The global demand of the volume of woody biomass (such as wood, logging residue, sawdust and so on) is huge and increased annually, due to its new application for the energy/fuel production during recent years. Pyrolysis is termed as a promising thermo-chemical technology to convert woody biomass to liquid, gas and solid fuels/chemicals. The better understanding of the pyrolysis mechanism of woody biomass is demanding considering the thermal performance of individual components (hemicellulose, cellulose and lignin) and their interactions. In order to develop the current understanding of the pyrolysis of the individual components (hemicellulose, cellulose and lignin) in woody biomass and fill the knowledge gap on their interactions under pyrolytic conditions, the on-line pyrolysis and off-line pyrolysis study of the model compounds of the components and their “synthesized biomass” samples has been extensively investigated employing TGA-FTIR and fast pyrolysis unit, in terms of the mass loss variation against temperature together with the on-line identification of the evolved volatiles by FTIR, yield of pyrolyzed products (gas, bio-oil and char) from the fast pyrolysis unit, variation of the compositions in bio-oil and gas products against the fluidized-bed-reactor temperature, the chemical pathways for the chemical structure change of the macromolecules and the cracking of the primary fragments, and the interactions among the chemical components. The proposed chemical pathways, indicating the possible competitive and/or consecutive relationship among the prominent compounds in bio-oil and gaseous product, give hints to improve the current kinetic scheme of the individual components. Notably, the vapor-phase interaction among the components in the fluidized-bed reactor is investigated in terms of the product yield and variation of the prominent compounds in bio-oil and gaseous product, but their interactions in solid/liquid phase are not involved.

The focus of this thesis is on the prediction of sound attenuation through a lined duct, based on a mathematical model. Ducts with a single section as well as multi-segmented sections are discussed. The duct of interest has a rectangular cross-section as normally used for ventilation purposes. The mean flow in a ventilation duct is very low and can be neglected. In this thesis, two-dimensional analytical models are developed for sound transmission in a series of different duct configurations. Two models of the lining behaviour are considered, either locally-reacting or bulk-reacting. The models are used first to obtain the transverse and axial wavenumbers of various modes of the duct. The required finite numbers of wavenumbers are tracked using Müller’s method. The wavenumbers are traced from a very low frequency to high frequency using small frequency steps. It is found that, for a duct with a bulk-reacting lining, the number of modes with a transverse wavenumber below a particular value may exceed the corresponding number of modes in a duct with a locally-reacting lining. These additional modes are termed lining modes. The number of lining modes depends on the lining thickness. Dispersion curves are presented for both types of lining. The transmission of sound through the duct is then calculated using the mode-matching technique. The mode-matching model allows analysis of multi-modal wave propagation in the duct. The model is first developed for an infinitely long rigid duct with a finite length of lined insert. The estimation from the locally reacting model, that is widely available in the literature, is compared with the estimation from the newly developed bulk-reacting model. Although the locally reacting model often overestimates the performance of a bulk-reacting lining it is found that this is not always the case, especially for a small lining thickness and at lower frequencies where the locally reacting model may under-estimate the performance. The analytical model is then extended to a multi-segmented lining where the lined section is uniformly segmented with rigid walled sections in a periodic manner. For a bulk-reacting lining, the segmented arrangement renders the lining more similar to the behaviour of a duct with a locally-reacting lining and improves the peak attenuation. Little improvement is found in the case of a multi-segmented locally-reacting lining. The effect of duct height, lining thickness and lining flow resistivity on sound attenuation is studied using the analytical model. Experiments are presented which validate the analytical model.

In this work, a new thermo-mechanical model is developed by improving on an existing one, applicable to large deep seated landslides and rockslides consisting of a coherent mass sliding on a thin clayey layer. The considered time window is that of catastrophic acceleration, starting at incipient failure and ending a few seconds later, when the acquired displacement and velocity are such that the sliding material begins to break up into pieces. The model accounts for temperature rise in the slip zone due to the heat produced by friction, leading to thermoplastic collapse of the soil skeleton and subsequent increase of pore water pressure. This in turn drastically decreases the resistance to motion and allows the overlying mass to move downslope ever more freely. The proposed model is implemented numerically and validated by back-analysing the two well-documented catastrophic landslide case histories of Vajont and Jiufengershan. The model is then employed to carry out a parametric study to systematically investigate the development of catastrophic failure in uniform slopes. It was found that the most influential parameters in promoting catastrophic collapse are (1) the static friction-softening rate a1, (2) the slope inclination β, (3) the soil permeability kw, (4) the dynamic residual friction angle rd φ and (5) the overburden thickness H. The most dangerous situation is when a1, β and H are very large and kw and rd φ are very low. Of the above, the ‘thermo-mechanical parameters’ kw and H deserve more attention as they have been introduced by the thermo-mechanical model and are not normally considered in standard stability analyses of uniform slopes. A second parametric study was performed to demonstrate that thermo-mechanical parameters alone can make a difference between a relatively non-catastrophic event and a catastrophic one. Hence, further insight into the design of landslide risk mitigation measures can be gained if, in addition to the standard site investigations, the permeability of the soil is measured and the depth of an existing or expected failure surface is measured or estimated respectively.

Food and energy security are two key environmental challenges currently faced by mankind. The principles behind organic farming are to promote environmental sustainability; however within the organic standards the use of renewable energy is only a suggested method with which to achieve this. If organic farmers can successfully utilise anaerobic digesters, they could contribute towards the provision of both food and energy security using one holistic system. Within this thesis, the suitability of anaerobic digesters on organic farms was explored using methods from ecological, sociological and environmental sciences. This enabled both the practical and theoretical issues behind the question of whether it is suitable for anaerobic digesters to be used on organic farms to be addressed. Field and laboratory experiments were used to compare the effects digestate and slurry had on earthworms, grass and weeds. Digestate and slurry had species dependent effects on earthworms during both LD50 / LT50 experiments and behavioural bioassays; Lumbricus terrestris survived longer in slurry and showed a behavioural preference towards slurry over digestate, whereas Eisenia fetida showed the opposite responses. Fertiliser application rates over 170 kg N ha-1 were found to be harmful to both species of earthworm. Suppressed germination effects were seen on thistles treated with digestate compared with no treatment (F0.56,19.66 =4.66, P < 0.01), whilst grass fertilised with digestate had a greater total mass than grass fertilised with slurry or left unfertilised (F2,27 =17.92, P < 0.001). Questionnaires and interviews were used to obtain a better understanding of the opinions farmers had about anaerobic digesters. Organic farmers believed renewable energy generation fitted well within organic principles, but using an anaerobic digester on an organic farm was less practical than on a conventional farm. This was due to multiple reasons including lack of information, poor associated finances, and that existing digesters are currently unsuitable for small organic farms. There was also support for anaerobic digesters to be on dairy farms- this was regardless of whether the farm was organic or conventional. Two case-study farms were used to assess the impact an anaerobic digester would have on the farms total GHG emissions. An anaerobic digester on the dairy farm was calculated to reduce GHG emissions by up to 24%, while for the mixed farm, the maximum reduction was by 20%. This was primarily due to the fact that the dairy farm benefitted from a higher volume of feedstock and proposed to use the biogas in a more energy efficient manner by producing electricity rather than vehicle fuel. Due to the high emissions associated with keeping livestock, both case studies needed to import additional feedstock if the farms were to achieve zero net GHG emissions. The answer to whether anaerobic digesters can be suitable for organic farms was judged on how well they complimented or conflicted with IFOAM’s definition of organic farming. Three main aspects of their definition were chosen and evidence from each chapter used to address the main question of the thesis. In conclusion, anaerobic digesters are theoretically suitable for use on organic farms, but are generally more practical for use on conventional farm systems. Across both farm systems the most suitable enterprises to adopt anaerobic digesters are dairy farms. This highlights the need for suitability of new systems to be assessed on a case-by-case scenario when trying to maximise positive impacts from new technologies.

No description available.

The search for alternative landfill operation and management strategies has triggered the development of the concept of a landfill as a bioreactor. The application of the concept requires the recirculation of liquids and hence a better understanding of fluid flow and transport processes that are strongly controlled by the physical structure of the media. It is generally accepted that as a result of the deposition in progressive layers, compaction and heterogeneity; solid waste develops a strong and anisotropic structure. Also, that due to their flat shape and orientation, materials such as plastics and textiles can influence flow behavior. The aim of this research was to provide a better understanding of the structure that develops when solid wastes are landfilled and the influence of this structure on fluid flow. The research included a characterization and description of specimens of raw household waste (MSW) and pretreated wastes (MBT) using PSD mathematical models, an study of the changes caused to particle size and shape by degradation processes, a study of the effect that flat shaped particles have on the fluid flow characteristics of a porous medium, and an investigation of the structure of a MSW specimen applying invasive and non-invasive radiographic techniques. The study revealed that the characteristics of particle size and shape differ between waste materials and also change with degradation. An MBT specimen that had gone a dual anaerobic aerobic treatment showed statistically insignificant changes in particle size and shape with degradation, whilst partially treated MBT and MSW specimens showed significant changes in the particle size and in the content of flat shaped materials. PSD models were successfully fitted to the different specimens investigated suggesting that analytical expressions can be incorporated into existing waste behavioural mathematical models to characterise the particle size. Flat shaped particles that comply to be at least 15 times larger than the matrix particles and constitute at least 7.3% by dry mass were found to reduce the hydraulic conductivity by a factor of more than 30%. The reduction factor is controlled by the relative content and size of the intrusive particles and it is always within one order of magnitude. The use of dye tracer visualization, thin sectioning and μCT techniques were pioneered during this research for the study of preferential flow and the structure in solid waste. This study evidenced that the presence of high content of inert coarse flat shaped materials in a specimen of MSW resulted in the development of a strongly layered structure, with large pores horizontally connected and that favoured preferential flow.

Anaerobic digestion of source segregated domestic food waste (SS-DFW) offers a sustainable management route for reclaiming potential energy in the form of a fuel gas, and nutrients which can be recycled back to land. However, the biochemical characteristics of SS-DFW can lead to free ammonia nitrogen (FAN) concentrations that are inhibitory to the digestion process causing unstable operation and in some cases complete process failure, particularly in thermophilic systems. With the purpose of reducing the total ammoniacal nitrogen (TAN) in the digester, side-stream and in situ biogas stripping technologies were tested. Mesophilic and thermophilic temperatures were evaluated under moderate and complete biogas mixing rates (0.4 l min-1 – 2.6 l min-1) in a batch system. Laboratory investigations showed that TAN reductions in an in situ bubbling reactor with moderate and complete gas mixing rates were non-existent at mesophilic temperatures and minimal at thermophilic temperatures. For this reason, it is unlikely that in situ biogas stripping would be adequate to prevent TAN concentrations greater than 2500 mg N l-1 in a food waste digester and thus will not mitigate ammonia inhibition in a thermophilic system. Semi-continuous trials carried out on SS-DFW in laboratory-scale digesters, fed daily at an organic loading rate (OLR) of 2 kg VS m-3 day-1 and coupled to stripping columns at low bleed rates (2 – 3.5 % digester volume per day treated in the stripping process) were effective in reducing ammonia concentrations to below thermophilic toxic levels (TAN concentration of 2500 – 3500 mg N l-1). The experiments also confirmed that removal of a proportion of the digester contents and their exposure to thermophilic conditions with pH adjustment to 10 had no adverse effects on performance in terms of biogas production (0.83 ± 0.03 l g-1 VS without stripping, 0.84 ± 0.05 l g-1 VS with stripping) or VS destruction (81.8 % without stripping, 88.5 % with stripping). The process required high pH and temperature (≥70 ⁰C) to achieve a TAN concentration below the toxic threshold for thermophilic digestion, and it is unlikely that stripping at 55 ⁰C and pH 10 would achieve the target reduction. The research showed the way forward for the application of side-stream stripping to prevent the build-up of ammonia under thermophilic conditions, if the digester is started up with a non-inhibitory FAN concentration in the inoculum.

The EU landfill directive requires the amount of wastes going to landfills to be reduced signifi-cantly in compliance with the sustainable waste management principles. However, the disposal has been and will continue to play a significant role, and the overall aim is an improved design and operation of the landfill sites, and reduction of their negative environmental impact towards sustainable landfilling. Waste has been recognised by other researchers as the primary structural element in landfills; therefore for better understanding of its behaviour, the physical and engineering properties of its components must be well known. The main aspect of this research was focused on investigation of particle compressibility and its effect on the overall compressibility and settlement of the waste body. A methodology to measure particle compressibility in saturated conditions at various stress levels was developed, using synthetic deformable materials and mechanically-biologically treated (MBT) waste. MBT waste sample with particle size reduced to 9 mm showed a response to loading similar to soils, hence soil mechanics principles will be applicable. Simultaneously, a categorisation of different types of pre-treated wastes was carried out by some of their physical and geometrical properties. The results were interconnected into a newly developed waste classifcation system, which allowed an assessment and comparison of their geomechanical and flow properties, and predict to some extent their futurebehaviour in landfills. About a third of the MBT samples by mass comprised a matrix (�ne material of <5 mm) into which the larger particles were embedded. The large 2D elements (mainly presented by plastics, glass and metal foils) will play an important role for stability and flow transportation, taking about 25% by mass. On one hand, they will have a reinforcing effect but on the other, they will modify, divert, or impede the flow paths in the waste which may result in reduced permeability or preferential flows. Highly compressible synthetic materials were also used to simulate the deformable materials in landfills (such as hollow 3D elements). They tend to embed into each other and form a horizontal highly dense structure which reduces significantly or completely the volume of voids. In large scale, this will lead to modified or blocked the flow paths and hence reduce the flow rates and impede the flushing of contaminants in landfills. Compressible particles reach their maximum compressibility at certain stress thresholds and progressively change their shape from 3D compressible to 2D incompressible. At the end of the study, a simplified phase relationship model was suggested, considering changes in the solid phase due to both particle compressibility and decomposition. The applicability of the conventional effective stress theory on highly compressible materials was questioned as well.

Hydraulic conductivity is a measurement of the ease of movement of a fluid through a medium and is therefore a key parameter in the design of landfill leachate management systems. Hydraulic conductivity of landfilled wastes may be affected by several factors such as overburden stress from the weight of overlying waste, water content, the type, age and pre-processing of the waste, and the presence of landfill gas. A further factor that may affect leachate movement through wastes is the predominantly horizontal orientated structure of compacted wastes. This anisotropic structure may result in hydraulic conductivity in the horizontal direction being greater than that in the vertical direction. However existing research has been effectively limited to evaluating hydraulic conductivity in a single plane and so the presence of anisotropic flow in waste remains unproven. Consequently, modelling of leachate and contaminant movement in landfills may be compromised by the use of isotropic, or assumed anisotropic, hydraulic conductivity values. The object of this research has been to assess for the first time the inherent anisotropy of two different waste samples by measuring and comparing the vertical and horizontal hydraulic conductivities over a range of stresses typical of landfill conditions. In this thesis, factors affecting the measurement of hydraulic conductivity of wastes are discussed, and details of the samples tested and test methodology are given. The results of the tests are shown and alternative test methods are discussed. The effects of gas accumulation and pore water pressure on waste hydraulic conductivity encountered during testing are also reported as further research has developed from this important finding.

A considerable amount of work has been conducted developing exposure estimate models for quantitative evaluation of Hg intake and human health risks, but few have assessed the applicability and the validity for evaluating the risks posed by Hg in the environment and have achieved very mixed results. The present study focused on verifying the daily Hg intake estimates using exposure estimate models. Deterministic methods and the probabilistic methods (the Monte Carlo) were applied to simulate the daily Hg intake doses which were verified by comparing the estimates to those established from measured Hg concentrations in the hair of 289 participants. The results showed that the single-value deterministic method for simulating Hg exposure levels overestimated the level of risk by a factor of 1.5 when compared with the highest concentration of the Hg observed in the hair of the study population. The average daily Hg intake doses simulated using the probabilistic simulation were similar in distribution to the biomarker data, with the variability of 23%. The difference between the probabilistic simulation and the data derived from hair Hg levels was considered to be most likely due to the uncertainties in unconfirmed questionnaire-based survey data, small sampling sizes and the surrogates used in the exposure models. When the reference dose (RfD) of 0.1 μg/kg body weight/day was adopted as the acceptable dose for daily intake rate, there were approximately 19% estimated to have potential Hg exposure risks based on the Monte Carlo simulation. This percentage was favourably similar to the 17% determined from Hg concentrations in the hair samples. The findings implied that the existing exposure models together with the probabilistic approach were appropriate for the research of human exposure to Hg. On the other hand, low Hg levels in the participants’ hair indicated that Hg accumulated in the study population was not very serious, probably due to the good Hg absorptivity of the on-site fly ash. However, it should be advised that consumption of river fish elevates the health risks to the local population.