 1996)). The TCLP fluid simulates the worse case acid conditions that might develop in a MSW landfill where biodegradable waste was decomposing and producing acids. The TCLP leachates were acid digested and the digestates were analyzed using GF AAS or rcp AES. For toxicity characterization, the concentrations measured in the leachates are compared to the TC limits in the regulations; if the leachate concentrations are higher, the solid waste is a hazardous waste. 3. The SPLP. The SPLP was designed in a similar fashion as the TCLP, but a synthetic rainwater is used. The SPLP utilizes two inorganic acids (nitric and sulfuric acid) to simulate acidic rainwater (EPA SW -846 method 1312; (U.S.EPA 1996). Metal analysis was the same as the TCLP. 4. The WET The WET is a Califomiaspecific leachate test used to determine whether solid wastes are hazardous wastes. This test is similar to the TCLP in that it uses a buffered organic acid solution as the extraction fluid. The main difference lies in the choice of the acid; the TCLP uses an acetic acid mixture, while the WET uses a buffered citric acid solution (CCR 1998). The liquid to solid ratio (1: 1) and the extraction time (48 hours) also differs from the TCLP and SPLP. 5. Lysimeter Tests. Leaching colunm experiments (lysimeter tests) were carried out in stainless steel leaching lysimeters. See Brantley and Townsend (1999) for a complete description of these devices. One ft of ash was placed in three 4-feet tall, 15- cm diameter, lysimeters. The ash was placed in eight 1.S-inch lifts, with each lift representing one of the eight samples. Simulated rain water was applied to the top of the lysimeter and leachate was regularly collected from a reservoir at the bottom of each colunm. Leachate samples were digested and analyzed in the same fashion as described for the batch leachate samples. 146

RESULTS Table 1 presents the mean concentration of the total concentrations of all metals analyzed (mg/kg). The percentages following the averages represent the relative standard deviation. Calcium had the highest concentration, with an average concentration of 185, mg/kg. Calcium is a common component of wood ash (wood ash is often used a liming agent for soils). Iron and zinc had the next highest concentrations; both of these metals are likely a result of the combusted tires. Trace amounts of the more toxic metals were detected (As 35 mg/kg, Cr 4 mg/kg, Pb 54 mg/kg). general, the WET extracted the highest concentration of metals, followed by the TCLP, and then the SPLP and Dr water. This is partially due to the organic acid used in the extraction (Buchholz and Landsberger 1995; Hopper et al. 1998). Citric acid has a greater ability to complex many metals than acetic acid does. Inorganic acids like the ones that are used with the SPLP do not have the same complexing ability as organic acids. This is supported by the fact that metals concentrations in the Dr water extraction test were at the same level as those of the SPLP extraction tests (Wiles 1996)..2S Table 1: Metal Concentration in Wood and Tire Ash Metal Concentration (mglkg) Al 3,26±18% As 35.2±13% Ba 33.5±18% Ca 185,OO±22% Cd 2.35±13% Co 111±18% Cr 4.±11% Cu 143±18% V 7.26±4% Fe 31, 2±14% K 6,25±11% Ph 53.9±16% Mg 4,53±23% Mn 254±25% Na 1,54±9% Ni 14.2±21% Zn 15,9±19% Arsenic and chromium could have resulted from CCA-treated wood, a small amount of which is burned at the facility. Lead might have resulted from lead-based-paint on wood waste and possible from leaded tire weights. The batch extraction tests were analyzed for 16 different metals (see Townsend et al. 23). Figure 1 presents the average leaching results for several selected metals (Cr, Pb, and Cu) for the different batch leaching tests employed. Metals concentrations in the TCLP leachate did not exceed the TC limit thus the ash was not a characteristic hazardous waste. The final extraction ph for all four-extraction tests was approximately 12. The alkaline ph was caused by an abundance of calcium oxide, a common component of wood ash. In.2 O.OS _er I!2Z!Ia Pb _Sa. -. 1 SPLP TCLP WET Figure 1: Metal Leachability in Batch Tests Of the eighteen metals examined in this study, only five (lead, zinc, iron, and barium) were detected on a consistent basis in the lysimeter leachate. Other metals were primarily below their respective detection limits. Two dominant leaching trends were observed. Barium and iron (iron presented in Figure 2) leached most in the initial phase of the experiment (wash-off phase) followed by lower concentrations over time (a more diffusion controlled phase). Lead and zinc behaved differently (lead is presented in Figure 3). The concentration of these two metals started lower and increased to approach a relatively steady concentration. Lead started at a concentration of less than 1 JLg/L and reached an average concentration approximately 5 JLg/L. 147

....7 ;-.,.6 e.5 f -- 'p.4 &3.3 2 u.2 U i J'fltl.1.... 1 2 3 4 5 6 7 Leachate Volume (L) Figure 2: Iron Concentration in Lysimeter Leachate.1 ;-.,.8 -- ' ' '.c.6 ' ' '. ' ' <II ' ' tl ' ' '.<tp<9 <U CQpO' 6 u.4 cp U ' <II.2 <U...l >. 1 2 3 4 5 6 7 Leachate Volume (L) Figure 3: Lead Concentration in Lysimeter Leachate COMPARISON WITH RISK BASED STANDARDS The results of the total concentration analyses were compared (see Table 2) to the direct exposure SCTLs and arsenic exceeded by the greater amount. Arsenic concentration (35.2 mglkg) is 4 times greater than the residential SCTL (.8 mglkg) and ten times than the industrial SCTL (3.7 mglkg). Copper and iron exceeded their respective SCTLs residential standards (but not the industrial SCTLS). None of the other detected metals exceeded the direct exposure SCTLs. Note: An actual beneficial use demonstration would require that more samples would be run and the 95% upper confidence level concentration for a given metal would be compared to the SCTL. The risk to groundwater via leaching was first assessed by comparing the total concentrations to the leaching SCTLs (see Table 2). It is noted that not all of the metals tested have assigned leaching SCTLs. The total concentration (mglkg) of 3 of the 7 metals with assigned leaching SCTLs exceeded their respective leaching SCTLs: As, Cr and Zn. Arsenic and chromium were both very near the target level, while zinc was approximately 4 times greater. The chromium leaching SCTL is based on hexavalent chromium; no chromium speciation was performed as part of this study. As a second approach to evaluate leaching risk, the SPLP leachate concentrations were compared to the GWCTLs (see Table 3). Only those metals detected are presented (along with their respective GWCTL). None of the metal concentrations in the SPLP leachates exceed a GWCTL with the exception of lead. Lead exceeded by a little over three times. None of the metals predicted to be a leaching risk using the leaching SCTL were found to be exceed the GWCTL using the SPLP. Table 2: Metal Concentration in Wood and Tire Ash Ash Florida's SCTLs Metal Con entr ation (mg/kg) (mg/kg) Residential Industrial Al 3,26 7,2 NA As 35.2.8 3.7 29 Ba 33.5 11 87, 1,6 Cd 2.35 75 1,3 8 Co 111 4,7 11, Cr 4. 21 42 38 Cu 143 11 76, V 7.26 15 7,4 98 Fe 31,2 23, 48, Ph 4 92 Mn 1,6 22, Ni 14.2 11 28, 13 Zn 15,9 23, 56, 6, 53.9 254 Table 3: Batch Tests Extraction Results. Ash SPLP M e t a I Concentration (mg/l) Ba.218 Cr.7 Fe.116 Na 32.5 Pb.52 Zn 1.72 Florida's GWCTL (mgfl) 2..1.3 16,.15 5. 148

::J OIl 2- c g c '" u c U " '" 1 8 6 4 2 2 ------\---- 4 Leachate Volume (L) SPLP Concentration Figure 4: Lead Concentrations in Lysimeter Leachate and SPLP Leachate The lysimeter leachates were analyzed for all of the metals discussed previously, but only a few were consistently measured above detection limit (see Townsend et al. 23). The only metal encountered in the lysimeter leachate above a GWCTL was lead. As presented previously, lead concentrations started low but increased to a steady value over time. Figure 4 shows the concentration of leachate measured in the lysimeters as a function of volume leached; the dotted line represents the concentration measured using the SPLP. For this ash sample, the lead concentration in the SPLP matches well with the steady state lead concentration in the lysimeters. The question is often raised "if dilution is appropriate for a given reuse scenario, does one apply a dilution factor to the results of the SPLP?" Because of the large liquid-to-solid ratio in the SPLP, it has been argued that dilution is already accounted for in the test itself, and thus a dilution factor should not be applied. On the other hand, for an ash such as the one tested here, it can be argued that the SPLP concentrations are truly the same as the pore water concentrations and thus a dilution factor should be applied if dilution is appropriate to that application scenario. The authors note, however, that this phenomenon is not universal; some soils and ashes do get diluted using the SPLP and thus a dilution factor might not be appropriate. Approaches to deal with the question of whether a dilution factor should be applied to SPLP require development. 6 CONCLUSION Florida, along with many states, has developed policies for determining when a non-hazardous industrial solid waste such as combustion ash can be land applied in a beneficial manner. As part of research investigating the use of leaching tests for risk-based decision making in solid waste management, ash from a facility that combusts wood debris and tires for fuel was characterized. From a direct human exposure pathway, arsenic was found to be the most limiting metal. This is likely to be the case with many combustion ashes, as Florida has relatively low risk based clean soil levels for arsenic. Even ash from the combustion of clean wood will have arsenic concentrations greater than the SCTL for arsenic. Iron and copper also exceeded their respective SCTLs for residential application, but not for industrial application. It is noted that unlike arsenic (which is a carcinogen), copper and iron are listed only based on toxicity. With respect to leaching, two different approaches were compared: comparing total concentrations (mglkg) to the leaching SCTLs and comparing actual leachate concentrations (mgil) to GWCTLs. Comparison with the leaching SCTLs indicated that arsenic, chromium and zinc would pose a potential risk to ground water. The SPLP results did not find these metals to pose a risk, but found lead instead. This suggests that using leaching SCTLs that are developed for soil is not appropriate for application to combustion ash. The SPLP results showed elevated levels of lead (above the GWCTL). When compared to steady state concentrations measured in the 1 ft lysimeters, SPLP lead concentrations matched very well. This suggests that SPLP concentrations were reflective of the pore water concentration for this ash and that a dilution factor should be applied if one is appropriate for the particular land application scenario. The authors note, however, that SPLP concentrations for other wastes and metals may not always be representative of pore water concentrations. 149

ACKNOWLEDGEMENTS This work was funded by the Florida Center for Solid and Hazardous Waste Management (www.floridacenter.org). The authors thank the Polk County Solid Waste Division for their support. Thabet Tolayrnat is a graduate research assistant in the Department of Environmental Engineering Sciences at the University of Florida. Timothy Townsend is an associate professor in the same department (ttown@ufl.edu). Hopper, K., Iskander, M., Sivia, G., Hussein, F., Hsu, J., Deguzman, M., Odion, Z., Ilejay, Z., Sy, F., Peters, M., and Simmons, B. (1998). "Toxicity Characteristic Leaching Procedure Fails to Extract Oxoanion Forming Elements that Are Extracted by Municipal Solid Waste Leachates." Environ. Sci. Technol., 32, 3825-383. Kanungo, S. B., and Mohapatra, R. (2). "Leaching Behavior of Various Trace Metals in Aqueous medium From Two Fly Ash Samples." Journal Environmental Quality(29), 118-196. REFRENCES Berggren, D. (1999). "The solubility of aluminium in two Swedish acidified forest soils: An evaluation of lysimeter measurements using batch titration data." Water Air and Soil Pol/ution, 114(1-2), 137-153. Brantley, A, and Townsend, T. (1999). "Leaching of Pollutants from Reclaimed Asphalt Pavement." Environ. Eng. Sci., 16(2), 15-116. Buchholz, B. A, and Landsberger, S. (1995). "Leaching Dynamics Studies of Municipal Solid Waste Incinerator Ash." Journal of Air & Waste Management Association, 45, 579-59. Magid, J., Christensen, N., and Nielsen, H. (1992). "Measuring phosphorus fluxes through the root zone of a layered sandy soil: comparisons between lysimeter and suction cell solution." J. Soil Sci., 43, 739-747. Saranko, c., HaImes, C., Tolson, K., and Roberts, S. (1999). "Development Of Soil Cleanup Target Levels (SCTLs) For Chapter 62-777, F.AC." Center for Environmental & Human Toxicology. University of Florida., Gainesville Fl. Townsend, T., Solo-Gabriele, H., Tolayrnat, T., and Stook, K. (22). "The Impact of Chromated Copper Arsenate (CCA) in Wood Mulch." Sci. Tot. Environ., Submitted for Publication. CCR. (1998). California Code of Federal Regulations, Title 22 Chapter 11, Article 5, Appendix II. Florida Department of Environmental Protection (21). Guidance for Preparing Municipal Waste to Energy Ash Beneficial Use Demonstrations. Version 1, February 27, Tallahassee, Florida. Hageman, P., Briggs, P., Desborough, G., Lamothe, P., and Theodorakos, P. (2). "Synthetic Precipitation Leaching Procedure (SPLP) Leachate Chemistry Data for Solid Mine Waste Composite Samples from Southwestern New Mexico, and Leadville, Colorado." Department of Interior USGS, Denver, CO. Townsend, T., Jang, Y., Tolayrnat, T. (23). "Leaching Tests for Evaluating Risk in Solid Waste Management Decision Making." Draft report submitted to the Florida Center for Solid and Hazardous Waste Management, Gainesville, FL. U.S.EPA (1996). Test Methods For Evaluating Solid Waste, SW846, 3, Office of Solid Waste and Emergency Response, Washington D. C. Wiles, C. (1996). "Municipal Solid Waste Combustion Ash: State-of-the-Knowledge." Journal of Hazardous Materials, 47,325-344. 15