Leachate Recirculation Research Articles

Quantification of leachate discharged to groundwater using the water balance method and the Hydrologic Evaluation of Landfill Performance (HELP) model

Landfills are a source of groundwater pollution in Gaza Strip. This study focused on Deir Al Balah landfill, which is a unique sanitary landfill site in Gaza Strip (i.e., it has a lining system and a leachate recirculation system). The objective of this article is to assess the generated leachate quantity and percolation to the groundwater aquifer at a specific site, using the approaches of (i) the hydrologic evaluation of landfill performance model (HELP) and (ii) the water balance method (WBM). The results show that when using the HELP model, the average volume of leachate discharged from Deir Al Balah landfill during the period 1997 to 2007 was around, 6800 m3/year. Meanwhile, the average volume of leachate percolated through the clay layer was 550 m3/year, which represents around 8% of the generated leachate. Meanwhile, the WBM indicated that the average volume of leachate discharged from Deir Al Balah landfill during the same period was around 7660 m3/year--about half of which comes from the moisture content of the waste, while the remainder comes from the infiltration of precipitation and re-circulated leachate. Therefore, the estimated quantity of leachate to groundwater by these two methods was very close. However, compared with the measured leachate quantity, these results were overestimated and indicated a dangerous threat to the groundwater aquifer, as there was no separation between municipal, hazardous and industrial wastes, in the area.

Estimating Moisture Content of Landfilled Municipal Solid Waste without Drilling: Innovative Approach

AbstractThe understanding of moisture content distribution within municipal solid waste (MSW) in a landfill due to leachate recirculation plays an important role in designing and optimizing the operation of a leachate recirculation system. Electrical resistivity imaging (ERI) is one of the many methods that have been used in the field to monitor the moisture distribution and moisture movement within the MSW in a landfill. The objective of this paper is to develop a correlation between electrical resistivity and moisture content of waste so that in situ moisture content of MSW can be determined without direct sampling and laboratory testing. To achieve this objective, an experimental program was developed to study the variation of electrical resistivity of MSW with moisture content and other factors that affect resistivity. The electrical resistivity of fresh MSW samples collected from the working face and partially degraded landfilled MSW samples collected from closed sections of the landfill using a buck...

Aerobic in situ stabilization of Landfill Konstanz Dorfweiher: Leachate quality after 1 year of operation

Modern landfill understanding points out controlled operation of landfills. Emissions from landfills are caused mainly by anaerobic biodegradation processes which continue for very long time periods after landfill closure. In situ landfill stabilization aims controlled reduction of emissions towards reduced expenditures as well as aftercare measures. Since April 2010, a new in situ stabilization technique is being applied at a pilot scale landfill (BAIV) within Landfill Konstanz Dorfweiher. This new method utilizes intermittent aeration and leachate recirculation for waste stabilization. In this study, influence of this technique on leachate quality is investigated. Among many other parameters, leachate analyses were conducted for COD, BOD5, NH4–N, NO2–N, NO3–N, TKN and chloride besides continuously on site recorded pH, electrical conductivity and oxidation–reduction potential (ORP). Results from leachate quality analyses showed that biological activity in the landfill was accelerated resulting in initial higher leachate strength and reduced emission potential of landfill. During full scale in situ aeration, ambient conditions differ from optimized laboratory scale conditions which mainly concern temperature increase and deficient aeration of some landfill parts (Ritzkowski and Stegmann, 2005). Thus, as a field application results of this study have major importance on further process optimization and application.

Design considerations for a farm-scale biogas plant based on pilot-scale anaerobic digesters loaded with rice straw and piggery wastewater

Two pilot-scale (1 m3) digesters filled with untreated rice straw and co-digested with raw pig wastewater were operated to obtain design parameters for a farm-scale biogas plant. Both digesters contained 50 kg of dry straw mixed with diluted pig wastewater to create dry digestion conditions (20% TS) and operated for 189 days with leachate recirculation. Digester A was designed for optimum performance (150 L of pig wastewater and mesophilic temperatures) while Digester B was designed to establish minimum inputs (60 L of pig wastewater at ambient temperatures). The pig wastewater provided sufficient buffering capacity to maintain appropriate pH values (between 7.0 and 8.1) and nutrient balances (TOC to TKN ratios of 20 in Digester A and 32 in Digester B). Total biogas production was 22,859 L in Digester A and 1420 L from Digester B, resulting in specific methane yields of 231 and 12 L CH4/kgVS added, respectively. Gas production in Digester A was directly correlated with temperature, but the overall lack of methanogenic activity was caused primarily by the reduced wastewater volume. Two theoretical farm-scale scenarios (considering both untreated and pretreated rice straw) were developed for a 100-ha rice farm. Either scenario can produce 100,000 m3CH4 per year, yielding 328 MWh. Major differences including heat input, space requirements, loading frequency, digester volume, engine size, wastewater quantities, and additives are quantitatively defined. The appropriate choice for a farm-scale operation is the simplest model using untreated rice straw without additives, although six times more heat and twice as much reactor volume is required.

Enhanced solid waste stabilization in aerobic landfills using low aeration rates and high density compaction

Historically, municipal solid waste landfills have been designed and operated as storage facilities with suboptimal degradation under anaerobic conditions resulting in slow waste stabilization, gaseous emissions and leachate formation. This article examines the aerobic bioreactor alternative combining the recirculation of high strength leachate [chemical oxygen demand (COD): 89,000-95,600 mg/l; biological oxygen demand (BOD): 75,700-80,000 mg/l)] with low aeration rates (0.0125-0.05 l/min.kg) at high initial waste compaction (657-875 kg/m3) to promote and control biodegradation of solid waste in laboratory-scale columns (diameter = 60 cm, height = 1 m). Low aeration rates coupled with high initial density demonstrated improved performance with increased levels of stabilization with COD and BOD attenuation reaching up to 96%, final C:N ratio of 25 and waste settlement up to 55%.

Enhanced leachate recirculation and stabilization in a pilot landfill bioreactor in Taiwan

This study focused on the treatment of municipal solid waste (MSW) by modification and recirculation of leachate from a simulated landfill bioreactor. Hydrogen peroxide was added to recirculated leachate to maintain a constant oxygen concentration as the leachate passed again through the simulated landfill bioreactor. The results showed that leachate recirculation increased the dissolved oxygen concentration in the test landfill bioreactor. Over a period of 405 days, the biochemical oxygen demand (BOD(5)) in the collected leachate reduced by 99.7%, whereas the chemical oxygen demand (COD) reduced by 96%. The BOD(5)/COD ratio at the initial stage of 0.9 improved to 0.09 under aerobic conditions (leachate recirculation with added hydrogen peroxide) compared with the anaerobic test cell 0.11 (leachate recirculation alone without hydrogen peroxide). The pH increased from 5.5 to 7.6, and the degradation rate of organic carbon was 93%. Leachate recirculation brings about the biodegradation of MSW comparatively faster than the conventional landfill operation. The addition of a constant concentration of hydrogen peroxide was found to further increase the biodegradation. This increased biodegradation rate ultimately enables an MSW landfill to reach a stable state sooner and free up the land for further reuse.

Moisture Distribution in Bioreactor Landfills: A Review

Municipal solid waste (MSW) generation has been increasing every year in the United States and other parts of the world, as recent studies document. Therefore, landfill design, operations and treatment play an important role in managing MSW. Bioreactor landfills were recently introduced as a mechanism by which to overcome the issue of prolonged waste biodegradation in the conventional landfill. In a bioreactor landfill, the leachate that is generated is collected from the leachate collection removal system and then recirculated into the landfill to increase the moisture content of MSW. That increased moisture content then helps to distribute the microbes and nutrients required for suitable MSW biodegradation. However, the body of knowledge on the effective operation of bioreactor landfill is limited. Few studies have documented the performance of bioreactor landfill in the context of moisture distribution in the MSW. Both improper leachate recirculation and an empirical approach to the design of leachate recirculation systems (LRS) have led to a large variation in the performance of these systems. A detailed literature review on moisture distribution in bioreactor landfills is reported in this paper. The studies reported in the literature review are divided into laboratory studies, field studies, combined laboratory and field studies, and mathematical models. Based on the literature review, it is evident that the LRS design is based on either exceptionally limited information from laboratory and field observations or the insufficient or improper selection of MSW properties. Further, the assumption of that MSW is homogeneous isotropic and ignoring the effect of unsaturated hydraulic properties and effect of temperature can lead to large variation in the actual performance of bioreactor landfill.

Stabilisation of biodried municipal solid waste fine fraction in landfill bioreactor

The biodrying process of solid waste is a pre-treatment for the bio-stabilisation of the municipal solid waste. This study aims to investigate the fate of the municipal solid waste fine fraction (MSWFF) resulting from a biodrying treatment when disposed in landfills that are operated as bioreactors. Biodried MSWFF was apparently stable due to its low moisture content that slows down the microbial activity. The lab-scale anaerobic bioreactors demonstrated that a proper moisture content leads to a complete biodegradation of the organic matter contained in the biodried MSWFF. Using a pilot-scale landfill bioreactor (LBR), MSWFF stabilisation was achieved, suggesting that the leachate recirculation could be an effective approach to accomplish the anaerobic biodegradation and biostabilisation of biodried MSWFF after landfilling. The biostabilisation of the material resulting from the LBR treatment was confirmed using anaerobic and aerobic stability indices. All anaerobic and aerobic indices showed a stability increase of approximately 80% of the MSWFF after treatment in the LBR. The similar values of OD7 and BMP stability indices well agree with the relationship between the aerobic and anaerobic indices reported in literature.

Microorganisms in landfill bioreactors for accelerated stabilization of solid wastes

Landfill bioreactors (LBRs) with management of leachate and biogas have presented numerous advantages such as accelerated stabilization of solid wastes, reduced amount of leachate, and in situ leachate treatment. Such advantages have minimized environmental risks, have allowed extension of the useful life of the landfill site, and have fostered cost reduction. LBRs of three types have been developed using both anaerobic and aerobic modes: anaerobic, aerobic, and hybrid. Microorganisms in landfills cause various reactions related with organic fractions and heavy metals. Such functions have been stimulated in LBRs by recirculation of leachate with or without aeration. To date, most studies of microorganisms in LBRs have analyzed bacteria and archaea based on 16S rRNA genes and have analyzed fungi based on 18S rRNA genes from a taxonomical viewpoint. Indicator genes for specific functions in LBRs such as nitrification, denitrification, and methane production have also been monitored. The population dynamics of microorganisms in LBRs have been partially clarified, but the obtained data remain limited because of highly heterogeneous features of solid wastes inside LBRs. Systematic monitoring of microorganisms should be established to improve LBR performance.

Optimization of landfill leachate management in the aftercare period

The management of sanitary landfills after closure is an important engineering, economic and sustainability issue and is referred to as the greatest unresolved landfill challenge. Most sanitary landfills are operated according to the dry tomb principle, resulting in aftercare periods of hundreds of years. To study landfill body behaviour, long-term leachate emissions were studied with anaerobic landfill simulators, and a forecast model was developed targeting the behaviour of NH(4)-N, COD and chlorides as a function of temperature and the L/S-ratio (liquid-to-solid). It was found that NH(4)-N is the decisive factor in leachate management, requiring the highest L/S-ratio (around 6) to meet the direct discharge limit values. Various scenarios were constructed to find optimal leachate management strategies both in large (waste height H = 25 m) and medium-sized landfills (H = 10 m) with corresponding temperature ranges. The results show that by minimizing the aftercare period length with leachate pre-treatment and recirculation, both sustainability and economic benefits can be achieved. The results provide new views on how to manage the long-term leachate aftercare problem. In the case of large landfills, further efforts are needed to reach stabilization within a reasonable time frame.

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 0.47yr−1 and 0.21yr−1. These results expectedly exceeded the United States Environmental Protection Agency’s rate constants for dry and conventional landfills (0.02–0.05yr−1), but they are comparable to wet landfill rate constants derived using landfill gas data (0.1–0.3yr−1).

Possible interactions between recirculated landfill leachate and the stabilized organic fraction of municipal solid waste

The stabilized organic fraction of municipal solid waste (SOFMSW) is a product of the mechanical/biological treatment (MBT) of mixed municipal solid waste (MMSW). SOFMSW is considered a 'grey' compost and the presence of pollutants (particularly heavy metals) and residual glass and plastic normally prevents agricultural use, making landfills the typical final destination for SOFMSW. Recirculation of leachate in landfills can be a cost-effective management option, but the long-term sustainability of such a practice must be verified. Column tests were carried out to examine the effect of SOFMSW on leachate recirculation. The results indicate that organic matter may be biologically degraded and metals (copper and zinc) are effectively entrapped through a combination of physical (adsorption), biological (bacterial sulfate reduction), and chemical (precipitation of metal sulfides) processes, while other chemicals (i.e. ammonia nitrogen and chloride) are essentially unaffected by filtration through SOFMSW.

Effect of various leachate recirculation strategies on batch anaerobic digestion of solid substrates

Various leachate recirculation strategies were applied to a batch-wise operated solid-phase digestion system in laboratory-scale tests. Comparative experiments with both continuous and intermittent leachate recirculation revealed no advantages of a continuous flow. Results suggest that leachate recirculation should not be carried out continuously during process initialisation when methanogenesis is the rate-limiting step. Continuous watering resulted in the accumulation of Volatile Fatty Acids (VFA) during process start-up. In addition, no need for continuous water circulation was found for the following digestion process when hydrolysis was rate-limiting. Even in the absence of liquid recirculation, degradation was only slightly retarded when the biomass moisture content was adjusted.

Root Analogous Solid Waste Management System (RA-MSW for Biocells)

Root Analogous Municipal Solid Waste System “RA-MSW” is a novel management system that manages waste, biogas, and leachate in bioreactor landfill. Different than conventional disposal at landfills, waste is penetrated by synthetic roots that serve dual mission for biogas collection and leachate recirculation. RA-MSW roots are permeable hydropho- bic polymer material that are formed on-place or prefabricated at factory from recyclable material available on the dumping area. Since the material is hydrophobic, it does not contain water in the voids providing more space for gas transport and collection. The roots are also interchangeably used for leachate recirculation where the parameters of wa- ter content, nutrients, pH, and temperature are optimized to enhance biogas production simultaneously with leachate treatment. RA-MSW provides new approach of waste management and control; it has new virtues of landfill operation; new material medium for biogas collection; new biocell design configuration; new manipulation for leachate and biogas. The approach adds new merits for solid waste management, bio-energy utilization, and the concept of 5 R’s cycle for MSW management.

Intelligent MSW Biocell Approach for Efficient Methane Production

The aim of this research is to provide approach to enhance methane production and to convert CO2 released into methane via anaerobic degradation. Despite CH4 has more global warming potential than CO2 but it is less available in the environment and it has fuel value. This research suggests approach that methane is being stimulated and carbon dioxide is being converted to methane. The methane enhancement herein is achieved via technical and intelligent processes. The technical processes entail leachate and carbon dioxide recirculation. The recirculated leachate is controlled via fuzzy intelligent system that acquires values of abiotic factors such as C:N:P, pH, temperature, and moisture content, and then these values are introduced to trained fuzzy system to decide the value of methane production quality. The fuzzy logic proceeds in systematic sequence as input, inference through rules, and output. If the fuzzy logic output decision indicates bad production, then the value of aboitic factors are dynamically altered with optimized combination of values. Carbon dioxide is being re-circulated in order to convert it biologically to methane by hydrogenotrophic methanogens. The hydrophobic permeable membranes are used as planes through the solid waste. These selective membranes are used to separate biogas and to have smooth and fast transfer of biogas from waste to the storage. The approach of this research is believed to be as a new generation of sustainable green bio-fuel biocells.

Instrumented large scale subsurface liquid injection model for bioreactor landfills

Abstract Bioreactor landfills are complex unsaturated systems where liquids are injected at relatively high pressures in on/off dosing cycles. In order to simulate hydraulic scenarios to improve understanding of leachate recirculation systems for landfills, 86 cm long by 30 cm wide by 56 cm tall unsaturated flow physical model was designed and fabricated. A permeable blanket was installed in the model to inject water. The blanket was 50 cm long × 30 cm wide × 2 cm thick and was made up of pea gravel. Uniform fine and coarse sands, which were thoroughly characterized for their hydraulic properties, were used in separate experiments to simulate waste. Pressure transducers and water content sensors were embedded in the model to monitor the migration of injected water in the blanket and in the underlying soils. Water was injected at flow rates ranging from 20 to 150 cm3/s in continuous and on/off modes to achieve transient and steady-state conditions. The responses of the pressure transducers embedded in the blanket in the model mimicked the responses of the pressure sensors embedded in an instrumented field-scale (55 m long × 9 m wide × 0.15 m thick) permeable blanket made up of crushed recycled glass used for recirculation of leachate at a municipal solid waste landfill. The effect of entrapped air present in the voids was evident from greater pressures developed during wetting which dissipated as the entrapped air escaped the system. This finding highlights the need to use of dual phase models for simulating pressures in bioreactor landfills.

Waste stabilization mechanism by a recirculatory semi-aerobic landfill with the aeration system

The main purpose of this research is to clarify and compare the mechanism of waste stabilization by a recirculatory semi-aerobic landfill with the aeration system. Our research is proposing the semi-aerobic landfill system for developing countries because of the simple and low-cost technology for the final disposal. Moreover, this system with leachate recirculation can be a more effective system for waste stabilization because of the improvement of leachate quality as an organic pollutant and, also, nitrogen removal. In this research, five different systems of landfill (Ae: aerobic, An: anaerobic, Se: semi-aerobic, SeR: recirculatory semi-aerobic landfill, and SeRA: recirculatory semi-aerobic landfill with aeration system) are compared with lysimeters which are 1 m high with a diameter of 0.3 m. The results of the leachate quality shows that the leachate treatment effect of the SeRA system can be observed to be as high as the Ae system. To determine the mechanism of this process, all lysimeters are dismantled after 1,100 days in the experimental period and the waste composition, the dissolution test, the mass balance of carbon and nitrogen, the determination of bacterial counts, etc., were analyzed. In this research, it was proven that the SeRA system has an optimal leachate treatment effect that is the same as the Ae system. And, from the results of the mass balance of carbon and nitrogen, the SeR and SeRA systems show higher waste stabilization effectiveness and nitrogen removal than the other systems. Moreover, the number of the aerobic bacteria can be observed to be higher in the SeR and SeRA systems. To determine these results, the waste stabilization mechanism is considered by the results of leachate quality, the mass balance of carbon and nitrogen, and, also, the bacterial numbers.

Hydrologic evaluation of landfill performance (HELP) modeling in bioreactor landfill design and permitting

The practice of operating municipal solid waste landfills as bioreactor landfills has become more common over the past decade. Because simulating moisture balance and flow is more critical in such landfills than in dry landfills, researchers have developed methods to address this problem using the hydrologic evaluation of landfill performance (HELP) model. This paper discusses three methods of applying the HELP model to simulate the percolation of liquids added to landfill waste: the leachate recirculation feature (LRF), the subsurface inflow (SSI) feature, and additional rainfall to mimic liquids addition. The LRF is simple to use but may not be able to bring the landfill to bioreactor conditions. The SSI feature provides a convenient user interface for modeling liquids addition to each layer. The additional rainfall feature provides flexibility to the model, allowing users to estimate the leachate generation rate and the leachate head on bottom liner associated with daily variation in the liquids addition rate. Additionally, this paper discusses several issues that may affect the HELP model, such as the time of model simulation, layers of liquids addition, and the limitations of the HELP model itself. Based on the simulation results, it is suggested that the HELP model should be run over an extended period of time after the cessation of liquids addition in order to capture the peak leachate generation rate and the head on the liner (HOL). From the perspectives of leachate generation and the HOL, there are few differences between single-layer injection and multiple-layer injection. This paper also discusses the limitations of using the HELP model for designing and permitting bioreactor landfills.

Effects of Intermixed Soils and Decomposition on Hydraulic Conductivity of Municipal Solid Waste in Bioreactor Landfills

AbstractTo estimate the generated leachate and design of a leachate recirculation system, a clear understanding of the hydraulic conductivity of municipal solid waste with degradation, and the effects of intermixed cover soils, is necessary. Two sets of laboratory-scale bioreactor landfills were simulated and sampled at various phases of decomposition. The state of decomposition was quantified by methane yield, pH, and volatile organic content. The matrix structure of the degradable solid waste component was broken down because of decomposition. However, daily cover soil, a nondegradable constituent of municipal solid waste, remained constant. Therefore, interaction between daily cover soil and municipal solid waste particles are expected to affect hydraulic characteristics resulting from degradation. The current study shows that the hydraulic conductivity of municipal solid waste with cover soil is lower than that without any intermixed cover soils. Based on experimental results, hydraulic conductivity o...

Enhancement of methane production and bio-stabilisation of municipal solid waste in anaerobic bioreactor landfill

The aim of the experiment was to enhance biodegradation and methane production of municipal solid waste (MSW). Two groups of simulated anaerobic bioreactor landfill were used; one group of mixed MSW with three bioreactors (R1, R2 and R3) and second group was compostable MSW with two bioreactors (R4 and R5). The different combinations of operational parameters were aeration with addition of aerobic microbial culture, anaerobic sludge, coarse gravel mixing, intermediate soil cover and varied leachate recirculation rate. The results observed at the end of 270days prevail that the process combination of above operational parameters adopted in compostable MSW bioreactor was more efficient approach for stabilization of MSW. It has accelerated the methane production rate (141.28Lkg−1dry waste) by 25%. It was also observed that the degradation time of MSW was reduced by 25% compared to maximum values quoted in the literature. The nonlinear regression of the cumulative biogas production and digestion time shows that Gompertz growth equation fits the results well.