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Förslaget inkom 2007-05-02

Biogas residues as fertilizers – effects on plant growth, soil microbiology, and emission of green house gases

MicroDrivE – MSc Project School
Environmental and economic reasons motivate focused research on biofuel production. The new research programme MicroDrivE – Microbially Derived Energy, offers a series of MSc projects within bio-preservation, enzymatic pre-treatments, ethanol fermentation, bioprocessing of byproducts, biogas production and fertility effects of bioresidues. The projects are supervised by scientists from the Departments of Microbiology, Molecular Biology, and Chemistry at the Swedish University of Agricultural Sciences (SLU), Uppsala. MicroDrivE cooperates with a number of biotech and bioenergy companies. For information on the other MSc projects use the search function ”Fritext” to search for MicroDrive.

Goal and background
The overall objective of this work is to evaluate fertilizing effects, changes in microbial soil quality, and nitrous oxides emissions of application of organic residue from biogas processes based on arable crops.

Animal manure and slurry are well-known sources of plant nutrients for crop production, while the use of biogas residues from treatment of organic waste is less well documented. During anaerobic digestion a large part of the energy contained in the organic waste is transformed into methane. At the same time, the nitrogen is conserved in the biogas residue, predominantly as ammonium, which when added to soil is immediately available to plants. In addition phosphorus, potassium and magnesium, as well as trace elements essential to the plant, are preserved in the residue.

Obviously, an increased recirculation of biogas residues to arable soils has several environmental benefits. However, the rapid development within the biogas area regarding both technologies and substrates treated, results in new organic residues that have to be evaluated before large-scale use as soil conditioners and fertilizers. This calls for reliable tests to assess changes in soil quality, as well as effects on crop and risks for spreading plant pathogens. In addition, the residue has a high water content which makes it expensive to handle and to spread in the field. Handling and spreading may also pose an environmental risk, not only due to leakage of nitrate to recipient waters, but also due to substantial gaseous losses of ammonia and the greenhouse gas nitrous oxide. On the other hand, upon drying, as much as 90% of the ammonium might be lost as ammonia.

The work
A. Pot experiments with plants to evaluate plant growth and to assess short-term changes in soil respiration and potential denitrification rates.

B. Incubation experiments in gastight chambers of soil cores collected in the field. Rates of nitrous oxide emission is measured after addition of biogas residue.

Greenhouse plant growth; soil respirometry; acetylene inhibition technique for measurement denitrification rates; gaschromatography;

We are looking for a student within the microbiology and biotechnology area, interested in future technologies for biofuel production and environmental concerns.

For information on the Department of Microbiology, SLU, visit our Web-site: http://www.mikrob.slu.se


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