The Pyruvate dehydrogense complex (PDH) is a primarily aerobic enzyme which catalyses pyruvate to acetyl-CoA and carbon dioxide. Its counterpart in anaerobic metabolism is pyruvate formate lyase (Pfl) which converts pyruvate to acetyl-CoA and formate. A novel fermentation pathway involving PDH rather than Pfl (or equivalent), which retains the reducing equivalents from pyruvate oxidation, could provide a novel route for ethanol production, as well as changes in redox balance opening up opportunities for the production of higher alcohols such as butanol. Utilising PDH for the production of biofuels has been investigated in three microorganisms: Geobacillus thermodenitrificans, Bacillus subtilis, and E. coli. Geobacillus thermodenitrificans does express Pfl, thus PDH is always active in the G. thermodenitrificans regardless of whether the bacterium is growing in aerobic or anaerobic conditions. To utilise this PDH in the production of ethanol a bi-functional alcohol dehydrogenase (AdhE) was introduced to G. thermodenitrificans K1041. Further optimisation of ethanol production was achieved by knocking-out lactate dehydrogenase (Ldh), which would otherwise compete with ethanol for flux from acetyl-CoA, and activity of the PDH promoter verses potential alternative promoters to increase the expression of the native PDH was investigated. Like G. thermodenitrificans, Bacillus subtilis also does not have a PFL pathway, but does have a native Adh so can undergo fermentation, albeit poorly. To increase ethanol production competing fermentation pathways were knocked-out, however this resulted in strains which were unable to grow anaerobically. The activity of the native PDH promoter was investigated, and PDH subsequently upregulated. The production of 1-butanol from B. subtilis was also achieved using expression of Clostridial genes encoding a butanol synthetic pathway from a plasmid and from chromosomal integrations. PDH in Gram-negative bacteria such as E. coli are not active during anerobic growth due to fermentation resulting in elevated levels of intracellular NADH; which in turn triggers negative feedback inhibition of PDH. A consequence of this is E. coli strains which are engineered to produce increased titres of ethanol by knocking-out pfl are unable to grow anaerobically. To alleviate this problem a PDH from gram-positive bacteria was expressed in E. coli. The effect of these PDH was also used to assess their potential benefits on 1-butanol in E. coli, by introducing Clostridial genes encoding a butanol synthetic pathway via plasmids.

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The present study is in two parts, the first part describes an investigation that was undertaken to determine the feasibility and hydrodynamic behaviour of a cold model circulating fluidized bed system proposed for the continuous combustion-gasification of biomass. The design is based on the principle that the char produced in the gasifier is circulated with the bed material and combusted in a separate reactor to generate the heat required for the gasification process. While high solid circulation rates are required to maintain the heat balance, product and flue gas mixing between the two units must be minimised or eliminated. The design of the circulating bed simply consists of two fluid bed units connected two together via a riser and a downcomer fitted with a non-mechanical valve. Various aspects such as solid circulation rate, gas mixing, solids mixing, and pressure component around the circulating loop were studied. Results show that the solid circulation and gas mixing are strongly influenced by the riser gas velocity, total solids inventory, and position of the riser from the riser gas jet. Solid circulation fluxes of up to 1 l5kg/m 2s were attained and easily controlled. The flue gas crossflow was less than 4% over the range studied. By analysing the experimental data, a series of mathematical correlations were obtained which successfully predict the exponential relationship that exists between the solid circulation rate, gas mixing and the operating parameters. The potential of this system for its purpose is highlighted. The second part of the study focuses on the design and development of a heated fluidized bed reactor with an on-line gas and solids sampling technique to study the steam gasification of biomass (almond shells). Experiments were conducted at temperatures of up to 800°C to investigate the gasification rates of biomass char under different operating conditions. Understanding the gasification and combustion rates of biomass char is an important step towards the proper designing of biomass gasifiers. In the heated fluid bed, the extent of the gasification of biomass increased with increasing temperature as indicated by an increase in the quantity of gaseous products. A hydrogen content of up to 43% by volume was obtained. The sampling technique adopted allows the collection of the bed sample at gasification conditions which can be used to predict the composition of the bed. The gasification rate of biomass (almond shell) char was found to be affected by the gasification temperature. In order to evaluate the char gasification rate constants, the shrinking core model with reaction controlling step (SCM) was applied to the char gasification data. The rate constant values obtained from the SCM were 5.14E-5, 7.67E- 5, and 1.26E-4 s' for temperatures of 712, 753, and 806 °C respectively. The activation energy was evaluated as 89 kJ/mol. These values were in close agreement with those published in the literature. SEM pictures of the surface of the chars shows that at high temperatures, the char formed is very porous and hence very reactive. With regards to practical gasifiers, the results obtained have been used to evaluate an --mum volume for a typical biomass gasifier operating at 850 °C. The aim of the present work were satisfactorily achieved.

Forest is one of the natural resources that are facing a serious threat in the world today. Overexploitation of forest resources for timber, fuelwood and agricultural land is increasing faster, to the extent that the future prospects for most forest in the world are open to question. While there are various reasons responsible for the decline in vegetation, this study explores the situation of the Northern Nigerian region arid zone forest by studying the changing pattern of vegetation in relation to the cooking fuel situation in the region using both national and regional statistics and a local area case study. The study uses multiple methodologies (Remote Sensing, Geographical Information Systems and a local survey using household survey, focus group discussion and participant observation) to examine various aspects of the overall problem at different geographical scales. The combined methods serve as a triangulation strategy to identify causal linkages between changes in forest cover, fuelwood consumption and cooking fuel supply problems in the region. Past studies have used some of the methodologies, singly or in combination. However, no previous study has utilised the full range of methodologies listed above to examine the fuelwood problem across all scales from the national to local level, which is a contribution to knowledge that this present study offers. The study commences by using a time series analysis of Landsat satellite images of the North-Eastern part of Nigeria (NEN), covering a period of about three decades, using the technique of Remote Sensing (RGB-NDVI model), with a view to identifying areas where deforestation is evident in the vegetated areas of the region. The results indicate that the vegetation of the area has drastically reduced since 1970s. However, both the pattern and causes of the observed change were non-linear. Similarly, evidence from ground truthing investigation has shown that fuelwood collection is among the major factors of deforestation in the region, mainly due to lack of alternative energy sources in the region. This initiated a wider national exploration of fossil fuel supply and consumption in the country, with a view to examining whether there are any spatial patterns of such inequalities amongst households across the 36 states of Nigeria (and Abuja the capital city). Spatial analysis of the distribution and consumption of cooking fuel is conducted using Geographical Information Systems (GIS). The results show that fossil fuel supply is precarious in the country. The majority of the northern states are deprived of sufficient fossil fuel supply, and this is closely correlated with their dependence on traditional fuels (fuelwood), leading to considerable pressure on the region’s scarce vegetation resources. Further investigation of the national findings relating to fossil fuel supply is undertaken using a local survey, which explores the pattern of household fuel consumption and commercial fuelwood activities in some selected areas of North-Eastern Nigeria. The results also reveal that there are some local inequalities in the choice of cooking fuel among households (in favour of fuelwood), which is related to the unreliability in the supply of fossil fuel in the region (cooking fuel poverty). This has paved the way for the expansion of organised commercial fuelwood vending in the region to supply households with fuelwood.

Disposal of large quantities of surplus straw, which lie in the fields after harvest, is a major annual problem to cereal farmers. The current preferred solution of burning the straw where it lies is environmentally unsatisfactory and appears to be a huge waste of a potentially valuable, renewable energy source. None of the currently available straw packaging systems provides an economically viable alternative. A process is proposed for producing industrial quality fuel briquettes using a tractor towed implement. The economic feasibility of such a system is investigated and comparisons are made with existing straw disposal methods. The projected cost of fuel, produced in this way, is compared with prevailing fossil fuel prices. A multistage continuous process machine concept is described and the various stages are proven workable both experimentally, in the laboratory, and analytically. Laboratory experiments determine the forces required to produce acceptable quality briquettes and comparisons are made between the power available from the tractor, the economical throughput rate and the energy consumed in the compaction process. The mechanism of bonding within the straw packages, under compression, is examined so that the parameters necessary to give the optimum machine design may be understood. The effect, on briquette quality, of variations in die shape within the constraints imposed by the machine concept is fully investigated. Experiments extend to compression at speeds representative of 'live' field operation and a die shape is developed which produces packages of consistently good durability. Many of the design ideas put forward in this thesis have now been incorporated in an original prototype machine, built and successfully field-tested by the company who has supported this project and now holds the relevant patents.

Since wood fuel when used sustainably provides an energy source that does not contribute to greenhouse warming, its use in future is likely to increase. Contractors prefer to chip trees and residues green to minimise power required and machinery wear. For non-specialised combustion systems the green woodchips should then be dried to increase their calorific value and to allow buffer storage without significant dry matter loss or the development of hazardous fungal spores. As the drying of wood chips has never been rigorously defined, a study was undertaken to determine the drying characteristics of green woodchips. A drying bin was built to simulate storage drying in one dimension. Data from three drying runs using spruce and birch whole tree provided data to validate a one-dimensional heat and mass transfer drying model converted from an existing grain drying routine. The specific energy consumption varied from 2.0 MJ/kg of moisture removed using unheated air during summer drying to 5.0 MH/kg during winter when dried with air warmed by 28°C. Dry matter loss in birch during drying and a period of two months cool storage was approximately 2%. Mean evaporation rate ranged from 1.9 kg/h in winter to 2.9 kg/h in summer. This gave a drying rate of 1% and 2.2% per day, inwinter and summer respectively. Hardwoodbirch released its moisture more readily than softwood Sitkaspruce. Airflow rates used ranged from 0.26-0.63 m³/s pertonne of dry matter. The dust levels on the woodchips ranged from 3.0 mg/m³ ofair before drying up to 55 mg/m³ of air after drying. The concentrations of colony forming units on woodchips ranged from2.0 X 10⁴ cfu/m³ of air before drying up to 8.0 X 10⁵cfu/m³ of air after drying.

The thesis examines the process of technical change in industrialized and developing country situations, and extracts lessons from this analysis for the design and implementation of forest energy development programmes. It notes how the role of technology users is of great importance in innovation" whether this process involves "high technology" development in large, competitive firms, or "appropriate technology" development to meet basic needs in poor, rural communiti~s. In reviewing the results of the past ten years of work in renewable energy programmes in developing nations, it finds that a major factor in the poor performance of such work is the lack of provision for user participation in innovation. Forest energy development programmes, which have been an important part of renewable energy development assistance, also have suffered from this insufficient attention to technology users. It is postulated that new approaches to forest energy development that provide for a more interactive relationship between R&D establishments and technology Llsers will have greater. success in bringing about innovations in this sector. The experience of charcoal production, charcoal stove, and forestry development under the Sudan Renewable Energy Project, supported by the Sudan Energy Research Council and the US Agency for International Development, demonstrates the positive results of just this sort of interactive innovation strategy. The SREP, in its ~ priori commitment to user participation, uncovers valuable resources of indigenous technical knowledge and skills, which play an integral part in the design and dissemination of these 3 forest energy technologies. The project's success provides an empirical justification of the importance of technology users to the innovation process, and its example h~s larger implications for renewable energy development, government R&D management, and development assistance policy.

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