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Process optimization is needed for the development and expansion of the biogas industry and to meet the ever growing demand for methane. This thesis explores process technologies for the development of the anaerobic digestion process and includes pre-treatments, studies on the effects of different mixing modes and evaluation of a water treatment technology. Two pre-treatments were evaluated, mechanical and electroporation, for treatment of ley crop silage. Digester mixing has an effect on the digestion result. The performed review and experiments show that the mixing demand increases with organic loading.

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Process optimization is needed for the development and expansion of the biogas industry and to meet the ever growing demand for methane. This thesis explores process technologies for the development of the anaerobic digestion process and includes pre-treatments, studies on the effects of different mixing modes and evaluation of a water treatment technology.

Two pre-treatments were evaluated, mechanical and electroporation, for treatment of ley crop silage. Digester mixing has an effect on the digestion result.

The performed review and experiments show that the mixing demand increases with organic loading. Excessive mixing during process start up, instabilities and shock loads leads to increased volatile fatty acid concentrations and process inhibition. Reduction of mixing reduces the effects of process instabilities and periodical mixing with mixing breaks has been shown to be beneficial for biogas production.

Improved separation can increase the capacity of the substrate pre-processing and reduce process related problems. However, even though the membrane filtration unit shows promising results it would demand a relatively high energy consumption and lead to limited benefits to a process already at it maximum organic loading.

Previous studies on substrates for biogas production have shown that different types of pre-treatments make the material more accessible for microbial degradation by breaking down the complex structure of the organic material, thereby increasing their potential for gas production. In this paper, two different mechanical pre-treatment apparatus, i. The treatments were investigated with regard to their effects on particle size, methane potential, capacity and energy balance.

The energy balance was positive for Gd and around the break-even point for Kd. Analysis of the setup showed that Kd had almost twice the capacity of the Gd. All rights reserved. Exploiting the full biogas potential of some types of biomass is challenging. The complex structures of lignocellulosic biomass are difficult to break down and thus require longer retention times for the nutrients to become biologically available.

It is possible to increase the digestibility of the substrate by pre-treating the material before digestion. This paper explores a pre-treatment of ley crop silage that uses electrical fields, known as electroporation EP. Different settings of the EP equipment were tested, and the results were analyzed using a batch digestion setup.

The energy balance of the EP treatment suggests that the yield, in the form of methane, can be up to double the electrical energy input of the process. Mixing in an anaerobic digester keeps the solids in suspension and homogenizes the incoming feed with the active microbial community of the digester content. Experimental investigations have shown that the mixing mode and mixing intensity have direct effects on the biogas yield even though there are conflicting views on mixing design.

This review analyzes and presents different methods to evaluate the mixing in a digester chemical and radioactive tracers and laboratory analysis , tools for digester design computational fluid dynamics and kinetic modeling and current research on the effects of mixing on the anaerobic digestion process.

Empirical data on experiments comparing different mixing regimes have been reviewed from both a technical and microbial standpoint with a focus both on full scale digesters and in lab-scale evaluations.

Lower mixing intensity or uneven mixing in the anaerobic digestion process can be beneficial during the startup phase to allow for methanogenic biomass growth and alleviate process instability problems.

Intermittent mixing has been shown to be able to yield a similar gas production as continuous mixing but with the possibility to reduce the maintenance and energy demands of the process.

Problems often experienced with experimental design include the effect of mixing on the solids retention time, and measurement of steady state gas production because of startup instabilities. Further research should be aimed at studying the effects of mixing on a chemical and microbial level and on the different stages of anaerobic digestion hydrolysis, acidogenesis, acetogenesis and methanogenesis. The focus should be on the effects of mixing on a multiple stage digestion process and also finding new methods to evaluate the effects of mixing in the one stage digestion process rather than evaluating a wider range of mixing modes, intensities and substrates.

Mixing inside an anaerobic digester is often continuous and is not actively controlled. The selected mixing regime can however affect both gas production and the energy efficiency of the biogas plant.

This study aims to evaluate these effects and compare three different mixing regimes, RPM and 25 RPM continuous mixing and minimally intermittent mixing for both digestion of fresh substrate and post-digestion of the organic fraction of municipal solid waste.

The results show that a lower mixing intensity leads to a higher biogas production rate and higher total biogas production in both cases. The lower gas production at RPM could not be explained by the inhibition of volatile fatty acids.

Cumulative biogas production until day 31 was As well as increasing gas production, optimal mixing can improve the energy efficiency of the anaerobic digestion process. Waste water from a biogas process is often recirculated and mixed with the incoming organic material to produce a feed for the digester.

The dry matter DM content of the final mixture should be as high as possible to maximise the capacity of the plant without exceeding the capability of the pumps. This means that the DM content of the recirculated process water has a large impact on the amount of substrate that can be processed.

Experiments to reduce the dry matter content of the recirculated process water were carried out using a ceramic ultrafiltration UF membrane. The energy required to heat the membrane when using heat recovery is small compared to the energy of the methane produced from the additional added substrate.

The lifespan of the membranes and uncertainties in the substrate DM content are showed to be important for the economic result. Please wait English Svenska Norsk. Cite Export. Permanent link. Citation style. More styles. More languages. Output format. Create Close. Evaluating the effects of electroporation pre-treatment on the biogas yield from ley crop silage.

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Exploiting the full biogas potential of some types of biomass is challenging. The complex structures of lignocellulosic biomass are difficult to break down and thus require longer retention times for the nutrients to become biologically available. It is possible to increase the digestibility of the substrate by pre-treating the material before digestion. This paper explores a pre-treatment of ley crop silage that uses electrical fields, known as electroporation EP. Different settings of the EP equipment were tested, and the results were analyzed using a batch digestion setup. The energy balance of the EP treatment suggests that the yield, in the form of methane, can be up to double the electrical energy input of the process. Process optimization is needed for the development and expansion of the biogas industry and to meet the ever growing demand for methane.

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