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The increasing demand for sustainably produced timber and the expansion of land-based greenhouse gas removal technologies is driving the growth of the forestry sector in the U.K. This is creating increased competition for the finite land resource. Historic planting on nutrient limited upland soils, coupled with open nutrient cycles due to high intensity silvicultural systems, is creating a productivity crisis across upland plantation forestry. Climate change is expected to further impact the productivity of U.K forests and managing soil health is vital in ensuring crop resilience to our changing climate. Biochar is an established greenhouse gas removal technology (GGR) that can increase the carbon storage capacity of land and enhance the efficacy of other land based GGR technologies, such as woodland creation. The agronomic benefit of biochar is well understood, however, there has been minimal research thus far on the potential application of biochar in productive silvicultural systems as a novel method of forest fertilisation. This thesis explores the potential utilisation of targeted biochar application to improve seedling growth on nutrient poor soils during the establishment phase of forest cycles. A selection of distinct biochar types, ranging from high to low available phosphorus concentration, were tested in a controlled environment growth experiment on Scots pine (Pinus sylvestris L.), Sitka spruce (Picea sitchensis (Bong.) Carr.) and Douglas fir (Pseudotsuga menziesii (Mirbel) Franco) along with conventional phosphorus fertilisation intervention. A specified biochar was also developed to address the primary soil limitations on seedling establishment in phosphorus limited soils. The vascular cambial zone of roundwood is relatively high in phosphorus and is a readily available sawmill co-product produced during ring debarking. This feedstock was used to create VCZ biochar. The physical and chemical properties of this specified biochar address the limitations of low phosphorus upland forest soils. Biochar amendment was further tested in a large-scale field experiment on a typical phosphorus limited restock establishment site. The effects of biochar on seedling growth and morphology were variable, according to biochar properties, dose and seedling species. The moderate native biochar phosphorus content of VCZ biochar, coupled with high porosity and internal surface area, improved above ground biomass growth, stimulated root proliferation and enhanced mycorrhizal abundance. Optical and SEM microscopy was used to investigate the importance of root and hyphal interaction with biochar structure and the accessibility of available nutrients within biochar particles in relation to seedling nutrient uptake strategies. High phosphorus fertilisers and high phosphorus biochar were found to limit the development of below ground biomass and suppress mycorrhizal fungi, in turn impacting above ground biomass development. The mechanisms which contribute to the effect of specified biochar on seedlings was explored. Biochar is a direct source of micro and macro-nutrients and can also improve localised soil nutrient availability and accessibility through sorption, pH and biofertilisation. Foliar analysis showed that biochar can be used to alleviate seedling phosphorus deficiency. The effect of biochar on soil water holding capacity (WHC) was also found to be a critical factor in improving establishment and increasing drought resilience. This thesis details the impact of biochar on forest carbon. The implication of forest establishment practices, including biochar amendment, on carbon balance and year of net carbon storage was modelled to assess the optimal scenarios for carbon storage on nutrient poor soils. Early growth improvements from low dose targeted biochar amendment have the potential to reduce the time to net carbon storage by three to six years on low yield organomineral planting sites. It can be concluded that the targeted application of specified biochar can improve early-stage seedling growth and enhance the development of the rhizosphere, providing greater silvicultural benefit compared to conventional forest fertilisation. This in turn can create longer term benefits to forest health, crop stability and future rotation yields. Enhancing the localised soil conditions through specified biochar amendment should be considered as a viable management intervention to increase forest resilience, species suitability, carbon sequestration and close nutrient cycles.

Over decades anaerobic digestion (AD) has been successfully established as technology to treat organic wastes. The perspective of turning organic wastes into biogas, a source of renewable energy and profit, through a low-cost process, has gained increased interest around this technology. The AD as biological process is strongly dependent on the environmental conditions such as temperature, pH, presence of inhibitors, and nutrients content, that, in particularly unfavourable situations, can attribute to undesirable drop in performance and even for detrimental failures. Therefore, several strategies such as feedstock pre-treatment and process optimization have been developed to secure AD performance. However, these approaches do not remove inhibitor from the process, which may result in accumulation of the inhibitor and further destabilization of the AD system. From this point of view, it is beneficial to develop methods that remove and/or reduce the mobility and bioavailability the inhibitor within the digestion process. In this study, char derived from lignocellulosic wastes was added to anaerobic digestion to elucidate their roles on process performance and efficiency. The results of this analysis suggest that changes of AD performance (i.e. biogas production and intermediates concentrations) are strongly correlated to biochemical characteristics of char materials. Furthermore, the impact of changes in inhibitor concentrations on the digester's performance was observed, and found that inhibition tolerance of AD was improved by the presence of selected char materials. However, contrary to the initial hypothesis based on previous studies in related hydrochar application, the addition of RH hydrochar led to reduction in biogas production but an enhanced methane content in biogas was observed. Except from batch AD tests, a larger-scale AD system (semi-continuous stirring tank reactor) was used to determine the possibility of biochar on enhancing digestate structure and reduce the sensitivities towards environmental factors such as pH and other inhibitors. The further outcome from scale-up study revealed that biochar had improved ammonium tolerance (1.59 mg NH4-N/kg) by recovering 12-16.4% biogas production. This study also investigated effects of iron impregnated-thermal activation on physiochemical properties of the resultant biochar. Effects of these modified biochars on gas production and volatile fatty acids concentration was also measured and significant changes was observed. Overall, char material had a positive effect on AD system stability and promoted bio-methanation during the long run operations.

As a derivative of biomass energy, biochar materials have been widely used in soil improvement, soil remediation, water pollution treatment, carbon fixation and other fields. The biochar generated by the pyrolysis and carbonisation of biomass has a high and stable carbon content, reducing the carbon emissions from biomass combustion. In addition, bio-oil and syngas produced during biomass pyrolysis are also potential fuels that can replace fossil energy in the future. Therefore, biochar is considered an eco-friendly material due to its many advantages. Firstly, based on literature research, the thesis investigates the CO₂ adsorption performance of various biochar materials under different activation conditions. CO₂ adsorption studies were mainly carried out with bamboo charcoal, charcoal and coconut shell charcoal as the main adsorbents. In addition, porous structure generating was carried out under specific conditions of physical and chemical activation to enable the biochar to increase its adsorption activity. Meanwhile, there are no uniform standards regarding the CO₂ adsorption activity of biochar, and the work also uses three different assays for comparing the CO₂ capture capacity of biochar. Additionally, it was concluded that specific chemical activation is helpful for the improvement of the CO₂ adsorption capacity of lignocellulosic biochar, where the 15 % CO₂ adsorption capacity (25°C, 1 bar) of bamboo biochar and wood pellet biochar increased from 0.59 mmol g⁻¹ and 0.28 mmol g⁻¹ to 0.88 mmol g⁻¹ and 0.66 mmol g⁻¹, respectively, under the activation condition of an equal mass of KOH and 550°C activation for the one-hour duration. Secondly, after studying the mechanism and properties of carbon dioxide adsorption by biochar, charcoal was used to carry out 15% carbon dioxide adsorption, while the effect of water vapour during the adsorption process was explored. As biochar is used as a carbon dioxide adsorbent, environmental influences have to be considered. Therefore, the presence of large amounts of water vapour in the flue gas of a plant is one of the factors affecting the adsorption activity and stability of biochar that is worth discussing. As the results obtained from the experiments, the capture ability of biochar decreased as CO₂ concentration decreased from 100% to 15%. The relative humidity had a negative impact on CO₂ capture over biochar. The CO₂ capture capability of biochar materials treated by steam decreased by 31.38% to 62.89% as the relative humidity rose from 8.8% to 87.9%. Furthermore, the lifetime of biochar samples at various relative humidity shows that increased relative humidity had a negative impact on CO₂ adsorption due to water molecules occupying active sites. In addition, it is also necessary to try using biochar for direct carbon capture after it has been verified that it can adsorb carbon dioxide. Direct air capture is an emerging technology that has specific social development prospects. In this work, KOH-activated bamboo biochar shows a CO₂ capture capacity of 3.49 mmol g⁻¹ (25°C, 1bar), and it is used as an adsorbent to perform direct air capture using a fixed-bed reactor with an ambient CO₂ capture capacity of up to 51.74 μmol g⁻¹. Furthermore, the effect of relative humidity on CO₂ adsorption by biochar was investigated and exhibited promising stability under 2.7% relative humidity. However, the biochar activity for CO₂ capture is reduced to 63.88% under 67.1% humidity after 50 cycles. Eventually, the application of porous biochar for phosphorus-containing wastewater treatment has also been investigated to study biochar's sustainability. In this study, the irrigation of dirty water phosphorus treatment by biochar samples derived from digestate of anaerobic digestion was investigated. The biochars were further activated by steam activation with different duration time, and KOH activation with different introducing ratios, the textural properties of biochars was optimised after activation from the aspect of biochar characterisation. Notably, the biochar demonstrates a remarkable adsorption effect of phosphorus, with an adsorption efficiency of 8.99 mg g⁻¹. Besides, the effect of biochar dosage on phosphorus removal, adsorption kinetics, and thermodynamic isotherms are studied. According to the adsorption kinetics, the adsorption of phosphorus from dirty water fits the Elovich equation (R² = 0.95). Furthermore, the thermodynamic isotherm results illustrate the process of phosphorus removal by biochar is endothermic (ΔH0 =17.93 kJ mol⁻¹) and spontaneous (ΔS=96.24 J mol⁻¹ K⁻¹). Therefore, this work suggests a promising solution to phosphorus-related environmental challenges in industry and agriculture.

The present global efforts to tackle climate change stipulate an objective of limiting global temperature rise to 2°C by the end of the century while pursuing measures to keep it below 1.5°C. An in-depth investigation of climate change mitigation strategies was carried out, detailing 3 major approaches, namely emissions reduction, atmospheric carbon removal and radiative forcing geoengineering. On the basis of the findings, it was determined that current emission reduction efforts, as well as future emission reduction commitments announced globally, are insufficient to meet the 2015 Paris agreement targets, and that carbon removal must be integrated with emission reduction efforts in order to reduce global temperatures over the coming decades. Based on an assessment of the prominent carbon removal technologies, it was determined that carbon removal via industrial biochar systems is a very promising approach. Accordingly, the dimensions related to biochar-based carbon removal systems were explored in detail. This covered potential feedstocks, feedstock analytical techniques, potential production technologies, biochar properties with a special focus on carbon stability, the impact of processing configurations on production yield and biochar properties, as well as potential by-product valorization routes. Furthermore, the investigation discussed the concept of biochar as a negative emissions technology and introduced potential carbon reservoirs and a variety of value-adding applications. Moreover, the current status of the emerging carbon removal economy and participation requirements were presented. Overall, with the emergence of the new carbon removal economy, research focused on system design, process optimization, and techno-economic-environmental assessments of biochar-based carbon removal projects was found to be critical moving forward. As prospective feedstocks, several materials, including olive tree pruning residues, sesbania sesban, and cotton stalks, were investigated experimentally. Kinetic models were developed for the pyrolytic degradation of such materials using a sophisticated thermo-kinetic tool, Advanced Kinetics and Technology Solutions (AKTS), and conversion predictions were constructed under various heating configurations. The results of the investigations provided a comprehensive understanding of the materials' behaviour during pyrolysis and the information aided in subsequent modelling and optimization. Moreover, olive tree pruning residue biomass was selected for further investigation. Finally, the carbon removal potential of an industrial biochar system in Spain was holistically examined. The objective was to assess the techno-economic environmental aspects of large-scale olive tree pruning residue pyrolysis for atmospheric carbon removal, using an integrated assessment framework that is based on current market dynamics. The framework included i) biochar production and optimization, ii) biochar characterization, iii) plant design and process modelling, iv) life cycle analysis, v) carbon removal quantification, and vi) economic modelling. Production optimization using Response Surface Methodology (RSM) was carried out, aiming to maximize yield, production throughput and stable carbon content while prioritizing stability. It was determined that optimized biochar production was attained at 650°C and 15 min residence time. Furthermore, a biochar plant with a biomass processing capacity of 6.5 tonne per hour (20% moisture content) was designed for further analysis. A thermodynamic model was developed using Advanced System for Process Engineering (ASPEN Plus) software, and the process was determined to be self sufficient with the availability of surplus energy. Moreover, a life cycle assessment (cradle-to-grave) revealed that approximately 2.68 tCO2 are permanently removed from the atmosphere per tonne of biochar produced, after accounting for the carbon footprint of the entire process. This corresponds to a carbon removal capacity of 3.26 tCO2 per hour and the removal of approximately 24,450 tCO2 annually. The economic assessment revealed that the project is profitable; however, profitability is sensitive to pricing of the carbon removal service and biochar. A project internal rate of return (IRR) of 22.35% was achieved at a price combination of EUR 110 per tonne CO2 removal and EUR 350 per tonne biochar, and a feedstock cost of EUR 45 per tonne (delivered with 20% moisture), where service and product pricing are both within the lower bound of market pricing. If the project was exclusively designed to offer a carbon removal service, a minimum price of EUR 206 per tonne CO2 removal is required to achieve project profitability, based on the same feedstock cost. The results indicate the feasibility of biochar-based carbon removal systems, however, the business model, type of feedstock, choice of technology, pricing decisions and ability to negotiate favourable terms and prices for feedstock supply are critical to the success of this approach. The findings demonstrate the viability of immediately deploying large-scale biochar-based carbon removal via pyrolytic conversion of olive tree pruning residues to address the climate crisis.

Mining has serious environmental impacts including effects on water quality. Slate quarrying is neglected as with regards environmental impacts in the literature. Specifically, the geochemical effect of slate quarrying on water is an under-researched field. The effects of climate change may have future impacts with regards mining perhaps worsening any effects. Two metals which are of prime importance in this dynamic are Aluminium (Al) and Copper (Cu), which are found to be the most enriched in the river Barlwyd, they are also the most toxic to aquatic life. This thesis explores the geochemistry, hydrology, sediment effects and remediation in the Ffestiniog area, an area synonymous with historical and current slate mining. The first aim was to quantify the temporal and spatial pollution of Al/Cu from slate quarrying on the rivers Barlwyd and Bowydd in line with the European Water Framework (EWFD) guidelines. This involved a yearlong study which was completed to establish a baseline. Samples were taken at 20 different sites throughout the year during different weather conditions. On the Bowydd concentrations of Al were 0.0015-0.8698 mg/L. Sample concentrations ranged for the Barlwyd ranged between 0.020 mg/L at B1 and 21.2656 mg/L at B12 and were spatially dependent. pH ranged between 3.4 at B12 and 7.62 at B1. Turbidity was negligible. Geochemical parameters were correlated to metal concentrations. This demonstrated that slate quarrying influences river water quality. This effect is most pronounced in the summer months when metal sample water concentrations are at their peak, as the water is more concentrated due to water availability. Geographically, Al and Cu were found to be enriched in the river Barlwyd and in the river Bowydd near sources of slate pollution/slate tips. Al/Cu also showed a temporal pattern of expression in this riverine environment, with higher concentrations in summer months when there was less rainfall. Al and Cu concentrations found by this research place the river in this area are poor status as with regards to the EWFD and are outside guidelines. Geochemical parameters also showed extreme tendencies, with low pH and high electroconductivities, outside recommended guidelines. Flux illustrated heavy loads on the river, explaining the poverty of aquatic life found in the river. It is concluded that slate mining has a significant impact on the river water quality. Chapter 4 in this study aimed to establish the influence of storm-driven hydrological change on Al/Cu concentrations and associated aqueous geochemistry of the of the Afon Barlwyd. Samples collected from 20 sites during storm events, showed an initial increase in Al and Cu concentrations (Site B4 0.319 mg/L and Cu 20.2 μg/L, Site B12 8.563 mg/L and 216.64, Site B14 0.0265- 0.0544 mg/L, 1.7523-2.72) and increase in pH to circa neutral levels over the course of the storm. This is evidence of a flushing effect, and as the storm progresses there is a physical dilution. Concentration: time relationships during the storm events demonstrated a clockwise hysteresis relationship, indicating that it could be as Doty and Carter (1965) claim that that the material decreases because of hydrological processes, or as Novotny (1980) suggests that the decrease in rainfall levels in the storm retreat means there is less polluted material carried into the water channel. Eh/pH relationships indicate that the speciation of Cu and Al are found in free ion states, suggesting it is more toxic to aquatic life. The key overall conclusion is that storms have a negative effect on aquatic life in the river as a flush of material causes toxicity from quarrying activity. The aim of Chapter 5 was to estimate the sorption/desorption of the metals Al/Cu from sediment into the dissolved water fraction. The end goal was to work towards establishing better guidelines for the EWFD, by estimating the relative contribution of slate quarrying sediment to the Al/Cu load in the river. To examine the effect of sediment on the river water in the Barlwyd, sediment - aquatic phase exchange experiments modelling natural conditions were conducted. The study showed ambiguous results between sites and temperature and there was no overall clear pattern as there could sometimes be absorption and sometimes be desorption. This study indicated that sediment was not enough to explain the levels of metals in the water. Sediment analysis using TxRF revealed that the rock was rich in Al, and Cu, and laser ablation showed and that it was enriched in clay particles. To explain the results, it is concluded that a pH dependent mechanism is responsible for the dissolution of minerals, and this could be due to clay presence in the rock. The final aim was to evaluate two methods of remediation, biochar and zerovalent iron on removal of Al/Cu from samples of slate quarrying affected river water. Modelled lab trials with microcosms revealed that biochar was effective at removal of Cu but not as effective at removal of Al. Percentage removal of Al ranged from 44-97% biochar and 34-86.9% with FeO. The removal of Cu with biochar was not as efficient as with biochar with 44-76.9% removal. Percentage removal of Cu with FeO was 63-97 %. It is concluded that again the pH of the river water may play a crucial part in the mechanism of removal. It is demonstrated that viable remediation options could include the use of Biochar and FeO in the future.

Intensification of agricultural practices is necessary to support a growing global population. Water movement and storage in soils are very crucial for successful intensification of agriculture. They are important for nutrient delivery to plant and overall crop productivity. Climate change and population growth have been predicted to limit water supply especially in arid regions. Therefore, there is an urgent need to proffer solutions that would help maintain or even increase soil moisture retention. The use of biochar for improving soil hydraulic properties is a current and growing area of research. Biochar is a stable form of charcoal gotten from heating natural organic materials in a high temperature and low oxygen process known as pyrolysis. Biochar physical and chemical properties vary due to the pyrolysis process conditions, the type of feedstock, and the ratios of lignin, cellulose, and hemicellulose in the biomass. These change the structure of the biochar and will invariably affect to what extent it can improve soil water retention. To understand how biochar affects soil water properties we must understand the specific characteristics of biochar that influence these changes. Understanding the mechanisms is important for easy prediction of when and by how much biochar will improve soil water properties. The aim of this thesis is to provide new and extensive insight into 4D structural changes of biochar produced from different feedstock and pyrolysis conditions and how these affects soil moisture characteristics of different soil textures. The first aspect of the thesis was to carry out a meta-analysis of the available literature to quantify the effect of biochar on soil hydraulic properties. To enable matching of biochar to soil constraints and application needs, a thorough understanding of the impact of biochar properties on relevant soil parameters is necessary. This meta- analysis of the available literature for the first time quantitatively assessed the effect of not just biochar application, but different biochar properties on the full sets of key soil hydraulic parameters. The review shows that the key factors influencing biochar performance were particle size, specific surface area and porosity indicating that both soil-biochar inter-particle and biochar intra-particle pores are important factors. Next, the role of biochar particle size and hydrophobicity in controlling soil water movement and retention was assessed. Softwood pellet biochar in five particle size ranges was used for the experiment. These particle sizes were tested on two soil types at four different application rates in the laboratory. The results clearly show that both biochar intraporosity (pores inside biochar particles) and interporosity (pore spaces between biochar and soil particles) are important factors affecting amended soil hydraulic properties. Biochar interpores affect mainly hydraulic conductivity; both interpores and intrapores control soil water retention properties. Our results suggest that for a more effective increase in soil water retention of coarse soils, the use of hydrophilic biochar with high intraporosity is recommended. The third aspect of the thesis was to assess the 4D structural changes and pore network model of standard biomass feedstock during pyrolysis. Biochar properties are highly variable and are dependent on the biomass feedstock and production conditions. Despite these variabilities, there has been no study that uses a single sample to study the development of microstructural properties of biomass and biochar through the full range of pyrolysis temperatures. In this study, synchrotron x-ray micro-tomography (SµCT) was used to visualize the internal structure and characterise pore structure of biochar from several feedstock during pyrolysis (50 - 800 °C). The results show a wide range of variation in the pore structural characteristics of the biochar depending on feedstock and pyrolysis temperature, with observed porosity in the range of 7.41 - 60.56 %. The results from this study are not only important for the use of biochar as soil amendments but also a range of other applications relying on biochar pore characteristics, such as biochar as habitat for microbes, water, and wastewater treatments, as an absorbent for the removal of acid gases, or an additive in construction or engineering materials. In addition, the in-depth insights into changes in biomass structure during heating are valuable for research and applications related to fire safety. Finally, the data set from the SµCT was used to produce statistical models enabling the prediction of the effect of biochar on soil water holding capacity from biochar microstructural properties. The results of this thesis, therefore, clearly establish the mechanisms with which biochar improves soil hydraulic properties. It also demonstrates that by appropriately matching microstructural properties of biochar to those of the target soil, it is possible to achieve considerable improvement in soil properties using relatively low application rates of biochar. The relationship between biochar structural properties and its effect on soil moisture characteristics of specific soil texture, is an attractive pathway towards development of precisely tailored biochars aimed to enhance water use efficiency and provide low-dose, high-efficiency benefits.

Carbon dioxide removal technologies present an opportunity to alleviate some of the worst consequences of climate change by actively removing CO2 from the atmosphere while the decarbonization of our economies progresses. Biomass valorization through the production of biochar is a unique carbon negative technology as it comprises benefits beyond carbon sequestration, from the utilization of agricultural waste, the co-production of renewable energy to the use as an adsorbent. However, widespread adoption of biochar is still lacking due to economic obstacles in monetizing its various environmental benefits and high production prices compared to fossil materials. I address these obstacles by evaluating current biochar systems and developing an alternative concept to increase the economic competitiveness of biochar. I argue that the price of biochar can be significantly reduced by changing the perception of biochar as a product. Utilization systems specifically designed to monetize biochar's multifunctional properties are capable to reduce its price without requiring lower production costs. The developed concept of sequential biochar systems is based on the perception of biochar as a carrier for environmental services rather than a product. Within this service-oriented concept, biochar is rented out and recycled rather than sold, enabling an iterative valorization of its properties while retaining its carbon sequestration value. This approach centers around the novel concept of biochar recycling to effectively decouple the price of biochar from its production costs by distributing these costs over several applications. To evaluate the prospects of sequential biochar systems, I conducted an experimental proof-of-concept trial assessing a sequence of three applications connected by two recycling steps. Engineered biochars were designed with a parallel focus on increased application capacity and recycling performance to provide synergies throughout the sequence. The applications targeted the use of biochar in wastewater and gas filtration as high value applications with emerging use scenarios for biochar. Recycled biochars showed comparable performance to commercial materials, and recycling displayed environmental advantages to current methods by retaining carbon throughout the sequence. The exploratory work in this thesis provides various starting points for further research on effective biochar utilization strategies, which are urgently needed to accelerate the development of biochar into an economically self-sustaining carbon dioxide removal technology.

Greenhouse gas removal technologies (GGRT) are needed to meet the UNFCCC aim to limit the global average temperature increase to 2°C above pre-industrial levels. GGRTs vary in carbon sequestration potential, readiness level, scalability, cost, required surrounding environment and related environmental and social effects. Quantifying these components in every context is critical to ensure maximum greenhouse gas removal efficiency while minimising negative effects. In this thesis I use life cycle assessment (LCA) to assess the carbon sequestration potential of three GGRTs: enhanced weathering, biochar and reforestation. I use case studies in São Paulo, Brazil for biochar and enhanced weathering, and in the Peruvian Amazon for reforestation. In addition, I use LCA to identify the most important processes in each system and to determine context-specific limits that switch the systems from net GHG sequestration to net GHG emission. Overall, this work promotes the use of LCA to consider GGRTs in their entirety and predict their context-specific carbon capture potential, along with their limitations and potential caveats to guide both the science and policy communities.

Water contamination and municipal waste management are two problems of global significance. The amount of municipal waste generated is expected to increase over the coming century as populations increase and become more urban in nature as developing countries become more developed. Furthermore, water contamination will also become an increasingly significant problem as developing countries become more industrialised. For this reason, solutions are needed to remove contamination from water, and to reduce the amounts of municipal waste being disposed of in unsustainable ways. The main objective of this thesis was to assess the adsorption ability of biochar produced from mixed municipal discarded material (MMDM) in a novel heat pipe reactor. Another novelty of this thesis is that the use of heat pipes limits the pyrolysis temperature for safety reasons, dependent on the working fluid used. Consequently, biochar produced in the heat pipe reactor contains more oxygen containing functional groups. These interact with aqueous metals in complexation interactions and participate in hydrogen bonding with functional groups present in some organic contaminants. The biochar adsorbent was characterised using scanning electron microscopy, energy dispersive x-ray analysis, x-ray diffraction crystallography, Fourier transmission infra-red spectroscopy, and Raman spectroscopy. Following characterisation, batch adsorption experiments were conducted using either copper, methylene blue or tetracycline as the target adsorbate. Batch adsorption experiments were analysed using kinetic, diffusion and isothermal models. This thesis used the non-linear equations of adsorption kinetics and isotherms to remove the transformation errors caused through using the linear kinetic and isothermal models that are commonly used in literature. This thesis shows that biochar produced using MMDM in a heat pipe reactor can produce an adsorbent that is comparable to other biochar in literature. Copper adsorption reached a maximum of 6.3mg/g, methylene blue adsorption reached a maximum of 7.3mg/g, and tetracycline adsorption reached a maximum of 9.84mg/g. Typically, Elovich and pseudo second order kinetic models were the best fitting adsorption kinetics, with the Langmuir isotherm best describing copper adsorption, and the dual mode isotherm best describing the methylene blue and tetracycline adsorption. Biochar produced from MMDM is shown to be a promising adsorbent material that could be used in various water treatment applications. Further activation/functionalisation could produce an adsorbent material from discarded materials that could rival current commercial activated carbons. This highlights how this material could be used in a holistic circular economy approach to waste management and water treatment.

Phosphorus (P) is a irreplaceable element essential for life. It is relied upon, as mineral-derived phosphate fertilisers, for maintaining global agricultural productivity. Excess P in surface water causes eutrophication, where hypoxic effects and algal toxins degrade the environment and are hazardous to health. Therefore, the removal of P from wastewater, before the discharge of effluents to the environment, is important. Additionally, due to the finite nature of geological sources of mineral P, it is now crucial that P is not only removed from wastewater but captured in forms suitable for its direct reuse as recovered fertiliser. There are various routes to achieving this, however approaches developed can be limited to large wastewater treatment plants or have limited ability to remove P to the low concentrations (<1 mg P/L) increasingly required by legislation. Biochars, as adsorbents for the recovery of P, are attractive due to their known native soil ameliorant and carbon sequestration properties. Biochar-based materials saturated with P could have further benefit as being a recovered P fertiliser. This thesis has critically reviewed the feasibility and trends in the various technological approaches for the recovery of P from wastewater treatment plants and also the state-of-the-art in the development of biochar and biochar-based materials for the capture of P. Complimentary characterisation approaches suitable for biochar analysis related with its environmental uses were assessed before subsequent work investigated the forces driving the capture of P with biochar derived from various sources. This work found that the concentration of Ca and Mg within various unmodified biochars was the main driver of P adsorption, with CO[sub]2 activation (carried out to increase biochar surface area and porosity) providing only a limited improvement. Building on this initial work, the thesis has culminated in the development of novel modified biochars with enhanced properties for the efficient recover of P. Various biochar composites removed >90% of P from an initial concentration of 10 mg P/L and presented moderate release of P after extraction at mildly acidic and basic pH, which attempted to replicate soil solutions. Upon further study through isotherm and kinetics experiments the adsorption was found to occur at a rapid rate (reaching equilibrium within < 5 min); whilst maximum capacities were modest in most cases (10-15 mg P/g composite), the heat of adsorption was found to be higher than commonly reported in the literature. This thesis has made a significant contribution to the analysis, use, and mechanisms involved in biochar-P interactions, and has furthered the development of biochar composites with improved properties for P recovery through novel routes.

Peat is a type of soft soil with very high organic and water contents. It lacks any kind of structure, which makes it extremely compressible and weak. These are highly undesirable physical characteristics when considering a site for construction, as they significantly increase the risk of large differential settlement. In countries like Malaysia and Indonesia where peat covers about 8 and 14% of the land areas, it is not always possible to avoid construction on peaty regions. Geotechnical engineers have developed several techniques to circumvent the issue and build safely on peatland. One of the most common techniques uses chemical binders with cementitious properties where hydration reactions create bonds reinforcing and strengthening the peat soil matrix. Among the selection of binders available, Ordinary Portland Cement is the most common due to its wide availability. Past experiences and research have reported the cement stabilisation of peat to be largely effective. However, one of the main disadvantages is the large quantity of binders required before stabilisation is effective, making it uneconomical. Sand is often used as a supplementary material in cement stabilisation of peat in an effort to reduce the amount of binder required. However, both sand and cement are produced or mined from rapidly depleting natural resources. Therefore, in recent years, there has been a concentrated effort to research the use of alternative materials from more sustainable sources or recycled waste materials. Biochar is a product of pyrolysis where biomass is decomposed in the absence of oxygen and has been widely researched for its exceptional soil amendment qualities to improve crop yields, carbon sequestration potential and the ability to remediate contaminated lands. No research has been conducted on its potential use as a supplementary material in chemical soil stabilisation. In the early stages of this investigation, a proof of concept study was set up to evaluate its potential in cement stabilised peat. The outcome of the study was overwhelmingly positive with the biochar enhanced cement stabilised peat performing noticeably better even at a very low dosage (10%). The main objectives of this investigation are to evaluate the static and dynamic performance of biochar enhanced cement stabilised peat. The results of the static tests show that biochar crushed to a size smaller than 75 µm performs significantly better than sand as a filler. Samples with 10% cement and 40% biochar matched the performance of the control sample with 20% cement only, without biochar. This gives confidence that biochar has the potential to partially replace cement binder while retaining similar performance for a more cost-effective and environmentally friendly application. Scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) tests were used to study how the mechanisms of hydration change to the inclusion of biochar. The micrographs from SEM confirmed that the inclusion of biochar crushed to a size smaller than 75 µm produced a much more homogenous soil matrix which correlates to a performance increase. The results from XRD also showed a decrease in $C_2S$ clinker material in the biochar enhanced samples which is a good indication of an increased hydration. The findings from the bender elements tests and cyclic triaxial tests showed that the shear stiffness increased with the inclusion of biochar. And finally, the increase in performance in biochar samples translated to a small amount of cumulative plastic strain under cyclic loading.

Abandoned metal mines and the large quantity of tailings deposited around these mines, which are rich in heavy metals, represent a significant threat to terrestrial, aquatic and atmospheric environments. The heavy metal content of mine tailings is a serious contamination issue worldwide. These elements can be transferred through the food chain and accumulate in the human body, causing considerable harm due to their carcinogenicity, mutagenicity and teratogenicity. Thus, it is extremely important to remove heavy metals from polluted media (tailings, soils and water) and/ or to inactivate them within these media in order to conserve human health and permit continued use and development of urban and rural land. Therefore, the remediation of multi heavy metal-contaminated sites was investigated using different approaches and under various conditions to reduce the phytoavailability of cadmium (Cd), zinc (Zn), lead (Pb) and copper (Cu) in mine tailings collected from Parys and Britannia copper mines, and Pandora lead mine located in North Wales, UK. A sequential extraction protocol was applied to examine the distribution of studied heavy metals among different geochemical fractions and to evaluate the effectiveness of the remediation strategies in reducing target metal availability. The metal fractionation results obtained showed that the chemical dynamics of target metals were similar in Parys and Britannia copper mines with the majority of studied metals associated with the residual fraction. However, the exchangeable fraction retained high proportions of investigated metals in Pandora tailings. Organic and inorganic amendments individually and in combination with the phytoremediation technique were examined in terms of their ability to reduce the mobility and phytoavailability of target metals to plant and soil biota. Application of 2% of several organic and inorganic amendments (zero valent iron (Fe0), zeolite, green waste biochar and green waste compost) to Pandora and Parys tailings was investigated during a 1-year pot experiment under uncontrolled conditions in Henfaes research station. The application of 2% of amendments modified several physiochemical properties of treated tailings particularly highly acidic tailings with various effects on the bioavailability of target metals. The added amendments reduced the metal availability at the beginning of study, but with time the mobility of investigated metals fluctuated and was higher than in the control treatments on several occasions. We concluded that 2% of amendments was not sufficient to reduce the mobility of several metals. A greenhouse trial using different mixtures of tailings and uncontaminated soil (US) was conducted using ryegrass as a bio-indicator of phytoremediation technology. The results showed that applying US enhanced plant biomass production and ryegrass roots accumulated higher levels of heavy metals than shoots with lower levels of heavy metals toxicity indicated e.g., shortness of plant shoots and roots and chlorosis. Ryegrass roots accumulated higher levels of target metals with low translocation of heavy metals to the vegetative parts, with the exception of Zn. Thus, ryegrass may be an effective plant to use for the phytostabilisation of heavy metals in both sites, and a hyperaccumulator plant appropriate for the treatment of Pb in Pandora mine tailings. The metal content in grass tissue depends on the phytoavailable fraction of the metal. Plants grown in Pandora tailings accumulated higher concentrations of heavy metals in their roots than grass planted in Parys tailings, reflecting the higher occurrence of studied metals in the exchangeable fraction in Pandora tailings compared with Parys tailings. The co-amending mine tailings experiment was conducted to examine the effect of applying phytoremediation (ryegrass) in combination with two types of amendment (Fe0 and green waste compost, added separately to target tailings). Results indicated that the applied amendments increased the pH of severally acidic tailings (Parys tailings) more effectively and compost was more effective than Fe0 particularly at a higher dosage to promote ryegrass biomass productivity. Fe0 did not show significant enhancement of grass biomass production even at a higher dosage. The amendments had various effects on of target metal phytoavailability, metal uptake and translocation within plant tissues. Compost reduced the translocation of Cu, Zn, Pb and Cd within grass tissues in treated Parys mine tailings. For Pandora tailings both amendments increased Cu translocation within grass tissues, but Zn immigration from roots to shoots decreased. Also, the uptake of Zn and Cd by grass roots increased, but Pb uptake was reduced by the addition of amendments to Pandora tailings. Pb isotopic studies suggested that geogenic routes seemed to be the main source of Pb fingerprinting in Parys tailings, but in Pandora mine tailing the ore processing of Pb appeared to be the major route of Pb pollution. In addition, the applications of compost and Fe0 did not result in a significant alteration in the Pb isotopic content of ryegrass tissues. Overall, application of green waste compost supported the establishment of ryegrass cover on mine sites, thus reducing the erosion of mine tailings by wind and rain. This approach also promoted the growth of deep grass roots, which increased the ability of ryegrass to take up heavy metals for storage in the roots or translocate them to aboveground parts prior to harvesting and safe disposal. The application of ryegrass and compost can be used to amend soils exposed to heavy metal contamination by any source including mine tailings. Further studies are necessary in controlled and uncontrolled conditions to examine the feasibility of using several native plant species supported by organic matter application for phytoremediation of mine tailings.

Contaminated land is a widespread, global issue affecting millions of people. Atrazine is a commonly used herbicide which often contaminates groundwater and drinking water supplies and is associated with adverse health outcomes. Biochar is the solid product of pyrolysis and is associated with several environmental benefits. It may be an effective remediation tool when used as a soil amendment. This thesis investigates the mechanisms through which biochar can immobilise atrazine, and the implications of the mechanisms for remediating contaminated land. Nine biochar samples were obtained from the United Kingdom Biochar Research Centre , which were produced from softwood pellets (SWP), wheat straw pellets (WSP), miscanthus straw pellets (MSP), rice husk (RH) and oil seed rape (OSR) each at pyrolysis temperatures of 550°C and 700°C (excluding OSR at 700°C). The sorption mechanisms controlling atrazine sorption to these biochars were determined through various characterisation methods and batch sorption experiments. The sorption tests showed that sorption to each of the standard biochars occurs via multiple simultaneously occurring mechanisms, which are each promoted under certain conditions. Studies investigating sorption kinetics, isotherms and interactions with humic acids showed that for all biochars in this study, pore filling was a significant process through which atrazine is transported to adsorption sites, although poor intraparticle diffusion for softwood and oil seed rape biochars can prevent efficient transport. Wheat straw and rice husk biochars showed effective pore diffusion, resulting in high sorption capacities. Partitioning was associated with poor remediation outcomes and was significant to softwood biochars, although adsorption dominated overall sorption for all other biochars. pH was shown to significantly influence the occurrence of various sorption mechanisms. At low pH values, most biochars showed evidence of electrostatic repulsion between positive atrazine species and the positively charged biochar surface. At intermediate pH values, all biochars showed strong hydrogen bonding between H+ groups on the surface of the biochar and atrazine. A meta-analysis of previous relevant studies provided further evidence for hydrogen bonding of atrazine to biochar and showed that hydrophobic effects likely play little role in adsorption after accounting for the effects of surface area. Varying contributions of π-π EDA interactions, hydrogen bonding involving biochar O- groups, and interactions with ash minerals resulted in different sorption profiles for each biochar at high pH values. In order to further determine the mechanisms controlling sorption at high pH, surface compositions of SWP550, RH700 and OSR550 biochars were modified using hydrofluoric acid. Modification with hydrofluoric acid successfully removed the ash contents of rice husk and oil seed rape biochars and reduced atrazine removal at high pH values. This suggested that the ash fraction increases atrazine removal at high pH through complexation or catalytic hydrolysis. The roles of the various mechanisms are related to remediation outcomes in a novel manner allowing for the improved design of biochar for environmental remediation.

Methane is a potent greenhouse gas with a global warming potential 21 times that of carbon dioxide. Globally, ruminants are the main anthropogenic contributors to methane release to the atmosphere. Methane is produced in the gastrointestinal tract of ruminants, mostly within the rumen by methanogenic archaea. However, methane production represents a loss of 2 to 12% of dietary gross energy for the animal, which could otherwise be available for growth or milk production. Therefore, mitigation of methane production by ruminants could produce both economic and environmental benefits, with more sustainable and energy efficient livestock, and offering a promising way of slowing global warming. Despite extensive research undertaken to find ways of reducing methane emissions from ruminants, progress has been relatively limited. Furthermore, there is still a lack of studies linking rumen microbiology and ruminant nutrition and production. The central purpose of this research was to investigate feed additives to reduce methane emissions and to understand associated changes that occur in the rumen microbiota. For the first experiment (Chapter 2), biochar was evaluated as an antimethanogenic compound for beef cattle. The in vitro gas production technique was used to study the effects of biochar on rumen fermentation and methane production. Overall, methane production was reduced by 5% by the addition of biochar compounds (10 g/kg of substrate). The observed reduction in methane produced was not associated with a change in volatile fatty acid profile suggesting biochar primarily inhibited fermentation. Ammonia concentration was significantly reduced with biochar inclusion. Because different biochars had different effects on methane production, further investigation of relationships between the physicochemical properties of biochars and antimethanogenic effects are necessary. However, due to the small reduction in methane production recorded, research with biochar was discontinued. Encapsulated nitrate was then explored as an antimethanogenic additive and as an alternative non-protein nitrogen source to urea (Chapter 3). The effect of using encapsulated nitrate as a replacement for urea or dietary protein, plus the addition of inorganic sulphur, on enteric methane emissions, nutrient digestibility, nitrogen utilization and microbial protein synthesis from crossbred beef steers were studied. In addition, nitrate toxicity and eating behaviour were investigated. The inclusion of encapsulated nitrate reduced methane production compared to urea and a true protein source, with no adverse effects on rumen fermentation or nitrogen metabolism and no effects with the inclusion of elemental sulphur. The level of addition of encapsulated nitrate (14.3 g nitrate /kg DM) and the time of adaptation chosen for this study (14 days) were adequate to avoid nitrate toxicity. Finally, the effects of adding nitrate inclusion to different basal diets on rumen microbial populations and relationships of these populations with methane production were investigated (Chapter 4). The V4 hypervariable regions of the bacterial and archaea 16S rRNA genes were amplified and sequenced. Effects on microbial population induced by nitrate were dependant on the basal diet but nitrate altered specific archaeal and bacterial OTUs consistently between studies. A direct and strong correlation between some archaea taxonomic groups and OTUs with methane production was observed.

Despite recent instability in the global supply of phosphate-rock derived fertiliser and the potential for this to continue into the future, the recovery of phosphorus (P) from wastewater treatment systems, where P is abundant and accessible, is well below maximum potential. Considerable resource is spent on removing P from wastewater in order to comply with environmental standards and to protect aquatic ecosystems from eutrophication, yet there is little emphasis on capturing the P in a way that is optimised for re-using it as agricultural fertiliser. To address this lack of innovation in the face of climate change and food insecurity, a concept for a material capable of capturing P from wastewater was developed, with an emphasis on the utilisation of otherwise waste materials and the use of carbon neutral or negative production technologies. Based on the demonstrated P capture properties of coal minewater treatment waste (ochre) and biochar made from anaerobically digested feedstocks, a range of biochars were designed and produced using different mixtures of ochre (“OC”), sourced from the UK Coal Authority Minto minewater treatment scheme in Fife, Scotland and anaerobically digested sewage sludge (“AD”), sourced from the Newbridge wastewater treatment plant in Edinburgh. A first generation of materials consisting of either AD or a 1:1 mixture (dry weight basis) of OC and AD were produced in a small-scale batch pyrolysis unit at two pyrolysis highest treatment temperatures (HTTs) (450 and 550°C) to give the biochars AD450, AD550, OCAD450 and OCAD550. These were tested for their P capture properties in repeated P-exposure experiments with pH buffering in comparison to unpyrolysed ochre, activated carbon and a natural zeolite. After 5 days of repeated exposure to a P solution at a wastewater-relevant concentration (20 mg P l-1) replenished every 24 h, relatively high masses of P were recovered by ochre (1.73 ± 8.93×10-3 mg P g-1) and the biochars OCAD550 (1.26 ± 4.66×10-3 mg P g-1), OCAD450 (1.24 ± 2.10×10-3 mg P g-1), AD450 (1.06 ± 3.84×10-3 mg P g-1), and AD550 (0.986 ± 9.31×10-3 mg P g-1). The biochar materials had higher removal rates than both activated carbon (0.884 ± 1.69×10-2 mg P g-1) and zeolite (0.130 ± 1.05×10-2 mg P g-1). To assess the extractability of recovered P and thus potential plant bioavailability, P exposure was followed by repeated extraction of the materials for 4 days with pH 7-buffered deionised water. The AD biochars retained 55% of the P recovered, OCAD biochars 78% and ochre 100%. Assessment of potentially toxic element (PTE) concentrations in the biochars against guideline values indicated low risk associated with their use in the environment. A second generation of materials were produced to examine the scalability of the concept. Mixtures of AD and OC were pelletised with a lignin binder (89.1:9.9:1.0 ratio, dry weight basis) and AD was pelletised with binder (99:1 ratio, dry weight basis). The pelletised feedstocks were pyrolysed in a bench-scale continuous flow pyrolysis kiln at the same two HTTs to give the pelletised biochars PAD450, PAD550, POCAD450 and POCAD550. Analysis of digested biochar samples compared to the previous generation of biochars showed general similarities between the two groups, apart from the substantially lower Fe content. Sub-samples of the pelletised biochars were exposed to a 20 mg l-1 P solution over 6 days, with the solution replaced every 24 h to give the P-exposed biochars EPAD450, EPAD550, EPOCAD450 and EPOCAD550. To probe the mechanisms of P capture by these materials and how feedstock preparation and pyrolysis conditions affected these, spectroscopic analysis using laser-ablation (LA) ICP-MS, X-ray diffraction, X-ray photo-electron spectroscopy (XPS) and scanning electron microscopy coupled with energy dispersive X-ray was performed. The results highlighted the general importance of Fe minerals in P capture and subsidiary roles for Al, Ca and Si. A 3-week barley (Hordeum vulgare) seedling growth experiment was conducted using the pelletised and P-exposed biochars, in comparison with other biochars produced using feedstock which contained high amounts of PTEs. The biochars were also extracted using a range of different methods used to assess the bioavailability of PTEs and nutrients in soils, and the results compared to digests of barley leaves to identify whether any of these could reliably predict plant bioavailability in biochar. The above ground biomass and its total P concentration of barley grown in a 5% mixture of EPOCAD550 in sand was significantly higher than the control (p < 0.05 and p < 0.01, respectively). A significant positive correlation between mean leaf P mass and dry weight leaf yield (R2 = 0.865, p < 0.001) was found, indicating that dry weight yield could be used as an indicator for the P fertilising capability of biochar for barley seedlings. Element concentrations in unbuffered and buffered and (pH 7) 0.01 M CaCl2 biochar extractions were significantly positively correlated with plant leaf concentration for 6 of the 18 elements investigated, more than any of the other extractions. A longer barley growth experiment was conducted, using rhizoboxes, to test the bioavailability of P in the biochars compared to conventional fertiliser. The pelletised and Pexposed biochars were applied to a sandy loam soil with P constraints. Biochar application rates were based on 2% formic acid extractable P, calculated for summer barley using Index 0 soil. Analysis of total leaf length at harvest (12 weeks), dry weight yield, leaf P concentration and leaf P mass showed no significant differences between the biochar treatments, NPK fertilised and NK fertilised controls. This shows that biochar, when applied at low total application rates based on extractable P, is as effective as conventional fertiliser. Now that AD biochar materials have been shown to have useful phosphorus recycling properties in laboratory experiments, additional work is required to optimise their use in wastewater and agricultural systems. The next stage of research should determine their performance in flow-through filtration systems with simulated and real wastewater effluent, as well as their performance in field trials with different crops of interest to demonstrate their potential as viable alternative fertilisers.

Maintaining an adequate level of soil organic matter and nutrients cycling is crucial to the success of any soil management in the humid tropics. Cover crops, compost, or manure additions have been used successfully to supply nutrients to crops but the benefits of such amendments are often short-lived in the tropics, since decomposition rates are high. This study focused on charcoal which, when utilised as a soil amendment is termed ‘biochar’. Throughout this thesis, the terms ‘charcoal’ and ‘biochar’ are used interchangeably depending on the context. Charcoal exhibits physiochemical properties potentially suitable for soil improvement as well as for the safe and long-term storage of carbon in the environment. As a way of investigating its recalcitrance as a carbon store, O:C ratios have been shown to reflect the extent of oxidation and therefore decomposition of charcoal. This study aimed to fill a gap in the research by describing the effects of biochar on the water retention capacity of soil under laboratory conditions. It also provides a detailed snapshot of the first ten years of recalcitrance under natural conditions, using X-Ray Photoelectron Spectroscopy (XPS) to determine elemental oxygen and carbon ratios of whole charcoal fragments and how these are affected by the surrounding environment over time. Mechanisms of oxidation are described, showing how both biotic and abiotic factors influence the degradation of charcoal in the soil. It also investigated how these properties affect the nutrient and water retention capability of charcoals of different ages in the laboratory. Results of charcoal/soil mixtures showed significant reduction in nitrate leachate losses with no reduction in performance over a ten year period of residing in the soil. It was also shown that charcoal addition to a sandy soil resulted in a significantly increased available water content. Both these results were argued to support the idea that charcoal is of potential beneficial amendment to sandy, degraded soils.

Biochar has been heralded as a promising technology for climate change mitigation that can also benefit soils. Biochar is a carbonaceous solid produced by pyrolysis of biomass – the thermal decomposition of plant and plant-derived matter in the absence of oxygen. When added to soils, biochar has the potential to increase crop yields and suppress soil emissions of greenhouse gases, whilst sequestering carbon in a stable form. In addition to biochar, biomass pyrolysis produces liquids and gases that can serve as biofuels. Biochar production systems that generate excess heat or power are particularly environmentally and economically attractive. Rotary kilns are the favoured process reactor in many industries, given their potential to handle a wide range of feedstocks and provide good process control. This thesis investigates the potential to coproduce biochar and excess biofuels by slow pyrolysis in a pilot-scale rotary kiln. The work attempts to progress towards the ultimate aim of scaling up the rotary kiln and optimising its operating conditions to produce biochar of good quality along with an excess of useful biofuels. Experimental work, involving the development and application of new methodologies, was used to gain a better understanding of the process. The data gathered were then used to support preliminary numerical simulation efforts towards the development of a comprehensive process model. Five biomass feedstocks were considered: softwood pellets, miscanthus straw pellets, wheat straw pellets, oilseed rape straw pellets and raw rice husks. The granular flow of biomass feedstocks was observed in a short closed drum faced with acrylic and resting on rollers. All pelletized feedstocks displayed similar angles of repose, validating the use of softwood pellets as a model biomass for these feedstocks. Bed mixing, which can improve product uniformity, was slow under typical operating conditions, requiring 5 min to complete at 4 rpm for softwood pellets. Mixing quickened considerably at higher rotation rates. A digital image analysis method was developed to measure the distribution of solid residence times inside the rotary kiln. The mean residence time of softwood pellets ranged from 19 to 37 min under typical operating conditions, decreasing with increases in kiln rotation rate, but mostly unaffected by feeding rates. These findings show that kiln rotation rates must be selected to balance the residence time of solids inside the kiln with bed mixing levels. Thermogravimetry and differential scanning calorimetry were performed on samples of ground softwood pellets under five different heating profiles to study the kinetics and heat flows of the pyrolysis process. Both exothermic and endothermic regions were identified, with most reactions taking place between 250°C and 500°C. Results suggest that exothermic pyrolysis reactions can be promoted by altering the process heating rate, thereby improving net biofuel yield from the process. The thermogravimetric data collected was used to develop a distributed activation energy model (DAEM) of the kinetics of softwood pellet pyrolysis for integration into a comprehensive model of the process. The applicability of the kinetic model to large-scale processes was confirmed using a simplified process model developed to simulate biomass pyrolysis inside the pilot-scale rotary kiln. Although crude, the simplified process model produced sufficiently accurate estimates of char yield for preliminary design purposes. The simplified model also allowed important process parameters, such as kiln filling degree, solid residence time and heating rate, to be evaluated. A series of pyrolysis experiments was performed on the pilot-scale rotary kiln to evaluate the yields of biochar and biofuels and determine the temperature profile inside the kiln. This work required the design of a suspended thermocouple system that measures temperatures along the kiln, both in the gas phase and inside the solid bed. For most experiments at 550°C, a region of high temperature gas and solids was observed, possibly indicative of exothermic reactions. Biochar yield varied from 18% to 73% over the range of feedstocks and operating conditions tested. A vapour sampling methodology that relies on the use of a tracer gas was developed to determine the yield of pyrolysis liquids and gases. Due to analytical difficulties, it was not possible to obtain accurate mass closure with this method. However, the methodology revealed significant air ingress into the pilot-scale rotary kiln that is responsible for partially combusting biofuels produced by the process, thereby reducing their calorific value. Energy balances on the kiln confirmed that the calorific content of pyrolysis liquids and gases exceeds the energetic demand of the process, yielding between 0.3 and 11 MJ in excess biofuels per kg of biomass feedstock. An attempt was made to develop a multiphase model of the flow of vapours and solids inside the rotary kiln using computational fluid dynamics (CFD), but the continuous modelling approach was found inadequate to simulate the dense bed of biomass inside the kiln. The discrete element method (DEM) was sought as an alternative to model the granular flow of biomass inside the kiln. Extensive parameter calibration was required to reproduce the experimental behaviour of softwood pellets observed in the short closed drum. A model of the pilot-scale rotary kiln was constructed to simulate particle residence times. Further parameter calibration was required to replicate softwood pellet holdup inside the kiln. The calibrated model was able to reproduce the mean residence time of softwood pellets within 10% under different kiln operating conditions. However, simulated residence time distributions could not be established as a result of the long execution times required for this modelling work. Few data are currently available on large-scale continuous biomass pyrolysis processes; the experimental data gathered in this thesis help to fill this gap. Along with the numerical simulation work presented herein, they provide the foundation for the development of a comprehensive model of biomass pyrolysis in rotary kilns. Such a numerical model would prove invaluable in scaling up the process and maximizing its efficiency. Future work should consider the agronomic value and carbon sequestration potential of biochar produced under different operating conditions. In addition, the performance and efficiency of different conversion technologies for generating heat and power from biofuels need to be investigated.

For widespread use of biochar in agriculture and horticulture, it must be ensured that application will neither adversely affect soil and plants, nor exceed legislated contaminant concentrations. The most relevant groups of contaminants in biochar are potentially toxic elements (PTEs), polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOC). In this thesis, the concentrations of these groups of contaminants were analysed in 90 different biochars produced by slow pyrolysis. Subsequently, the concentrations were compared to legislation/guideline threshold values and linked to production conditions. The risk these contaminants pose to plant growth was also assessed, to give recommendations on production of safe biochar. PTEs can neither be formed nor destroyed, which means their presence in biochar is predominantly determined by feedstock type. However, significant levels of Cr, Fe and Ni were introduced into biochar from the furnace steel, whilst PTEs with low boiling points, such as As, Cd and Zn, partially evaporated during pyrolysis. PTEs were not responsible for phytotoxic effects observed for PTE-rich biochars despite biochar’s exceedance of available and total PTE threshold values for soil and soil amendments. Although initial tests were promising, the risk that PTE-rich biochars as amendment for soil and growing media pose, needs further investigation. The PAH concentration in biochar was markedly reduced by increasing carrier gas flow rate, and the type of feedstock also influenced the PAH content. However, there was no clear dependence of pyrolysis temperature on PAH concentrations, which was attributed to PAHs being increasingly formed and evaporated at higher pyrolysis temperatures. Ultimately, condensation of pyrolysis vapours and deposition on biochar was identified as the main risk for biochar contamination with PAHs, as this resulted in elevated concentrations of high-risk, higher molecular weight PAHs. Weaknesses in the pyrolysis unit design, such as cold zones, resulted in elevated concentrations of VOCs, as well as PAHs, in biochar. Comparing concentrations and phytotoxic potential of both compound groups, it was concluded that observed toxic effects were much more likely caused by VOCs in biochars containing both contaminants. Overall, formation of VOCs and PAHs cannot be prevented, but their presence in biochar resulting from retention and deposition can be minimised.

Biochar has often been described as a "win-win" technology for soil fertility, agronomic yields, carbon sequestration and poverty reduction. However, despite a growing body of physical research evidence to support these claims, there is much less socio-economic evidence for biochar's potential to achieve these "winwin" outcomes in real-world systems. Consequently, debates about biochar and its potential to contribute to sustainable development have often been polarised between extremes of opinion, with some claiming it is a key technology for mitigating climate change, and others warning of potentially dire effects for ecosystems and vulnerable populations. This inspired the objective for this PhD, which is to generate research that can inform and moderate the debate on biochar's win-win potential. Guided by the theory of ecological modernisation, this PhD aimed to generate a body of applied, policy-relevant research on the economic and environmental potential of biochar as a win-win use of biomass resources. It was important to adopt geographical and biomass boundaries for the research to provide a meaningful and focused contribution, therefore the research is focused on China and its agricultural straw residues. One of the central claims for biochar is that it can improve crop yields and, consequently, reduce poverty for smallholder farmers. This thesis investigated this from a socio-economic perspective using farm-scale linear programming models with primary data from interviews conducted across four contrasting Chinese agricultural systems. The results suggest that biochar is unlikely to provide even minor economic gains, let alone poverty-reducing change, to smallholder farmers in these systems. If biochar is not economic for farmers, there is a possibility that economies of scale made possible by business ventures could reduce the marginal costs per unit of biochar product and/or that governments/climate finance institutions may be interested in subsidising this technology where it has significant carbon mitigation impacts. Thus the next research question was whether biochar might be a profitable investment for businesses in China, and further whether businesses might also profit from carbon credits/subsidies where biochar's carbon sequestration potential is valued either by carbon markets or by climate conscious governments willing to provide appropriate incentives. Life-cycle and cost-benefit analyses demonstrated that, when compared to the main competing uses for straw feedstocks (briquetting for combustion in boilers, and gasification for electricity generation), pyrolysis of straw to produce biochar makes a financial loss under all subsidy scenarios considered, and is the least cost-effective technology for carbon sequestration. Overall it seems biochar made from China's straw feedstocks is not currently a win-win option for smallholder farmers, business investors or national/international climate mitigation strategies. In light of the relative dominance of bioenergy over biochar production as a financial and climate mitigating option for China's straw, the focus of the thesis shifts to explore win-win scenarios in this domain. Here the results are more promising. Combining a unique geographical dataset of China's coal fired powerstations and straw location with data on energy economics, the model suggests a small tweak to China's bioenergy subsidy system (an extension of the existing feed-in-tariff to include low energy replacement ratio cofiring) could contribute 42-62% of China's 2020 target to install 30GW of renewable energy generation capacity: a classic win-win scenario for the Chinese government's bioenergy targets, bioenergy investors and global climate change. Overall this thesis offers two main findings to the literature. Firstly it demonstrates that, within its current high application rate model, biochar will struggle to compete as a win-win strategy when viewed through financial and carbon sequestration lenses. However, secondly, it suggests that win-win strategies are available for China's straw resources under cofiring bioenergy applications. The thesis concludes with a critical discussion of these results in relation to the theory of ecological modernisation and the concept of win-wins.

Biochar is the solid, carbon-rich by-product obtained from pyrolysis. It offers the prospect of long-term carbon sequestration and soil conditioning with agronomic benefits, often referred to as the ‘biochar effect‘. These multiple direct or indirect changes in the soil plant interface have also been associated with the control of plant diseases by influencing the host’s systemic induced resistance. The biological impact of biochar on the phytopathology of a major cereal grain has not yet been investigated. The most damaging foliar disease of barley in the UK is Rhynchosporium leaf blotch caused by the hemibiotrophic fungal pathogen Rhynchosporium commune. The aim of this project was to evaluate biochar performance and effectiveness as a disease control agent in the barley – R. commune – pathosystem, and attempted to identify underlying mechanisms by which biochar may function in the interaction between barley and the causal pathogen. Therefore, a unique set of nine slow pyrolysis biochars were established along a 350 to 800°C pyrolysis temperature gradient, with eight of these made from pelleted softwoods and a single one made from Miscanthus straw. A comprehensive biochar quality assessment was undertaken and established that the biochars differed in their chemical composition, which largely depended on production parameters, predominantly temperature (P < 0.05). The analysis proposed that biochar 9, made from Miscanthus at 800°C, showed added value as a soil conditioner over softwood biochars, due to higher pH, mineral ash and macronutrient recoveries, which pointed towards a possible liming potential. Regardless of the feedstock, biochars pyrolysed above 600°C indicated potential use for carbon sequestration purposes, due to higher carbon stability. Short-term controlled bioassays showed significant restricted growth of R. commune mycelium on defined medium to direct (1.0% w/w) and indirect volatile exposure from certain biochars (P < 0.001). The findings suggested a synergistic effect of the softwood biochars acidic nature and presence of fungicidal compounds, with observed inhibition of 100% attributed to re-condensation of tarry vapours onto biochar surfaces during pyrolysis. Qualitative biochar volatile organic compound analysis was conducted and identified biocide active phenolic and organic acid compounds, similar to those commonly found in smoke, bio-oils or wood vinegars. These findings proposed possible application for mitigation of inoculum pressure in field-grown barley, but the toxic nature of volatiles raised concerns over risks to human and environmental health, as also evidenced by detrimental barley growth effects. Subsequent controlled in vivo and in planta experiments revealed significant (P < 0.05) symptomatic barley leaf blotch reduction effects of up to 100%, following 5% (w/w) application of biochars 4, 5, 8 and 9. Barley plants transcriptional changes in ISR-dependent LOX2 and SAR-dependent PR1-b expression in planta verified systemic induced resistance as mechanisms behind the significant disease suppression of barley plants grown in soil amended with biochar 5 and 8. Disease reduction and biochar mediated induced resistance was attributed to either low concentrations of phytotoxic compounds, a direct toxicity effect from fungicidal compounds or indirect promotion of beneficial microbes. The results provided evidence, that in the case of the studied pathosystem, there is potential for biochar with specific characteristics to be considered as a soil amendment, offering not only carbon sequestration, but also possible improved disease resistance.

Nitrous oxide (N2O) is a powerful greenhouse gas (GHG) which has a global warming potential 296 times greater than that of carbon dioxide (CO2). Agriculture is a major source of N2O and in the UK approximately 71 % of N2O emissions are produced by agricultural soils, mainly as a result of the application of nitrogenous fertilisers. Despite previous research into agricultural N2O emissions which has demonstrated that N2O emissions have high spatial and temporal variability, there is still a lack of knowledge surrounding the factors that influence the magnitude of emissions from agricultural soils. Agricultural N2O emissions for the UK’s annual GHG inventory are currently estimated using a 1.25 % emission factor (EF) (to be decreased to 1 % in 2015) which assumes that 1.25 % of applied nitrogen (N) fertiliser is emitted as N2O. The EF does not take into account influencing factors such as location or fertiliser type. Mitigation of N2O emissions is vital if future climate change is to be prevented, yet this must also be combined with the need to intensify agricultural production to feed the increasing global population. Biochar which is a carbon rich material produced during the pyrolysis of biomass has been identified as a potentially useful soil amendment with the ability to mitigate N2O emissions. However, most previous research has focused on laboratory scale experiments and there is a need to investigate the use of biochar in a field environment. Other N2O mitigation options such as nitrification inhibitors, or altering fertiliser management practices, require testing under different conditions to assess their suitability for use. This thesis aims to investigate a). The factors affecting N2O emissions from synthetically and organically fertilised arable soils, and b). To explore the potential of various N2O mitigation options for arable systems, including biochar. This thesis firstly investigates N2O emissions from synthetically fertilised arable soil. Varying application rates of ammonium nitrate fertiliser were applied to a Scottish arable soil during a year long field experiment and the effects of mitigation options such as a nitrification inhibitor (DCD) were assessed. N2O emissions were shown to be significantly affected by soil water filled pore space and the 1.25 % EF was demonstrated to be generally greater than those calculated in this experiment. The use of DCD significantly decreased N2O emissions and crop yields. A second year long field experiment was carried out to investigate N2O and NH3 emissions from an organically fertilised arable soil and to explore the effect of the timing, form and method of organic fertiliser application on emissions and EFs. Slurry, poultry litter, layer manure and farmyard manure were applied in the autumn and the spring. Cumulative N2O emissions were generally greater from the autumn applications and NH3 emissions were greater from the spring applications, due to wetter soil conditions and incorporation of fertiliser during the autumn. The type of fertiliser applied affected the magnitude of emissions with the greatest cumulative N2O and NH3 emissions from the layer manure. The method of fertiliser application had no effect on emissions. The following experiment investigated the ability of different biochars to retain N from a solution and the effect of biochar particle size on retention. A batch sorption experiment was used to test the affinity and capacity of six biochars for ammonium (NH4+) and nitrate (NO3-) from different concentrations of NH4NO3 solution. All of the biochars studied demonstrated the ability to retain NH4+ and NO3- from solution although greater NH4+ retention was observed. Differences in biochar affinity for N could be explained by pyrolysis temperature, but there was no effect of particle size or pH. Oil seed rape straw biochar was demonstrated to have the greatest NH4+ and NO3- retention capacity and as such was chosen for use in the next experiment. This work investigated the potential for oil seed rape straw biochar to decrease emissions of N2O, CH4 and CO2 from stored slurry and whether any GHG mitigation effects would continue following application of the slurry to arable soil. The effect on emissions of amending the biochar and slurry mixture with DCD after application to the soil was also explored. There was no significant effect of the biochar on GHG emissions from the stored slurry although the slurry initially acted as a sink for N2O and CO2. There were no significant differences between emissions from any treatments following application to the soil. The overall results of these studies indicate that N2O emissions are highly dependent on weather conditions, and hence location, in addition to fertiliser type and application timing. It was concluded that the use of a standard 1.25 % EF for synthetic and organic N fertiliser applications for the whole of the UK is inappropriate. Mitigation options such as the use of DCD, altering fertiliser application season or fertiliser type have been shown to possess the potential to mitigate N2O emissions but tradeoffs between N2O and NH3 emissions, and impacts on crop yields must be considered. Biochar was demonstrated to retain NH4+ and NO3- ions and this property may account for biochar’s N2O mitigation capabilities as observed by previous researchers. However, if N retention is taking place, the N appears to still be available for production of N2O and crop uptake.

Artificial soils have been employed within the Biomes of the Eden Project since its construction in 2000. Produced from sand, bark, composted green waste and lignite clay, these soils were designed to have their nutrient concentrations controlled through careful fertiliser applications. However, following variable environmental conditions, management practices and planting, the soils across the site are performing variably with regard to nutrient retention and storage. Experiments were conducted to assess the performances of an artificial soil in terms of nutrient cycling. This was carried out in three phases: Firstly, soils from the Humid Tropics and Outdoor biomes were sampled and examined, using a range of analytical techniques, to determine the nutrient characteristics of the established artificial soils from across the Eden Project site. This demonstrated that many of the nutrient concentrations of the artificial soils were consistent with those reported for naturally formed soils within comparable environments. All soil samples were of sandy loam texture (ISO 14688-1), with the sand-sized fraction representing > 50 % of the particle size composition. Statistical analyses suggested that management practices had a greater impact on the nutrient characteristics of artificial soils than environmental conditions. Secondly, an artificial soil was produced, following the Eden Project protocol, to examine its performance under controlled environmental conditions. This was packed into 4 columns (1 m height by 110 mm diameter), maintained at 15 ˚C and subjected to an irrigation regime for 52 weeks. Following 26 weeks of irrigation, 2 of the 4 columns were fertilised. Leachate was analysed for dissolved constituents as were solid samples of the fresh soil and of soil samples collected from the columns following 52 weeks irrigation. Leachate concentrations for all nutrients, excepting phosphate, were observed to decline over the irrigation period. Leached phosphate concentrations increased from weeks 0 to 2, and then remained relatively constant. Low nitrogen concentrations within the leachate from weeks 2 to 38 were caused by nitrogen immobilisation within the soil, whilst subsequent mineralisation resulted in increased concentrations from Week 38. Analyses of solid phase constituents determined little variation with depth. Fertiliser application demonstrated a significant (p < 0.05) increase in leachate concentrations for some dissolved organic nitrogen and nitrate, phosphate, magnesium and calcium and a decrease in pH. Fertiliser application observations showed less prominent differences for the extracted and solid phase constituents. Thirdly, biochar was applied to the artificial soil at three concentrations (10 %, 5 % and 2 %) plus a control (0 %), to determine whether biochar application may improve nutrient characteristics of artificial soils. The biochar amended soils were packed into mesocosms and maintained at 15 ˚C for 6 weeks. In general, leachate analyses demonstrated a decrease in nutrient losses to leaching with increasing biochar concentration, highlighting the potential for improved nutrient retention within the soils.

Biochar production and application to soil can mitigate climate change and improve soil quality. This thesis investigated the influence of biochar preparation methods and application rates on the hydrological and erosional characteristics of biochars themselves and the soils to which they were applied. Biochar hydrophobicity was influenced by feedstock and decreased with increasing highest treatment temperature (HTT). Biochar did not influence soil wettability and the effect of HTT on biochar porosity was more important for soil water-holding capacity than its effect on hydrophobicity. HTT affected biochar yield, cation exchange-capacity and provision of fungal substrates. HTT also significantly influenced the effect of biochar on soil suction. Smaller feedstock particles produced biochars that were slightly more hydrophobic than those produced from larger particles. The effects of biochar application on the properties of sandy loam were influenced by biochar particle size, because larger particles had less effect on bulk density and had slower water uptake. A low biochar application rate (5 g kg-1) had no effect on the aggregate stability of a silt loam and did not affect the hydrological and erosional response of the soil under simulated rainfall. Application rates of 25 and 50 g kg-1 reduced aggregate stability, which led to surface sealing and overland flow generation occurring more readily. However, there was no more erosion of these soils than those with low or zero biochar content, and the crusts formed by seal drying were much weaker than those formed on soils with low or zero biochar. Biochar was preferentially eroded from the soils, regardless of the application rate used. HTT and particle size can have important implications both for the properties of biochar itself and for its effects on soil properties. However, biochar may only substantially influence soil hydrology and erosion when applied at sufficiently high rates.

Growing concerns about climate change and the inevitable depletion of fossil fuel resources have led to an increased focus on renewable energy technologies and reducing GHG emissions. Limiting the atmospheric level of CO2 is essential to prevent the most damaging effects of climate change. Among renewable energy resources, biomass combustion has the largest potential to contribute to global energy demands, however it is considered to be a carbon neutral solution and so only limits CO2 concentrations rather than reducing them. Through pyrolysis rather than combustion, biomass can lead to carbon negative liquid, gaseous and solid fuels while also offering a route for long term carbon storage in the form of biochar. Biochar is a carbonaceous material which has shown potential for improving soil fertility, reducing GHG emissions and most importantly long term C storage in the environment. However many questions still remain unanswered with regard to biochar, especially the influence that process conditions can have on its performance in soil as well as any potential trade-offs between soil amendment, C sequestration and heat/power generation. This thesis is therefore focused on assessing the influence that process conditions and feedstock selection have on biochar properties related to carbon stabilisation, improving soil fertility (functional properties) as well as the distribution of energy amongst the pyrolysis co-products. To achieve this, a systematic set of biochar samples was produced, using a wide range of pyrolysis parameters (highest treatment temperature (HTT), heating rate, residence time, carrier gas flow rate and feedstock type), and analysed for physicochemical and functional properties. Pyrolysis HTT consistently showed a dominant influence on determining the final yields and properties of biochar, while the effect of other production parameters was varied. In this thesis the candidate first studied the effect that process conditions had on the long term stability of biochar, as an important indicator of its ability to sequester carbon. While increasing the HTT resulted in a decrease in biochar yield, overall the yield of stable-C increased with temperature. This meant that by applying a higher HTT during pyrolysis a higher C sequestration potential for biochar was achieved. Next to be examined was the influence that process conditions had on other functional properties (labile-C yield, biochar pH, extractable nutrients and cation exchange capacity (CEC)) was then examined. The labile-C yield of biochar decreased with increasing HTT due to the release of volatile matter, while the CEC and concentration of extractable nutrients tended to be higher in biochar produced at 450oC rather than greater HTTs. Biochar pH was also highly alkaline at elevated HTT. This indicated that while high HTT favoured C sequestration and biochar pH, lower HTT may be more favourable for other functional properties. Furthermore by assessing the mass and energy distribution amongst the solid, liquid and gaseous fractions, it was possible to determine the energy balance of the process and through this evaluate the trade-off between the C sequestration potential of biochar and the energy output of the liquid and gas fractions. As the severity of pyrolysis was raised, the total energy stored within the liquid and gaseous co-products increased at the expense of the energy content of biochar, therefore increasing the available energy output of the system and reducing the energy lost when using biochar for carbon storage rather than for bioenergy. This also demonstrated that the pyrolysis process could be fine-tuned to increase the amount of stored C while also improving the heat/power generation of the system. The higher energy content of the gas stream at elevated HTT was also seen to contain sufficient energy to sustain the pyrolysis process, which would free up the solid and liquid fractions for higher value applications while reducing the necessity for external fuel sources. Finally, the data set was used to produce statistical models enabling the prediction of biochar stable-C yield as well as the heating value of biochar. The results of this thesis therefore demonstrate that through applying high HTT the potential energy output of the pyrolysis system can be increased while producing a biochar product with high C sequestration potential and positive functional properties for soil amendment. Due to potential trade-offs, the final choice of process conditions and feedstock would then be made based on the specific requirements of a selected site for biochar application. Understanding the influence that production conditions have on the functional properties of biochar as well as the energy balance of the system is critical to developing specifically engineered bespoke biochar, be it for agricultural use, carbon storage, energy generation or combinations of the three.

A loss of soil organic matter (SOM), whether through natural means or management practices, results in soil degradation. Biochar as a soil amendment can alter soil properties, ultimately affecting the availability of nitrogen and water to plants and thus crop growth. The effects of biochar are not definitive, and often dependent on both the soil type and the biochar applied. Biochar properties can change according to the feedstock and production parameters, thus for their effective use further investigation is required to link biochar properties to its effects in soil. A high-temperature (600˚ C) biochar from a mixed-hardwood feedstock was investigated. The biochar increased the soil water retention, as demonstrated by a water release curve and field trials. This retention was predominant at higher water potentials, which was attributed to the greater number of meso (storage) pores in the biochar. Biochar did not affect the soil’s saturated hydraulic conductivity; this is thought to be due to the low number of macro (transmission) pores in the biochar. Thus there was no effect on the transmission rate in the soil. Biochar reduced gross ammonium levels in the soil via adsorption, but resulted in increased non-exchangeable ammonium levels, possibly due to physical entrapment. Where carbon was already abundant in the organically managed soil, the adsorbed ammonium reduced nitrification through lower substrate availability. The range of carbon fractions added as a result of the biochar amendment increased the total organic carbon (TOC) content of the soil, but this supplementary carbon was released by the microorganisms as carbon dioxide. Microorganisms in the relatively carbon poor conventionally managed soil (with lower TOC), assimilated the additional labile carbon increasing microbial biomass. The higher microbial biomass, combined with improvements in pH and the higher ammonium levels (as a result of the ammoniacal fertiliser) increased nitrification. These changes in water and nitrogen availability did not alter crop yields as measured in the glasshouse and field trials. The effects of this biochar in a sandy agricultural soil depended on the type and level of carbon and nitrogen present in the soil, thus consideration of these factors should be taken when applying.