Environ. Sci. Technol. 2004, 38, 1897-1900
Ecotoxicity Assessment of Stabilized/Solidified Foundry Sludge A L B E R T O C O Z , * A N A A N D R EÄ S , A N D AÄ N G E L I R A B I E N Departamento de Ingenierı´a Quı´mica y Quı´mica Inorga´nica, Universidad de Cantabria, Avda de los Castros s/n, 39005 Santander, Spain
The aim of this study is to evaluate the toxicity of the leachates from a foundry sludge and the derived products based on the stabilization/solidification (S/S) processes. Foundry sludge is an industrial hazardous waste containing inorganic and organic pollutants. The immobilization of the foundry waste has been performed using different S/S procedures based on cement or lime as binder agents and foundry sand fines, calcium-magnesium lignosulfonate, silica fume, activated carbon and black carbon as additives. The waste and stabilized/solidified derived products have been evaluated according to environmental considerations. The relation between the chemical composition and the ecotoxicity of the leachates has been studied in this paper. The ecotoxicity of the leachates has been related to the heavy metals and the organic pollutants by an empirical logarithmic linear expression. Different parameters of the logarithmic fitting have been obtained for the studied binder agents and additives allowing the establishment of a relationship between the S/S process and the ecotoxicity of the derived products. Results of this study have wide-ranging implications for immediate management strategies of waste with organic and inorganic pollutants in addition to application in long-term remediation efforts.
Introduction Some biological tests have been developed for the technical evaluation of the ecotoxicity of waste with many pollutants and waste of complex character (organic and inorganic pollutants) by means of a single bioassay. The advantage of the biotests is that the toxicity of the waste stream is measured and may be compared. Thus, the toxicity of the contaminants is estimated, taking into account bioavailability and synergistic or antagonistic effects. There are some basic requirements for ecotoxicological testing (1). It must be representative, reproducible, and simple to enable the frequent control of effluents by short-term testing and must be cost-effective. Several test system hierarchies have been considered for these purposes (1): toxicity test with simple species (e.g., fish, daphnia, algae, and bacteria) or suborganism test systems (e.g., fish cell tests). However, there is not any test system that completely fulfills the above-mentioned criteria. For example, toxicity tests with single organisms cannot perfectly fulfill the expectations for ecosystem relevance. Whereas such a test is representative for the same species * Corresponding author phone: +34-942201359; fax: +34942201591; e-mail:
[email protected]. 10.1021/es034913f CCC: $27.50 Published on Web 02/13/2004
2004 American Chemical Society
and related organisms, a single species test does not reflect basic interactions in the ecosystem. There is a need to develop fast, robust, and peer-reviewed techniques based on biochemical mechanisms to assist toxicological parameters. Bacteria and enzyme systems have great potential; certain species of marine luminescent bacteria, in particular Vibrio fischeri (formerly known as Photobacterium phosphoreum), are useful surrogates for toxicological assessment (2). In the literature, different biotests (fish, daphnia, algae, and luminescent bacteria) have been compared (1, 3-6). The bacterial bioluminescence assay has been considered in this paper because it is a rapid, robust, highly sensitive method. The results show reproducibility, they are costeffective, and the reference limits are given in the Spanish Regulations. Furthermore, the bioluminescence assay has a worldwide application and standarization for regulatory purposes; it is preferred over other bacterial screening techniques. This work takes a foundry sludge generated from wet cleaning of gases and listed as hazardous waste in the European Waste Catalogue 2001, identifying this waste with the code 100213* (7). Table 1 shows the results of the waste characterization (8, 9). According to the Spanish Regulations, based on the inhibition of the luminescence of a marine bacteria (limit 3000 mg/L) (10), the waste is ecotoxic with EC50 lower than 1000 mg/L. EC50 (mg/L) is expressed as the effective concentration of toxicant that causes a 50% decrease in the light output. The ecotoxicity of the waste may be related to organic compounds (phenols) and inorganic elements (zinc) as the main pollutants. These pollutants and the high proportion of water in the sludge make it difficult to handle and to manage the waste. In previous studies (9, 11), several immobilization processes have been developed in order to obtain a waste for disposal. Stabilization/solidification (S/S) processes were applied because they are known techniques for the treatment of industrial waste and they are technically and economically feasible. In this work, lime and cement are used as binder agents and foundry sand fines; calcium-magnesium lignosulfonate is used as a superplasticizer; and silica fume, activated carbon, and black carbon are used as additives. Leaching tests have been carried out in order to evaluate the stabilized/solidified derived products following the European Regulation (12). The chemical parameters were the phenol index and the zinc concentration. Bioluminescence tests with V. fischeri and Microtox standard tests have been carried out to determine the ecotoxicity of the leachates according to the Spanish Regulations (10) and to check the influence of the chemical composition on the ecotoxicity. Although many papers have reported the leaching behavior of heavy metals and organic pollutants in waste and derived products (13-19), few results have been reported on the ecotoxicity of S/S products and the relationship between ecotoxicity and chemical composition (3, 4, 20, 21). Correlations between parameters have been mentioned (2224), but the cumulative effect of inorganic (zinc) and organic (phenols) pollutants has not been described in the literature. The experimental results allow us to formulate a correlation relating ecotoxicity of the stabilized/solidified derived products with the chemical composition, both organic (phenols) and inorganic (zinc). These relations are useful in optimizing the S/S processes for hazardous waste treatment before disposal. VOL. 38, NO. 6, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Results of Foundry Sludge Characterization composition range
parameter water content (%) Zn (mg/L) in TCLP leachate other heavy metals: Pb, Cr, Cu, Ni, Cd, Hg, As, Ba, Se, Ag (mg/L) in TCLP leachate TOC (mg/L) in EN leachate phenol index (mg/L) in EN leachate AOX (mg/L) in EN leachate Heavy metals: Zn, Pb, Cr, Cu, Ni, Cd Hg, As (mg/l) in EN leachate Ecotoxicity EC50 (mg/l)
49.43-63.04 1958-2239 0.0049-0.73 40.1-79.8 11.8-35.4 0.02 0.0025-0.77 396-804.5
TABLE 2. S/S Formulations binder (%) S/S waste product (%)
lime
additive (%)
foundry silica activated black cement sands fume lignos. carbon carbon
0 100 1-4 60-90 10-40 5-10 35-90 5-30 0-50 11-14 70 25-30 0-5 15-23 28-70 12-30 0-60 24-29 70 15-29, 0-10 0.5-5 5 30-33 70 15-29 0-10 34-37 70 15-29 0-10 38-41 70 15-29 0-10 1-5
1-5 1-5
Experimental Section Materials. Foundry sludge (FS) from a factory located in Cantabria (Spain) was used in the experimental study. Portland cement type I 42,5 R (Cementos ALFA, Cantabria) and commercial lime (Calcinor, S.A., Cantabria) were used as binders. Foundry sand fines, byproduct from the foundry activities, activated carbon reagent grade, calcium-magnesium lignosulfonate (superplasticizer Curtexil 55L from Lignotech Ibe´rica, S.A., Cantabria), silica fume (SikacreteHD from Sika, Spain) and black carbon Columbian Carbon Spain, S.A., Cantabria, were studied as additives. Stabilization/Solidification Procedures. The formulation of the stabilized/solidified products are shown in Table 2. The quantities of additives used in S/S processes with FS, according to the literature, is in the range of Table 2. The waste was mixed with binders and additives in a CEMEX W-20, X-02-G laboratory-scale solid mixer prototype. Each product was transferred to a plastic bag at room temperature for 28 or 56 days of curing. Leaching Tests. The samples were characterized using the leaching tests EN 12457 and U.S. EPA-TCLP regulated procedures (10, 12, 25). In the U.S. EPA-TCLP, acetic acid is used as a leachant to simulate the organic acid generation in municipal waste landfills, while in the EN procedure distilled water is used in order to evaluate the mobility of the pollutants. Chemical Analysis. The metal concentration Zn in the TCLP leachate was measured using an atomic emission spectrometer ICP (inductively coupled plasma), Perkin-Elmer 400. Phenol index in EN leachate was determined according to the norm DIN 38409-H16 “Determination of Phenol Index 4-Aminoantipyrine Spectrometric Method after Distillation” (26). The equipment used was the Spectrophotometer PerkinElmer, Lambda 2UV/VIS. Zinc concentration has been analyzed in the TCLP leachate in order to correlate the mobility results with the ecotoxicity. However, the phenol index has been performed on the EN test due to fact that phenolic pollutants are soluble on distilled water and the mobility does not depend on the pH in the studied range (9). 1898
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FIGURE 1. Results of zinc mobility in TCLP leachate vs ecotoxicity in all products. Chemical composition of leachates were compared with the limits established by the EU Council Decision (12) in order to classify the treated waste as inert, hazardous, or nonhazardous for the purpose of landfilling. Bioassays. The microbial bioassay has been applied to TCLP leachates following the Spanish Regulation (10), which is based on the inhibition of the luminescence of the marine bacteria V. fischeri. The presence of toxic or bioreactive substances that disrupt or inhibit cellular metabolism will ultimately affect the electron transport system and can be readily quantified by measuring the change in light output of the test cell suspension. The lyophilized bacterial reagent was supplied by Microbics. The Microtox bioassay was conducted at a constant time and temperature (15 min, 15 °C). Bioassays were performed according to the standard procedure in a Microtox model 500. Results were expressed as 15 min EC50 values calculated with the Microtox reduction software supplied by Microbics Corp., where EC50 (mg/L) is expressed as the effective concentration of toxicant (leachate) that causes a 50% decrease in the light output. Results were compared to the values given by the Spanish Regulation (EC50 e 3000 mg/L) to establish if a waste is hazardous based on the ecotoxicity (H14, ecotoxicity property) (10). Another way to express toxicity is by means of toxicity units (TU), which are calculated as the inverse of EC50 being expressed as a percentage. A substance is considered toxic when its ecotoxicity value, expressed in TU, is greater than 3.3 (20).
Results and Discussion Stabilization/Solidification Derived Products Results. Figure 1 shows the results of the zinc mobility of the TCLP leachate versus the ecotoxicity for the stabilized/solidified products and the FS. The regulated limits for nonhazardous (EC50 >3000 mg/L, zinc concentration
