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A detailed review of literature reveals that although soil scientists have reported that soil is an excellent stabiliser of land applied waste, there is little evidence to assess the extremely complex reactions that occur when landfill leachate interacts with soil. In order to examine this, studies of mineralogical content, exchangeable cation status and chemical composition of soils were undertaken. Soil-leachate interactions were studied by column and batch techniques. When dealing with materials as variable and complex as soils, it is difficult to accurately identify the solid phase prior to contact. Owing to the large number and variety of concentrations of leachate constituents, it is considerably more difficult to quantitatively establish the results of interaction and assign alteration values to responsible mechanisms. However, this investigation did reveal the following: - 1. interaction does occur, but this interaction is not unlimited; 2. the degree of interaction is different for different soil types; 3. the relative influence of the mechanisms of interaction; 4. the influence of soil types, soil to leachate ratios and contact -times; and 5. soils previously thought to attenuate leachate have been found not to do so.

A multi-stage (5-vessel) chemostat was used to enrich and isolate from landfill a microbial association capable of dissimilating hexanoic acid (5 mM) under anoxic conditions. Two possible catabolic mechanisms existed : (i) that hexanoate was mineralised completely to carbon dioxide, although this has only been reported in sulphate-reducing bacteria (Widdel, Kohring & Mayer, 1983); and (ii) that a syntrophic association was involved in which the hydrogen produced, during hexanoate catabolism to acetate, was removed by a hydrogen-oxidising species such as a methanogen or sulphate-reducing bacterium. The multi-stage chemostat was primarily used to facilitate spatial separation of the component species of the microbial association. Examination of the formation and subsequent utilisation of metabolites, however, indicated that no such separations were attained. Sulphate concentration increases from 1,4 to 5 mM and from 5 mM to 10 mM did, eventually, result in a partial shift in the metabolic activity of the methanogens from the first vessel to the second at the final concentration. The results indicated that at least four groups of bacteria were present in the association :a hydrogen-producing acetogen, a hydrogen-utilising sulphate reducer, a hydrogen-oxidising homoacetogen and an aceticlastic methanogen. It was thus apparent that a syntrophic association was present in which in the presence of sulphate a sulphate-reducing bacterium was the dominant hydrogen utiliser whereas in the absence of this electron acceptor an association between a homo-acetogen and a methanogen dominated. Acetate was metabolised exclusively by the methanogen both in the presence and absence of sulphate. To assess the effect of a non constant dilution rate regime on the microbial association a 3-stage chemostat was constructed in which the volume was increased from an initial 310 ml in the first vessel to 700 ml in the second and finally to 1600 ml in the third. The imposed dilution rate of 0.05 h-1 in the first vessel, together with an influent sulphate concentration of 1.4 mM, resulted in the displacement of the methanogenic population. Although maximum sulphate reduction remained in the first vessel complete dissimilation of hexanoic acid was only effected in the presence of the whole association. To investigate the metabolic processes of the microbial association closed culture studies were made in which it was found that maximum rates of hexanoate degradation, by Y-oxidation, required the intervention of sulphate reduction. Since the overall pattern of metabolism remained unchanged it was apparent that the sulphate-reducing bacteria outcompeted both the methanogens and acetogens for hydrogen. The methanogenic component of the association was found to catabolise acetate to methane via an aceticlastic reaction although this mechanism was inhibited in the presence of hydrogen supplementation. Thus it was apparent that hydrogen removal to facilitate not only catabolism of hexanoate but also the subsequent dissimilation of the metabolic intermediate, acetate, was an essential requirements.

Thesis advisor: Rudolph Hon / A groundwater plume beneath a capped landfill in north-central Massachusetts contains dissolved arsenic concentrations exceeding 10,000 ppb at several locations. The landfill closed in the early 1990's and contains minimally documented solid waste materials deposited over the course of nearly a century. The source(s), fate, and transport of arsenic in the landfill aquifer have been studied extensively over the past decade; however, the source and pathways of arsenic are not yet fully defined. The primary source of arsenic likely involves a combination of the landfill waste material, the peat, the underlying overburden sequence, and/or bedrock minerals. Arsenic mobilization is most likely assisted by reducing conditions created by the decomposition of organic materials within the landfill and underlying peat present prior to the initiation of waste disposal. Another possibility is an arsenic-bearing groundwater discharging from the underlying bedrock from the oxidation of naturally occurring sulfides. Aqueous arsenic species, including inorganic arsenite [As(III), As(OH)3] and arsenate [As(V), AsO(OH)3], and organic monomethylarsonic acid [MMA(V), CH3AsO(OH)2] and dimethylarsinic acid [DMA(V), (CH3)2AsO(OH)], provide information as to where the arsenic is primarily originating from and how it is transported through the aquifer. Furthermore, the analysis of major ions, metals, and groundwater parameters from different zones of the landfill with varying arsenic concentrations will aid in the delineation of probable arsenic sources, the mobilization processes, and arsenic transport modes within the aquifer. A more complete conceptual site model with respect to arsenic speciation and groundwater chemistry will lead to a better understanding of geochemical processes within and beneath the landfill waste pile and also assist with future remediation of the aquifer. Using arsenic speciation and groundwater chemistry data, it was determined that although all four potential arsenic sources likely contribute to the total arsenic concentrations, the overall contribution from the landfill material, peat layer, and bedrock is minimal relative to the iron-oxyhydroxides coated on the sands particles throughout the aquifer which acts as the primary arsenic source. Oxidation-reduction potential and dissolved oxygen are the controlling factors in relation to mobilization and transport of arsenic species from aquifer features and an understanding of these processes at the local level can be further applied to global-scale arsenic contamination. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

Chapter I presents general information about landfill leachate, characteristics of leachates in Vietnam and review of general leachates treatment situation in the country. In chapter II, a careful bibliographical study on biological processes of nitrification and denitrification is done. In chapter III, existing activated sludge models are briefly reviewed, focusing on ASM1 and ASM3. The ASM3 model then is studied in more detail with focuses on state variables, processes; kinetic and stoichiometric parameters of the model. A careful bibliographical study on sequencing batch reactor (SBR) is done in chapter IV. Chapter V presents materials and methods that will be applied in the experiments in laboratories and modelling processes of this study. In chapter VI, an SBR bench-scale is set up in the laboratory to study partial nitrification process. Chapter VII presents the experimental studies on maximum nitrification and denitrification capability, then determination of kinetic and stoichiometric parameters that will be used for calibration in the next steps. Chapter VIII presents a study on partial nitrification by applying data analysis and experimental planning method. In chapter IX (the key part of the Thesis), the modelling of the partial nitrification and denitrification in SBR is presented. It is hoped that, this study will contribute to the major issue of leachate treatment in Vietnam, especially in the North of the country where leachate characteristics and variations are the same as what was used during our experiments. Partial nitrification seems to be easily achieved in an SBR bench-scale using leachate in Nam Son landfill site. Some important characteristics of the studied leachate, are high alkalinity, high pH leading to high free ammonia concentration in the system. This free ammonia is known as a growth rate inhibitor for nitrite oxidizing bacteria, thus limiting oxidation of nitrite to nitrate and accumulating nitrite during the nitrification period. DO concentration is also known as an important influencing factor in partial nitrification in many previous studies. But in our case, its influence is just significant when the nitrification process is nearly complete: no more ammonium remains in the system, alkalinity concentration is reduced leading to a lower buffer capacity, lower pH, and then nitrite is easily oxidized to nitrate. A sufficiently high DO concentration in this case, expresses its importance in bringing about the best nitrification efficiency, while saving aeration energy. The SBR technique has demonstrated its advantages, especially the flexibility in changing the working volume, and the operating time. Modeling of partial nitrification and denitrification processes for landfill leachate treatment using the SBR technique was the main objective of this study. The simulation software - WEST® program was very useful tool to implement this task. With this program, the available model base for activated sludge model (ASM1, ASM 2, ASM 3 etc,), presented in the Peterson matrix, the variables, kinetic, stoichiometric parameters, processes can be easily modified to another activated sludge model suitable in the scope of our study. In the present case, based on the ASM3, the ASM3_2step was developed and applied, in which nitrification and denitrification are divided into two steps with nitrite as an intermediate product. The modified ASM3_2step has shown its high accuracy during calibration process. It could be use also for the other processes/techniques using activated sludge, by adding more equations and parameters. Calibration and validation were implemented for two cases: Partial nitrification and denitrification with and without carbon addition. Good results were obtained where the simulations fit well the experimental data. The kinetic and stoichiometric parameters found are very important for the other simulations, especially in process optimisation. It also demonstrates that, through process optimisation, general productivity of the SBR system can be increased. Controlling DO, changing operating time cycle mechanisms can improve the total nitrogen removal efficiency, save some aeration energy for nitrification and carbon source for denitrification. As our results are very promising, the next step could be to implement the ANAMMOX process. Key words: Partial nitrification and denitrification, ASM3_2steps, SBR, modeling.

The energy consumption throughout the world has increased substantially over the past few years and the trend is projected to continue indefinitely. The primary sources of energy are conventional fuels such as oil, natural gas and coal. The most apparent negative impacts of these conventional fuels are global warming, poor air-quality, and adverse health effects. Considering these negative impacts, it is necessary to develop and use non-conventional sources of energy. Landfill gas (LFG) generated at landfills can serve as a source of cleaner energy. LFG has substantial energy generation potential and, if cleaned of certain impurities, can be used for several applications such as electricity generation and conversion to high Btu gas. This thesis considers another application of LFG, which consists of using it as a vehicular fuel for refuse trucks. Currently, limited research has been performed on the development of such a methodology to evaluate the application of LFG as a vehicular fuel for refuse truck operations. The purpose of this thesis is to develop a methodology that can be used to evaluate the use of LFG generated at landfills as a Liquefied Natural Gas (LNG) fuel source for refuse trucks in Texas. The methodology simulates the gas generation process at a landfill by using standard models developed by the Environmental Protection Agency. The operations of a refuse truck fleet are replicated by using generic drive cycles developed as part of this research. The economic feasibility is evaluated by estimating the costs required for cleaning the LFG and converting the truck fleet from diesel to LNG as well as quantifying the benefits obtained due to change in fuel consumption and emission generation by the refuse trucks. The methodology was applied to a potential landfill in Texas. The results show that the methodology offers an innovative tool that allows the stakeholders to evaluate the economic feasibility of using LFG for refuse truck operations. The methodology also provides a flexible framework wherein each component can be changed or tailored to meet the specific needs of the stakeholders.

Landfill leachate production is an unavoidable by-product of landfilling solid waste. Mitigation of the adverse environmental impacts of landfill leachate is required at all active and closed landfill sites. Since leachate production continues long after the landfill is closed and no longer generating revenue, management strategies including low-cost passive and naturalized landfill leachate treatment systems are ideal. The past practice of dumping solid waste into unused tracts of land has created many brownfield sites with uncontrolled discharges of leachate to the receiving environment. Belle Park in Kingston, Ontario is an example of such a site that has been reclaimed for recreational use. A seep management strategy, which included the installation of leachate extraction wells, has been implemented at the site. Passive treatment systems, a coastal fringe wetland and a phreatophyte plots, were installed to evaluate their effectiveness in conjunction with the leachate seep management. Modelling estimated that originally, the pumping wells decreased leachate discharge by 60%, and with the newer wells in 2007 the discharge was decreased by 75- 85%. In situ pilot-scale evaluations of treatments systems are required to ensure adequate treatment of the leachate. The Merrick Landfill in North Bay, Ontario currently captures leachate produced on site and is assessing the potential of a hybrid-passive landfill leachate treatment system. This design process started with bench-scale design and assessment of active pretreatment options, followed by an evaluation of passive and semi-passive treatment systems at the bench-scale (treating 2-3 L/day) at both room (24oC) and cold (2oC) ambient temperatures. The design process culminated with a pilot-scale assessment of hybrid-passive treatment systems (treating 2000 L/d). Assessment of flow in passive treatment system is usually conducted with tracer evaluations. Vertical-flow passive treatment systems with intermittent dosing of leachate for passive aeration have both saturated and unsaturated flow regions. This research shows that tracer evaluation of these types of system was insufficient to measure the clogging within the pore spaces. Therefore a time-lagged flux method was created, based on the pilot-scale hybrid passive treatment system at the Merrick Landfill. This analytical solution quantified the changes in saturated hydraulic conductivity in the treatment system cells. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2011-09-30 15:55:45.73