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PubMed2001

Nitrogen fertilizer rate and crop management effects on nitrate leaching from an agricultural field in central Pennsylvania.

Eighteen pan lysimeters were installed at a depth of 1.2 m in a Hagerstown silt loam soil in a corn field in central Pennsylvania in 1988. In 1995, wick lysimeters were also installed at 1.2 m depth in the same access pits. Treatments have included N fertilizer rates, use of manure, crop rotation (continuous corn, corn-soybean, alfalfa-corn), and tillage (chisel plow-disk, no-till). The leachate data were used to evaluate a number of nitrate leaching models. Some of the highlights of the 11 years of results include the following: 1) growing corn without organic N inputs at the economic optimum N rate (EON) resulted in NO3--N concentrations of 15 to 20 mg l(-1) in leachate; 2) use of manure or previous alfalfa crop as partial source of N also resulted in 15 to 20 mg l(-1) of NO3--N in leachate below corn at EON; 3) NO3--N concentration in leachate below alfalfa was approximately 4 mg l(-1); 4) NO3--N concentration in leachate below soybeans following corn was influenced by fertilizer N rate applied to corn; 5) the mass of NO3--N leached below corn at the EON rate averaged 90 kg N ha(-1) (approx. 40% of fertilizer N applied at EON); 6) wick lysimeters collected approximately 100% of leachate vs. 40-50% collected by pan lysimeters. Coefficients of variation of the collected leachate volumes for both lysimeter types were similar; 7) tillage did not markedly affect nitrate leaching losses; 8) tested leaching models could accurately predict leachate volumes and could be calibrated to match nitrate leaching losses in calibration years, but only one model (SOILN) accurately predicted nitrate leaching losses in the majority of validation treatment years. Apparent problems with tested models: there was difficulty estimating sizes of organic N pools and their transformation rates, and the models either did not include a macropore flow component or did not handle macropore flow well.

Agriculture↗
PubMed1978

Landfill disposal systems.

The current status of landfill disposal of hazardous wastes in the United States is indicated by presenting descriptions of six operating landfills. These landfills illustrate the variety of techniques that exist in landfill disposal of hazardous wastes. Although some landfills more effectively isolate hazardous waste than others, all landfills must deal with the following problems. Leachate from hazardous waste landfills is generally highly polluted. Most landfills attempt to contain leachate at the site and prevent its discharge to surface or groundwaters. To retain leachate within a disposal area, subsurface barriers of materials such as concrete, asphalt, butyl rubber, vinyl, and clay are used. It is difficult to assure that these materials can seal a landfill indefinitely. When a subsurface barrier fails, the leachate enters the groundwater in a concentrated, narrow band which may bypass monitoring wells. Once a subsurface barrier has failed, repairs are time-consuming and costly, since the waste above the repair site may have to be removed. The central problem in landfill disposal is leachate control. Recent emphasis has been on developing subsurface barriers to contain the wastes and any leachate. Future emphasis should also be on techniques for removing water from hazardous wastes before they are placed in landfills, and on methods for preventing contact of the wastes with water during and after disposal operations. When leachate is eliminated, the problems of monitoring, and subsurface barrier failure and repair can be addressed, and a waste can be effectively isolated.A surface seal landfill design is recommended for maintaining the dry state of solid hazardous wastes and for controlling leachate. Any impervious liner is utilized over the top of the landfill to prevent surface water from seeping into the waste. The surface barrier is also the site where monitoring and maintenance activities are focused. Barrier failure can be detected by visual inspections and any repairs can be made without disturbing the waste. The surface seal landfill does not employ a subsurface barrier. The surface seal landfill successfully addresses each of the four environmental problems listed above, provided that this landfill design is utilized for dry wastes only and is located at a site which provides protection from groundwater and temporary perched water tables.

Chemical Industry↗
PubMedDate not supplied

Fly ash and lime-stabilized biosolid mixtures in mine spoil reclamation: simulated weathering.

The use of large quantities of neutral coal fly ash (NFA) may be facilitated by co-application with a lime-stabilized biosolid (LSB) for the reclamation of acid mine spoil (AMS). Although NFA may not aid in the mitigation of acid drainage, questions concerning the leachability and mineralogy of native and NFA- and LSB-born metals must be addressed. In this study, the potential long-term influence of LSB and NFA on AMS leachate chemistry and trace element mineralogy was evaluated using laboratory weathering and selective dissolution techniques. The application of LSB at a rate sufficient to neutralize the potential acidity of the AMS increased leachate pH from approximately 3 to 7.5 for the duration of the study. Fly ash rates (1X, 1.5X, and 2X LSB rate) did not affect leachate pH. The dominant electrolytes in all leachates were Ca and SO4, the concentrations of which were mirrored by solution electrical conductivity (EC). Leachate concentrations of Al, Fe, Mn, K, Cu, Ni, and Zn were significantly reduced by LSB application, whereas concentrations of Ca, SO4, Mg, Cl, F, B, and P were increased. Nitrate concentrations were not affected by LSB. With the exception of leachate B, which increased with increasing NFA rate and was regenerated during the weathering study, NFA did not affect leachate composition. Sequential selective dissolution indicated a transformation of Co, Cr, Cu, Ni, Pb, and Zn into less labile mineral pools with weathering. The results of these evaluations suggest that the application of NFA during AMS reclamation would have little effect on leachate chemistry or the mineralogy of trace elements. Thus, the high-volume application of NFA to AMS during reclamation may offer an additional opportunity for the use of this combustion by-product.

Calcium Compounds↗
PubMed2004

Response of biofilm bacteria to dissolved organic matter from decomposing maple leaves.

Stream bacteria play an important role in the utilization of dissolved organic matter (DOM) leached from leaves, and in transfer of this DOM to other trophic levels. Leaf leachate is a mixture of labile, recalcitrant, and inhibitory compounds, and bacterial communities vary in their ability to utilize leachate. The purpose of this study was to determine the effects of DOM from sugar maple leaves on bacterial populations in biofilms on decomposing leaf surfaces. Populations of Acinetobacter calcoaceticus, Burkholderia cepacia, and Pseudomonas putida were enumerated on decomposing maple leaves in a northeast Ohio stream using fluorescence in situ hybridization. Additionally, artificial substrata consisting of PVC-end caps filled with agar supplemented with leaf leachate and covered with cellulose filters were used to determine bacterial response to leachate from leaves at different stages of decomposition. Population sizes of bacterial species exhibited different responses. Leachate did not affect A. calcoaceticus. B. cepacia was tolerant of phenolic compounds released from leaves and the population size increased when DOM concentrations were greatest. In contrast, P. putida was inhibited by phenolic components of leachate when total DOM concentrations were greatest. Differences in response of the bacterial species to components of leaf leachate indicate the complexity of microbial population dynamics and interactions with DOM. Differences among species in response to DOM have the potential to influence transport and retention of organic matter in stream ecosystems.

Acer↗
PubMed2006

Characteristics of the bioreactor landfill system using an anaerobic-aerobic process for nitrogen removal.

A sequential upflow anaerobic sludge blanket (UASB) and air-lift loop sludge blanket (ALSB) treatment was introduced into leachate recirculation to remove organic matter and ammonia from leachate in a lab-scale bioreactor landfill. The results showed that the sequential anaerobic-aerobic process might remove above 90% of COD and near to 100% of NH4+ -N from leachate under the optimum organic loading rate (OLR). The total COD removal efficiency was over 98% as the OLR increased to 6.8-7.7 g/l d, but the effluent COD concentration increased to 2.9-4.8 g/l in the UASB reactor, which inhibited the activity of nitrifying bacteria in the subsequent ALSB reactor. The NO3- -N concentration in recycled leachate reached 270 mg/l after treatment by the sequential anaerobic-aerobic process, but the landfill reactor could efficiently denitrify the nitrate. After 56 days operation, the leachate TN and NH4+ -N concentrations decreased to less than 200 mg/l in the bioreactor landfill system. The COD concentration was about 200 mg/l with less than 8 mg/l BOD in recycled leachate at the late stage. In addition, it was found that nitrate in recycled leachate had a negative effect on waste decomposition.

Aerobiosis↗
PubMed2005

Implication of chromium speciation on disposal of discarded CCA-treated wood.

The wood preservative chromated copper arsenate (CCA) contains hexavalent chromium [Cr(VI)] and the conversion of Cr(VI) to trivalent chromium [Cr(III)] drives fixation of the treatment chemicals to the wood fibers. Since the toxicity of Cr depends on its valence state, an assessment of the Cr species occurring in CCA-treated wood, as well as leachates and ashes from CCA-treated wood, is helpful when assessing implications for disposal. In this study, both new and weathered wood samples of CCA-treated wood and their ashes were evaluated for total Cr and Cr(VI) within the solid matrices and within leachates. Results show that for both new and weathered CCA-treated wood, Cr(VI) occurred in the range of 0.7-4% of the total Cr. Greater Cr leaching occurred at the pH extremes, with Cr(VI) only measured under alkaline pH values (pH > 9.0). Total chromium concentrations from synthetic precipitation leaching procedure (SPLP) leachates from CCA-treated wood were consistently less than 3mg/L with Cr(VI) below detection limits. The results suggest that leaching of Cr(VI) from discarded CCA-treated wood should not be a concern in most landfill environments. One exception would be disposal in landfills with alkaline leachate; Cr(VI) was observed to leach from CCA-treated wood in the presence of alkaline leachate from crushed concrete. When CCA-treated wood is combusted, chromium becomes concentrated in the ash. Cr(VI) in ash from the combustion of CCA-treated wood was found between 4 and 7% of the total chromium. In ash from the combustion of wood recovered from construction and demolition (C&D) debris (which contained some CCA-treated wood), Cr(VI) accounted for as much as 43% of the total Cr. Nearly, all of the Cr in SPLP leachates produced from the ash was in the Cr(VI) form. The degree of Cr(VI) leaching from the ash was highly dependent upon the alkalinity of the ash, with higher ash leachate pH resulting in greater concentrations of Cr(VI).

Arsenates↗
PubMed2006

Metal concentrations of simulated aerobic and anaerobic pilot scale landfill reactors.

Leachate and solid waste samples from aerobic and anaerobic simulated landfill reactors operated with and without leachate recirculation were characterized in terms of metals such as Fe, Ca, K, Na, Cd, Cr, Cu, Pb, Ni, and Zn. Metal concentrations of aerobic landfill reactor leachate samples are always below the regulation limits. The higher concentrations in anaerobic landfill leachate samples decreased to regulation limits after the landfill becomes methanogenic. The effect of leachate recirculation is determined in anaerobic landfills more clearly than aerobic landfills. Metal precipitation resulted in a decrease in leachate metal content and an increase in solid waste metal content as expected. Result of the study show that the metal content of landfill leachate samples is not a major concern for both aerobic and anaerobic landfills.

Aerobiosis↗
PubMed2006

Leaching potential of heavy metals (Cd, Ni, Pb, Cu and Zn) from acidic sandy soil amended with dolomite phosphate rock (DPR) fertilizers.

There is an increasing concern on heavy metal leaching from the soils amended with sewage sludge. A column study was conducted to examine the extent of leaching of five important heavy metals (Cd, Ni, Pb, Cu and Zn) from an acidic sandy soil amended with different dolomite phosphate rock (DPR) fertilizers (an application rate of 1% fertilizers) developed from DPR and N-Viro (consisting of biosolids and fly ash) at 0%, 10%, 20%, 30%, 40%, 50% and 100% DPR. Ten leaching events were carried out with each event done at an interval of 7 days and with total leaching volume of 1183mm, which is equivalent to the mean annual rainfall of this region during the period of 2001-2003. Leachate was collected after each leaching event and analyzed for heavy metals. The maximum leachate concentrations of Cd, Ni, Pb, Cu and Zn were all below drinking water quality guidance limits set by Florida Department of Environmental Protection and World Health Organization, suggesting that the application of DPR fertilizers may not pose a threat to water quality by leaching. Most of leachate concentrations of Cd, Ni and Pb were below their detection limits and there were no significant differences between the control and the treatments with different DPR fertilizers. By contrast, there were higher leachate concentrations of Cu and Zn (ranging from 0.7 to 37.1mug Cu/l and 5.1 to 205.6mug Zn/l for all treatments) due to their higher contents in both the soil and different DPR fertilizers compared with Cd, Ni and Pb. The leachate concentrations of Cu and Zn for each treatment decreased with increasing leaching events. The differences in leachate concentrations of Cu and Zn between the control and the treatments with different DPR fertilizers containing N-Viro were significant, especially in the first several leaching events and, moreover, they increased with increasing proportion of N-Viro in the DPR fertilizers. There were similar trends in total losses of Cu and Zn after ten leaching events. Greater differences in both leachate concentrations and total losses of Zn between the control and the treatments containing N-Viro were noted. Total losses of Zn for the treatments containing N-Viro were 3.0-5.1 times higher than those for the control compared with 1.4-2.2 times higher for total losses of Cu, suggesting that greater proportions of Zn losses came from the DPR fertilizers due to the greater mobility of Zn in the DPR fertilizers compared with Cu.

Fertilizers↗
PubMed2006

Evaluation and prediction of emissions from a road built with bottom ash from municipal solid waste incineration (MSWI).

In autumn 2001, a full-scale test road was built with municipal solid waste incineration (MSWI) bottom ash at the Dåvamyran landfill, Umeå, Northern Sweden. Leachates were collected from asphalted sections with either bottom ash or gravel as filling material. In this research, 12 months of ash leachate sampling were evaluated with respect to emissions of contaminants such as trace metals and chlorides (Cl). The usefulness of regression models describing trace metal mobility from bottom ash was also tested as predictive tools for reusability applications of MSWI bottom ash. Cl, Cu, and Cr had the highest mobility (considering leachate concentrations) in the ash leachate, though concentrations of Cl and Cu decreased during the sampling period (Cl from 10,000 to 600 mg l(-1); Cu from 1600 to 500 microg l(-1)). An increased mobility of Cr during the autumns (about 3-4 times higher compared to the summer) was noted with a maximum value of nearly 70 microg l(-1) during autumn 2001. Pb showed a very low mobility over the entire year with leachate concentrations of around 3-4 microg l(-1). Chemical equilibrium calculations using Minteq indicated that several Cu minerals were oversaturated in the leachate, thus mineral precipitation could be responsible for declining amounts of Cu in the leachate. Adsorption to iron oxides was found to be a probable explanation for the low mobility of Pb. A reasonably good agreement between regression models and field values were achieved for Ni, Pb, Zn, and Cu, while the models for Cd and Cr were less promising. Even though a large part of the variation (R2=61-97%) in the leaching experiment could be explained by only pH and L/S, field data were much more scattered than expected from field pH.

Chlorides↗
PubMed2000

Field studies of the leachability of aged brown coal ash.

The environmental management of ash produced from the brown coal power stations of the Latrobe Valley region of Australia has been studied. Current practice consists of slurrying fly and bottom ash, a short distance to an ash disposal pond. However, storage facilities are approaching capacity and alternative ash management strategies are required in the near future. Initially, the ash produced within the power stations is known to possess a large soluble mass, which can leach rapidly to generate a saline leachate with minor trace metal content. After slurrying and deposition within the ash pond, it has been demonstrated that the soluble mass is significantly lower and the ash can be considered as aged or "leached" ash - a more benign waste that meets the criteria for fill material. In order to assess the long-term behaviour of the leached ash and its suitability for co-disposal in engineered sites within overburden dumps, two field cells were constructed and monitored over a period of 1 year. Each cell was 5 x 5 m in area, 3-m deep and HDPE lined with a coarse drainage layer and leachate collection pipe. The first cell only collected natural rainfall and was known as the Dry Cell. The second cell had an external tank of 5000 l installed (200-mm rainfall equivalent) and water was spray-irrigated regularly to simulate higher rainfall and accelerate the leaching process. The cumulative inflow and outflow for each cell has been calculated using a linear relationship and the leachate quality was monitored over time. The results demonstrate that the ash behaves as an unsaturated porous material, with the effect of evaporation through the profile being dominant and controlling the production of leachate. The leachate quality was initially moderately saline in both cells, with the concentration dropping by nearly 95% in the Wet Cell by the end of the field study. The leachate chemistry has been analysed using the PHREEQC geochemical model. The log activity plots of various species suggest the mineralogical controls on these species in leachate. The full results from this study are presented.

Australia↗
PubMed2001

A simple model for the distribution and fate of organic chemicals in a landfill: MOCLA.

A simple mathematical model (MOCLA: Model for Organic Chemicals in Landfills) is presented, describing the distribution of organic chemicals between leachate, gas and solid waste. The model also predicts the fate of the chemicals in terms of emissions with leachate and landfill gas and in terms of degradation and transformation in the landfill. Local equilibrium is assumed for the distribution of the chemicals in the landfill as expressed by Henry's Law for the leachate-gas interface, and by the linear partition coefficient based on the waste solid organic carbon content for the waste-leachate interface. Degradation of the chemicals is expressed as a first order reaction. Annual specific leachate and gas generation data in combination with data on landfill area and volume allow for prediction of main emission routes. Model simulations involving two landfill scenarios for a number of chemicals with different physico-chemical characteristics indicate that volatilisation is a likely route for some chemicals (e.g. vinyl chloride, and some of the freons), while other chemicals (e.g. phenol, lower chlorinated aliphatic compounds) more likely will appear as dissolved in the leachate. However, many chemicals will be strongly associated with the solid waste (e.g. dichlorobenzene, naphthalene, and higher Polycyclic Aromatic Hydrocarbons (PAHs), and the pool available will be able to supply the landfill gas and leachate with organic trace components for decades unless these are degraded in the landfill. The model suggests that, in addition to the physico-chemical characteristics of the organic chemical, the presence of free phases of organic chemicals and the degradability of the chemicals are the main factors controlling the fate and emissions of organic chemicals in the landfill environment.

Forecasting↗
PubMed2005

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.

Biological Availability↗
PubMed2001

Nitrogen and sulfate attenuation in simulated landfill bioreactors.

The characteristics of leachate from landfills vary according to site-specific conditions. Leachates from old landfills are often rich in ammonia nitrogen, posing potential adverse environmental impacts in the case of uncontrolled discharge. At landfills where leachate recirculation is practiced, leachate ammonia concentrations may accumulate to higher levels than during the single pass leaching. Using leachate recirculation with system modifications, separate aerobic and anoxic zones for nitrification and both autotrophic and heterotrophic denitrification can be provided. Results from simulated landfill bioreactors indicated that both nitrogenous and sulfur compounds can be attenuated through autotrophic denitrification, and leachate nitrate concentrations of 750 mg/L reduced to less than 1 mg/L by denitrification to nitrogen gas promoting this very common process in a landfill environment results in the reduction of both leachate ammonia and sulfate concentrations.

Ammonia↗
PubMed2005

Methanogenesis acceleration of fresh landfilled waste by micro-aeration.

When municipal solid waste (MSW) with high content of food waste is landfilled, the rapid hydrolysis of food waste results in the imbalance of anaerobic metabolism in the landfill layer, indicated by accumulation of volatile fatty acids (VFA) and decrease of pH value. This occurrence could lead to long lag time before the initiation of methanogenesis and to the production of strong leachate. Simulated landfill columns with forced aeration, with natural ventilation, and with no aeration, were monitored regarding their organics degradation rate with leachate recirculation. Hydrolysis reactions produced strong leachate in the column with no aeration. With forced aeration, the produced VFA could be effectively degraded, leading to the reduction in COD of the leachate effluent since the week 3. The CH4 in the landfill gas from the column with aeration rate of 0.39 m3/(m3 x d) and frequency of twice/d, leachate recirculation rate of 12.2 mm/d and frequency of twice/d, could amount to 40% (v/v) after only 20 weeks. This amount had increased up to 50% afterward even with no aeration. Most of COD in the recirculated leachate was removed. Using natural ventilation, CH4 could also be produced and the COD of the leachate effluent be reduced after 10 weeks of operation. However, the persistent existence of oxygen in the landfill layer yielded instability in methanogenesis process.

Biodegradation, Environmental↗
PubMed2005

Leachability of protein and metals incorporated into aquatic invertebrates: are species and metals-exposure history important?

To partially simulate conditions in fish intestinal tracts, we leached six groups of metals-contaminated invertebrates at pH 2 and pH 7, and analyzed the concentrations of four metals (Cd, Cu, Pb, and Zn) and total protein in the leachates. Four of the groups of invertebrates were benthic macroinvertebrates collected from metals-contaminated rivers (the Clark Fork River in Montana and the Coeur d'Alene River in Idaho, USA); the other two groups of invertebrates (one of which was exposed to metals in the laboratory) were laboratory-reared brine shrimp (Artemia sp.). Additionally, we fractionated the pH 2 leachates using size-exclusion chromatography (SEC). Protein content was 1.3 to 1.4x higher in Artemia than in the benthic macroinvertebrates, and leachability of metals and protein differed considerably among several of the groups of invertebrates. In SEC fractions of the pH 2 leachates from both groups of Artemia, Cu and protein co-eluted; however, Cu and protein did not co-elute in SEC fractions of the leachates from any of the benthic macroinvertebrate groups. Although none of the other three metals co-eluted with protein in any of the pH 2 leachates, one or more of the metals co-eluted with lower-molecular-weight molecules in the leachates from all of the groups of invertebrates. These results suggest fundamental differences in metal-binding properties and protein leachability among some invertebrates. Thus, different invertebrates and different histories of metals exposure might lead to different availability of metals and protein to predators.

Animals↗
PubMed2004

Effect of alkalinity on the performance of a simulated landfill bioreactor digesting organic solid wastes.

This study investigated the effects of alkalinity on the anaerobic treatment of the organic solid wastes collected from the kitchen of Engineering Faculty in Dokuz Eylul University, Izmir, Turkey and the leachate characteristics treated in three simulated landfill anaerobic bioreactors. All of the reactors were operated with leachate recirculation. One reactor was operated without alkalinity addition. The second reactor was operated by the addition of 3 g l-1 d-1 of NaHCO3 alkalinity to the leachate and the third reactor was operated by the addition of 6 g l-1 d-1 NaHCO3 alkalinity to the leachate. After 65 d of anaerobic incubation, it was observed that the chemical oxygen demand (COD), volatile fatty acids (VFA) concentrations, and biochemical oxygen demand to chemical oxygen demand (BOD5/COD) ratios in the leachate samples produced from the alkalinity added reactors were lower than the control reactor while the pH values were higher than the control reactor. The COD values were measured as 18900, 3800 and 2900 mg l-1 while the VFA concentrations were 6900, 1400 and 1290 mg l-1, respectively, in the leachate samples of the control, and reactors containing 3 g l-1 NaHCO3 and 6 g l-1 NaHCO3 after 65 d of anaerobic incubation. The total nitrogen (TN), total phosphorus (TP) and ammonium nitrogen (NH4-N) concentrations in organic solid waste (OSW) significantly reduced in the reactor containing 6 g l-1 NaHCO3 by d 65. The values of pH were 6.54, 7.19 and 7.31, after 65 d of anaerobic incubation, respectively, in the aforementioned reactors results in neutral environmental conditions in alkalinity added reactors. Methane percentage of the control, reactors containing 3 g l-1 NaHCO3 and 6 g l-1 NaHCO3 were 37%, 64% and 65%, respectively, after 65 d of incubation. BOD5/COD ratios of 0.27 and 0.25 were achieved in the 3 and 6 g l-1 NaHCO3 containing reactors, indicating a better OSW stabilization. Alkalinity addition reduced the waste quantity, the organic content of the solid waste and the biodegradation time.

Bacteria, Anaerobic↗
PubMed2004

Leaching of CCA-treated wood: implications for waste disposal.

Leaching of arsenic, chromium, and copper from chromated copper arsenate (CCA)-treated wood poses possible environmental risk when disposed. Samples of un-weathered CCA-treated wood were tested using a variety of the US regulatory leaching procedures, including the toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP), extraction procedure toxicity method (EPTOX), waste extraction test (WET), multiple extraction procedure (MEP), and modifications of these procedures which utilized actual MSW landfill leachates, a construction and demolition (C and D) debris leachate, and a concrete enhanced leachate. Additional experiments were conducted to assess factors affecting leaching, such as particle size, pH, and leaching contact time. Results from the regulatory leaching tests provided similar results with the exception of the WET, which extracted greater quantities of metals. Experiments conducted using actual MSW leachate, C and D debris leachate, and concrete enhanced leachate provided results that were within the same order of magnitude as results obtained from TCLP, SPLP, and EPTOX. Eleven of 13 samples of CCA-treated dimensional lumber exceeded the US EPA's toxicity characteristic (TC) threshold for arsenic (5 mg/L). If un-weathered arsenic-treated wood were not otherwise excluded from the definition of hazardous waste, it frequently would require management as such. When extracted with simulated rainwater (SPLP), 9 of the 13 samples leached arsenic at concentrations above 5 mg/L. Metal leachability tended to increase with decreasing particle size and at pH extremes. All three metals leached above the drinking water standards thus possibly posing a potential risk to groundwater. Arsenic is a major concern from a disposal point of view with respect to ground water quality.

Arsenates↗
PubMed2005

Modelling the leaching of Pb, Cd, As, and Cr from cementitious waste using PHREEQC.

A leaching model was developed using the United States Geological Survey public domain PHREEQC geochemical package to simulate the leaching of Pb, Cd, As, and Cr from cementitious wastes. The model utilises both kinetic terms and equilibrium thermodynamics of key compounds and provides information on leachate and precipitate speciation. The model was able to predict the leaching of Pb, Cd, As, and Cr from cement in the presence of both simple (0.1 and 0.6M acetic acid) and complex municipal landfill leachates. Heavy metal complexation by the municipal landfill leachate was accounted for by the introduction of a monoprotic organic species into the model. The model indicated Pb and As were predominantly incorporated within the calcium silicate hydrate matrix while a greater portion of Cd was seen to exist as discrete particles in the cement pores and Cr (VI) existed mostly as free CrO4(2-) ions. Precipitation was found to be the dominant mechanism controlling heavy metal solubility with carbonate and silicate species governing the solubility of Pb and carbonate, silicate and hydroxide species governing the solubility of Cd. In the presence of acetic acid, at low pH values Pb and Cd acetate complexes were predominant whereas, at high pH values, hydroxide species dominated. At high pH values, the concentration of As in the leachate was governed by the solubility of Ca3(AsO4)2 with the presence of carbonate alkalinity competing with arsenate for Ca ions. In the presence of municipal landfill leachate, Pb and Cd organic complexes dominated the heavy metal species in solution. The reduction of As and Cr in municipal landfill leachate was crucial for determining aqueous speciation, with typical municipal landfill conditions providing the reduced forms of As and Cr.

Adsorption↗