599 research outputs found
Biogas for Rural Areas
Bioenergy is renewable energy obtained from biomassâany organic material that has stored sunlight in the form of chemical energy. Biogas is among the biofuels that can be obtained from biomass resources, including biodegradable wastes like manure, sewage sludge, the organic fraction of municipal solid wastes, slaughterhouse waste, crop residues, and more recently lignocellulosic biomass and algae. Within the framework of the circular economy, biogas production from biodegradable waste is particularly interesting, as it helps to save resources while reducing environmental pollution. Besides, lignocellulosic biomass and algae do not compete for arable land with food crops (in contrast with energy crops). Hence, they constitute a novel source of biomass for bioenergy.Biogas plants may involve both high-tech and low-tech digesters, ranging from industrial-scale plants to small-scale farms and even households. They pose an alternative for decentralized bioenergy production in rural areas. Indeed, the biogas produced can be used in heaters, engines, combined heat and power units, and even cookstoves at the household level. Notwithstanding, digesters are considered to be a sustainable technology that can improve the living conditions of farmers by covering energy needs and boosting nutrient recycling. Thanks to their technical, socio-economic, and environmental benefits, rural biogas plants have been spreading around the world since the 1970s, with a large focus on farm-based systems and households. However, several challenges still need to be overcome in order to improve the technology and financial viability
Biogas for rural areas
This is a reprint of articles from the Special Issue published online in the open access journal Energies (ISSN 1996-1073) (available at: www.mdpi.com/journal/energies/special issues/BiogasRural Areas).Peer ReviewedObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No ContaminantObjectius de Desenvolupament Sostenible::6 - Aigua Neta i SanejamentPostprint (published version
Biological processing in oscillatory baffled reactors (OBRs)
EngD ThesisBioprocessing involves using complete cells or any of their components for the manufacture of products such as pharmaceuticals, fuel, health products and precursor compounds for plastics. Bioprocessing can provide sustainable routes for the manufacture of products which are traditionally manufactured from fossil-derived chemicals. The stirred tank reactor (STR) is the prevalent fermenter/reaction vessel in industry due to its simplicity and cost. However; the basic design has not changed for centuries. This thesis describes the use of oscillatory baffled reactors (OBRs) for bioprocessing. Generally, the âniche applicationâ of OBRs is in performing âlongâ processes in plug flow conditions, so they should be suitable for many bioprocesses.
In this thesis, four research projects using OBRs are presented: modelling of plug flow and OBR design; enzymatic saccharification; microalgae culture; and anaerobic digestion (AD).
A robust method to maximise plug flow in various OBR designs is described. Second order, polynomial models (R2=92.1% and 97.3%) were used to maximise plug flow at Κ=1.9. The net flow rate (Q) was shown to affect the quality of plug flow which has implications for OBR design.
Enzymatic saccharification was conducted in reactors based on OBR and STR technology. The OBR required 94-99% less power to achieve the necessary mixing intensities to maximise glucose production.
Chlamydomonas reinhardtii was cultured in a modified OBR for use as a photobioreactor (PBR). Maximum growth rates were increased by 95% in the OBR compared to cultures conducted in T-flasks. A flotation effect was observed that suggests that a dual culture and harvest device for microalgae is possible.
Anaerobic digestion of dairy slurry and co-digestion with glycerol was conducted in digesters based on OBR and STR technology. The OBR achieved a maximum specific methane yield 28% higher than the STR. However, blockages occurred in the OBR and 89% less power was required for temperature control in the STR, predominantly due to differences in surface areas to volume ratios.
Overall, OBR technology was successfully used in three bioprocesses, with improvements demonstrated over traditional technologies such as STR and/or T-
flasks. Commercial systems based on OBR technology could be designed, provided that sufficient data is generated to overcome the risks associated with adoption of a novel technology such as OBRs.The Centre for Process Innovation (CPI):
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IMPROVED BIOMASS UTILIZATION THROUGH REMOTE FLOW SENSING
The growth of the livestock industry provides a valuable source of affordable, sustainable, and renewable bioenergy, while also requiring the safe disposal of the large quantities of animal wastes (manure) generated at dairy, swine, and poultry farms. If these biomass resources are mishandled and underutilized, major environmental problems will be created, such as surface and ground water contamination, odors, dust, ammonia leaching, and methane emission. Anaerobic digestion of animal wastes, in which microorganisms break down organic materials in the absence of oxygen, is one of the most promising waste treatment technologies. This process produces biogas typically containing {approx}65% methane and {approx}35% carbon dioxide. The production of biogas through anaerobic digestion from animal wastes, landfills, and municipal waste water treatment plants represents a large source of renewable and sustainable bio-fuel. Such bio-fuel can be combusted directly, used in internal combustion engines, converted into methanol, or partially oxidized to produce synthesis gas (a mixture of hydrogen and carbon monoxide) that can be converted to clean liquid fuels and chemicals via Fischer-Tropsch synthesis. Different design and mixing configurations of anaerobic digesters for treating cow manure have been utilized commercially and/or tested on a laboratory scale. These digesters include mechanically mixed, gas recirculation mixed, and slurry recirculation mixed designs, as well as covered lagoon digesters. Mixing is an important parameter for successful performance of anaerobic digesters. It enhances substrate contact with the microbial community; improves pH, temperature and substrate/microorganism uniformity; prevents stratification and scum accumulation; facilitates the removal of biogas from the digester; reduces or eliminates the formation of inactive zones (dead zones); prevents settling of biomass and inert solids; and aids in particle size reduction. Unfortunately, information and findings in the literature on the effect of mixing on anaerobic digestion are contradictory. One reason is the lack of measurement techniques for opaque systems such as digesters. Better understanding of the mixing and hydrodynamics of digesters will result in appropriate design, configuration selection, scale-up, and performance, which will ultimately enable avoiding digester failures. Accordingly, this project sought to advance the fundamental knowledge and understanding of the design, scale up, operation, and performance of cow manure anaerobic digesters with high solids loading. The project systematically studied parameters affecting cow manure anaerobic digestion performance, in different configurations and sizes by implementing computer automated radioactive particle tracking (CARPT), computed tomography (CT), and computational fluid dynamics (CFD), and by developing novel multiple-particle CARPT (MP-CARPT) and dual source CT (DSCT) techniques. The accomplishments of the project were achieved in a collaborative effort among Washington University, the Oak Ridge National Laboratory, and the Iowa Energy Center teams. The following investigations and achievements were accomplished: Systematic studies of anaerobic digesters performance and kinetics using various configurations, modes of mixing, and scales (laboratory, pilot plant, and commercial sizes) were conducted and are discussed in Chapter 2. It was found that mixing significantly affected the performance of the pilot plant scale digester ({approx}97 liter). The detailed mixing and hydrodynamics were investigated using computer automated radioactive particle tracking (CARPT) techniques, and are discussed in Chapter 3. A novel multiple particle tracking technique (MP-CARPT) technique that can track simultaneously up to 8 particles was developed, tested, validated, and implemented. Phase distribution was investigated using gamma ray computer tomography (CT) techniques, which are discussed in Chapter 4. A novel dual source CT (DSCT) technique was developed to measure the phase distribution of dynamic three phase system such as digesters with high solids loading and other types of gas-liquid-solid fluidization systems. Evaluation and validation of the computational fluid dynamics (CFD) models and closures were conducted to model and simulate the hydrodynamics and mixing intensity of the anaerobic digesters (Chapter 5). It is strongly recommended that additional studies be conducted, both on hydrodynamics and performance, in large scale digesters. The studies should use advanced non-invasive measurement techniques, including the developed novel measurement techniques, to further understand their design, scale-up, performance, and operation to avoid any digester failure. The final goal is a system ready to be used by farmers on site for bioenergy production and for animal/farm waste treatment
The importance of high crop residue demand on biogas plant site selection, scaling and feedstock allocation â A regional scale concept in a Hungarian study area
In regions characterised by intensive agriculture, livestock manure is a commonly used feedstock for biogas production. Due to its expensive transportation, manure sources are often the sole criteria during biogas plant site selection, regarding feedstock supply. Encouraging biogas plant operators to use larger amounts of crop residues in the feedstock is favourable from an energy management viewpoint, but its spatial projection on resource logistics and its significance on biogas plant selection is less investigated. In this study, scenarios were created with different feedstock compositions considering constant manure and varying crop residue ratios. Based on their potential biogas yields and the location of livestock farms, a manure source-oriented site selection and facility scaling was made in a Hungarian study area. The applied GIS-based feedstock allocation and logistic analysis defined the crop acquisition possibilities and optimal transportation routes, assuming multiple resource-competitive biogas plants. The results indicate that feedstock composition can indirectly impact the site selection procedure and supply security if high crop residue demand is considered. Resource acquisition possibilities and economic feasibility are significantly affected by the location and density of the proposed biogas plants and their relative position to the crop supply areas. Due to the geographical heterogeneity of the supply side and the demand points, the transportation costs of crop residues and the digestate exceed those of the manure in all scenarios, which draws attention to the importance of spatial availability of crop residues during biogas plant site selection and scaling
Optimisation of Methane Production from Anaerobically Digested Cow Slurry Using Mixing Regime and Hydraulic Retention Time
AD is regarded as a sustainable technology that could assist the UK Government meet internationally agreed GHG emission targets by 2050. However, the mature status of the technology is based on expensive systems that rely on high energy feedstock to be profitable. Meanwhile, the natural biodegradation of cow slurry is a recognised contributor to climate change despite having a relatively low CH4 potential because of the large volumes produced. Economic mixing is essential to the cost-effectiveness of farm AD but techniques applied are not always appropriate as slurry is a shear thinning thixotropic Herschel-Bulkley fluid and therefore challenging to mix. The apparent viscosity of slurry and the shear stress induced was most influenced by solids content (exponential change) followed by temperature (linear). Most shear thinning occurred before a rising shear rate of 20s-1 was achieved with the fluid acting near-Newtonian above. Thixotropic recovery occurred within 1 hour of resting. Rheological values were also much higher than previously reported. Highest CH4 production occurred in the first 10 days of the batch process using a range of mixing regimes with different shear rates and rest periods. During fed-batch operations, changing shear rate had a minimal effect on CH4 production using a 30-day HRT whereas shorter rest periods increased production. Specific CH4 production rate was highest when feeding and mixing coincided. However, when HRT was reduced (OLR increased) the CH4 produced by all mixed regimes significantly increased with highest values being achieved using high intensity mixing rested for short periods. Lower HRTs also requires smaller digesters. Parasitic mixing energy invariably had the most influence on net energy production. Signs of instability were evident after 20 days using the low HRT. Significant microbial adaptation was also observed as the experiments progressed. The research outcomes demonstrate that mixing regime and HRT can be managed to maximise net energy production whilst reducing capital expenditure.European Social Fun
Co-benefits of mitigation options in the CCAFS- Mitigation Options Tool (CCAFS-MOT)
This work is the result of a collaboration among the University of Aberdeen, CCAFS, and the Gund Institute for Environment, University of Vermont. CCAFS, which is carried out with support from the CGIAR Trust Fund and through bilateral funding agreements. For details please visit ttps://ccafs.cgiar.org/donors. The views expressed in this document cannot be taken to reflect the official opinions of these organizations. In addition to support from CCAFS and its donors, research and development of CCAFSMOT has been supported by the British Research Councilâs Natural Environment Research Council (NERC), the United States Agency for International Development (USAID), and the United States Department of Agriculture (USDA).Publisher PD
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