Characterization of pollutants in Florida street sweepings for management and reuse

Disposal and beneficial-use options for street sweeping residuals collected as part of routine roadway maintenance activities in Florida, USA, were assessed by characterizing approximately 200 samples collected from 20 municipalities. Total concentrations (mg/kg or μg/kg) and leachable concentrations (mg/L or μg/L) of 11 metals and a number of organic pollutant groups (volatile organics, semi-volatile organics, pesticides, herbicides, carbamates) in the samples were measured. The synthetic precipitation leaching procedure (SPLP) was performed to evaluate the leachability of the pollutants. From the total metal analysis, several metals (e.g., arsenic, barium, chromium, copper, nickel, lead, and zinc) were commonly found above their detection limits. Zinc was found to have the highest mean concentration of all metals measured (46.7 mg/kg), followed by copper (10.7 mg/kg) and barium (10.5 mg/kg). The metal with the smallest mean concentration was arsenic (0.48 mg/kg). A small fraction of the total arsenic, barium, lead, and zinc leached in some samples using the SPLP; leached concentrations were relatively low. A few organic compounds (e.g., 4,4′-DDT, endrin, and endosulfan II) were detected in a limited number of samples. When the total and leaching results were compared to risk-based Florida soil cleanup target levels and groundwater cleanup target levels, the street sweepings were not found to pose a significant human-health risk via direct exposure or groundwater contamination.     

Leachability of printed wire boards containing leaded and lead-free solder

Due to environmental concerns and regulatory initiatives, electronics manufacturers are replacing the tin/lead solder commonly used on printed wire boards (PWBs) with alternative solders. To determine the potential waste management impacts of the alternative solders versus the tin/lead solder, two leaching tests on PWBs manufactured with five alternative types of solder were performed: the toxicity characteristic leaching procedure (TCLP) and the synthetic precipitation leaching procedure (SPLP). These tests are commonly used in the US regulatory community to assess pollutant leachability in different disposal scenarios. The article discusses the application and limitations of these tests. The five types of solders investigated were 63Sn/37Pb, 99.3Sn/0.7Cu, 95.5Sn/4Ag/0.5 Cu, 96Sn/2.5Ag/1Bi/0.5Cu, and 42Sn/1Ag/57Bi. The leaching tests were conducted on four PWB sections, each with a unique configuration and solder density. The largest lead concentrations were observed from the PWBs containing Sn/Pb solder, with concentrations exceeding the hazardous waste toxicity characteristic (TC) in TCLP leachates. Silver, the other regulated element used in the solders, was rarely detected, with none of the samples exceeding the TC limit for silver. High copper concentrations were observed and were determined to result from the PWB itself, not from the copper-containing solders.     

Accelerated weathering of biosolid-amended copper mine tailings

Application of municipal biosolids to mine tailings can enhance revegetation success, but may cause adverse environmental impacts, such as increased leaching of NO3- and metals to ground water. Kinetic weathering cells were used to simulate geochemical weathering to determine the effects of biosolid amendment on (i) pH of leachate and tailings, (ii) leaching of NO3- and SO4(2-), (iii) leaching and bioavailability (DTPA-extractable) of selected metals, and (iv) changes in tailing mineralogy. Four Cu mine tailings from southern Arizona differing in initial pH (3.3-7.3) and degree of weathering were packed into triplicate weathering cells and were unamended and amended with two rates (equivalent to 134 and 200 Mg dry matter ha(-1)) of biosolids. Biosolid application to acid (pH 3.3) tailings resulted in pH values as high as 6.3 and leachate pH as high as 5.7, and biosolids applied to circumneutral tailings resulted in no change in tailing or leachate pH. Concentrations of NO3--N of up to 23 mg L(-1) occurred in leachates from circumneutral tailings. The low pH of the acidic tailing apparently inhibited nitrification, resulting in leachate NO3--N of <5 mg L(-1). Less SO4(2-)-S was leached in biosolid-amended versus unamended acid tailings (final rate of 0.04 compared with 0.11 g SO4(2-)-S wk(-1)). Copper concentrations in leachates from acidic tailings were reduced from 53 to 27 mg L(-1) with biosolid amendment. Copper and As concentrations increased slightly in leachates from biosolid-amended circumneutral tailings. Small increases in DTPA-extractable Cu, Ni, and Zn occurred in all tailings with increased biosolid rate. Overall, there was little evidence of potential for adverse environmental impacts resulting from biosolid application to these Cu mine tailings.     

Properties of steel foundry electric arc furnace dust solidified/stabilized with Portland cement

Electric arc furnace dust from steel production is generated in considerable amounts worldwide and needs to be treated as hazardous waste. The aim of this study was to investigate the properties of electric arc furnace dust solidified/stabilized by using Portland cement. Mortar and paste samples were prepared with varying waste-to-binder ratios between 0% and 90%. A comprehensive experimental program was designed including XRF characterization, setting time, unconfined compressive strength, and toxicity characteristics leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP), and acid neutralization capacity (ANC) tests. The results were evaluated in order to determine if the solidified /stabilized product can be disposed of at a landfill site with domestic waste or at a segregated landfill. The effect of using sand on S/S performance was also investigated. The results indicated that the solidification /stabilization process using PC helps the heavy metals to be bound in the cement matrix, but the TCLP leaching results exceeded the EPA landfilling limits. The SPLP leaching results conformed to the limits implying that the waste or S/S products can be disposed of at a segregated landfill; however the low ANC of the S/S products reveals that there may be leaching in the long-term. The sand used in the mortar samples adversely affected the S/S performance, causing higher heavy metal leaching levels, and lower pH levels in the leachate after the TCLP extraction than those measured in the leachate of the paste samples.     

Characteristics of a bioxalate chelating extraction process for removal of chromium,copper and arsenic from treated wood

The disposal of wood waste treated with chromated copper arsenate (CCA) is a problem in many countries. We have proposed a novel chelating extraction technique for CCA-treated wood using bioxalate, a solution of oxalic acid containing sufficient sodium hydroxide to adjust the pH to 3.2, which is an effective way to obtain an extraction efficiency of 90% for chromium, copper, and arsenic. The purpose of the present study was to investigate the characteristics of bioxalate extraction of CCA-treated wood. Extractions of CCA-treated western hemlock chips with solutions of bioxalate, oxalic acid, and sodium hydroxide were carried out. The use of bioxalate was confirmed as the most effective extraction technique for chromium, copper and arsenic, with an efficiency of 90%. Extraction with simple oxalic acid was ineffective for copper (less than 40% extraction efficiency), but effective for chromium and arsenic, with 90% efficiency. Sodium hydroxide showed a similar tendency, being ineffective for chromium and copper (less than 20% extraction efficiency), but relatively effective for arsenic (around 70–80% efficiency). We also discovered an interesting phenomenon whereby the addition of sodium hydroxide to a simple oxalic acid solution during the oxalic acid extraction progress resulted in dramatically increased extraction efficiency for copper, chromium and arsenic, up to 90%. Although oxalic acid was ineffective for copper extraction, the addition of sodium hydroxide during the oxalic acid extraction process rendered it effective.     

Phosphate treatment of firing range soils: lead fixation or phosphorus release?

Phosphate treatment of lead (Pb)-contaminated soils relies on the premise that Pb converts to the thermodynamically stable, insoluble mineral class of pyromorphites. Recent research showed that treatment performance is kinetically controlled and strongly dependent on soil pH; this study employed an acidic phosphate (P) form, monobasic calcium phosphate (MCP), to investigate treatment performance of Pb occurring in an alkaline-buffered and an acidic firing range soil. The results of leaching, X-ray powder diffraction (XRPD), and modeling analyses showed that P and Pb dissolution in the alkaline soil and transformation reactions were kinetically controlled, so that: (i) TCLP (toxicity characteristic leaching procedure) and SPLP (synthetic precipitation leaching procedure) results were poor to marginal even at high MCP dosages; (ii) brushite (Ca(HPO(4)).2H(2)O) and cerussite (PbCO(3)) persisted in XRPD patterns; and, (iii) geochemical modeling failed to predict leaching and phase assemblages. In the acidic soil, Pb-P reactions promoted further soil acidification, improved TCLP performance, and generated better agreement with the equilibrium-based model; however, SPLP and modeling results showed that Pb concentrations could not be reduced below 15 microg/L mainly due to the low soil pH. The marginal or inadequate Pb immobilization was observed in both soils despite the elevated MCP dosages, which were well in excess of the pyromorphite stoichiometric ratio (P/Pb = 0.6). Additionally, P leaching concentrations and rates were extremely high (>300 mg/L), under both SPLP and deionized (DI) water extraction conditions, and as predicted by thermodynamic equilibrium. The performance and sustainability of phosphate-based treatment therefore seem questionable.     

The characterization of total and leachable metals in foundry molding sands

Waste molding sands from the foundry industry have been successfully used as a component in manufactured soils, but concern over metal contamination must be addressed before many states will consider this beneficial use. Since there is little data available on this topic, the purpose of this study was to characterize total and leachable metals from waste molding sands. A total elemental analysis for Ag, Al, As, B, Ba, Be, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Sb, V, and Zn was conducted on 36 clay-bonded and seven chemically bonded molding sands. Total metal concentrations in the molding sands were similar to those found in agricultural soils. The leaching of metals (i.e. Ag, As, Ba, Be, Cd, Cr, Cu, Ni, Pb, Sb, and Zn) was assessed via the toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP), and ASTM water leach test. Based on the TCLP data, none of the 43 molding sands would meet the Resource Conservation and Recovery Act (RCRA) characteristic for toxicity due to high Ag, As, Ba, Cd, Cr, and Pb. Compared to the TCLP results, the metal concentrations were generally lower in the SPLP and ASTM extracts, which is likely related to the buffering capacity of the extraction fluids.     

Effect of tomato packinghouse wastewater properties on phosphorus and cation leaching in a spodosol

Land application of wastewater is a common practice. However, coarse-textured soils and shallow groundwater in Florida present favorable conditions for leaching of wastewater-applied constituents. Our objective in this study was to determine phosphorus (P) and associated cations (Ca, Mg, K, Na) leaching in a Spodosol irrigated with tomato packinghouse wastewater. We packed 12 polyvinyl chloride soil columns (30 cm internal diameter × 50 cm length) with two soil horizons (Ap and A/E) and conducted 30 sequential leaching events by irrigating with wastewater at low (0.84 cm d), medium (1.68 cm d), and high (2.51 cm d) rates. The control treatment received deionized water at 1.68 cm d Leachate pH was lower (6.4-6.5) and electrical conductivity (EC) was higher in the wastewater-treated columns (0.85-1.78 dS m) than in the control treatment (pH 6.9; EC, 0.12 dS m) due to the low pH (6.2) and high EC (2.16 dS m) of applied wastewater. Mean leachate P concentrations were greatest in the control treatment (0.70 mg L), followed by the high (0.60 mg L) and low and medium wastewater-treated columns (0.28-0.33 mg L). Leachate concentrations of Na, Ca, Mg, and K were significantly ( < 0.05) greater in wastewater-treated columns than in the control. Concentrations of P, Na, and K in leachate remained lower than the concentrations in the applied wastewater, indicating their retention in the soil profile. In contrast, leachate Ca and Mg concentrations were greater than in applied wastewater during several leaching events, suggesting that additional Ca and Mg were leached from the soil. Our results suggest that tomato packinghouse wastewater can be beneficially land-applied at 1.68 cm d in Florida's Spodosols without significant P and cation leaching.     

Use of adjuvants to minimize leaching of herbicides in soil

Excessive leaching of herbicides affects their efficacy against target weeds and results in contamination of groundwater. Use of adjuvants that can weakly bind herbicides and in turn release them slowly is a valuable technique to prolong the efficacy of herbicides and to minimize their leaching into groundwater. Effects of activated charcoal, three humic substances (Enersol SP 85%, Enersol 12%, and Agroliz), or a synthetic polymer (Hydrosorb) on the leaching of bromacil, dicamba, and simazine were investigated in leaching columns using a Candler fine sand (Typic Quartzipsamment). The addition of adjuvants had no harmful effects on physical properties of the soil as evident from lack of its affects on water percolation. When no adjuvants were used, 69%, 37%, and 4% of applied dicamba, bromacil, and simazine, respectively, were leached in the first pore volume of leachate (⋍3.2 cm rainfall). With five pore volumes of leachate (⋍16 cm rainfall), bromacil and dicamba were leached completely and only 80% of simazine was leached. Using Enersol 12% adjuvant resulted in a 13%–18% reduction in leaching of dicamba and bromacil in five pore volumes of leachate. The leaching of simazine was significantly decreased when any of the five adjuvants mentioned above were used. However, the decrease in leaching was significantly greater when using Enersol SP 85% or Enersol 12% (24%–28%) than when using the other adjuvants (12%–16%).     

Arsenic availability from chromated copper arsenate (CCA)-treated wood

Lumber used to construct raised garden beds is often treated with chromated copper arsenate (CCA). This project aimed to determine (i) how far As, Cu, and Cr had diffused away from CCA-treated wood surfaces in raised garden beds under realistic conditions, (ii) the uptake of these elements by crops, and (iii) the effect of CCA solution on soil bacteria. This study showed that As, Cu, and Cr diffuse into soil from CCA-treated wood used to construct raised garden beds. To determine crop uptake of these elements, contaminated soil 0 to 2 cm from the treated wood was obtained from two different beds (40-50 mg kg(-1) As); control soil was collected 1.5 m away from the treated wood (<3-10 mg kg(-1) As). Four replicates of carrot (Daucus carota var. sativus Hoffm. cv. Thumbelina), spinach (Spinacia oleracea L. cv. Indian Summer), bush bean (Phaseolus vulgaris L. cv. Provider), and buckwheat (Fagopyrum esculentum Moench cv. Common) were grown in pots containing these soils in a greenhouse. After harvest, plant materials were dried, ground, digested, and analyzed for As by inductively coupled plasma-hydride generation (ICP-HG). Concentrations of As in all crops grown in contaminated soils were higher than those from control soils. The levels of As in the crops remained well below the recommended limit for As set by the United States Public Health Service (2.6 mg kg(-1) fresh wt.). To determine if bacteria in soils 0 to 2 cm from the treated wood had higher resistance to Type C chromated copper arsenate (CCA-C) solution than those from reference soils, dilution plates were set up using quarter-strength tryptic soy agar (TSA) media and 0 to 22.94 g L(-1) (0-1.25% v/v) CCA-C working solution. The microorganisms from soils adjacent to treated wood had greater growth on the CCA-amended media than those from reference soils outside the bed.     

REGIONAL NITRATE LEACHING VARIABILITY: WHAT MAKES A DIFFERENCE IN NORTHEASTERN COLORADO

ABSTRACT: The high spatial variability of nitrate concentrations in ground water of many regions is thought to be closely related to spatially-variable leaching rates from agricultural activities. To clarify the relative roles of the different nitrate leaching controlling variables under irrigated agriculture in northeastern Colorado, we conducted an extensive series of leaching simulations with the NLEAP model using best estimates of local agricultural practices. The results of these simulations were then used with GIS to estimate the spatial variability of leachate quality for a 14,000 ha area overlying the alluvial aquifer of the South Platte River. Simulations showed that in the study area, differences in soil type might lead to 5–10 kg/ha of N variation in annual leaching rates while variability due to crop rotations was as much as 65 kg-N/ha for common rotations. Land application of manure from confined animal feeding operations may account for more than 100 kg-N/ha additional leaching. For a selected index rotation, the simulated nitrogen leaching rates across the area varied from 10 to 299 kg/ha and simulated water volumes leached ranged from 13 to 76 cm/yr depending on soil type, irrigation type, and use of manure. Resulting leachate concentrations of 3.5–140 mg/l NO₃ as N were simulated. Land application of manure was found to be the most important factor determining the mass flux of nitrate leached and the combination of sprinkler irrigation and manure application yields the highest leachate concentrations.     

Leaching of carbonated air pollution control residues using compliance leaching tests

The leaching characteristics of air pollution control (APC) residues collected in Shanghai, China, were compared by performing three compliance leaching tests. These were the standard Chinese method for determining the leaching toxicity of solid waste (GB 5086.1-1997), the USEPA's Toxicity Characteristic Leaching Procedure (TCLP), and the new European shake test (EN 12457-3). In particular, behaviors of raw samples and samples that had been subjected to natural aging were compared. Both the leaching tests and natural aging substantially affected the leaching results concerning the APC residue samples. Most importantly, EN and GB tests classified the raw APC residues as hazardous, but the residues passed the TCLP test as nonhazardous. After it had been naturally aged for 720 h, however, the aged sample was classified as hazardous by the TCLP and EN tests, but as nonhazardous by the GB test. Metals that are thought to have been immobilized by carbonation were released at pH 6.3. Model calculations based on the geochemical thermodynamic equilibrium model MINTEQA2 revealed that the formation of metal carbonates did not correspond to the noted change in the leaching behaviors in the three leaching tests. Rather, the partial neutralization of alkaline ash by dissolved CO2 changing the final pH of the leachate dominated the leaching characteristics. The leaching results showed a change in leachate pH.     

A novel extractant for removal of hazardous metals from preservative-treated wood waste

The purpose of this study was to develop a one-step metal extraction process that would effectively remove hazardous elements from wood powder or chips of western hemlock [Tsuga heterophylla (Raf.) Sarg.] treated with chromated copper arsenate (CCA) preservative. In addition, we tested this method for wood treated with other copper-based preservatives such as ammoniacal copper quaternary (ACQ) and copper, boron, and azole (CuAz). A bioxalate solution consisting of 0.125 M oxalic acid adjusted to pH 3.2 with sodium hydroxide was tested for its ability to extract chromium, copper, and arsenic from wood treated with CCA and copper from ACQ, CuAz, or a mixture of CCA-, ACQ-, and CuAz-treated wood in single step. The extraction proceeded efficiently with 6 h of treatment, and was insensitive to the differences in chemical characteristics, including solubility of individual elements. After 6 h of treatment, approximately 90% of chromium, copper, and arsenic were effectively removed from wood treated with CCA or a mixture of CCA, ACQ, and CuAz and 90% of copper from ACQ- and CuAz-treated wood. These results demonstrate that the solvent extraction technique using pH-adjusted bioxalate solution with sodium hydroxide is a promising method for pollution minimization by various types of wastes contaminated with heavy metals and arsenic.     

Nitrate leaching beneath a containerized nursery crop receiving trickle or overhead irrigation

Container production of nursery crops is intensive and a potential source of nitrogen release to the environment. This study was conducted to determine if trickle irrigation could be used by container nursery producers as an alternative to standard overhead irrigation to reduce nitrogen release into the environment. The effect of overhead irrigation and trickle irrigation on leachate nitrate N concentration, flow-weighted nitrate N concentration, leachate volume, and plant growth was investigated using containerized rhododendron (Rhododendron catawbiense Michx. 'Album') supplied with a controlled-release fertilizer and grown outdoors on top of soil-monolith lysimeters. Leachate was collected over two growing seasons and overwinter periods, and natural precipitation was allowed as a component of the system. Precipitation accounted for 69% of the water entering the overhead-irrigated system and 80% of the water entering the trickle-irrigated system. Leachate from fertilized plants exceeded the USEPA limit of 10 mg L(-1) at several times and reached a maximum of 26 mg L(-1) with trickle irrigation. Average annual loss of nitrate N in leachate for fertilized treatments was 51.8 and 60.5 kg ha(-1) for the overhead and trickle treatments, respectively. Average annual flow-weighted concentration of nitrate N in leachate of fertilized plants was 7.2 mg L(-1) for overhead irrigation and 12.7 mg L(-1) for trickle irrigation. Trickle irrigation did not reduce the amount of nitrate N leached from nursery containers when compared with overhead irrigation because precipitation nullified the potential benefits of reduced leaching fractions and irrigation inputs provided under trickle irrigation.     

Ryegrass cover crop effects on nitrate leaching in spring barley fertilized with 15NH415NO3

Cover crops are a management option to reduce NO3 leaching under cereal grain production. A 2-yr field lysimeter study was established in Uppsala, Sweden, to evaluate the effect of a perennial ryegrass (Lolium perenne L.) cover crop interseeded in barley (Hordeum vulgare L.) on NO3-N leaching and availability of N to the main crop. Barley and ryegrass or barley alone were seeded in mid-May 1992, in lysimeters (03-m diam. x 1.2-m depth) of an undisturbed, well-drained, sandy loam soil. Fertilizer N was applied at the same time as labeled l5NH415NO3 (10 atom % 15N) at a rate of 100 kg N ha(-1). In 1993, barley was reseeded in May in the lysimeters but with nonlabeled NH4NO3 and no cover crop (previous year's cover crop incorporated just prior to seeding). Barley yields and total and fertilizer N uptake in Year 1 (1992) were unaffected by cover crop. Total aboveground N uptake by the ryegrass was 28 kg ha(-1) at the time of incorporation the following spring. Recovery of fertilizer-derived N in May 1993 was about 100%; 53% in soil, 46% in barley, <2% in ryegrass, and negligible amounts in leachate. In May 1994, the corresponding figures were: 32% in soil, <3% in barley, and, again, negligible amounts in leachate. The cover crop reduced concentrations of NO3-N in the leachate considerably (<5 mg L(-1), compared with 10 to 18 mg L(-1) without cover crop) at most sampling times from November 1992 to April 1994, and reduced the total amount of NO3-N leached (22 compared with 8 kg ha(-1)).     

Landfill cover soil, soil solution, and vegetation responses to municipal landfill leachate applications

Municipal solid waste landfill leachate must be removed and treated to maintain landfill cover integrity and to prevent contamination of surface and ground waters. From 2003 to 2007, we studied an onsite disposal system in Ottawa County, Michigan, where leachate was spray irrigated on the vegetated landfill cover. We established six 20-m-diameter circular experimental plots on the landfill; three were spray irrigated as part of the operational system, and three remained as untreated control plots. We quantified the effects of leachate application on soil properties, soil solution chemistry, vegetative growth, and estimated solute leaching. The leachate had high mean levels of electrical conductivity (0.6-0.7 S m(-1)), Cl (760-900 mg L(-1)), and NH(4)-N (290-390 mg L(-1)) but was low in metals and volatile organic compounds. High rates of leachate application in 2003 (32 cm) increased soil electrical conductivity and NO(3)-N leaching, so a sequential rotation of spray areas was implemented to limit total leachate application to <9.6 cm yr(-1) per spray area. Concentrations of NO(3)-N and leaching losses remained higher on irrigated plots in subsequent years but were substantially reduced by spray area rotation. Leachate irrigation increased plant biomass but did not significantly affect soil metal concentrations, and plant metal concentrations remained within normal ranges. Rotating spray areas and timing irrigation to conform to seasonal capacities for evapotranspiration reduced the localized impacts of leachate application observed in 2003. Careful monitoring of undiluted leachate applications is required to avoid adverse impacts to vegetation or soils and elevated solute leaching losses.     

Bromide and nitrate movement through undisturbed soil columns

Field experiments often assume that Br-, 14NO3(-)-N, and 15NO3(-)-N have similar leaching kinetics. This study tested this assumption. Twenty-four undisturbed soil columns (15-cm diameter) were collected from summit-shoulder, backslope, and footslope positions of a no-tillage field with a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Each of the landscape positions had a different soil series. After conditioning the columns with 4 L of 0.01 M CaCl2 (2 pore volumes), 15N-labeled Ca(NO3)2 and KBr were applied to the soil surface and leached with 4 L of 0.01 M CaCl2. Leachate was collected, weighed, and analyzed for NO3(-)-N, NH4(+)-N, 15N, 14N, and Br-. The total amount of 15NO3(-)-N and 14NO3(-)-N collected in 1000, 2000, and 3000 mL of leachate was similar. These data suggest that 15N discrimination during leaching did not occur. Bromide leached faster through the columns than NO3(-)-N. The more rapid transport of Br- than NO3(-)-N was attributed to lower Br- (0.002 +/- 0.036 mg kg(-1)) than NO3(-)-N (0.17 +/- 0.03 mg kg(-1)) sorption. Results from this study suggest that (i) if Br- is used to estimate NO3(-)-N leaching loss, then NO3(-)-N leaching losses may be overestimated by 25%; (ii) the potential exists for landscape position to influence anion retention and movement in soil; and (iii) 15N discrimination was not detected during the leaching process.     

Leaching from organic matter-rich soils by rain of different qualities: I. Concentrations

Soil monoliths from an area exposed to acid precipitation and from an unpolluted area were used in a lysimeter experiment to study effects of different rain qualities on the chemical composition of the leachate from shallow soils rich in organic matter. The vegetation was either dominated by moorgrass [Molinia caerulea (L.) Moench] or heather [Calluna vulgaris (L.) Hull]. The lysimeters received either "acid rain" (pH 4.3) or "normal rain" (pH 5.3). High concentrations of dissolved organic carbon (DOC) were characteristic of the leachate. The different "rain" qualities had no significant influence on the DOC concentration. More DOC was, however, leached from lysimeters with heather vegetation. Roughly 50% of the aluminum (Al) was in complex with organic material and the Al charge was calculated to be between +1.4 and +2.0. Sulfate (SO4(2-)) was the only component that was significantly influenced by the treatment, as more was leached from lysimeters receiving "acid rain." Sulfate was poorly correlated with pH, suggesting that reduced SO4(2-) input would not necessarily lead to reduced acidity. Differences in the pH of the leachate due to the treatments were less than 0.15 pH units. Nitrate (NO3-) was only leached in very low concentrations and of little consequence for the leachate acidity. Some observations do, however, suggest that NO3- may contribute to acidification in episodes with high precipitation. High concentrations of Cl- in the leachate and a significant positive correlation between Cl-, H+, and base cations indicate that sea salt episodes may be important for soil acidification and acidity of the leachate.     

Leachate chemistry of field-weathered spent mushroom substrate

Passive leaching by rainfall and snowmelt is a popular method to treat piles of spent mushroom substrate (SMS) before its reuse. During this field weathering process, leachate percolates into the underlying soils. A field study was conducted to examine the chemistry of SMS leachate and effects of infiltration. Two SMS piles were deposited (90 and 150 cm in height) over a Typic Hapludult and weathered for 24 mo. Leachate was collected biweekly using passive capillary samplers. The SMS leachate contained high concentrations of dissolved organic carbon (DOC; 0.8-11.0 g L(-1)), dissolved organic nitrogen (DON; 0.1-2 g L(-1)), and inorganic salts. The pH, electrical conductivity, and acid neutralizing capacity were 6.6 to 9.0, 21 to 66 ds m(-1), and 10 to 75 mmolc L(-1), respectively. Inorganic chemistry of the leachate was dominated by K+, Cl-, and SO24-. Leachate DOC was predominantly low molecular weight (<1000 Da) organic acids. During 2 yr of weathering, the 90-cm SMS pile released (per cubic meter of SMS) 3.0 kg of DOC, 1.6 kg of dissolved N, and 26.6 kg of inorganic salts. The 150-cm pile released (per cubic meter of SMS) 2.8 kg of DOC, 0.7 kg of dissolved N, and 13.6 kg of inorganic salts. The 150 cm pile retained more water and exhibited lower net nitrification compared with the 90-cm pile. The top 90 cm of soil retained 20 to 89% of the leachate solutes. Weathering of SMS in piles of 90 cm depth or greater may adversely affect ground water quality.     

Decontamination of Fly Ash and Used Lime from Municipal Waste Incinerator Using Thiobacillus ferrooxidans

Thiobacillus ferrooxidans to leach metals from APCR to render them nonhazardous. The multistage solubilization process involves an alkaline aqueous phase that removes some Pb. In the second phase, the APCR are acidified to pH 4 with H₂SO₄, then inoculated with a bacterial culture that has been acclimated in the presence of 2% Fe (FeCl₃). Several rinses and decantings achieve removal of the leachable metals. The final step involves the addition of Ca(H₂PO₄)₂ and an increase in the treatment pH prior to the final filtration. Viability of thiobacilli in APCR was poor. Despite this problem, the removal of Pb was 35.9%, 46.0%, and 68.7% (for APCR containing 1594, 3026, and 5038 mg Pb/kg, respectively), which demonstrates greater metal removal with increased APCR contamination. Zn removal varied from 68.2% (8273 mg Zn/kg APCR) to 79.5% (16,873 mg Zn/kg APCR), which was positively correlated to the level of residue contamination, whereas Cu was removed in the proportions of 26.9% (495 mg Cu/kg APCR) to 68.2% (465 mg Cu/kg APCR). Cadmium removal appeared to be independent of the level of Cd in the APCR; Cd was removed to the greatest degree, with a variation of 92.0% (129 mg Cd/kg APCR) to 94.7% (267 mg Cd/kg APCR). The treated APCR were tested using four different leachate tests. The APCR released 43 mg Pb/liter during contact with water, and 7.40 mg Cd/liter during TCLP [the toxicity characterization leaching procedure of the United States Environmental Protection Agency (US EPA)]. After biological treatment, the leachate from TCLP was within the acceptance criteria of the US EPA, if the pH of the APCR was increased to pH 5 after the biological treatment. In the case of the Transport Canada leaching test, a betterment of the process is required in order to satisfy the stringent regulatory level of 0.5 mg Cd/liter (0.68 and 0.57 mg/liter).