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PubMed2003

A study of the leachate toxicity of metal-containing solid wastes using Daphnia magna.

This paper examines the ecotoxicity of different actual inorganic wastes containing some potentially toxic metals commonly found in many industrial residues and the reduction in ecotoxicity obtained when the wastes are submitted to a solidification/stabilization process. The ecotoxicity was assessed as defined in the Spanish regulations on hazardous wastes, by means of the Daphnia magna Straus acute toxicity test applied to the toxicity characteristic leaching procedure (TCLP) waste leachate. On the basis of the EC50 values of the individual metals and the effect of the pH of the aqueous medium on D. magna, we have explored a method for estimating the toxicity of the TCLP waste leachate by calculating its EC50 value in the D. magna test. Although the method is only valid in cases in which a clear cause for the toxicity exists, the procedure described allows us to more completely explain the observed effects on the daphnids. The ecotoxicity of the residues after stabilization is less than that of the untreated waste, generally as a consequence of the reduction in metal leachability achieved by the immobilization treatment. The stabilization process was analyzed in terms of both the chemical and the ecotoxicological parameters, and the influence of leachate pH on the objectives of waste treatment is discussed.

Animals↗
PubMed2003

A holistic approach to Concentration Assessment of hazards in the risk assessment of landfill leachate.

Risk assessment is a new research area. The risk assessment research area deals with a wide range of issues other than landfills. Examples of these issues are Radiation, Food Industry, Ecology, Epidemiology, etc. The authors have found that there are generic elements in risk assessment and these elements are independent of the subject areas mentioned above. An important example of these generic elements is the Concentration Assessment of hazards and is equally important from the perspective of landfill risk assessment. Furthermore, in the literature review of landfill risk assessment approaches, no evidence has been discovered of a holistic risk assessment methodology for landfill gas, leachate, or degraded landfill waste. A range of knowledge deficiencies has been found in the literature reviewed to date. One of these deficiencies in knowledge is the lack of a holistic procedure for carrying out Concentration Assessment. From the perspective of landfill leachate, this paper discusses the extent to which the Concentration Assessment of hazards is absent in landfill risk assessment approaches described in the literature reviewed to date, and the elements that should be added to the procedure of the Concentration Assessment in order to enhance the process of risk assessment. The paper also briefly outlines a holistic procedure for the Concentration Assessment and a corresponding computer model for the risk assessment of landfill leachate.

Animals↗
PubMed2003

Biogeochemistry and isotope geochemistry of a landfill leachate plume.

The biogeochemical processes were identified which improved the leachate composition in the flow direction of a landfill leachate plume (Banisveld, The Netherlands). Groundwater observation wells were placed at specific locations after delineating the leachate plume using geophysical tests to map subsurface conductivity. Redox processes were determined using the distribution of solid and soluble redox species, hydrogen concentrations, concentration of dissolved gases (N(2), Ar, and CH(4)), and stable isotopes (delta15N-NO(3), delta34S-SO(4), delta13C-CH(4), delta2H-CH(4), and delta13C of dissolved organic and inorganic carbon (DOC and DIC, respectively)). The combined application of these techniques improved the redox interpretation considerably. Dissolved organic carbon (DOC) decreased downstream in association with increasing delta13C-DOC values confirming the occurrence of degradation. Degradation of DOC was coupled to iron reduction inside the plume, while denitrification could be an important redox process at the top fringe of the plume. Stable carbon and hydrogen isotope signatures of methane indicated that methane was formed inside the landfill and not in the plume. Total gas pressure exceeded hydrostatic pressure in the plume, and methane seems subject to degassing. Quantitative proof for DOC degradation under iron-reducing conditions could only be obtained if the geochemical processes cation exchange and precipitation of carbonate minerals (siderite and calcite) were considered and incorporated in an inverse geochemical model of the plume. Simulation of delta13C-DIC confirmed that precipitation of carbonate minerals happened.

Environmental Monitoring↗
PubMed2002

Prediction of leachate pH for cement paste containing pure metal compounds.

Neural network models, to predict the leachate pH for single batch extraction leaching tests conducted on Portland cement pastes containing pure compounds, were constructed using existing data from the literature. The models were able to represent the known non-linear dependency of pH on acid addition, and were used to show that Cu increases, and Zn and NO3- decrease, the leachate pH for addition of 8 meq acid/g dry cement (to achieve a mid-alkaline pH). Ba, Cd, Cr(III), Ni, Pb, Cl- and OH- had no detectable effect on the acid neutralisation capacity (ANC) of the cement pastes in the concentration ranges investigated. The laboratory where testing was conducted was found to be an important predictive variable, which acted as a surrogate variable for laboratory specific variables that were not adequately reported in the literature, such as cement characteristics, sample preparation details, and leaching test and pH measurement details. This work has shown that development of good empirical predictive models for solidified product leachate pH is feasible, and is limited only by the availability of data.

Environmental Pollution↗
PubMed2002

Treatment of industrial landfill leachate by means of evaporation and reverse osmosis.

In this paper a process for the treatment of landfill leachate involving evaporation and reverse osmosis was proposed. Experimental tests were performed on an industrial landfill leachate. The leachate was subjected to evaporation so as to obtain a distillate containing a small amount of organic material and a substantial amount of inorganic substances (consisting primarily of metals and ammonium salts). The distillate of the evaporation treatment was then subjected to reverse osmosis. The reverie osmosis tests were performed using two different membranes: the AD membrane (thin two-ply film of polyamide) and the SC membrane (thin three-ply film of polyamide). Tests carried out at different values of pH showed a reduction of organic content of about 88% when AD membranes were used and about 80% with SC membranes independently of pH. As regards ammonium, comparable reductions of over 97% were registered for both types of membrane in the optimal conditions of pH = 6.4 (97.1% for AD membranes and 97.7% for SC).

Hydrogen-Ion Concentration↗
PubMed2002

Advanced mercury removal from gold leachate solutions prior to gold and silver extraction: a field study from an active gold mine in Peru.

Mercury contamination in the Gold-Cyanide Process (GCP) is a serious health and environmental problem. Following the heap leaching of gold and silver ores with NaCN solutions, portions of the mercury-cyano complexes often adhere to the activated carbon (AC) used to extract the gold. During the electrowinning and retorting steps, mercury can be (and often is) emitted to the air as a vapor. This poses a severe health hazard to plant workers and the local environment. Additional concerns relate to the safety of workers when handling the mercury-laden AC. Currently, mercury treatment from the heap leach solution is nonexistent. This is due to the fact that chelating ligands which can effectively work under the adverse pH conditions (as present in the heap leachate solutions) do not exist. In an effort to economically and effectively treat the leachate solution prior to passing over the AC, a dipotassium salt of 1,3-benzenediamidoethanethiol (BDET2-) has been developed to irreversibly bind and precipitate the mercury. The ligand has proven to be highly effective by selectively reducing mercury levels from average initial concentrations of 34.5 ppm (parts per million) to 0.014 ppm within 10 min and to 0.008 ppm within 15 min. X-ray powder diffraction (XRD), proton nuclear magnetic resonance (1H NMR), Raman, and infrared (IR) spectroscopy demonstrate the formation of a mercury-ligand compound, which remains insoluble over pH ranges of 0.0-14.0. Leachate samples from an active gold mine in Peru have been analyzed using cold vapor atomic fluorescence (CVAF) and inductively coupled plasma optical emission spectroscopy (ICP-OES) for metal concentrations before and after treatment with the BDET2- ligand.

Carbon↗
PubMed2003

Powdered activated carbon added biological treatment of pre-treated landfill leachate in a fed-batch reactor.

Biological treatment of landfill leachate usually results in low treatment efficiencies because of high chemical oxygen demand (COD), high ammonium-N content and also presence of toxic compounds such as heavy metals. A landfill leachate with high COD content was pre-treated by coagulation-flocculation followed by air stripping of ammonia at pH = 12. Pre-treated leachate was biologically treated in an aeration tank operated in fed-batch mode with and without addition of powdered activated carbon (PAC). PAC at 2 g l-1 improved COD and ammonium-N removals resulting in nearly 86% COD and 26% NH4-N removal.

Bacteria, Aerobic↗
PubMed2002

Allelochemical stress produced by the aqueous leachate of Callicarpa acuminata: effects on roots of bean, maize, and tomato.

The in vitro effects of an aqueous leachate (1%) of Callicarpa acuminata Kunth. (Verbenaceae) on radicle growth, protein expression, catalase activity, free radical production and membrane lipid peroxidation in roots of bean, maize, and tomato were examined. Aqueous extract of C. acuminata inhibited the radicle growth of tomato by 47%, but had no effect on root growth of maize and beans. 2D-PAGE and densitometry analysis showed that C. acuminata aqueous leachate modified the expression of various proteins in the roots of all treated plants. In treated bean roots, microsequencing analysis of an 11.3-kDa protein, whose expression was enhanced by leachate treatment, revealed a 99% similarity with subunits of alpha-amylase inhibitor of other beans. A 27.5-kDa protein induced in treated tomato showed 69-95% similarity to glutathione-S-transferases (GST) of other Solanaceae. Spectrophotometric analysis and native gels revealed that catalase activity was increased by 2.2-fold in tomato roots and 1.4-fold in bean roots. No significant changes were observed in treated maize roots. Luminol chemiluminescence levels, a measure of free radicals, increased 3.8-fold in treated tomato roots and 2.1-fold in treated bean roots. Oxidative membrane damage in treated roots was measured by lipid peroxidation rates. In tomato we observed a 2.4-fold increase in peroxidation, however, no effect was observed in maize or beans.

Journal Article↗
PubMed1999

Carbonate induced dissolution of uranium containing precipitates under cement leachate conditions.

The effects of carbonate on uranium (VI) solubility under aerobic and cementitious conditions have been investigated. The information is of relevance to low level nuclear waste disposal. Aqueous NaOH, KOH, Ca(OH)2 and a cement leachate solution were added to uranyl nitrate solution. Afterwards, increasing amounts of ammonium carbonate were added to re-dissolve the precipitates. The precipitates were characterised by means of X-ray powder diffraction (XRPD) measurements and modelling studies. The model calculations were performed using the MINTEQA2 speciation code, with an expanded database incorporating uranium stability constants taken from the HATCHES database. The measured and predicted amounts of CO3(2-) needed to dissolve the precipitates were compared. The knowledge gained from the 'pure' systems was used to rationalise the precipitation and re-dissolution behaviour observed in the leachate system. The lack of uranium solubility at low carbonate levels brought into question literature formation constants for UO2(OH)3- and UO2(OH)4(2-). An approximate log K value of 26.8 for K2U2O7 formation was estimated from the KOH results at pH 12. Generally, uranium solubilities are expected to be insignificant at low level nuclear waste sites because anaerobic conditions should persist. However, this study has demonstrated that solubility in leachate could rise at high pH and high carbonate levels, if aerobic conditions were to develop. Soluble U(VI) species would be formed. The novel part of the study has been to reproduce the effects and to correlate enhanced solubilities with model predictions. Consequently, the study has re-emphasised the need for appropriate environmental monitoring of such sites.

Carbonates↗
PubMed2004

Growth of water hyacinth in municipal landfill leachate with different pH.

Batch experiments were conducted to investigate the effect of municipal landfill leachate pH on the growth of water hyacinth (Eichhornia crassipes). These experiments were carried out in a green house environment on leachate samples collected from Essex-Windsor Regional Landfill, Windsor, Ontario, Canada. It was found that water hyacinth plants survived in a pH range of 4.0 to 8.0. Both alkaline pH (above 8.0) and highly acidic pH (below 4.0) had inhibitory effect on the growth of plants. The pH range, for optimum growth of the water hyacinth plants was found to be 5.8 to 6.0. At optimum growth, water hyacinth had an average mean relative growth rate of 0.043 d-1. It was found that nitrogen compounds underwent different transformations depending on the pH of leachate. Plant uptake, nitrification and volatilization were among these transformations.

Eichhornia↗
PubMed2004

Removal of metals in leachate from sewage sludge using electrochemical technology.

Heavy metals in acidic leachates from sewage sludge are usually removed by chemical precipitation, which often requires high concentration of chemicals and induces high metallic sludge production. Electrochemical technique has been explored as an alternative method in a laboratory pilot scale reactor for heavy metals (Cu and Zn) removal from sludge leachate. Three electrolytic cell arrangements using different electrodes materials were tested: mild steel or aluminium bipolar electrode (EC cell), Graphite/stainless steel monopolar electrodes (ER cell) and iron-monopolar electrodes (EC-ER cell). Results showed that the best performances of metal removal were obtained with EC and EC-ER cells using mild steel electrodes operated respectively at current intensities of 0.8 and 2.0 A through 30 and 60 min of treatment. The yields of Cu and Zn removal from leachate varied respectively from 92.4 to 98.9% and from 69.8 to 76.6%. The amounts of 55 and 44 kg tds(-1) of metallic sludge were respectively produced using EC and EC-ER cells. EC and EC-ER systems involved respectively a total cost of 21.2 and 13.1 CAN dollars per ton of dry sludge treated including only energy consumption and metallic sludge disposal. The treatment using EC-ER system was found to be effective and more economical than the traditional metal precipitation using either Ca(OH)2 and/or NaOH.

Conservation of Energy Resources↗
PubMed2001

Treatment of leachate from a domestic solid waste sanitary landfill by an electrolysis system.

This study deals with the characteristisation and the treatability of leachates from the new municipal domestic waste (DW) landfill site in Athens, Greece, using an electrolysis system. This site has been in operation since July 1998. The leachate from this site has mean COD and BOD5 values of 53300 and 30300 mg l(-1), respectively, and constitutes a major environmental problem that must be taken into serious consideration. An electrolysis system, using Ti/Pt electrode in alkaline conditions was used to treat the leachate. The study showed, that the COD was reduced by 84%, and that VSS, N-NH4 and Total Phosphorus were reduced by 100% within one hour of electolysis and at pH 9. The efficiency of electrolysis went up to 32 g COD removed (CODr)/h-A-m2 and the energy consumption was 12.6 kWh kg(-1)CODr.

Chloramines↗
PubMed2001

Variations of landfill leachate's properties in conjunction with the treatment process.

A study was done on the variations of water quality parameters, in conjunction with the processing steps, installed for the treatment of leachate from a sanitary landfill. The leachate was primarily subjected to biological treatment, composed of anaerobic digestion, aerobic treatment, and rotating biological contact in series. The effluent from the rotating biological contact process was further treated by combination of flocculation-sedimentation and adsorption processes. Finally, it was polished by the reverse osmosis process before discharge. The quality of raw leachate, of influents to and of effluents from the reverse osmosis process was assessed and compared. To determine size--dependent behavior of organic materials, analyses were also made for the fractionated samples through ultrafiltration. The overall treatment efficiency was about 98% for removal of organic materials. Most of the organic materials were in the low molecular weight range. In particular, about 95% of the biological oxygen demand was found to be exerted by the fraction of organic material of which cut -off molecular weight was less than 500. The analysis of molecular weight distribution confirmed that the organic materials resistant to the removal by the treatment process were humic substances, of which cut off molecular weight was greater than 500. The reverse osmosis process showed a high efficiency for removal of high molecular weight constituents. However, the final effluent showed an unexpectedly high oxygen demand.

Adsorption↗
PubMed2005

[Study of the metal precipitation from decontamination leachates of municipal wastes fly ash incinerators].

This research work focuses on the development of a new process for the decontamination of municipal wastes incinerators fly ashes. The objective of this study was to evaluate different total and selective precipitation methods for metals removal from ash decontamination leachates. The tested options include 1) use of hydrated lime and caustic soda for selective (pH 5.0) and total (pH 8.5) metal precipitation; 2) addition of different chemicals (H3PO4, Na2S and FeCl3) in a pH range from 6.0 to 9.0. Fly ash decontamination assays using alkaline and acid washing steps were initially performed using optimal conditions previously established. Treated fly ashes respected the standards based on the TCLP leaching test for all studied metals and SPLP. Total metal precipitation tests carried out at pH 8.5 achieve removal yields for all metals > or = 90% using hydrated lime and > or = 83% using caustic soda. Selective precipitation tests alone at pH 5.0 show removal yields > or = 97% for Cr and between 75 and 87% for Al and Pb. Moreover, assays carried out using a stoechiometric addition of Na2S have allowed the separation of Cd (> or = 99%) and Zn (> or = 71%) as metal sulphides (CdS and ZnS). From an economical point of view, the most interesting option seems to be the leachates neutralization at pH 7.0 using Ca(OH)2 combined with the reuse of the treated leachates in the fly ash leaching steps. Metal precipitation cost at pH 7.0 has been estimated to be 22.7 CAN dollars tct-1 using Ca(OH)2, and 26.7 CAN dollars tct-1 using NaOH.

Carbon↗
PubMed2006

Characteristics of blast furnace slag leachate produced under reduced and oxidized conditions.

A laboratory study was conducted to determine the environmental conditions necessary to reproduce leachates observed emerging from blast furnace slag acting as the foundation of highways in northwest Indiana. The leachates in the field are often highly alkaline with a pungent sulfur odor, a distinct green or milky-white in color, and sulfate concentrations exceeding 2,000 mg/L. Slag was equilibrated in the laboratory under both oxidized and anoxic environments and at various slag:water ratios. Constant anoxic conditions were required to produce to green colors in the slag, but high sulfate concentrations were observed only when the suspensions were fully oxidized. Leachate from the study site appears to form as a result of a series of complex chemical reactions including fluctuating oxidized and reduced conditions.

Adsorption↗
PubMed2006

Sustainable approach for leachate treatment: electricity generation in microbial fuel cell.

Electricity generation from landfill leachate was examined by using both a dual-chamber microbial fuel cell (MFC) and a single chamber MFC. Experimental results showed that the maximum power density of 2060.19 mW/m3 in the dual-chamber MFC and that of 6817.4 mW/m3 in the single chamber MFC were obtained. It was recognized that the difference in internal resistance for two MFC systems was the main reason for resulting in the difference of power generation. Power generation as function of chemical oxygen demand (COD) in single chamber MFC showed a Monod-type relationship with Pmax of 5920.96 mW/m3 and Ks of 251.39 mg/L at an external resistance of 500 Omega. Cyclic voltammetry showed that electrons were directly transferred onto the anode by bacteria in biofilms, rather than self-produced mediators of bacteria in the solutions. At low COD concentration, electricity generation was limited by the anode due to kinetic limitation; while at high COD concentration, the cathode was shown to have more significant effects on the electricity generation than the anode. COD in leachate could be removed when it increases, mainly because oxygen diffused from the cathode was substantially reduced by aerobic or anoxic bacteria in the anode chamber, leading to the substrate loss. Removal of ammonium-nitrogen was not observed in the single chamber MFC. This novel technology provides an economical route for electricity energy recovery in leachate treatment.

Bacteria↗
PubMed2001

Application of various bod test methods in landfill leachates.

This study examined the determination of BOD in landfill leachates by dilution (D-Method) and manometric methods (M-Method). The discrepancies between these methods were discussed and statistical tests were carried out. The effects of sample dilution and seeding on BOD results were examined. In comparison to the D-Method the M-Method was found to be more sensitive to increases in chloride and Total Kjeldahl Nitrogen (TKN) concentrations in leachate samples. However, in the M-Method the positive interference of nitrogenous BOD (NBOD) to carbonaceous BOD (CBOD) was more successfully prevented. The BOD rate constant k and the ultimate BOD (BODu) were estimated by non-linear regression. With the M-Method these parameters could be more reliably estimated than the D-Method. Based on these results, suggestions were made for BOD analyses in landfill leachates in future studies.

Environmental Monitoring↗
PubMed2002

Use of coagulant and zeolite to enhance the biological treatment efficiency of high ammonia leachate.

Most landfill leachates in Korea, herein defined as the contaminated liquid resulting from the percolation of water through a landfill, are high in ammonium nitrogen, which inhibits biological treatment processes and deteriorates rivers. A laboratory experiment investigated the effect of pre-removal of ammonium nitrogen using zeolite on the efficiency of organic treatment of the following activated-sludge process. Ferric chloride was initially used as a coagulant for solids removal. A clinoptilolite and mordenite rich rock from the Guryongpo area, the Yeongil Basalt, in Korea, reduced the ammonia nitrogen concentrations of leachate from 1300-1500 to 110-130 mg/l in a 24h batch operation. Three activated sludge reactors were operated to compare treatment efficiency under different influent conditions. In reactor 1, leachate having high concentration of chemical oxygen demands (COD) and suspended solids (SS) was directly fed to the reactor without pretreatment. The supernatant, after the coagulation process that remove some suspended solids and COD, was fed to reactor 2. As the use of coagulation process alone is not effective to remove ammonium nitrogen, supernatant treated by both coagulation focusing on the removal of COD and the zeolite concentrating on the removal of ammonium nitrogen was fed to reactor 3. As the result of experiment, greater efficiency in lowering the chemical oxygen demand (83%, influent COD; 1800-3000 mg/l, effluent COD; 300-500 mg/l) was achieved in reactor 3. Meanwhile, 63% (influent COD; 4000-5000 mg/l, effluent COD; 1470-1840 mg/l) and 66% (influent COD; 2400-3300 mg/l, effluent COD; 820-1100 mg/l) removal efficiency of COD were achieved in reactors 1 and 2, respectively. Thus, ammonia pre-removal by zeolite remarkably improved the lowering of chemical oxygen demand and the solids separation in the activated sludge process.

Ammonia↗