Synthetic Leachate Research Articles

Effects of Thickness on the Aging of HDPE Geomembranes

The results of an accelerated aging test program to evaluate the effect of thickness on the depletion of antioxidants from high-density polyethylene HDPE geomembranes and subsequent degradation of the physical properties are reported. Three commer- cially available HDPE geomembranes having nominal thicknesses of 1.5, 2.0, and 2.5 mm were examined. The geomembranes were immersed in a synthetic leachate at 85, 70, 55, and 22° C and tested for oxidative induction time, crystallinity, melt index MI, tensile properties, and stress-crack resistance. The antioxidant depletion rate for the 1.5 mm geomembrane was faster than for the 2.0 and 2.5 mm geomembranes. Antioxidant depletion time was predicted at representative landfill temperatures of 20- 60° C using Arrhenius modeling and was found to increase with geomembrane thickness for the three geomembranes examined. Based on the results of crystallinity, MI, and stress-crack resistance, the degradation of the geomembrane was slowest for the thickest geomembrane. These results suggest that a thicker geomembrane may have a longer service life other things being equal.

Impact of landfill liner time–temperature history on the service life of HDPE geomembranes

The observed temperatures in different landfills are used to establish a number of idealized time-temperature histories for geomembrane liners in municipal solid waste (MSW) landfills. These are then used for estimating the service life of different HDPE geomembranes. The predicted antioxidant depletion times (Stage I) are between 7 and 750 years with the large variation depending on the specific HDPE geomembrane product, exposure conditions, and most importantly, the magnitude and duration of the peak liner temperature. The higher end of the range corresponds to data from geomembranes aged in simulated landfill liner tests and a maximum liner temperature of 37 degrees C. The lower end of the range corresponds to a testing condition where geomembranes were immersed in a synthetic leachate and a maximum liner temperature of 60 degrees C. The total service life of the geomembranes was estimated to be between 20 and 3300 years depending on the time-temperature history examined. The range illustrates the important role that time-temperature history could play in terms of geomembrane service life. The need for long-term monitoring of landfill liner temperature and for geomembrane ageing studies that will provide improved data for assessing the likely long-term performance of geomembranes in MSW landfills are highlighted.

Permeation of BTEX through Unaged and Aged HDPE Geomembranes

The effects of aging of high-density polyethylene (HDPE) geomembranes on the diffusion and partitioning of a group of volatile organic compounds (VOCs) are examined. Two different 1.5 mm thick HDPE geomembranes were aged in the laboratory at 85°C by immersing in a synthetic leachate for up to 32 months. The results of partitioning and diffusion tests performed at room temperature on both unaged and aged geomembranes using a dilute aqueous solution containing four VOCs commonly found in landfill leachates [benzene, toluene, ethylbenzene, and xylenes (BTEX)] are reported. The diffusion and partitioning coefficients decreased with increased aging. The calculated permeation coefficients decreased by 36–62% after aging the geomembrane for about 10–32 months. This decrease in diffusion, partitioning, and permeation coefficients is related to the increase in geomembrane crystallinity during aging. A relationship between partitioning, diffusion, and permeation coefficients with the geomembrane crystallinity is established and could potentially be used to evaluate the migration of VOCs through HDPE geomembranes. Aging of HDPE geomembrane did not increase diffusive transport of organic contaminants.

Migration of Leachate from Uncollected Solid Waste Dumpsite

This paper examines the composition and concentration of leachates from a dumpsite in Nairobi University and the variation of the concentration of the constituents of the leachate with depth. Soil samples at varying depths below the dumpsite and solid waste samples at the dumpsite were subjected to synthetic leachate precipitation in the laboratory. The composition of the leachate was then measured. TDS, total hardness, conductivity, turbidity, COD and nitrates concentration were found to decrease with an increase in depth while alkalinity, chlorides, pH and DO were found to increase as depth increased. Keywords : Leachate, pollution, solid waste Journal of Civil Engineering Research and Practice Vol. 5 (1) 2008: pp. 79-90

Behavior of kaolinite and illite-based clays as landfill barriers

The technical requirements for the landfill of municipal wastes in the European Union (EU) are given in the Council Directive 1999/31/EC. A geological barrier of at least 1 m thickness with a hydraulic conductivity (HC) of 1 · 10 − 9 m/s is required. Where the geological barrier does not naturally meet the above conditions, a geological barrier of at least 0.5 m thick must be artificially established. We studied at controlled conditions, the ability of some clays (kaolinite or illite based) to act as landfill barriers. Several Spanish ceramic clays were compacted in columns (0.5 m length) and characterized for mineralogical, physical–chemical and heavy metal ions adsorption properties after 10 months leaching experiments. Zn, Cd, Pb and Cr salts were dosed in the synthetic leachates in order to test their in-depth retention. The specific surface area decreased in the material located near the clay–leachate interface region (< 6 cm) due to biofilm formation around clay particles, but bulk mineralogical properties were not affected. Although all the clays fulfilled the HC requirements, the diffusion of anions (chloride) reached more than 30 cm in kaolinite–illite or pure illite clays. The presence of significant traces of smectite (< 5%) was critical in anion transport retardation. Heavy metal ions were generally retained in the first 10 cm but in high surface-area illitic clays, the anions and heavy metal ions transport was stopped at < 6 cm. The clay mineralogy and the presence of carbonates and soluble salts greatly influenced the behavior of the barrier materials. Carbonate dissolution and precipitation affected < 6 cm depth. Divalent cations of carbonates selectively occupied the exchangeable positions and inhibited the retention of Na +, NH 4 + and K +, in the leachates. Sulphate was reduced at a depth of 20–30 cm. This biogeochemical process contributed to cadmium retention, presumably precipitated as sulphide.

Parameter estimation for modelling clogging of granular medium permeated with leachate

A numerical model called BioClog is used to backcalculate biological activity rate constants using measured values of water quality and clog chemical characteristics from well-controlled laboratory column experiments that contained a granular-sized material permeated with synthetic and real leachates. BioClog is a multispecies, reactive chemical transport model capable of predicting clogging of a porous media caused by the accumulation of biofilms, chemical precipitates, and entrained particles. Monod kinetic constants for acetate- and butyrate-degrading bacteria were obtained through inverse modelling of granular-sized material permeated with synthetic leachate. The model predicted the changes in concentrations of volatile fatty acids and dissolved calcium and it predicted the changes in clog composition from a juvenile clog containing biofilm to a mature clog containing biofilm with mineral matter. The kinetic constants were then applied to predict spatial and temporal water quality and clog composition for a granular-sized material permeated with real leachate. The kinetic constants deduced through inverse modelling of the synthetic leachate column experiments provided reasonable predictions of the behaviour of the columns permeated with real leachate.

Leachate chemical composition effects on OIT depletion in an HDPE geomembrane

Results of series of tests examining the effect of different chemical constituents found in municipal solid waste leachate on the degradation of a high-density polyethylene (HDPE) geomembrane are reported. Geomembrane samples were incubated in four synthetic leachates consisting of different combinations of volatile fatty acids, inorganic nutrients, trace metal solution, and surfactant at temperatures of 85°C, 70°C, 55°C, 40°C and 22°C. It is shown that the leachate should be replaced every two weeks to maximise the depletion of antioxidants from the geomembrane. Arrhenius modelling gave activation energies for antioxidant depletion of between 62.5 and 64.0 kJ/mol. The small difference in activation energies implies that the four leachates examined are similar in terms of antioxidant depletion rate. There was no evident effect of the difference in these leachates on crystallinity, MFI, or tensile properties during the testing period. However, the fastest antioxidant depletion was observed for the simplest leachate, comprising trace metals and surfactant in water. Results are also reported for a second series of tests involving 18 different immersion media with different concentrations of trace metals and surfactant. Based on an examination of solutions with pH between 4 and 10, it is found that antioxidant depletion is the fastest for relatively acidic or basic solutions and the slowest for neutral solutions. Antioxidant depletion is the most sensitive to the presence of surfactant. As the surfactant concentration increases to about 1 ml/l the majority of the effect is evident. There was no further increase in effect for any increase in concentration beyond 5 ml/l.

Aerobic Bio-oxidation with Ozonation for Recalcitrant Wastewater Treatment

AbstractThe aim of the present research was to find a combination of biological and chemical oxidation processes that improves the purification efficiency of recalcitrant wastewater treatment at reduced ozone consumption. The following wastewater treatment processes were experimentally studied: conventional aerobic biooxidation, post-ozonation of biologically treated wastewater, a combined process - aerobic bio-oxidation with ozonation in a re-circulation system - and aerobic bio-oxidation with direct introduction of ozone-containing water into a bioreactor. A synthetic landfill leachate corresponding in its composition to leachate of young landfills, thermo-mechanical pulping water, and phenolic effluent from the Estonian oil shale industry were used as wastewaters. It was established that compared with conventional aerobic bio-oxidation, the combined process enables an improvement in purification efficiency even at relatively low ozone doses (10 to 60 mgO

Removal of heavy metals from synthetic leachate using a biologically generated electric field

Removal of heavy metals from aqueous solutions was investigated in batch reactors using a biologically generated electric field. An electric field with a potential difference of 50 mV to 100 mV was generated using an anaerobic culture and an aerobic culture couple. The electric field was applied to a synthetic leachate solution made up using cadmium, zinc or nickel salts using titanium-coated mesh electrodes. After 72 hours of exposure, at 15 mm electrode spacing, less than 40% removal of cadmium and zinc was observed while nearly 80% nickel removal occurred. After 72 hours and at an electrode spacing of 25 mm, nearly 40% removal of cadmium occurred, 60% of zinc was removed, and 80% of nickel was removed from solution. After 72 hours and at 45 mm electrode spacing, nearly 70% of cadmium, 60% of zinc, and over 80% of nickel was removed. The tendency for zinc and cadmium to form more hydroxy complexes as compared to nickel may have contributed to these results. Cadmium and zinc removal were lower at an electrode spacing of 15 mm and 25 mm, compared to removal at an electrode spacing of 45 mm. Electrode spacing did not affect nickel removal.

Factors affecting measurement of hydraulic conductivity in low-strength cementitious materials

The hydraulic conductivity (water permeability) is one of the most significant transport properties of concrete and measuring it is a key step in predicting the performance of concrete as a barrier to the movement of fluids and ions. The transport properties are critical for the performance of the cover layer in protecting embedded reinforcement as waste containments barriers (which are considered in this paper) and other applications such as dams. The measurements are difficult to interpret due to experimental effects of sample size and changes of flow with time and the chemistry of the fluid used. The intrinsic permeability to water and synthetic leachate was determined and the relationship between the eluted volume passing and permeability was established for mortar mixtures having compressive strengths ranging from 5 to 20 MPa. Two mortar mixtures containing portland cement and one without portland cement and incorporating cement kiln dust, lagoon ash, and Ferrosilicate slag were tested. The effects of the sample size were also investigated. The results indicate a decrease in hydraulic conductivity for lower strength mixtures and a slight increase in permeability coefficient for the higher strength mixtures with increasing permeating volumes. Increasing the testing specimen size also slightly increased the coefficient of permeability in lower strength mixtures and decreased the coefficient in higher strength mixtures. The permeability coefficient did not change significantly with pore solution pressure.

Kinetic and Mass Balance Analysis of Constructed Wetlands Treating Landfill Leachate

Experiments were conducted to investigate the feasibility of applying constructed wetlands to treat a sanitary landfill leachate containing high nitrogen (TN) and bacterial contents. Two-pilot scale subsurface-flow constructed wetland (SFCW) units located at the Asian Institute of Technology, Thailand, campus, were fed with a synthetic wastewater and landfill leachate collected from a nearby sanitary landfill. Under the tropical conditions (temperature of about 30°C), the SFCW units operating at the hydraulic retention time(HRT) of 8 days yielded the best treatment efficiencies with BOD5 removal of 91 %, TN removal of 96 %, total and fecal coliforms (TC and FC) removal of more than 99 % and cadmium removal of 99.7 %. The treatment performance was found to follow first-order reaction rate, in which the k20 values of BOD5, COD, TN, TC, FC and Cd were 0.201, 0.121, 0.247, 0.346, 0.354 and 0.690 d−1, respectively. Mass balance analysis, based on TN contents of the plant biomass and dissolved oxygen (DO) and oxidation– reduction potential (ORP) values, suggested that 88 % of the input TN were uptaken by the plant biomass; 8 % removed by nitrification–denitrification reactions and adsorption on the wetland media, while the remaining 4 % were discharged with the effluent.

Selenium(IV) and (VI) Sorption by Soils Surrounding Fly Ash Management Facilities

Leachate derived from unlined coal ash disposal facilities is one of the most significant anthropogenic sources of selenium to the environment. To establish a practical framework for predicting transport of selenium in ash leachate, sorption of Se(IV) and Se(VI) from 1 mM CaSO4 was measured for 18 soils obtained down‐gradient from three ash landfill sites and evaluated with respect to several soil properties. Furthermore, soil attenuation from lab‐generated ash leachate and the effect of Ca2+ and SO42− concentrations as well as pH on both Se(IV) and Se(VI) was quantified for a subset of soils. For both Se(IV) and Se(VI), pH combined with either percentage clay or dithionite‐citrate‐bicarbonate (DCB)‐extractable Fe described &gt;80% of the differences in sorption across all soils, yielding an easy approach for making initial predictions regarding site‐specific selenium transport to sensitive water bodies. Se(IV) consistently exhibited an order of magnitude greater sorption than Se(VI). Selenium sorption was highest at lower pH values, with Se(IV) sorption decreasing at pH values above 6, whereas Se(VI) decreased over the entire pH range (2.5–10). Using these pH adsorption envelopes, the likely effect of ash leachate‐induced changes in soil pore water pH with time on selenium attenuation by down gradient soils can be predicted. Selenium sorption increased with increasing Ca2+ concentrations while SO42− suppressed sorption well above enhancements by Ca2+ Soil attenuation of selenium from ash leachates agreed well with sorption measured from 1 mM CaSO4, indicating that 1 mM CaSO4 is a reasonable synthetic leachate for assessing selenium behavior at ash landfill sites.

Passive treatment of municipal landfill leachate in a granular drainage layer

This paper describes a laboratory investigation that simulates in situ treatment of leachate representative of that generated by a municipal solid waste (MSW) landfill. The objective of the investigation is to demonstrate that recycle of leachate and treatment within a leachate collection system (LCS) coupled with a nitrification reactor can provide significant decreases in leachate chemical oxygen demand (COD) and ammonia concentration. In the investigation five 15 cm (6 in.) diameter polyvinyl chloride (PVC) columns were packed with drainage media of various sizes consisting of natural gravel and (or) crushed concrete (washed and screened). Geotextiles were placed between the various media as filter–separators and to promote bacterial growth. Synthetic leachate was continuously fed into the top of each column and recirculated from the bottom at rates representative of operating field conditions. For each column, effluent was discharged to a nitrification reactor before recirculation. The tests were conducted under anaerobic and unsaturated conditions in the columns. The results obtained from the experiment show that in situ treatment at landfills using this approach is viable. A 97% decrease in COD and about 98% conversion of the ammonia to nitrogen gas was observed. The denitrification process did not significantly inhibit COD depletion or methane production. Further, the biogas produced contained only a small fraction of CO2, which could suggest a potential benefit in terms of decreasing the potential of clogging in the LCS and extending the service life of a landfill gas (LFG) collection network by generating a less corrosive environment.Key words: leachate treatment, chemical oxygen demand (COD) removal, nitrification, denitrification, biogas production, sanitary landfill.

Effect of pH, competitive anions and NOM on the leaching of arsenic from solid residuals

Implementation of the new arsenic MCL in 2006 will lead to the generation of an estimated 6 million pounds of arsenic-bearing solid residuals (ABSRs) every year, which will be disposed predominantly in non-hazardous landfills. The Toxicity Characteristic Leaching Procedure (TCLP) is typically used to assess whether a waste is hazardous and most solid residuals pass the TCLP. However, recent research shows the TCLP significantly underestimates arsenic mobilization in landfills. A variety of compositional dissimilarities between landfill leachates and the TCLP extractant solution likely play a role. Among the abiotic factors likely to play a key role in arsenic remobilization/leaching from solid sorbents are pH, and the concentrations of natural organic matter (NOM) and anions like phosphate, bicarbonate, sulfate and silicate. This study evaluates the desorption of arsenic from actual treatment sorbents, activated alumina (AA) and granular ferric hydroxide (GFH), which are representative of those predicted for use in arsenic removal processes, and as a function of the specific range of pH and concentrations of the competitive anions and NOM found in landfills. The influence of pH is much more significant than that of competing anions or NOM. An increase in one unit of pH may increase the fraction of arsenic leached by 3–4 times. NOM and phosphate replace arsenic from sorbent surface sites up to three orders of magnitude more than bicarbonate, sulfate and silicate, on a per mole basis. Effects of anions are neither additive nor purely competitive. Leaching tests, which compare the fraction of arsenic mobilized by the TCLP vis-a-vis an actual or more realistic synthetic landfill leachate, indicate that higher pH, and greater concentrations of anions and NOM are all factors, but of varying significance, in causing higher extraction in landfill and synthetic leachates than the TCLP.

Evaluation of Granular Activated Carbon, Shale, and Two Organoclays for Use as Sorptive Amendments in Clay Landfill Liners

Four materials with high sorptive capacities for organic compounds [granular activated carbon (GAC), shale, benzyltriethylammonium-bentonite (BTEA-bentonite), and hexadecyltrimethylammonium-bentonite (HDTMA-bentonite)] were evaluated for their use in compacted clay landfill liners by conducting laboratory sorption and permeability experiments with both a 0.002 N CaS O4 solution (to simulate the ionic strength of ground water) and a synthetic leachate. Results from equilibrium sorption experiments with 0.002 N CaS O4 indicate that all four amendments have a very high sorptive capacity for the three organic solutes tested: benzene, trichloroethylene, and 1,2-dichlorobenzene. GAC exhibited the highest sorptive capacity for all three solutes, followed by BTEA-bentonite, HDTMA-bentonite, and shale. Experiments conducted with synthetic leachate indicate that GAC and BTEA-bentonite did not exhibit competitive sorption effects with the synthetic leachate constituents, while shale did exhibit some competitive sorp...

Evolution of clog formation with time in columns permeated with synthetic landfill leachate

Laboratory column tests conducted to gain insight regarding the biological and chemical clogging mechanisms in a porous medium are presented. To seed the porous medium with landfill bacteria, a mixture of Keele Valley Landfill and synthetic leachate permeated through the column under anaerobic conditions for the first 9 days of operation. After this, 100% synthetic leachate was used. The synthetic leachate approximated Keele Valley Landfill leachate in chemical composition but contained negligible suspended solids and bacteria compared with real leachate. The removal of volatile fatty acids (VFAs), primarily acetate, in leachate as it passed through the medium was highly correlated with the precipitation of calcium carbonate (CaCO 3(s)) from solution. The columns experienced a decrease in drainable porosity from an initial value of about 0.38 to less than 0.1 after steady state chemical oxygen demand (COD) removal, resulting in a five-order magnitude decrease in hydraulic conductivity. The decrease in drainable porosity prior to steady state COD removal was primarily due to the growth of a biofilm on the medium surface. After steady state COD removal, calcium precipitation was at least equally responsible for the decrease in drainable porosity as biofilm growth. Clog composition analyses showed that CaCO 3(s) was the dominant clog constituent and that 99% of the carbonate in the clog material was bound to calcium.

Some factors controlling the adsorption of potassium ions on clayey soils

The adsorption of contaminants is one of the key mechanisms governing the transport of contaminants in the clay liner at landfill sites. This study presents an investigation of some factors controlling the adsorption of potassium (K +) onto two soils, named Ariake clay and Akaboku soil. The KCl solution and multi-salt solution containing KCl, NaCl and CaCl 2 were selected as the synthetic leachates. The results show that with the increase of the solid/solution ratio, the adsorbed amount of K + decreased for both soils. This dependence of adsorption behavior on the solid/solution ratio was found more significant for the Ariake clay. Both soils arrived an equilibrium condition in short time less than the contact time prescribed by the ASTM and US EPA standard batch-type tests. It was observed that both soils adsorbed larger amount of K + in the case of KCl solution condition than in the case of multi-salt condition.

TCLP underestimates leaching of arsenic from solid residuals under landfill conditions.

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

Accelerated weathering and biodegradation of E-glass polyester composites

Abstract Successful material performance of composites depends on the environmental conditions to which they are exposed. Biological factors in aquatic environments may accelerate material deterioration. Simultaneously, leached constituents can adversely affect the surrounding ecosystem. An accelerated weathering was used to demonstrate the ease of coupon biodeterioration. In 3 months, 21 mg l −1 of organics were leached, aquatic bacteria numbers increased by 43%, and biofilm growth was accelerated. Degradability of leached compounds was tested in experiments with water collected from the accelerated weathered coupons and a synthetic leachate. The first experiment verified isophthalaldehyde as a polyester biodegradation byproduct. Although the rate of biodegradation was twice that of the abiotic system, microbial numbers had reduced from 5.0×107 to 5.4×10 4 CFU l −1 . Synthetic resin experiments showed that the bacteria were able to use the resin as a carbon source. However, compound toxicity prevented exponential growth of the bacteria.

Application of electrochemical process for landfill leachate treatment with emphasis on heavy metal and organic removal

This study was conducted to investigate the mechanisms of electrochemical treatment of a landfill leachate with emphasis on lead and organic removal. Laboratory electrochemical experiments were conducted using both synthetic wastewater and landfill leachate samples. From the synthetic wastewater experiments, the lead removal efficiencies were found to be more than 99%. The lead removal was observed to be dependent on: the electrical current, ratio between reacting surface area and volume of reactor and operation time, and following a first‐order reaction. Similar results on lead removal were obtained when the landfill leachate samples were treated in the electrochemical reactor; the percent removal of soluble biological oxygen demand and soluble chemical oxygen demand concentrations from the landfill leachate during the electrochemical treatment were 30–60%, while the color removal was 70%. The sludge generated from the electrochemical reactions using the synthetic lead wastewater, analyzed by X‐ray diffractometry, was found to be composed mainly of maghemite, magnetite, and laurionite. Based on the X‐ray fluorescence spectrometry analysis, the percent contents of iron and lead were 68.6% as maghemite and 10.1% as lead oxide, respectively. The sludge generated from the landfill leachate treatment containing lead, analyzed by X‐ray diffractometry, was found to be composed mainly of maghemite. Based on the X‐ray fluorescence spectrometry analysis, the percent contents of iron and lead in the sludge were 69.49% as maghemite and 0.63% as lead oxide, respectively. The sludge volume index, capillary suction time and teachability values of the sludge were in suitable range for settling, dewatering and disposal.