Measuring seasonal variations of moisture in a landfill with the partitioning gas tracer test

Seven pilot-scale partitioning gas tracer tests (PGTTs) were conducted to assess the accuracy and reproducibility of this method for measuring water in municipal solid waste landfills. Tests were conducted in the same location over a 12-month period, and measured moisture conditions ranged from possible dry waste to refuse with a moisture content of 24.7%. The final moisture content of 24.7% was in reasonable agreement with gravimetric measurements of excavated refuse, where the moisture content was 26.5+/-6.0 CI%. Laboratory tests were used to assess the utility of the PGTT for measuring water in small pores, water sorbed to solid surfaces, and the influence of dry waste on PGTTs. These experiments indicated that when refuse surfaces are not completely solvated with water, PGTTs may produce misleading results (negative estimates) of water saturation and moisture content.     

Enhanced methane recovery by food waste leachate injection into a landfill in Korea

The current food waste leachate (FWL) disposal practice in Korea warrants urgent attention and necessary action to develop an innovative and sustainable disposal strategy, which is both environmentally friendly and economically beneficial. In this study, methane production by FWL injection into a municipal solid waste landfill with landfill gas (LFG) recovery facility was evaluated for a period of more than 4 months. With the target of recovering LFG with methane content ~50%, optimum LFG extraction rate was decided by a trial and error approach during the field investigation in five different phases. The results showed that, upon FWL injection, LFG extraction rate of ~20 m(3)/h was reasonable to recover LFG with methane content ~58%. Considering the estimated methane production potential of 31.7 m(3) CH(4) per ton of FWL, methane recovery from the landfill was enhanced by 14%. The scientific findings of this short-term investigation indicates that FWL can be injected into the existing sanitary landfills to tackle the present issue and such landfills with efficient liner and gas collection facility can be utilized as absolute and sustainable environmental infrastructures.     

Municipal solid waste in situ moisture content measurement using an electrical resistance sensor

Moisture content (MC) is a crucial parameter for degradation of solid waste in landfills. Present MC measurement techniques suffer from several drawbacks. A moisture sensor for measurement of in situ moisture content of solid waste in landfills was developed. The sensor measures the electrical resistance across the granular matrix of the sensor, which in turn can be correlated to moisture content. The sensor was also equipped with a thermocouple and tubing that permits simultaneous measurement of temperature and gas sampling. The electrical conductivity of the surrounding moisture and the temperature in the matrix both affect the resistance measurements. This paper describes the results of laboratory experiments designed to select the appropriate granular media particle size, measure the influence of moisture electrical conductivity and temperature, and develop calibration relationships between measured resistance and gravimetrically determined moisture content. With a few limitations, the sensor is able to detect MC of solid waste under conditions allowing moisture movement into the sensor. The application of this technique shows promise for use in bioreactor landfills where high moisture contents are expected and desired.     

Methane production potential of leachate generated from Korean food waste recycling facilities: a lab-scale study

This paper examines the applicability of food waste leachate (FWL) in bioreactor landfills or anaerobic digesters to produce methane as a sustainable solution to the persisting leachate management problem in Korea. Taking into account the climatic conditions in Korea and FWL characteristics, the effect of key parameters, viz., temperature, alkalinity and salinity on methane yield was investigated. The monthly average moisture content and the ratio of volatile solids to total solids of the FWL were found to be 84% and 91%, respectively. The biochemical methane potential experiment under standard digestion conditions showed the methane yield of FWL to be 358 and 478 ml/g VS after 10 and 28 days of digestion, respectively, with an average methane content of 70%. Elemental analysis showed the chemical composition of FWL to be C(13.02)H(23.01)O(5.93)N(1). The highest methane yield of 403 ml/g VS was obtained at 35 degrees C due to the adaptation of seed microorganisms to mesophilic atmosphere, while methane yields at 25, 45 and 55 degrees C were 370, 351 and 275 ml/g VS, respectively, at the end of 20 days. Addition of alkalinity had a favorable effect on the methane yield. Dilution of FWL with salinity of 2g/l NaCl resulted in 561 ml CH(4)/g VS at the end of 30 days. Considering its high biodegradability (82.6%) and methane production potential, anaerobic digestion of FWL in bioreactor landfills or anaerobic digesters with a preferred control of alkalinity and salinity can be considered as a sustainable solution to the present emergent problem.     

Estimation and field measurement of methane emission from waste landfills in Hanoi, Vietnam

A methodology for estimating the methane emissions from waste landfills in Hanoi, Vietnam, as part of a case study on Asian cities, was derived based on a survey of documents and statistics related to waste management, interviews with persons in charge, and field investigations at landfill sites. The waste management system in Hanoi was analyzed to evaluate the methane emissions from waste landfill sites. The quantity of waste deposited into the landfill was evaluated from an investigation of the waste stream. The composition of municipal waste was surveyed in several districts in the Hanoi city area, and the quantities of degradable organic waste that had been deposited into landfill for the past 15 years were estimated. Field surveys on methane emissions from landfills of different ages (0.5, 2, and 8 years) were conducted and their methane emissions were estimated to be 120, 22.5, and 4.38 ml/min/m², respectively. The first-order reaction rate of methane generation was obtained as 0.51/year. Methane emissions from waste landfills were calculated by a first-order decay model using this emission factor and the amount of landfilled degradable waste. The estimates of methane emissions using the model accorded well with the estimates of the field survey. These results revealed that methane emissions from waste landfills estimated by regional-specific and precise information on the waste stream are essential for accurately determining the behavior of methane emissions from waste landfills in the past, present, and future.     

Forest products decomposition in municipal solid waste landfills

Cellulose and hemicellulose are present in paper and wood products and are the dominant biodegradable polymers in municipal waste. While their conversion to methane in landfills is well documented, there is little information on the rate and extent of decomposition of individual waste components, particularly under field conditions. Such information is important for the landfill carbon balance as methane is a greenhouse gas that may be recovered and converted to a CO(2)-neutral source of energy, while non-degraded cellulose and hemicellulose are sequestered. This paper presents a critical review of research on the decomposition of cellulosic wastes in landfills and identifies additional work that is needed to quantify the ultimate extent of decomposition of individual waste components. Cellulose to lignin ratios as low as 0.01-0.02 have been measured for well decomposed refuse, with corresponding lignin concentrations of over 80% due to the depletion of cellulose and resulting enrichment of lignin. Only a few studies have even tried to address the decomposition of specific waste components at field-scale. Long-term controlled field experiments with supporting laboratory work will be required to measure the ultimate extent of decomposition of individual waste components.     

Induction of enhanced methane oxidation in compost: temperature and moisture response

Landfilling is one of the most common ways of municipal solid waste disposal. Degradation of organic waste produces CH(4) and other landfill gases that significantly contribute to global warming. However, before entering the atmosphere, part of the produced CH(4) can be oxidised while passing through the landfill cover. In the present study, the oxidation rate of CH(4) was studied with various types of compost as possible landfill cover. The influence of incubation time, moisture content and temperature on the CH(4) oxidation capacity of different types of compost was examined. It was observed that the influence of moisture content and temperature on methane oxidation is time-dependent. Maximum oxidation rates were observed at moisture contents ranging from 45% to 110% (dry weight basis), while the optimum temperature ranged from 15 to 30 degrees C.     

Estimation of methane emission potential using the Clean Development Mechanism (CDM) tool for municipal solid waste landfill in Mandalay,Myanmar

Journal of Material Cycles and Waste Management - Municipal solid waste (MSW) landfills are the third largest source of global methane emissions as biogas (11%). In developing countries, MSW...     

Indirect measurements of field-scale hydraulic conductivity of waste from two landfill sites

Management and prediction of the movement and distribution of fluids in large landfills is important for various reasons. Bioreactor landfill technology shows promise, but in arid or semi-arid regions, the natural content of landfilled waste may be low, thus requiring addition of significant volumes of water. In more humid locations, landfills can become saturated, flooding gas collection systems and causing sideslope leachate seeps or other undesirable occurrences. This paper compares results from two different approaches to monitoring water in waste. At the Brock West Landfill in eastern Canada, positive pore pressures were measured at various depths in saturated waste. The downward seepage flux through the waste is known, thus the vertical saturated hydraulic conductivity of the waste at this landfill was determined to be 3 × 10(-7)cm/s. By comparison, the Spadina Landfill in western Canada is predominantly unsaturated. The infiltration of moisture into the waste was measured using moisture sensors installed in boreholes which determined arrival time for moisture fronts resulting from major precipitation events as well as longer-term change in moisture content resulting from unsaturated drainage during winter when frozen ground prevented infiltration. The unsaturated hydraulic conductivity calculated from these data ranged from approximately 10(-6)cm/s for the slow winter drainage in the absence of significant recharge to 10(-2)cm/s or higher for shallow waste subject to high infiltration through apparent preferential pathways. These two very different approaches to field-scale measurements of vertical hydraulic conductivity provide insight into the nature of fluid movement in saturated and unsaturated waste masses. It is suggested that the principles of unsaturated seepage apply reasonably well for landfilled waste and that the hydraulic behavior of waste is profoundly influenced by the nature and size of voids and by the degree of saturation prevailing in the landfill.     

Evaluating the biochemical methane potential (BMP) of low-organic waste at Danish landfills

The biochemical methane potential (BMP) is an essential parameter when using first order decay (FOD) landfill gas (LFG) generation models to estimate methane (CH₄) generation from landfills. Different categories of waste (mixed, shredder and sludge waste) with a low-organic content and temporarily stored combustible waste were sampled from four Danish landfills. The waste was characterized in terms of physical characteristics (TS, VS, TC and TOC) and the BMP was analyzed in batch tests. The experiment was set up in triplicate, including blank and control tests. Waste samples were incubated at 55 °C for more than 60 days, with continuous monitoring of the cumulative CH₄ generation. Results showed that samples of mixed waste and shredder waste had similar BMP results, which was in the range of 5.4–9.1 kg CH₄/ton waste (wet weight) on average. As a calculated consequence, their degradable organic carbon content (DOCC) was in the range of 0.44–0.70% of total weight (wet waste). Numeric values of both parameters were much lower than values of traditional municipal solid waste (MSW), as well as default numeric values in current FOD models. The sludge waste and temporarily stored combustible waste showed BMP values of 51.8–69.6 and 106.6–117.3 kg CH₄/ton waste on average, respectively, and DOCC values of 3.84–5.12% and 7.96–8.74% of total weight. The same category of waste from different Danish landfills did not show significant variation. This research studied the BMP of Danish low-organic waste for the first time, which is important and valuable for using current FOD LFG generation models to estimate realistic CH₄ emissions from modern landfills receiving low-organic waste.     

Geotechnical properties of fresh municipal solid waste at Orchard Hills Landfill, USA

This paper presents the results of a laboratory investigation to determine the geotechnical properties of fresh municipal solid waste (MSW) collected from the working phase of Orchard Hills Landfill located in Davis Junction (Illinois, USA). Laboratory testing was conducted on shredded MSW to determine the compaction, hydraulic conductivity, compressibility, and shear strength properties at in-situ gravimetric moisture content of 44%. In addition, the effect of increased moisture content during leachate recirculation on compressibility and shear strength of MSW was also investigated by testing samples with variable gravimetric moisture contents ranging from 44% to 100%. Based on Standard Proctor tests, a maximum dry density of 420 kg/m(3) was observed at 70% optimum moisture content. The hydraulic conductivity varied in a wide range of 10(-8)-10(-4)m/s and decreased with increase in dry density. Compression ratio values varied in a close range of 0.24-0.33 with no specific trend with the increase in moisture content. Based on direct shear tests, drained cohesion varied from 31 to 64 kPa and the drained friction angle ranged from 26 to 30 degrees. Neither cohesion nor friction angle demonstrated any correlation with the moisture content, within the range of moisture contents tested. The consolidated undrained triaxial shear tests on saturated MSW showed the total strength parameters (c and phi) to be 32 kPa and 12 degrees, and the effective strength parameters (c' and phi') to be 38 kPa and 16 degrees. The angle of friction (phi) decreased and cohesion (c) value increased with the increase in strain. The effective cohesion (c') increased with increase in strain; however, the effective angle of friction (phi') decreased first and then increased with the increase in strain. Such strain-dependent shear strength properties should be properly accounted in the stability analysis of bioreactor landfills.     

Wet landfill decomposition rate determination using methane yield results for excavated waste samples

An increasing number of landfills are operated to accelerate waste decomposition through liquids addition (e.g., leachate recirculation) as a wet landfill. Landfill design and regulation often depend on utilizing landfill gas production models that require an estimate of a first-order gas generation rate constant, k. Consequently, several studies have estimated k using collected gas volumes from operating wet landfills. Research was conducted to examine an alternative approach in which k is estimated not from collected landfill gas but from solid waste samples collected over time and analyzed for remaining gas yield. To achieve this goal, waste samples were collected from 1990 through 2007 at two full-scale landfills in Florida that practiced liquids addition. Methane yields were measured from waste samples collected over time, including periods before and after leachate recirculation, and the results were applied to a first-order decay model to estimate rate constants for each of the sites. An initial, intensive processing step was conducted to exclude non-biodegradable components from the methane yield testing procedure. The resulting rate constants for the two landfills examined were 0.47 yr(-1) and 0.21 yr(-1). These results expectedly exceeded the United States Environmental Protection Agency's rate constants for dry and conventional landfills (0.02-0.05 yr(-1)), but they are comparable to wet landfill rate constants derived using landfill gas data (0.1-0.3 yr(-1)).     

First-order kinetic gas generation model parameters for wet landfills

Landfill gas collection data from wet landfill cells were analyzed and first-order gas generation model parameters were estimated for the US EPA landfill gas emissions model (LandGEM). Parameters were determined through statistical comparison of predicted and actual gas collection. The US EPA LandGEM model appeared to fit the data well, provided it is preceded by a lag phase, which on average was 1.5 years. The first-order reaction rate constant, k, and the methane generation potential, L(o), were estimated for a set of landfills with short-term waste placement and long-term gas collection data. Mean and 95% confidence parameter estimates for these data sets were found using mixed-effects model regression followed by bootstrap analysis. The mean values for the specific methane volume produced during the lag phase (V(sto)), L(o), and k were 33 m(3)/Megagrams (Mg), 76 m(3)/Mg, and 0.28 year(-1), respectively. Parameters were also estimated for three full scale wet landfills where waste was placed over many years. The k and L(o) estimated for these landfills were 0.21 year(-1), 115 m(3)/Mg, 0.11 year(-1), 95 m(3)/Mg, and 0.12 year(-1) and 87 m(3)/Mg, respectively. A group of data points from wet landfills cells with short-term data were also analyzed. A conservative set of parameter estimates was suggested based on the upper 95% confidence interval parameters as a k of 0.3 year(-1) and a L(o) of 100 m(3)/Mg if design is optimized and the lag is minimized.     

Comparing field investigations with laboratory models to predict landfill leachate emissions

Investigations into laboratory reactors and landfills are used for simulating and predicting emissions from municipal solid waste landfills. We examined water flow and solute transport through the same waste body for different volumetric scales (laboratory experiment: 0.08 m³, landfill: 80,000 m³), and assessed the differences in water flow and leachate emissions of chloride, total organic carbon and Kjeldahl nitrogen. The results indicate that, due to preferential pathways, the flow of water in field-scale landfills is less uniform than in laboratory reactors. Based on tracer experiments, it can be discerned that in laboratory-scale experiments around 40% of pore water participates in advective solute transport, whereas this fraction amounts to less than 0.2% in the investigated full-scale landfill. Consequences of the difference in water flow and moisture distribution are: (1) leachate emissions from full-scale landfills decrease faster than predicted by laboratory experiments, and (2) the stock of materials remaining in the landfill body, and thus the long-term emission potential, is likely to be underestimated by laboratory landfill simulations.     

Achieving "Final Storage Quality" of municipal solid waste in pilot scale bioreactor landfills

Entombed waste in current sanitary landfills will generate biogas and leachate when physical barriers fail in the future, allowing the intrusion of moisture into the waste mass contradicting the precepts of the sustainability concept. Bioreactor landfills are suggested as a sustainable option to achieve Final Storage Quality (FSQ) status of waste residues; however, it is not clear what characteristics the residues should have in order to stop operation and after-care monitoring schemes. An experiment was conducted to determine the feasibility to achieve FSQ status (Waste Acceptance Criteria of the European Landfill Directive) of residues in a pilot scale bioreactor landfill. The results of the leaching test were very encouraging due to their proximity to achieve the proposed stringent FSQ criterion after 2 years of operation. Furthermore, residues have the same characteristics of alternative waste stabilisation parameters (low BMP, BOD/COD ratio, VS content, SO4(2-)/Cl- ratio) established by other researchers. Mass balances showed that the bioreactor landfill simulator was capable of practically achieving biological stabilisation after 2 years of operation, while releasing approximately 45% of the total available (organic and inorganic) carbon and nitrogen into the liquid and gas phases.     

Assessment of internal condition of waste in a roofed landfill

Recently, roofed landfills have been gaining popularity in Japan. Roofed landfills have several advantages over non-roofed landfills such as eliminating the visibility of waste and reducing the spread of offensive odours. This study examined the moisture balance and aeration conditions, which promote waste stabilisation, in a roofed landfill that included organic waste such as food waste. Moisture balance was estimated using waste characterization and the total amount of landfilled waste. Internal conditions were estimated based on the composition, flux, and temperature of the landfill gas. Finally, in situ aeration was performed to determine the integrity of the semi-aerobic structure of the landfill.With the effects of rainfall excluded, only 15% of the moisture held by the waste was discharged as leachate. The majority of the moisture remained in the waste layer, but was less than the optimal moisture level for biodegradation, indicating that an appropriate water spray should be administered. To assess waste degradation in this semi-aerobic landfill, the concentration and flow rate of landfill gas were measured and an in situ aeration test was performed. The results revealed that aerobic biodegradation had not occurred because of the unsatisfactory design and operation of the landfill.     

Detailed internal characterisation of two Finnish landfills by waste sampling

The aim of this study was to characterise the internal structure and composition of landfilled waste at two Finnish landfills to provide information for active and post-landfill operations. The two sites, Ämmässuo and Kujala, have been in operation for 17 and 48 years, respectively. Waste was sampled (total 68 samples) and analysed for total solids (TS), volatile solids (VS), total Kjeldahl nitrogen (TKN), biological methane potential (BMP) and leaching of organic material (determined as chemical oxygen demand, COD) and ammonium nitrogen (NH₄–N). The results showed high vertical and horizontal variability, which indicated that both the waste composition and state of degradation varied greatly in both landfills. Ämmässuo was characterised by 2- to 4-fold higher BMP, NH₄–N and COD leaching than Kujala. Moreover, the ratio of VS to TS was higher at Ämmässuo, while TS content was lower. The highest mean BMPs (68 and 44 m³/t TS), TKN content (4.6 and 5.2 kg/t dry weight) and VS/TS ratio (65% and 59%) were observed in the middle and top layers; and the lowest mean BMP (21 and 8 m³/t TS), TKN content (2.4 kg/t dry weight, in both landfills) and VS/TS ratio (55% and 16% in Ämmässuo and Kujala, respectively) in the bottom layers. In conclusion, waste sampling is a feasible way of characterising the landfill body, despite the high variation observed and the fact that the minimum number and size of samples cannot easily be generalized to other landfills due to different methods of waste management and different landfilling histories.     

Methane production from food waste leachate in laboratory-scale simulated landfill

Due to the prohibition of food waste landfilling in Korea from 2005 and the subsequent ban on the marine disposal of organic sludge, including leachate generated from food waste recycling facilities from 2012, it is urgent to develop an innovative and sustainable disposal strategy that is eco-friendly, yet economically beneficial. In this study, methane production from food waste leachate (FWL) in landfill sites with landfill gas recovery facilities was evaluated in simulated landfill reactors (lysimeters) for a period of 90 d with four different inoculum–substrate ratios (ISRs) on volatile solid (VS) basis. Simultaneous biochemical methane potential batch experiments were also conducted at the same ISRs for 30 d to compare CH₄ yield obtained from lysimeter studies. Under the experimental conditions, a maximum CH₄ yield of 0.272 and 0.294 L/g VS was obtained in the batch and lysimeter studies, respectively, at ISR of 1:1. The biodegradability of FWL in batch and lysimeter experiments at ISR of 1:1 was 64% and 69%, respectively. The calculated data using the modified Gompertz equation for the cumulative CH₄ production showed good agreement with the experimental result obtained from lysimeter study. Based on the results obtained from this study, field-scale pilot test is required to re-evaluate the existing sanitary landfills with efficient leachate collection and gas recovery facilities as engineered bioreactors to treat non-hazardous liquid organic wastes for energy recovery with optimum utilization of facilities.     

Relationships between analytical methods utilized as tools in the evaluation of landfill waste stability

In this study, the refuse from 12 landfills of various ages ranging from fresh refuse to material 11 years old was collected, and changes in the bio-stability parameters were determined. The parameters measured included cellulose, lignin, biochemical methane potential (BMP) and volatile solids, along with plastics. These parameters, along with the cellulose to lignin ratio were compared to determine which were most indicative of the bio-stability of the refuse. Lignin and volatile solids measurements were affected by plastics in refuse samples. Plastics increased both lignin and volatile solids measurements by approximately 10%. Cellulose and volatile solids measurements correlated well with age, each other, and with BMP measurements and were therefore considered the best parameters to determine stability. Data for the Riverbend landfill, a landfill with a moisture content of 48%, which is similar to that of bioreactor landfills, showed that degradation was nearly complete after 5 years as indicated by low values for cellulose and BMP.     

Improved methodology to assess modification and completion of landfill gas management in the aftercare period

Municipal solid waste landfills represent the dominant option for waste disposal in many parts of the world. While some countries have greatly reduced their reliance on landfills, there remain thousands of landfills that require aftercare. The development of cost-effective strategies for landfill aftercare is in society’s interest to protect human health and the environment and to prevent the emergence of landfills with exhausted aftercare funding. The Evaluation of Post-Closure Care (EPCC) methodology is a performance-based approach in which landfill performance is assessed in four modules including leachate, gas, groundwater, and final cover. In the methodology, the objective is to evaluate landfill performance to determine when aftercare monitoring and maintenance can be reduced or possibly eliminated. This study presents an improved gas module for the methodology. While the original version of the module focused narrowly on regulatory requirements for control of methane migration, the improved gas module also considers best available control technology for landfill gas in terms of greenhouse gas emissions, air quality, and emissions of odoriferous compounds. The improved module emphasizes the reduction or elimination of fugitive methane by considering the methane oxidation capacity of the cover system. The module also allows for the installation of biologically active covers or other features designed to enhance methane oxidation. A methane emissions model, CALMIM, was used to assist with an assessment of the methane oxidation capacity of landfill covers.