This database contains bibliographic descriptions of all Wageningen University PhD theses from 1920 onwards. It is updated on a daily basis by WUR Library.
Author abstracts and/or summaries are added to all descriptions. A link to the full text dissertation is added to the bibliographic description. In a few cases, no electronic version is available, mostly because of copyright issues.
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Abstract: The emission of nitrogen oxides (NOx) to the atmosphere is a major environmental problem. To abate NOx emissions from industrial flue gases, to date, mainly chemical processes like selective catalytic reduction (SCR) are applied. All these processes require high temperatures (>300 °C) and expensive catalysts. Therefore, biological NOx removal techniques using denitrification may represent promising alternatives for the conventional SCR techniques. However, water based biofiltration requires relatively long scrubber/bioreactor retention times, i.e. big reactor volumes, due to the slow mass transfer of NO from the gas into the liquid phase. BioDeNOx is in principle a welcome alternative for conventional NOx removal techniques like SCR and water-based biofiltration, since it does not need high temperatures and catalysts, while scrubber retention times can be very short (< 10 seconds) due to the chemically enhanced NO absorption. In this thesis, the BioDeNOx concept was investigated with special attention to the bioreactor key conversions: NO and Fe(III)EDTA- reduction. This study showed stable NO removal from the gas phase with efficiencies up to 80 %. It was found that the NO removal from the gas phase is primary determined by NO absorption kinetics. Therefore, a high Fe(II)EDTA2- concentration is required, i.e. the FeEDTA absorption liquor should be in the reduced state. However, a totally reduced system should be avoided, since this will induce sulfide accumulation. The latter process is unwanted, since already low sulfide concentrations showed an incomplete NO reduction due to inhibition of N2O reduction to N2. To achieve satisfying NO removal from the gas and to avoid sulfdogenic conditions, the redox potential of BioDeNOx reactors should be steered between -180 and -200 mV versus Ag/AgCl (pH 7.2±0.2). An ethanol dosing system that is controlled by the redox potential signal was shown to be a proper manner to do so
Abstract: Composting manure on farm can emit large quantities of ammonia and smell. This thesis focuses on improving the compost process by analysis of the process control, the feed composition and the bed structure. A low cost solution to the ammonia emission was developed. By composting at low oxygen concentration the ammonia emissions can be reduced with up to 78%. In order to optimise the feed mixture, an oxygen uptake measurement was modified so that the oxygen uptake rate of feed material can be measured on farm. A conceptual model of how the degradation can be predicted from the initial hydrolysis rate is presented. With these tools, the feed composition can be optimised. The analysis of the bed structure revealed the weakness of the compost bed’s structure at higher temperatures, was more important than the initial porosity. Finally, the results of this thesis are combined and it is shown how the acquired insight can be used to optimise the composting process.
Abstract: The number of people with (severe) overweight is increasing. More insight into the mechanism of food intake may help to develop foods for weight maintenance. There are indications that ghrelin is an important hunger signal. The role of ghrelin in the regulation of food intake was investigated in human volunteers at TNO Quality of Life in Zeist, in collaboration with the department of Human Nutrition of Wageningen University. Our studies showed that changes in ghrelin concentrations were related to changes in appetite, but these changes did not predict food intake. Suppression of ghrelin concentrations, however, did predict initiation of the next meal. Such suppression of ghrelin appears to depend on type of macronutrient and energy content of a meal. We conclude that ghrelin is a hunger signal that does not determine meal size (satiation), but that regulates next meal initiation (satiety). Foods that contain nutrients (for example dairy protein) that effectively suppress ghrelin concentrations, may help prevent overweight and obesity.
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