Municipal Solid Waste Stabilization Research Articles

Evaluation of bioplastics biodegradation under simulated landfill conditions.

Bioplastics that are generated from renewable sources have been regarded as an alternative to conventional plastics. Polylactic acid (PLA) is one of the mostly produced bioplastics because of its long shelf life for various applications. Even though bioplastics have drawn attention recently, their ultimate fate in landfills is still unknown. In this study, a standardized laboratory-scale lysimeter experiment was performed for the simulation of landfill conditions in order to evaluate the biodegradability of PLA during municipal solid waste stabilization. The reactors were loaded with municipal solid waste (MSW) taken from an operating landfill, certified PLA cups, and seed sludge. Various phases of landfill stabilization were simulated; hence, the reactors were operated under aerobic, semi-aerobic, and anaerobic conditions, respectively. Throughout the operation, both leachate and biogas generation in the reactors were regularly monitored. At the end of each phase, bioplastic cups were removed from the reactors, gently cleaned, weighed, and examined under a scanning electron microscope (SEM). The experimental results indicated that bioplastics did not undergo significant biodegradation during the first two stabilization phases (aerobic and semi-aerobic). On the other hand, it was observed that the cups were much softer and whiter at the end of the anaerobic phase. The weight of cups decreased by 12.8% on average, and their surfaces were prominently damaged after the completion of the last phase indicating the potential signs of biodegradation.

Lime sludge assisted anaerobic bioreactor landfilling of municipal solid waste for enhanced leachate stabilization and bioenergy yield

Bioreactor landfilling even being advanced technology for enhanced stabilization of municipal solid waste (MSW), often suffers with adverse acidogenic conditions. Such conditions reinforce poor leachate stabilization, and reduced biomethane yield. This work attempts to counter the challenges of adverse MSW landfilling conditions through incorporation of waste alkaline sludge from paper industry. The amendment in anaerobic bioreactor landfilling of MSW was practiced by adding lime sludge (LS) with MSW in three distinct proportions: 20 g LS/kg MSW (LS100), 50 g LS/kg MSW (LS250) and 100 g LS/kg MSW (LS500), keeping LS0 as control. Periodic leachate and biomethane analysis showed benefits of proportionate LS addition. The control reactor often experienced leachate ponding and inhibitory conditions for anaerobic digestion. However, reactor LS250 achieved highest decrease in leachate organic strength removal (76.47 %) and biomethane production (8.315 L) over the period of landfilling. The pH and volatile fatty acids (VFAs) were in coordination with LS proportions. The LS addition beyond 100 g LS/kg MSW (LS500) could decrease the leachate pollution removal and biomethane yield. Finally, the Gompertz growth model showed excellent fit (R2 >0.997) to recorded biomethane. The study expands the scope of utilizing similar sludges for amendment of existing landfilling practices for efficient bioconversion of organic fractions of MSW.

Impact of Leachate Recirculation on the Stabilization of Municipal Solid Waste in Anaerobic Bioreactors of Different Compositions

The aim of the current study is to determine the impacts of leachate recirculation on the degradation of three compositions of municipal solid waste in anaerobic bioreactors. The study was completed by using six columns with equal volume (0.042m3) containing different densities and compositions of solid waste, in order to follow waste degradation over a limited time. Three compositions of waste were studied: simulated fresh waste of standard composition, simulated fresh waste of fermentable composition, and actual aged waste. Measurements of the significant parameters including pH, leachate conductivity, Chemical Oxygen Demand (COD), and waste settlement, were carried out. The quantity of oxidized organic matter was increased by the leachate recirculation, and the degradation period was reduced by using leachate recirculation. After 300, 150, and 480 days, waste stabilization seemed to be reached for fresh, aged, and fermentable waste, whereas the organic content decreased to 650, 480, and 4000mg COD/L, respectively.

Effects of Environmental Factors on the Spatial Succession of the Bacterial Community in Municipal Solid-Waste Landfills

Secondary pollution control and rapid stabilization of municipal solid waste (MSW) landfills are closely associated with bacterial communities. The spatial variations in bacterial community structure and the environmental factors controlling it were studied by the 16S rRNA gene sequencing of MSW sampled at different depths in a large sanitary landfill (LSL) and a medium non-sanitary landfill (MNSL), respectively. The total nitrogen (TN) and total phosphorus (TP) content in the LSL and MNSL samples displayed a downward trend as the depth increased. However, the organic matter (OM) content followed the opposite trend. Diversity of microbes was highest in the middle layer of both the LSL and MNSL. Firmicutes and Proteobacteria were the dominant phylum both in the LSL and MNSL. In the LSL, the dominant bacteria genera succeeded from Psychrobacter, Pseudomonas to Clostridium, Savagea. However, in the MNSL, the genera succeeded from Uncultured, Pleomorphomonas to Hydrogenispora, Acetomicrobium. The type of landfill and the different environmental factors control the succession of the bacterial community in LSL and MNSL. The pH, OM, TN, and TP will change in the landfill as the landfill depth increased. The impact degree of landfill depth on pH, OM, TN, and TP content in the LSL was 15.3%, 16.1%, 4.9%, and 4.2%, respectively. These values were lower than those in the MNSL. In addition, depth and OM had the strongest correlations but no significance with the dominant bacteria both in the LSL (|Rdepth|average=0.48;|ROM|average=0.36) and MNSL (|Rdepth|average=0.51;|ROM|average=0.36). This indicated that bacterial community succession was mainly dependent on space, time, and MSW characteristics in different types of landfills.

Effect of geometry and material of municipal solid waste landfills on seismic response

The stability of municipal solid waste (MSW) landfills is a significant environmental concern. The performance of landfills during earthquakes should be evaluated to ensure their stability. The geometry and material types of MSW landfills are the main factors affecting their seismic response. In this study, the individual and coupled impact of these factors is investigated using numerical analyses. Amplification factors (AFs = Accsurface/Accbase) are investigated for six common MSW landfill types, namely canyon type, hill type, side-hill types 1 and 2 and stepped-base types 1 and 2. The results show that landfill types have significantly different behaviours due to their geometry and waste material properties. For low stiffness contrasts, the stepped-base landfill type has the minimum and the hill type experiences the maximum AF, 1.74 and 3.53, respectively. However, for high stiffness contrasts, the canyon type has the minimum AF (0.46) due to the effect of damping and thickness of the waste. Therefore, the proper geometry of the MSW landfills should be designed for specific waste material properties according to the seismic response.

DecoMSW: A Methodology to Assess Decomposition of Municipal Solid Waste for Initiation of Landfill Mining Activities

Biochemical decomposition of municipal solid waste (MSW) in landfills leads to the generation of leachate, gases and humus substances. In this context, a methodology to assess D ecomposition of MSW, designated as DecoMSW, has been developed; based on a series of tests conducted on samples of the fresh MSW and those retrieved from the active bioreactor landfill (BLF) cells of age from 13 to 48 months. Furthermore, spatial and temporal variation in the (i) physical (composition) and (ii) chemical (pH, volatile solids, total organic carbon, elemental analysis, ammonium and nitrate-nitrogen, biomethanation potential, lignocellulosic content) characteristics of the MSW samples exhumed from the landfill have been established. Finally, these characteristics were correlated vis-à-vis the respective values of the fresh MSW. From this exercise, it has been observed that except for nitrate-nitrogen, all other chemical parameters of MSW decrease exponentially with time until 20 months, and beyond that, they remain constant, which is an indication of stabilization of MSW. In short, it has been demonstrated that DecoMSW is instrumental in assessing the state of decomposition of MSW with respect to time in the BLF and facilitates initiation of the landfill mining activities.

Greenhouse gas emissions from semi-aerobic bioreactor landfills with different vent-pipe diameters.

The emission patterns of three greenhouse gasses (GHGs), viz. CH4, CO2, and N2O from landfills, were examined on a lab scale. Three simulated semi-aerobic bioreactor landfills (SABL1, SABL2, SABL3), with respective vent-pipe inner diameters (φ) of 25, 50, and 75mm, were used to investigate their effect on the greenhouse effect (GHE) during the municipal solid waste (MSW) stabilization process. We found that the vent-pipe φ influenced both MSW degradation and GHG emissions, increasing the vent-pipe φ which improved the removal of carbon and nitrogen-based pollutants. The GHG emissions were 364, 356, and 309kg CO2 equivalents per ton of MSW from the SABL2, SABL1, and SABL3, respectively, during the operation of 465days. Of the three GHGs, CH4 influenced the GHE the most, contributing 72.53%, 79.17%, and 71.42% in SABL1, SABL2, and SABL3, respectively. In the same sequence, CO2 (14.87%, 14.06%, and 21.9%) and N2O (12.6%, 6.77%, and 6.69%) were the second and third contributors to the GHE, respectively. Considering the rapidly MSW stabilization and the mitigation of GHG emissions, a vent pipe with φ of 75mm in the SABL column (φ of 800mm) was suggested. Moreover, the GHG mitigation in the SABL should be implemented by prioritizing CH4 collection and oxidation. The results provided a technical guidance for GHG mitigation in MSW management.

Effects of leachate recirculation quantity and aeration on leachate quality and municipal solid waste stabilization in semi-aerobic landfills

Although sanitary landfilling currently effectively treats municipal solid waste (MSW) semi-aerobic bioreactor landfills (SABLs) are designed to accelerate biological processes and shorten the landfill stabilization phase. In this study, the effects of SABLs with the joint treatment of leachate recirculation and preaeration on landfill stabilization were determined by four landfill reactors, one anaerobically as a control, and three semi-aerobically with different leachate recirculation treatments (reactor I, II and III: 300 mL leachate, 600 mL leachate, and 600 mL aerated leachate per week, respectively). Results showed that reactor III had the highest removal rates of chemical oxygen demand (COD) and ammonia-nitrogen (NH 4 + -N), reaching 97% and 88%, respectively. Degradation of the organic substances could be described using an exponential attenuation model; the rates of COD, NH 4 + -N and biochemical oxygen demand (BOD 5 ) in the SABLs increased from 0.019, 0.018, and 0.035 to 0.029, 0.025, and 0.053 day −1 , respectively, when leachate recirculation quantity was increased and preaeration was applied. Finally, classification index evaluation revealed that reactor III had the lowest I value of 312, indicating that the combination of increasing leachate recirculation quantity and preaeration could positively affect the MSW stabilization phase. This finding provides experimental evidence for improving landfill management for accelerating MSW stabilization in SABLs. • Different leachate quantity and preaeration were applied in semiaerobic landfills. • Higher pollutant removal rates were in semi-aerobic than in anaerobic reactor. • Greater recirculation quantities and preaeration accelerated waste stabilization. • The classification index method was used to evaluate landfill stabilization.

Characterization of Variability of Unit Weight and Shear Parameters of Municipal Solid Waste

The safety and stability of municipal solid waste (MSW) slopes are governed by unit weight (γ), cohesion (c), and friction angle (ϕ) of the MSW. Variability associated with the unit weight, cohesion, and friction angle of MSW is a major problem in the design of landfills because it negatively affects the performance of the slope. Variability associated with these properties may trigger catastrophic slope failures. The reported studies on the reliability-based design of MSW landfills adopted either Gaussian or lognormal distributions based on a reasonable approximation. The limitations are apparent when a coefficient of variation (COV) is higher. The accuracy of reliability-based designs depends on the selection of best-fit continuous and extreme value distributions (such as Gumbel and Weibull) that can model a high degree of variability precisely. The present study has undertaken to propose a suitable statistical model that gives a better representation of variability by optimizing the statistical parameters. A high degree of variability associated with the unit weight, cohesion, and friction angle of MSW is also investigated. A novel approach is proposed to determine reliable continuous probability density functions (PDFs) that can be fitted to the database consisting of 184 sample points collected from the most comprehensive experimental studies reported in the literature. The best-fit PDFs are recommended by optimizing the mean and standard deviation such that errors associated with quantiles (Q­­–Q), percentiles (P–P), and cumulative distribution functions (CDFs) are as minimum as possible. This study signifies the selection of optimized PDFs for the representation of parameter variability, and it is proved that the probability of failure is either underestimated or overestimated considerably when other conventional PDFs are chosen. The recommended mean, COV, and PDF can be useful in the reliability-based design of engineered MSW landfills and for judging the performance of existing MSW slopes.

Leachate after aerobic stabilization of municipal solid waste supplemented by waste glycerine from saponification to improve biogas production during co-digestion

Co-digestion of leachate from aerobic stabilization of OFMSW (leachateOFMSW) with waste glycerine (WG) from saponification is a promising approach for municipal waste and wastewater treatment. The effect of feedstock composition on co-digestion efficiency was examined. Two feedstocks with different contents of WG (6%, 13%) were used, which affected the COD:TKN ratios in those feedstocks (60, 100). LeachateOFMSW provided nitrogen and the micro- and macroelements. In both feedstocks, the N–NH4:TKN ratio was low (0.08), indicating that the dominant form of nitrogen was organic nitrogen (Norg). Co-digestion was carried out in upflow anaerobic-sludge blanket reactors (37 ± 2 °C; OLR, 4 kg COD m−3 d−1).This process ensured highly effective COD removal (over 97%). At a feedstock COD:TKN ratio of 60, specific biogas production (SBP) was ca. 0.22 m3 kg−1 COD, and methane content, 61.6%. Increasing the COD:TKN ratio to 100 significantly increased SBP to ca. 0.36 m3 kg−1 COD, but reduced biogas quality (54.2% CH4). Although Norg had to be ammonified to ammonium because of the low N–NH4:TKN ratio in the feedstocks, the ammonium concentration in the post-processing wastewater remained low. Moreover, the low ammonium concentrations meant that the pH (8.8) did not have a toxic effect on anaerobic co-digestion (free ammonia concentrations were merely ca. 28 and 5.5 mg L−1, respectively). However, at higher feedstock COD:TKN ratios than those tested, ammonium could be exhausted, which would impede methane production. These results indicate that WG is an effective co-substrate for leachateOFMSW if an appropriate amount of WG is added to the feedstock.

Scaling up laboratory column testing results to predict coupled methane generation and biological settlement in full-scale municipal solid waste landfills

Prediction of methane (CH4) generation and settlement of biodegrading municipal solid waste (MSW) is of primary interest to landfills aiming at biogas recovery for energy generation and MSW stabilization. We investigate these two concurring processes using datasets from 35 laboratory column tests and 8 pilot- and full-scale landfill cells available in the literature. We fit the datasets using three CH4 generation models, i.e., conventional first-order decay (FOD) model, coupled FOD model, and coupled Gompertz model. The latter two models are proposed in this study which couple CH4 generation with biological settlement strain (εB) instead of elapsed time. Each model requires only four to five input parameters which can be reasonably estimated a priori based on the initial conditions of the MSW and landfills. The performances of the models are compared using jackknife resampling approach and normalized root-mean-square error (NRMSE) values. The coupled Gompertz model results in on average 50% lower NRMSE when predicting the time-dependent CH4 generation in all the datasets compared to the other two models. Thus, we demonstrate that CH4 generation from biodegrading MSW in landfills can be better predicted using the corresponding εB than the elapsed time.

A constitutive model for municipal solid waste incorporating bounding surface plasticity and reinforcing effect

Seismic stability of municipal solid waste (MSW) landfills is of vital importance and increasingly encouraged to be analyzed through numerical modeling where a rational definition of the stress-strain relationship of MSW is essentially required. The complicated constituents and existence of fibrous materials lead to mechanical behaviors totally different from general soils. In this study, a constitutive model is proposed to describe the dynamic response of MSW. This model is based on the double-phase assumption, i.e. the behaviors of the MSW whole are governed by the basic and fibrous phase. The basic phase is described with a bounding surface plasticity model considering the degradation effect under dynamic loadings, and the fibrous phase is described with a pressure-dependent elastic model. An explicit integration algorithm with automatic error control is applied to solve it. The coupling of these two constitutive models facilitates the continuous development of effective stress path over the critical state line, which reflects the reinforcing effect of fibrous materials. Furthermore, the compression of MSW particles is considered for undrained conditions, enabling the accurate calculation of effective stress. This model is verified through comparison with triaxial test results and its features are demonstrated through parametric studies and application in specific problems.

A pilot-scale comparative study of bioreactor landfills for leachate decontamination and municipal solid waste stabilization

Many studies have sought to optimize operation parameters and enhance the treatment capacity of bioreactor landfills (BL) under ideal laboratory conditions. At pilot scale, conclusions drawn from laboratory-scale experiments will be different due to variations in actual landfill composition and changes in environmental conditions. However, comparative pilot-scale studies of traditional anaerobic landfills (AnL) and BLs are rare. In this study, three pilot-scale landfills, including an AnL, anaerobic BL (AnBL) and semi-aerobic BL (SABL), were monitored to examine the difference in performance at different scales and among types of landfills. Settlement amount followed the order SABL (25.45 cm) > AnBL (18.67 cm) > AnL (14.38 cm). Decomposition of organic matter (i.e., volatile fatty acids) was more rapid in SABL than in the other landfills and no hydrolytic acidification period was observed. Therefore, among the three landfills, SABL entered the methanogenic stage in a much shorter time and MSW stabilization was accelerated due to this landfill’s unique combination of aerobic-anoxic-anaerobic ambient. In addition, NH4+–N concentration in leachate from the SABL (~19.96 mg/L) was substantially lower than from AnL (338.28 mg/L) and AnBL (233.22 mg/L), and SABL leachate exhibited the least chloride pollution risk. This study provides theoretical support and strong evidence for using SABLs to treat MSW in practical applications.

Geoecological Assessment of the Сondition of Municipal Solid Waste Landfills

Methods for assessing the state of landfills for municipal solid waste (MSW) at various stages of the life cycle and their impact on the environment are considered. The results of a study assessing the degree of stability of waste of different periods of disposal according to physicochemical, biochemical, thermal parameters are presented. Based on the results of physicochemical and biochemical parameters, the stages of biodegradation and the degree of decomposition of the waste are determined relative to the disposal period of the waste. It was proposed to assess the stability of waste in an array of landfill by a number of thermal parameters of waste: the magnitude of thermal effects, the temperature of heat generation peaks, the rate of mass loss, the ratio of specific enthalpies of dry matter (DM) and organic dry matter (ODS). A method for integrated assessment of the stability of MSW in an array of landfill was developed, including the establishment of waste stability classes, boundary values of stability indicators and periods of their achievement. The method is intended for geoecological assessment of the condition of disposal of MSW and justify the choice of technical measures to reduce emissions.

Effect of Leachate Recirculation on Biological Stability of Municipal Solid Waste Under Simi-Arid Conditions

The present study was conducted to monitor the quality of leachate generated from solid waste landfills operated under different mode over a period of 335 days using a bench scale lysimeters. Sixty six kg waste sample reflecting the typical municipal solid waste (MSW) streams generated in Al-Diwaniyah city open dump was used to fill both sanitary and bioreactor lysimeters to study the influence of leachate recirculation on quality of leachate in landfills located in semi-arid areas. Leachate quality is frequently monitored in terms of pH, electrical conductivity (EC), chemical oxygen demand (COD), chloride, and total Kjeldahl nitrogen (TKN). The results show that pH and electrical conductivity values were clearly fluctuated in the rainy season, while in the dry season the values tend to decrease steadily with a close correlation between the chloride and electrical conductivity parameters. The study reveals that bioreactor landfill with leachate recirculation appears to be the most effective option in the removal of organic matter by 98% removal efficiency compared with 58% removal efficiency in a sanitary landfill. The main difference between recirculation and non-recirculation options is determined through leachate quality.

Conventional and fourier transform infrared characterization of waste and leachate during municipal solid waste stabilization

Solid waste and leachate samples from bench-scale anaerobic bioreactors and flushing bioreactors (FBs), containing mature waste were characterized using Fourier Transform Infrared Spectroscopy (FTIR) to provide a better understanding of the changes in waste characteristics when waste transitions from mature to stabilized. Humic acid (HA) extracted from mature waste and waste removed from the FBs were characterized using FTIR and 13C nuclear magnetic resonance. FBs were operated under three different treatment scenarios (flushing with clean water, recirculation of leachate treated by chemical oxidation, and recirculation of leachate treated by chemical oxidation with waste aeration. FTIR spectra of FB waste and leachate supported the stabilization of waste that occurred after the additional treatment. There was a shift in the dominance of organic to inorganic functional groups when compared to changes in conventional parameters that aligned with published values on waste stability. HA extracted from the mature waste were dominated by aliphatic carbon and aromatic carbon was less intense. Treatment by flushing resulted in a decrease in aliphatic carbon and an increase in aromatic carbon. HA extracted from reactors with oxidized leachate recirculation and aeration decreased in aliphatic carbon content, with minimal change in aromatic carbon. Therefore, the additional treatment did not result in an increase in the reactivity potential of the HA which aligns with FTIR and principal component analysis. Results suggest that spectroscopic techniques could be used to assess the stability of waste samples as opposed to more time-consuming analyses.

Modeling Coupled Hydro-Bio-Mechanical Processes in Bioreactor Landfills: Framework and Validation

Bioreactor landfills using leachate recirculation in municipal solid waste (MSW) undergo complex interrelated hydraulic, mechanical, and biochemical processes. In this study, the authors present a mathematical framework that combines and solves together a hydraulic model, a biodegradation model, and a mechanical model to simulate and predict the coupled hydro-bio-mechanical behavior of MSW in bioreactor landfills. The mathematical framework was implemented in Fast Lagrangian Analysis of Continua (FLAC), a finite difference code. The hydraulic model was a two-phase flow model where the fluid flow was governed by Darcy’s law while the saturated–unsaturated hydraulic behavior was governed by a soil-water retention model. The mechanical behavior of the MSW was evaluated by a plane-strain explicit formulation of the Mohr-Coulomb constitutive model, which accounted for concurrent changes in the MSW properties as a result of the MSW degradation. The MSW decomposition was modeled as a first-order decay kinetics biodegradation model similar to the LandGEM model used by the United States Environmental Protection Agency. The coupled mathematical framework was validated with a published large-scale laboratory experiment and a field-scale experiment. It was applied to simulate the coupled behavior of a typical bioreactor landfill cell undergoing hydro-bio-mechanical interactions. Overall, the study shows that the proposed mathematical framework accounted for both the spatial and temporal changes in the geotechnical properties of the MSW, including the extent of degradation, and predicted the landfill settlement and MSW stabilization time for a typical bioreactor landfill configuration subjected to coupled hydro-bio-mechanical processes. In addition, some of the limitations and key challenges associated with the numerical model are highlighted.

CFD modeling of hydro-biochemical behavior of MSW subjected to leachate recirculation.

The most commonly used method of operating landfills more sustainably is to promote rapid biodegradation and stabilization of municipal solid waste (MSW) by leachate recirculation. The present study is an application of computational fluid dynamics (CFD) to the 3D modeling of leachate recirculation in bioreactor landfills using vertical wells. The objective is to model and investigate the hydrodynamic and biochemical behavior of MSW subject to leachate recirculation. The results indicate that the maximum recirculated leachate volume can be reached when vertical wells are set at the upper middle part of a landfill (H W/H T = 0.4), and increasing the screen length can be more helpful in enlarging the influence radius than increasing the well length (an increase in H S/H W from 0.4 to 0.6 results in an increase in influence radius from 6.5 to 7.7m). The time to reach steady state of leachate recirculation decreases with the increase in pressure head; however, the time for leachate to drain away increases with the increase in pressure head. It also showed that methanogenic biomass inoculum of 1.0kg/m3 can accelerate the volatile fatty acid depletion and increase the peak depletion rate to 2.7 × 10-6kg/m3/s. The degradation-induced void change parameter exerts an influence on the processes of MSW biodegradation because a smaller parameter value results in a greater increase in void space.

Seismic Translational Failure Analysis of MSW Landfills Using Modified Pseudo-Dynamic Approach

For landfills situated in regions of high seismicity, seismic inertial forces may be a triggering factor for the translational stability of municipal solid waste (MSW) landfills. This paper applies a modified pseudodynamic method to the seismic translational stability analysis of landfills. In the present study, a closed-form solution is proposed to obtain the factor of safety and the yield acceleration coefficient for a typical side-hill-type landfill resting on a rigid base using limit equilibrium method. The acceleration ratio obtained in the present study compares well with that obtained using popular ground response analysis software for a given set of input parameters. The acceleration ratio is the ratio of seismic acceleration at the top of the landfill to the seismic acceleration at the base of the landfill. From parametric study, it is observed that the landfill is vulnerable to seismic damage in low-frequency input motions. At low frequencies, the seismic inertia force is in phase at all depths. The seismic force acting on the landfill mass is reduced at higher frequencies, where landfill mass is entering into higher modes of vibration, where some portion of landfill is moving in one direction and the remaining portion is moving in opposite direction. The results obtained are compared with the available literature sharing the same input parameters. The values of the factor of safety obtained in the present study are higher than those calculated using pseudostatic and pseudodynamic approaches. For the input parameters assigned in the comparison, the landfill mass in the third mode of vibration is the reason for the greater values of the factor of safety. Material damping may be also a reason for the higher factor of safety values. (C) 2017 American Society of Civil Engineers.

Application of landfill treatment approaches for stabilization of municipal solid waste

This research sought to compare the effectiveness of three landfill enhanced treatment approaches aimed at removing releasable carbon and nitrogen after anaerobic landfilling including flushing with clean water (FB 1), leachate recirculation with ex-situ treatment (FB 2), and leachate recirculation with ex-situ treatment and in-situ aeration (FB 3). After extensive treatment of the waste in the FB scenarios, the overall solids and biodegradable fraction were reduced relative to the mature anaerobically treated waste. In terms of the overall degradation, aeration did not provide any advantage over flushing and anaerobic treatment. Flushing was the most effective approach at removing biodegradable components (i.e. cellulose and hemicellulose). Leachate quality improved for all FBs but through different mechanisms. A significant reduction in ammonia–nitrogen occurred in FB 1 and 3 due to flushing and aeration, respectively. The reduction of chemical oxygen demand (COD) in FB 1 was primarily due to flushing. Conversely, the reduction in COD in FBs 2 and 3 was due to oxidation and precipitation during Fenton’s Reagent treatment. A mass balance on carbon and nitrogen revealed that a significant fraction still remained in the waste despite the additional treatment provided. Carbon was primarily converted biologically to CH4 and CO2 in the FBs or removed during treatment using Fenton’s Reagent. The nitrogen removal occurred through leaching or biological conversion. These results show that under extensive treatment the waste and leachate characteristics did meet published stability values. The minimum stability values achieved were through flushing although FB 2 and 3 were able to improve leachate quality and solid waste characteristics but not to the same extent as FB 1.