Leachate Recirculation Research Articles

Impact of a new Legislation on Volatile Organic Compounds Emissions in an Open Landfill in Tropical Insular Climate

Concentrations of airborne Volatile Organic Compounds (VOCs) were evaluated by monitoring landfill gases at the main municipal solid waste of Guadeloupe archipelago. Opened in 1973, the open landfill of La Gabarre is still operated nowadays. Over last decade, nature of stored waste and landfill configuration have evolved. Before 2008, waste was just spread out on the floor and there was no gas collection nor leachate recirculation systems installed. After 2009, new units were set up to collect and treat hazardous waste. VOCs measurements have been performed at La Gabarre for two distinct periods with two portable devices: an Open-Path Fourier Transform InfraRed (OPFTIR) spectrometer in 2003 and a Mass Spectrometer (MS 200) in 2012. Four VOCs commonly found in landfill plume were measured. Between 2003 and 2012, a sharp decrease is observed in the concentrations of benzene and trichloroethylene. Tetrachloroethylene was not detected by the OP-FTIR spectrometer. Taking acetaldehyde as an example, it was hypothesized that this decrease could not be related to the difference between measurement techniques. These results suggest that in recent years with the application of a new legislation and the installation of gas collection systems, emissions of VOCs in the atmosphere due to garbage have decreased at La Gabarre.

Axisymmetric gas flow model for bioreactor landfills incorporating MSW compression and leachate recirculation

To control the landfill gas (LFG) emission, LFG collection systems with vertical wells are extensively used in municipal solid waste (MSW) landfills. When investigating the LFG flow behavior, the solid–liquid–gas interactions cannot be neglected, especially in bioreactor landfills. In this study, an axisymmetric numerical model incorporating MSW compression and leachate recirculation was developed to describe the transient gas flow in bioreactor landfills. In the model, the porosity distribution was evaluated through circular computations, and the temporal and spatial changes in moisture were determined using the unsaturated–saturated seepage flow model. Based on these calculations, the governing equations of gas migration were solved using the finite element method. The influences of MSW properties, recirculation rate and well vacuum pressure were then investigated. The results show that the MSW compression and leachate recirculation have a significant impact on the distributions of gas generation, permeability and pressure. As the recirculation rate increases from 1 to 9 mm day−1, the gas permeability can decrease about 1 order of magnitude and thus the radius of influence decreases from 39 to 31 m. It is important to keep a balance between the acceleration of landfill stability and the recovery efficiency of LFG. These results provide helpful guidelines for the design of leachate recirculation and LFG control systems.

Effect of migration and transformation of iron on the endogenous reduction of H2S in anaerobic landfill

Hydrogen sulfide (H2S) is a major odor in landfill gas and needs urgent treatment. In this study, the effect of migration and transformation of iron on the endogenous reduction of H2S was investigated in two simulated landfills. The results showed that the H2S emission concentration from the landfill cover of conventional anaerobic landfill (CL) and anaerobic landfill with leachate recirculation (RL) could reach 19.4mgm−3 and 24.1mgm−3, respectively. However, the migration and transformation of iron in anaerobic landfill with different operational modes results in different endogenous reduction mechanism for H2S. The proportion of precipitation–reduction mechanism and oxidation–reduction mechanism in CL was 73.3% and 26.3%, respectively. But for RL, the function of oxidation was enhanced, and the sulfide content was reduced 23.1% compared with CL. The iron in landfill with leachate recirculation revealed good endogenous reduction effect on H2S control after a period of time landfilling.

Pilot-scale landfill with leachate recirculation for enhanced stabilization

A pilot-scale landfill and a two-phase (acidogenesis and methanogenesis) anaerobic sequencing batch reactor (anSBR) system was setup to treat leachate collected from the simulated landfill cell which had leachate recirculation (at <0.3% of total waste volume/day). It was noted there was already substantial acidogenic activity in the landfill cell before the acidogenic reactor. Development of the microbial communities in the two reactors was influenced by the acidogenesis in the landfill cell. A COD half-life of 10 weeks was achieved in the pilot-scale landfill system indicating very fast organics stabilization in the landfill. It was shown that with an ex-situ anSBR augmenting treatment of the landfill leachate, rapid landfill stabilization could be achieved even when leachate recirculation was at a relatively low rate.

Biotic and abiotic roles of leachate recirculation in batch mode solid-state anaerobic digestion of cattle manure

Solid state anaerobic digestion, with leachate recirculation, is suitable for exploiting manure with a high solid content. The biotic and abiotic effects of the leachates were studied in lab-scale leach bed reactors (LBRs). LBRs were fed with cow manure and four leachates either biologically active or inert. The biotic impact of leachate was assessed by monitoring the microbial communities in the manure and in the leachates. LBRs with biologically active leachates, regardless to their origin, produced equivalent methane volumes (114.52±19.05 and 99.79±6.4NL/kgVS) while LBRs with inert leachates produced half less methane (60.22±5.71 and 58.87±13.2NL/kgVS) attesting to the biotic role of leachate. Moreover, its beneficial abiotic role is mainly due to its initial nutrient content, pH, and buffering capacity. The microbial community in the manure was strongly involved in methane production, and no transfer of microorganisms from the liquid phase was found (p<0.05).

Impact of concentrated leachate recirculation on effectiveness of leachate treatment by reverse osmosis

The effect of concentrate recirculation on leachate quality and effectiveness of their treatment by reverse osmosis (RO) was investigated. The concentrate from reverse osmosis was characterized by a high concentration of sulphides (average of 828μg/l), sulphates (1898mg/l), chlorides (5608mg/l), electro-conductivity (8066μS/cm), moderate chemical oxygen demand (COD) value (1646mg/l) and low pH (6.7). Analysis of the leachate quality data showed that concentrate recirculation landfill produces stronger leachate especially in terms of inorganic compounds. Concentrate recirculation accelerated waste decomposition, therefore the concentration of COD, biochemical oxygen demand (BOD), ammonia nitrogen and COD/CODmax ratio value in leachate increased in first three months of recirculation. Changes in the leachate quality can influence the effectiveness of leachate treatment by RO. Correlation analysis has shown a negative correlation (−0.75) between iron concentration and COD removal, which is caused by fouling and bio-fouling induced by Fe. A negative correlation between the leachate pH and BOD removal (−0.78) was also observed, which was the result of electrostatic effects between the membrane surface and macromolecules of some organics.

Landfill aeration for emission control before and during landfill mining

The landfill of Modena, in northern Italy, is now crossed by the new high velocity railway line connecting Milan and Bologna. Waste was completely removed from a part of the landfill and a trench for the train line was built. With the aim of facilitating excavation and further disposal of the material extracted, suitable measures were defined. In order to prevent undesired emissions into the excavation area, the aerobic in situ stabilisation by means of the Airflow technology took place before and during the Landfill Mining. Specific project features involved the pneumatic leachate extraction from the aeration wells (to keep the leachate table low inside the landfill and increase the volume of waste available for air migration) and the controlled moisture addition into a limited zone, for a preliminary evaluation of the effects on process enhancement. Waste and leachate were periodically sampled in the landfill during the aeration before the excavation, for quality assessment over time; the evolution of biogas composition in the landfill body and in the extraction system for different plant set-ups during the project was monitored, with specific focus on uncontrolled migration into the excavation area.Waste biological stability significantly increased during the aeration (waste respiration index dropped to 33% of the initial value after six months). Leachate head decreased from 4 to 1.5m; leachate recirculation tests proved the beneficial effects of moisture addition on temperature control, without hampering waste aerobization. Proper management of the aeration plant enabled the minimization of uncontrolled biogas emissions into the excavation area.

Endogenous mitigation of H2S inside of the landfills.

Vast quantities of hydrogen sulfide (H2S) emitted from landfill sites require urgent disposal. The current study focused on source control and examined the migration and conversion behavior of sulfur compounds in two lab-scale simulated landfills with different operation modes. It aimed to explore the possible strategies and mechanisms for H2S endogenous mitigation inside of landfills during decomposition. It was found that the strength of H2S emissions from the landfill sites was dependent on the municipal solid waste (MSW) degradation speed and vertical distribution of sulfide. Leachate recirculation can shorten both the H2S influence period and pollution risk to the surrounding environment. H2S endogenous mitigation may be achieved by chemical oxidation, biological oxidation, adsorption, and/or precipitation in different stages. Migration and conversion mainly affected H2S release behavior during the initial stabilization phase in the landfill. Microbial activities related to sulfur, nitrogen, and iron can further promote H2S endogenous mitigation during the high reducing phase. Thus, H2S endogenous mitigation can be effectively enhanced via control of the aforementioned processes.

Characterization of a joint recirculation of concentrated leachate and leachate to landfills with a microaerobic bioreactor for leachate treatment

With comparison of a traditional landfill, a joint recirculation of concentrated leachate and leachate to landfills with or without a microaerobic reactor for leachate treatment was investigated in this study. The results showed that the joint recirculation of concentrated leachate and leachate with a microaerobic reactor for leachate treatment could not only utilize the microaerobic reactor to buffer the fluctuation of quality and quantity of leachate during landfill stabilization, but also reduce the inhibitory effect of acidic pH and high concentrations of ammonium in recycled liquid on microorganisms and accelerate the degradation of landfilled waste. After 390days of operation, the discharge of COD and total nitrogen (TN) from the landfill with leachate pretreatment by a microaerobic reactor was 7.4 and 0.9g, respectively, which accounted for 0.7% and 2.6% of COD, 1.9% and 7.5% of the TN discharge from the landfills without recirculation and directly recirculated with leachate and concentrated leachate, respectively. The degradation of the organic matter and biodegradable matter (BDM) in the landfill reactors could fit well with the first-order kinetics. The highest degradation of the organic matter and BDM was observed in the joint recirculation system with a microaerobic reactor for leachate treatment with the degradation constant of the first-order kinetics of 0.001 and 0.002.

Effects of Degradation on Geotechnical Properties of Municipal Solid Waste from Orchard Hills Landfill, USA

In bioreactor landfills, geotechnical properties of municipal solid waste (MSW) are believed to be affected by increased moisture content and accelerated biodegra- dation due to leachate recirculation; however, studies to quantify the changes in the MSW properties are scarce. This study quantifies the change in geotechnical properties of field MSW as a function of level of degradation. Fresh MSW samples were collected from the working phase of Orchard Hills landfill (Davis Junction, Illinois, USA) and were subjected to leachate recirculation and enhanced anaerobic degradation in specially designed laboratory bioreactors. Samples were exhumed from the bioreactors at different stages of degradation as determined by the amount and composition of biogas generated, and subse- quently tested for moisture content, organic content, unit weight, hydraulic conductivity, compressibility, and shear strength. Moisture content of MSW increased significantly, while organic content decreased with degradation. Bulk unit weight increased with degradation which led to decrease in saturated hydraulic conductivity. Primary compression ratio showed slight increasing trend with degradation, while the secondary compression ratio was not affected significantly with the degradation. The friction angle decreased from 30� to 12� , but cohesion increased from 29 to 65 kPa with degradation based on direct shear test results. The testing of saturated MSW in triaxial con- solidated undrained conditions resulted in lower shear strength with no distinct correlation of friction angle and cohesion with degradation. Additional large-scale, long- duration testing is recommended using the field MSW samples with the consistent composition to establish the correlations between the engineering properties and degree of degradation. Overall this study showed that the engi- neering properties of field MSW are affected by degrada- tion and these changes should be properly accounted in the analysis and design of bioreactor landfills involving lea- chate recirculation.

Stabilization of fine fraction from landfill mining in anaerobic and aerobic laboratory leach bed reactors

Fine fraction (FF, <20mm) from mined landfill was stabilized in four laboratory-scale leach bed reactors (LBR) over 180days. The aim was to study feasibility of biotechnological methods to treat FF and if further stabilization of FF is possible. Four different stabilization methods were compared and their effects upon quality of FF were evaluated. Also during the stabilization experiment, leachate quality as well as gas composition and quantity were analyzed. The methods studied included three anaerobic LBRs (one without water addition, one with water addition, and one with leachate recirculation) and one aerobic LBR (with water addition). During the experiment, the most methane was produced in anaerobic LBR without water addition (18.0LCH4/kgVS), while water addition and leachate recirculation depressed methane production slightly, to 16.1 and 16.4LCH4/kgVS, respectively. Organic matter was also removed via the leachate and was measured as chemical oxygen demand (COD). Calculated removal of organic matter in gas and leachate was highest in LBR with water addition (59gCOD/kgVS), compared with LBR without water addition or with leachate recirculation (51gCOD/kgVS). Concentrations of COD, ammonium nitrogen and anions in leachate decreased during the experiment, indicating washout mechanism caused by water additions. Aeration increased sulfate and nitrate concentrations in leachate due to oxidized sulfide and ammonium. Molecular weight distributions of leachates showed that all the size categories decreased, especially low molecular weight compounds, which were reduced the most. Aerobic stabilization resulted in the lowest final VS/TS (13.1%), lowest respiration activity (0.9–1.2mgO2/gTS), and lowest methane production after treatment (0.0–0.8LCH4/kgVS), with 29% of VS being removed from FF. Anaerobic stabilization methods also reduced organic matter by 9–20% compared with the initial amount. Stabilization reduced the quantity of soluble nitrogen in FF and did not alter concentration of soluble and insoluble phosphorus, and insoluble nitrogen. All four stabilization methods decreased organic matter and thus are possible stabilization methods for FF, but aerobic treatment was the most efficient in this study.

Modeling Coupled Hydromechanical Behavior of Landfilled Waste in Bioreactor Landfills: Numerical Formulation and Validation

AbstractBioreactor landfills involving leachate recirculation are emerging as the preferred option for managing municipal solid waste (MSW). Effective bioreactor landfill performance can be achieved by ensuring uniform and adequate moisture (leachate) distribution in landfilled MSW. This paper presents a numerical two-phase flow model as a tool to predict hydraulic behavior (moisture distribution and pore fluid pressures) in unsaturated MSW under leachate recirculation, mechanical response (stress-strain behavior), and coupled hydromechanical interactions of MSW in landfills. The selected mathematical model is the Fast Lagrangian Analysis of Continua (FLAC), which assumes leachate and landfill gas as two immiscible phases. The governing equations and numerical implementation are presented along with the general model implementation considerations. The model is validated by simulating the published laboratory studies, field studies, and published modeled studies. Overall, it is shown that the mathematical ...

Assessment of biogas production from MBT waste under different operating conditions

In this work, the influence of different operating conditions on the biogas production from mechanically–biologically treated (MBT) wastes is investigated. Specifically, different lab-scale anaerobic tests varying the water content (26–43% w/w up to 75% w/w), the temperature (from 20 to 25°C up to 55°C) and the amount of inoculum have been performed on waste samples collected from a full-scale Italian MBT plant. For each test, the gas generation yield and, where applicable, the first-order gas generation rates were determined. Nearly all tests were characterised by a quite long lag-phase. This result was mainly ascribed to the inhibition effects resulting from the high concentrations of volatile fatty acids (VFAs) and ammonia detected in the different stages of the experiments. Furthermore, water content was found as one of the key factor limiting the anaerobic biological process. Indeed, the experimental results showed that when the moisture was lower than 32% w/w, the methanogenic microbial activity was completely inhibited. For the higher water content tested (75% w/w), high values of accumulated gas volume (up to 150Nl/kgTS) and a relatively short time period to deplete the MBT waste gas generation capacity were observed. At these test conditions, the effect of temperature became evident, leading to gas generation rates of 0.007d−1 at room temperature that increased to 0.03–0.05d−1 at 37°C and to 0.04–0.11d−1 at 55°C. Overall, the obtained results highlighted that the operative conditions can drastically affect the gas production from MBT wastes. This suggests that particular caution should be paid when using the results of lab-scale tests for the evaluation of long-term behaviour expected in the field where the boundary conditions change continuously and vary significantly depending on the climate, the landfill operative management strategies in place (e.g. leachate recirculation, waste disposal methods), the hydraulic characteristics of disposed waste, the presence and type of temporary and final cover systems.

음식물류 폐기물 처리를 위한 준 회분식 액순환 건식 혐기성 소화법에 대한 기초연구

In this study, the experiment was carried out to produce methane by applying Semi-Continuous Leachate Recirculation Anaerobic Digestion System fed with source separated food waste from school cafeteria. There were two systems and each system consisted of a bioreactor and a liquid tank. Each bioreactor had a screen near the bottom of the reactor. 2.5L of separated liquid was transferred to the liquid tank for 30min each day by using a tubing pump and the liquid from the liquid tank was pumped to the bioreactor at the upper of the bioreactor as soon as the transfer was ended. Through this circulation, the liquid having high concentration of VFAs was supplied to the top of bioreactor. At the beginning of the experiment, food waste/inoculum anaerobic sludge volume ratio was 2:8 that is 9g VS/L of OLR(Organic Loading Rate). Feeding was conducted every two weeks. Experimental results showed that the contents of moisture, combustible matter, ash were 65.91%, 32.73%, and 1.36%, respectively. Two different food waste loading were studied. The average organic loading rates were 3.51g VS/d for System A and 3.86g VS/d for System B, respectively. The average produced methane based on food waste fed to bioreactor were observed as 6.30m 3 CH4/kgVS⋅d for system A and 4.94m 3 CH4/kgVS⋅d for System B, respectively.

Degradation of municipal solid waste in simulated landfill bioreactors under aerobic conditions

In this study the municipal solid waste degradation processes in simulated landfill bioreactors under aerobic and anaerobic conditions is investigated. The effect of waste aeration on the dynamics of the aerobic degradation processes in lysimeters as well as during anaerobic processes after completion of aeration is presented. The results are compared with the anaerobic degradation process to determine the stabilization stage of waste in both experimental modes. The experiments in aerobic lysimeters were carried out at small aeration rate (4.41⋅10−3lmin−1kg−1) and for two recirculation rates (24.9 and 1.58lm−3d−1). The change of leachate and formed gases composition showed that the application of even a small aeration rate favored the degradation of organic matter. The amount of CO2 and CH4 released from anaerobic lysimeter was about 5 times lower than that from the aerobic lysimeters. Better stabilization of the waste was obtained in the aerobic lysimeter with small recirculation, from which the amount of CO2 produced was larger by about 19% in comparison with that from the aerobic lysimeter with large leachate recirculation.

Leachate Quality Monitoring from Conventional, Retrofit, and Bio-Reactor Landfill Cells

AbstractThe recirculation of leachate is a common strategy to accelerate the decomposition of municipal solid waste in landfills. In this study, leachates from a conventional landfill cell without supplemental liquid addition (Control cell), a new landfill area that had a piping network installed as waste was being placed (As-Built cell), and a conventional landfill that was modified to allow for the recirculation of liquids (Retrofit cell) were monitored at the outer loop landfill bioreactor (OLLB) in Louisville, Kentucky. In general, leachates from the Retrofit cells were statistically different from leachates from the As-Built and Control cells. This is likely because the waste in Retrofit cells was about 6 years old when liquids were first introduced and the waste had already reached a more mature state prior to supplemental liquids addition. Based on time series data, the Retrofit cells, which received nitrified leachate, did not show signs of accelerated waste decomposition based on the leachate che...

Transformation of Dioctyl Phthalate in Bioreactor Landfill

Considering the refuse and leachate as one whole system, a conventional landfill (CL) was set as a control, transformation of dioctyl phthalate (DOP) in recirculated landfill (RL) and bioreactor landfill (BL) was studied. Results showed that DOP was detected in both leachate and refuse from CL, RL and BL. The initial DOP amount was 0.8 μg g-1 in the landfill refuse. At the day of 310, refuse sedimentation rates were 7.0%, 11.9% and 24.3% in CL, RL and BL, respectively. DOP removal rates were 17.4%, 30.8% and 31.7% in the refuse from CL, RL and BL, respectively. The residual amounts of DOP with significant differences well fitted exponential decay models in CL, RL and BL. DOP biodegradation was accelerated with the operation of leachate recirculation compared to the conventional operation, and it was further promoted with the introduction of methanogenic reactor.

Recent Advances of Biomass Waste to Gas Using Landfill Bioreactor Technology - A Review

The practice of disposing of waste in conventional dry-tomb landfills is not sustainable. A sustainable alternative is the landfill bioreactor and its variations. Landfill bioreactor approach includes specific design and operation techniques to enhance waste degradation and landfill gas (LFG) production. Although this approach has been known to landfill researchers and practitioners for a few decades, there are only a few successful field-scale landfill bioreactors in operation. This paper provides a comprehensive review of technological challenges with landfill bioreactors and associated design and operational details. A key issue that should be addressed by a landfill bioreactor designer is moisture and gas movement within a waste matrix that changes its properties continuously in time and space. The design components such as the leachate collection and removal system (LCRS), leachate recirculation system, and gas collection system could be severely impacted if the traditional landfill design and operation practice is not modified to take into consideration the behavior of waste matrix in time and space. Considering that a landfill bioreactor can be used as a biomass waste to energy facility, this paper details the LFG generation processes, the factors affecting the LFG generation and theoretical LFG generation estimation techniques as well as the important design, construction and operational issues associated with landfill bioreactors. Keywords: Anaerobic waste degradation, biocell, landfill bioreactors, leachate recirculation.

Carbon pools and flows during lab-scale degradation of old landfilled waste under different oxygen and water regimes

Landfill aeration has been proven to accelerate the degradation of organic matter in landfills in comparison to anaerobic decomposition. The present study aims to evaluate pools of organic matter decomposing under aerobic and anaerobic conditions using landfill simulation reactors (LSR) filled with 40year old waste from a former MSW landfill. The LSR were operated for 27months, whereby the waste in one pair was kept under anaerobic conditions and the four other LSRs were aerated. Two of the aerated LSR were run with leachate recirculation and water addition and two without. The organic carbon in the solid waste was characterized at the beginning and at the end of the experiments and major carbon flows (e.g. TOC in leachate, gaseous CO2 and CH4) were monitored during operation. After the termination of the experiments, the waste from the anaerobic LSRs exhibited a long-term gas production potential of more than 20NLkg−1 dry waste, which corresponded to the mineralization of around 12% of the initial TOC (67gkg−1 dry waste). Compared to that, aeration led to threefold decrease in TOC (32–36% of the initial TOC were mineralized), without apparent differences in carbon discharge between the aerobic set ups with and without water addition. Based on the investigation of the carbon pools it could be demonstrated that a bit more than 10% of the initially present organic carbon was transformed into more recalcitrant forms, presumably due to the formation of humic substances. The source of anaerobic degradation could be identified mainly as cellulose which played a minor role during aerobic degradation in the experiment.

Short tests to couple N2O emission mitigation and nitrogen removal strategies for landfill leachate recirculation

Landfills implemented with onsite leachate recirculation can efficiently remove pollutants, but currently they are reckoned as N2O emission hot spots. In this project, we evaluated the relationship between N2O emission and nitrogen (N) removal efficiency with different types of leachate recirculated. Nitrate supplemented leachate showed low N2O emission rates with the highest N removal efficiency (~70%), which was equivalent to ~1% nitrogen emitted as N2O. Although in nitrite containing leachates' N removal efficiencies also reached to ~60%, their emitted N2O comprised ~40% of total removed nitrogen. Increasing nitrogen load promoted N2O emission and N removal efficiency, except in ammonia type leachate. When the ratio of BOD to total nitrogen increased from 0.2 to 0.4, the N2O emission flux from nitrate supplemented leachate decreased from ~25 to <0.5μgN/kg-soil·h. We argue prior to leachate in situ recirculation, sufficient pre-aeration is critical to mitigate N2O surges and simultaneously enhance nitrogen removal efficiency.