TCLP underestimates leaching of arsenic from solid residuals under landfill conditions

Recent revision of the arsenic in drinking water standard will cause many utilities to implement removal technologies. Most of the affected utilities are expected to use adsorption onto solid media for arsenic removal. The arsenic-bearing solid residuals (ABSR) from adsorption processes are to be disposed of in nonhazardous landfills. The Toxicity Characteristic Leaching Procedure (TCLP) tests whether a waste is hazardous or nonhazardous; most solid residuals pass the TCLP. However, the TCLP poorly simulates the alkaline pH, low redox potential, biological activity, long retention time, and organic composition of mature landfills. These same conditions are likely to favor mobilization of arsenic from metal oxide sorbents. This study quantifies leaching of arsenic from Activated Alumina (AA) and Granular Ferric Hydroxide (GFH), two sorbents expected to be widely used for arsenic removal. The sorbents were subjected to the TCLP, the Waste Extraction Test (WET), an actual landfill leachate, and two synthetic leachate solutions. Up to tenfold greater arsenic concentration is extracted by an actual landfill leachate than by the TCLP. Equilibrium leachate concentrations are not achieved within 18 h (the TCLP duration) and an N2 headspace and end-over-end tumbling increase the rate of arsenic mobilization. However, tests with actual landfill leachate indicate the WET may also underestimate arsenic mobilization in landfills.     

Comparison between acetic acid and landfill leachates for the leaching of Pb(II), Cd(II), As(V), and Cr(VI) from cementitious wastes

The Toxicity Characteristic Leaching Procedure (TCLP) has been widely used to characterize the suitability of solid wastes for disposal in landfills. However, the widespread application of this test for the assessment of wastes disposed in different landfill types is often questionable. This paper investigates the leaching profiles of cement-stabilized heavy metal ions, namely, Pb (II), Cd (II), As(V), and Cr(VI), using acetic acid and leachates from municipal and nonputrescible Australian landfill sites. The leaching profiles of Pb, Cd, As, and Cr using acetic acid were found to be similar to the nonputrescible landfill leachate and differed markedly from the municipal solid waste (MSW) leachate. The additional presence of high amounts of organic and inorganic compounds in the municipal landfill leachate influenced the leaching profiles of these metal ions as compared to the acetic acid and the nonputrescible systems. It is postulated that the organic compounds present in the municipal landfill leachate formed complexes with the Pb and Cd, increasing the mobility of these ions. Moreover, the organic compounds in the municipal landfill leachate induced a reducing environment in the leachate, causing the reduction of Cr(VI) to Cr(III). It was also found that the presence of carbonates in the municipal landfill leachate affected the stability of calcium arsenate, with the carbonate competing with arsenate for calcium at high pH, forcing arsenate into the solution.     

Arsenic and lead leaching from the waste derived fertilizer ironite

The toxicity characteristic leaching procedure (TCLP) and the synthetic precipitation leaching procedure (SPLP) were performed on commercially purchased samples of the waste-derived soil amendment marketed as Ironite. Ten samples of the 1-0-0 grade (the most widely available in Florida) were tested. Two samples of the 12-10-10 grade and three samples of the 6-2-1 grade (a liquid version) were tested as well. TCLP leachate concentrations from the 1-0-0 grade samples ranged from 5.0 to 8.0 mg L(-1) for lead and 2.2 to 4.8 mg L(-1) for arsenic. SPLP concentrations from the 1-0-0 samples ranged from 0.62 to 3.1 mg L(-1) for lead and 1.9 to 8.2 mg L(-1) for arsenic. All of the 1-0-0 grade samples exceeded the U.S. hazardous waste toxicity characteristic (TC) limit for lead (5 mg L(-1)), while five of the 10 SPLP samples exceeded the TC limit for arsenic (5 mg L(-1)). The greater arsenic leachability in the SPLP relative to the TCLP was determined to be a result of lower pH conditions in the SPLP. A composite sample of the 1-0-0 grade was found to leach much greater concentrations of both arsenic and lead using California's waste extraction test (WET). Lead leachate concentrations were much lower in the two 12-10-10 samples (0.03 mg L(-1) or less); arsenic concentrations in these leachates (both TCLP and SPLP) exceeded 5 mg L(-1). None of the 6-2-1 samples contained lead or arsenic above TC limits. An experiment performed on the 1-0-0 grade which examined leachability as a function of pH found that at pH values in the range of what is encountered in the human digestive system (pH 4.0 to 1.5) lead leached 2-36% of its initial content, and arsenic leached 1-6% of its initial content. A simple gastric acid leaching experiment found 83 and 37% of the lead and arsenic present to leach, respectively.     

Arsenic speciation of solvent-extracted leachate from new and weathered CCA-treated wood

For the past 60 yr, chromate-copper-arsenate (CCA) has been used to pressure-treat millions of cubic meters of wood in the United States for the construction of many outdoor structures. Leaching of arsenic from these structures is a possible health concern as there exists the potential for soil and groundwater contamination. While previous studies have focused on total arsenic concentrations leaching from CCA-treated wood, information pertaining to the speciation of arsenic leached is limited. Since arsenic toxicity is dependent upon speciation, the objective of this study was to identify and quantify arsenic species leaching from new and weathered CCA-treated wood and CCA-treated wood ash. Solvent-extraction experiments were carried out by subjecting the treated wood and the ash to solvents of varying pH values, solvents defined in the EPA's Synthetic Precipitation Leaching Procedure (SPLP) and Toxicity Characteristic Leaching Procedure (TCLP), rainwater, deionized water, and seawater. The generated leachates were analyzed for inorganic As(III) and As(V) and the organoarsenic species, monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA), using high-performance liquid chromatography followed by hydride generation and atomic fluorescence spectrometry (HPLC-HG-AFS). Only the inorganic species were detected in any of the wood leachates; no organoarsenic species were found. Inorganic As(V) was the major detectable species leaching from both new and weathered wood. The weathered wood leached relatively more overall arsenic and was attributed to increased inorganic As(III) leaching. The greater presence of As(III) in the weathered wood samples as compared to the new wood samples may be due to natural chemical and biological transformations during the weathering process. CCA-treated wood ash leached more arsenic than unburned wood using the SPLP and TCLP, and ash samples leached more inorganic As(III) than the unburned counterparts. Increased leaching was due to higher concentrations of arsenic within the ash and to the conversion of some As(V) to As(III) during combustion.     

RCRA toxicity characterization of discarded electronic devices

The potential for discarded electronic devices to be classified as toxicity characteristic (TC) hazardous waste under provisions of the Resource Conservation and Recovery Act (RCRA) using the toxicity characteristic leaching procedure (TCLP) was examined. The regulatory TCLP method and two modified TCLP methods (in which devices were disassembled and leached in or near entirety) were utilized. Lead was the only element found to leach at concentrations greater than its TC limit (5 mg/L). Thirteen different types of electronic devices were tested using either the standard TCLP or modified versions. Every device type leached lead above 5 mg/L in at least one test and most devices leached lead above the TC limit in a majority of cases. Smaller devices that contained larger amounts of plastic and smaller amounts of ferrous metal (e.g., cellular phones, remote controls) tended to leach lead above the TC limit at a greater frequency than devices with more ferrous metal (e.g., computer CPUs, printers).     

Release of arsenic to the environment from CCA-treated wood. 2. Leaching and speciation during disposal

Wood treated with chromated copper arsenate (CCA) is primarily disposed within construction and demolition (C&D) debris landfills, with wood monofills and municipal solid waste (MSW) landfills as alternative disposal options. This study evaluated the extent and speciation of arsenic leaching from landfills containing CCA-treated wood. In control lysimeters where untreated wood was used, dimethylarsinic acid (DMAA) represented the major arsenic species. The dominant arsenic species differed in the lysimeters containing CCA-treated wood, with As(V) greatest in the monofill and C&D lysimeters and As(III) greatest in the MSW lysimeters. In CCA-containing lysimeters, the organoarsenic species monomethylarsonic acid (MMAA) and DMAAwere virtually absent in the monofill lysimeter and observed in the C&D and MSW lysimeters. Overall arsenic leaching rate varied for the wood monofill (0.69% per meter of water added), C&D (0.36% per m), and MSW (0.84% per m) lysimeters. Utilizing these rates with annual disposal data, a mathematical model was developed to quantify arsenic leaching from CCA-treated wood disposed to Florida landfills. Model findings showed between 20 and 50 t of arsenic (depending on lysimeter type) had leached prior to 2000 with an expected increase between 350 and 830 t by 2040. Groundwater analysis from 21 Florida C&D landfills suspected of accepting CCA-treated wood showed that groundwater at 3 landfills was characterized by elevated arsenic concentrations with only 1 showing impacts from the C&D waste. The slow release of arsenic from disposed treated wood may account for the lack of significant impact to groundwater near most C&D facilities at this time. However, greater impacts are anticipated in the future given that the maximum releases of arsenic are expected by the year 2100.     

Toxicity characteristic leaching procedure and iron treatment of brass foundry waste

The Toxicity Characteristic Leaching Procedure (TCLP) is used by the United States Environmental Protection Agency to determine if wastes contain extractable components subject to hazardous waste regulations. This paper examines the limitations of the TCLP and the way it is used by studying a particular example. Waste casting sand from brass foundries to which iron metal has been added passes the TCLP test but when placed in a landfill for several years may start to leach lead, copper, and zinc. Results of TCLP tests of waste sand alone and with the additives iron metal, zinc metal, hydrous ferric oxide, and hematite are reported. Three processes were studied: reduction by metallic iron, sorption by hydrous ferric oxide, and precipitation of hydroxides. Lead, copper, and zinc behave differently with respect to these three processes, and their measurement allows some deductions as to what is occurring in a TCLP test or a landfill. Iron addition does not result in long-term stabilization of a waste placed in the ground. The chemistry of a laboratory extraction can be very different from the chemistry of a waste placed in the environment. Wastes that are treated to pass the TCLP test, but are not permanently stabilized, are a threat to the environment.     

Impact of electronic waste disposal on lead concentrations in landfill leachate

Lead is the element most likely to cause discarded electronic devices to be characterized as hazardous waste. To examine the fate of lead from discarded electronics in landfills, five columns were filled with synthetic municipal solid waste (MSW). A mix of electronic devices was added to three columns (6% by weight), while two columns served as controls. A sixth column contained waste excavated from an existing MSW landfill. Leachate quality was monitored for 440 days. In columns with the synthetic waste, leachate pH indicated that the simulated landfill environment was characteristic of the acid phase of waste decomposition; lead leachability should be greater in the acid phase of landfill degradation as compared to the methanogenic phase. Lead concentrations ranged from 7 to 66 microg/L in the columns containing electronic waste and ranged from < 2 to 54 microg/L in the control columns. Although the mean lead concentrations in the columns containing electronic devices were greater than those in the controls, the difference was not found to be statistically significant when comparing the data sets over the entire monitoring period. Lead results from the excavated waste column suggest that lead concentrations in all columns will decrease as the pH increases toward more neutral methanogenic conditions.     

Relative leaching and aquatic toxicity of pressure-treated wood products using batch leaching tests

Size-reduced samples of southern yellow pine dimensional lumber, each treated with one of five different waterborne chemical preservatives, were leached using 18-h batch leaching tests. The wood preservatives included chromated copper arsenate (CCA), alkaline copper quaternary, copper boron azole, copper citrate, and copper dimethyldithiocarbamate. An unpreserved wood sample was tested as well. The batch leaching tests followed methodology prescribed in the U.S. Environmental Protection Agency toxicity characteristic leaching procedure (TCLP). The wood samples were first size-reduced and then leached using four different leaching solutions (synthetic landfill leachate, synthetic rainwater, deionized water, and synthetic seawater). CCA-treated wood leached greater concentrations of arsenic and copper relative to chromium, with copper leaching more with the TCLP and synthetic seawater. Copper leached at greater concentrations from the arsenic-free preservatives relative to CCA. Arsenic leached from CCA-treated wood at concentrations above the U.S. federal toxicity characteristic limit (5 mg/L). All of the arsenic-free alternatives displayed a greater degree of aquatic toxicity compared to CCA. Invertebrate and algal assays were more sensitive than Microtox. Examination of the relative leaching of the preservative compounds indicated that the arsenic-free preservatives were advantageous over CCA with respect to waste disposal and soil contamination issues but potentially posed a greater risk to aquatic ecosystems.     

Distribution and fate of inorganic and organic arsenic species in landfill leachates and biogases

The arsenic release from landfills requires special attention both due to its potential toxicity and due to the increasing global municipal solid waste production. The determination of arsenic species in both leachates and biogases has been performed in this work to determine the fate of arsenic in landfills. Both inorganic and methylated arsenic species occur in leachates with concentrations varying from 0.1 to 80 microg As L(-1). These species are representative of the leachate arsenic composition, as the mean recovery obtained for the speciation analyses is 67% of the total arsenic determined in elementary analyses. In biogases, both methylated and ethylated volatile arsenic species have been identified and semiquantified (0-15 microg As m(-3)). The landfill monitoring has emphasized close relationships between the concentrations of mono-, di-, and tri-methylated arsenic compounds in leachates. A biomethylation pathway has thus been proposed as a source of these methylated compounds in the leachates from waste arsenic, which is supposed to be in major part under inorganic forms. In addition, peralkylation mechanisms of both biomethylation and bioethylation have been suggested to explain the occurrence of the identified volatile species. This combined speciation approach provides a qualitative and quantitative characterization of the potential emissions of arsenic from domestic waste disposal in landfills. This work highlights the possible formation of less harmful organoarsenic species in both leachates and biogases during the waste degradation process.     

Arsenic leaching from mulch made from recycled construction and demolition wood and impacts of iron-oxide colorants

Mulch made from recycled construction and demolition (C&D) wood has been reported to contain elevated levels of arsenic from inadvertent inclusion of chromated copper arsenate (CCA)-treated wood. Such mulch is also commonly colored with iron oxide, a compound known to bind arsenic. The objectives of this study were to quantify the releases of arsenic from mulch made from C&D wood, to evaluate the impacts of an iron-oxide colorant in potentially decreasing arsenic leaching rates, and to evaluate the relative significance of additional variables on leachate concentrations. Atotal of 3 sets of mulch samples (0%, 5%, or 100% CCA-treated wood) were prepared containing a sample either with or without colorant addition. Each sample was subjected to two tests: a field leaching test and the Synthetic Precipitation Leaching Procedure (SPLP). Results showed that arsenic concentrations in the field leachate from the 0% treated wood mulches were consistently low (<0.003-0.013 mg/L) whereas leachates from 5 and 100% treated wood mulches were characterized by higher arsenic concentrations (0.059-2.23 mg/L for 5%; 0.711-22.7 mg/L for 100%). The mass of arsenic leached from the field samples during the 1-year monitoring period was between 10 and 15% of the initial mass of arsenic. The colorant reduced the leaching of arsenic by more than 20% for the field leachate and 50% for the SPLP leachate, on average. However, the study showed that the effect may not last for long periods. Besides colorant addition other factors were observed to affect the amount of arsenic leached from contaminated mulch. These include the proportion of CCA-treated wood in the mulch, time, and pH of rainfall.     

Landfill disposal of CCA-treated wood with construction and demolition (C&D) debris: arsenic, chromium, and copper concentrations in leachate

Although phased out of many residential uses in the United States, the disposal of CCA-treated wood remains a concern because significant quantities have yet to be taken out of service, and it is commonly disposed in landfills. Catastrophic events have also led to the concentrated disposal of CCA-treated wood, often in unlined landfills. The goal of this research was to simulate the complex chemical and biological activity of a construction and demolition (C&D) debris landfill containing a realistic quantity of CCA-treated wood (10% by mass), produce leachate, and then evaluate the arsenic, copper, and chromium concentrations in the leachate as an indication of what may occur in a landfill setting. Copper concentrations were not significantly elevated in the control or experimental simulated landfill setting (alpha = 0.05). However, the concentrations of arsenic and chromium were significantly higher in the experimental simulated landfill leachate compared to the control simulated landfill leachate (alpha = 0.05, p < 0.001). This indicates that disposal of CCA-treated wood with C&D debris can impact leachate quality which, in turn could affect leachate management practices or aquifers below unlined landfills.     

Leaching assessments of hazardous materials in cellular telephones

Protocols for assessing the risks of discarded electronic products (e-waste) vary across jurisdictions, complicating the tasks of manufacturers and regulators. We compared the Federal Toxicity Characteristic Leaching Procedure (TCLP), California's Waste Extraction Test (WET), and the Total Threshold Limit Concentration (TTLC) on 34 phones to evaluate the consistency of hazardous waste classification. Our sample exceeded TCLP criteria only for lead (average 87.4 mg L(-1); range = 38.2-147.0 mg L(-1); regulatory limit = 5.0 mg L(-1), but failed TTLC for five metals: copper (average 203 g kg(-1); range = 186-224 g kg(-1); limit = 2.50 g kg(-1), nickel (9.25 g kg(-1); range = 6.34-11.20 g kg(-1); limit = 2.00 g kg(-1)), lead (10.14 g kg(-1); range = 8.2211.60 g kg(-1); limit = 1.00 g kg-1), antimony (1.02 g kg(-1); range = 0.86-1.29 g kg(-1); limit = 0.50 g kg(-1)), and zinc (11.01 g kg(-1); range = 8.82-12.80 g kg(-1); limit = 5.00 g kg(-1). Thresholds were not exceeded for WET. We detected several organic compounds, but at concentrations below standards. Brominated flame retardants were absent. These results improve existing environmental databases for e-waste and highlight the need to review regulatory testing for hazardous waste.     

Leaching of arsenic from granular ferric hydroxide residuals under mature landfill conditions

Most arsenic bearing solid residuals (ABSR) from water treatment will be disposed in nonhazardous landfills. The lack of an appropriate leaching test to predict arsenic mobilization from ABSR creates a need to evaluate the magnitude and mechanisms of arsenic release under landfill conditions. This work studies the leaching of arsenic and iron from a common ABSR, granular ferric hydroxide, in a laboratory-scale column that simulates the biological and physicochemical conditions of a mature, mixed solid waste landfill. The column operated for approximately 900 days and the mode of transport as well as chemical speciation of iron and arsenic changed with column age. Both iron and arsenic were readily mobilized under the anaerobic, reducing conditions. During the early stages of operation, most arsenic and iron leaching (80% and 65%, respectively) was associated with suspended particulate matter, and iron was lost proportionately faster than arsenic. In later stages, while the rate of iron leaching declined, the arsenic leaching rate increased greater than 7-fold. The final phase was characterized by dissolved species leaching. Future work on the development of standard batch leaching tests should take into account the dominant mobilization mechanisms identified in this work: solid associated transport, reductive sorbent dissolution, and microbially mediated arsenic reduction.     

垃圾渗滤液处理技术研究进展

随着经济的快速增长以及工业化、城市化进程的加快,使固体废弃物的产量不断增加,而卫生垃圾填埋场是处理固体废物最常用的一种方法.但其存在的主要缺点是,雨水或地下水会渗入垃圾填埋场,从而产生垃圾渗滤液.垃圾渗滤液不仅会严重污染环境且难以处理,而传统的处理过程已无法去除渗滤液中所含的一些污染物,这些污染物最终会影响自然环境、生...     

Changes in landfill gas quality as a result of controlled air injection

Air addition has been proposed as a technique for rapid stabilization of municipal solid waste (MSW) in landfills. The objective of this study was to observe the change in concentration of trace constituents of landfill gas in response to air addition. Air injection tests were conducted at a MSW landfill in Florida, and the concentrations of several gaseous constituents at adjacent wells within the waste were measured. The concentrations of methane, carbon dioxide, and oxygen, as well as several trace constituents, were measured both prior to and during air addition. The trace components investigated included a suite of volatile organic compounds (VOCs), nitrous oxide (N20), carbon monoxide (CO), and hydrogen sulfide (H2S). A significant increase in CO was observed in 9 of 14 monitoring points; overall, CO concentrations were found to increase as the ratio of CH4 to CO2 decreased. A significant decrease in H2S was observed at 6 of 14 monitoring points. Air injection did not have a noticeable affect on VOC or N2O concentrations compared to initial levels.     

Arsenic leachability in water treatment adsorbents

Arsenic leachability in water treatment adsorbents was studied using batch leaching tests, surface complexation modeling and extended X-ray absorption fine structure (EXAFS) spectroscopy. Spent adsorbents were collected from five pilot-scale filters that were tested for removal of arsenic from groundwater in Southern New Jersey. The spent media included granular ferric hydroxide (GFH), granular ferric oxide, titanium dioxide, activated alumina, and modified activated alumina. The As leachability determined with the Toxicity Characteristic Leaching Procedure (TCLP, 0.1 M acetate solution) was below 180 microg L(-1) for all spent media. The leachate As concentration in the California Waste Extraction Test (0.2 M citrate solution) was more than 10 times higher than that in the TCLP and reached as high as 6650 microg L(-1) in the spent GFH sample. The EXAFS results indicate that As forms inner-sphere bidentate binuclear surface complexes on all five adsorbent surfaces. The As adsorption/desorption behaviors in each media were described with the charge distribution multisite complexation model. This study improved the understanding of As bonding structures on adsorptive media surfaces and As leaching behavior for different adsorbents.     

Lead analysis by anti-chelate fluorescence polarization immunoassay

Lead concentrations were determined by a fluorescence polarization immunoassay (FPIA) method that uses polyclonal antibodies raised against the lead(II) chelate of ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA). The technique is based on competition for a fixed concentration of antibody binding sites between Pb-EDTA, formed by treating the sample with excess EDTA, and a fixed concentration of a fluorescent analogue of the Pb-EDTA complex. The objective was to correlate results obtained by FPIA with those produced by conventional atomic spectroscopy analysis of soils, solid waste leachates (produced by the Toxicity Characteristic Leachate Procedure; TCLP), airborne dust, and drinking water. Linear regression analysis of FPIA results for 138 soil samples containing 0-3094 ppm Pb(II) by flame atomic absorption spectroscopy and 40 TCLP extracts containing 0-668 ppm Pb(II) by inductively coupled plasma atomic emission spectroscopy produced correlation coefficients (r2) of 0.96 and 0.93, respectively. Pilot studies of mineral acid extracts of airborne dust trapped on fiberglass filters and of two sources of drinking water demonstrated the feasibility of also measuring lead in these matrixes by FPIA. The limit of detection under conditions that minimized sample dilution was approximately 1 ppb, and cross reactivity with 15 nontarget metals was below 0.5% in all cases. The methods are simple to perform and are amenable to field testing and mobile laboratory use, allowing timely and cost-effective characterization of suspected sources of lead contamination.     

Municipal solid waste fueled power generation in China: a case study of waste-to-energy in Changchun City

With rapid economic growth and massive urbanization in China, many cities face the problem of municipal solid waste (MSW) disposal. With the lack of space for new landfills, waste-to-energy incineration is playing an increasingly important role in waste management. Incineration of MSW from Chinese cities presents some unique challenges because of its low calorific value (3000-6700 kJ/kg) and high water content (approximately 50%). This study reports a novel waste-to-energy incineration technology based on co-firing of MSW with coal in a grate-circulating fluidized bed (CFB) incinerator, which was implemented in the Changchun MSW power plant. In 2006, two 260 ton/day incinerators incinerated 137,325 tons, or approximately one/sixth of the MSW generated in Changchun, saving more than 0.2 million m3 landfill space. A total of 46.2 million kWh electricity was generated (38,473 tons lignite was also burned as supplementary fuel), with an overall fuel-to-electricity efficiency of 14.6%. Emission of air pollutants including particulate matters, acidic gases, heavy metals, and dioxins was low and met the emission standards for incinerators. As compared to imported incineration systems, this new technology has much lower capital and operating costs and is expected to play a role in meeting China's demands for MSW disposal and alternative energy.     

A two-front leach model for cement-stabilized heavy metal waste

Quantitative scanning electron microscope (SEM) studies of cement-stabilized waste specimens exposed to a leaching solution at constant pH in the range 4-7 have shown that the acid neutralization capacity (ANC) of the waste matrix is consumed at two consecutive leaching fronts. The first front is associated with the dissolution of portlandite (Ca(OH)2) and the partial reaction of calcium silicate hydrate (CSH) gel. The second front marks the dissolution of Ca-Al hydroxy sulfate minerals. The advancement of the first front is limited by the diffusion of OH- ions from the first front toward the leaching solution. The advancement of the second front, however, is controlled by the diffusion of H+ ions from the leaching solution toward the second front. Leaching of copper, zinc, and lead only occurs between the second front and the specimen surface. The leaching behavior of metals is modeled by considering that metals are leached from the waste matrix as a result of the advancement of the second front. The proposed model takes into account the leachable metal fraction in the waste matrix and the effect of metal remineralization on metal mobility.