<br/>In the composting process temperature and oxygen concentrations are essential parameters. A main objective of this thesis is to formulate a mathematical model which can predict these parameters. In this model a number of important material properties must be used: composition in terms of volume fractions of solid, liquid and gaseous phases, air permeability, oxygen diffusion coefficient, thermal conductivity coefficient, O <sub><font size="-2">2</font></sub> - consumption, CO <sub><font size="-2">2</font></sub> -production and heat production. Another main objective of this thesis is the determination of these properties. A mixture of wheat straw and chicken manure was chosen as composting material. For the above mentioned material properties some overall conclusions can be drawn.<p>The volume fractions of the distinguished phases varied with position due to the compressibility of the composting material. An equation was deduced to predict the air-filled volume fraction as a function of the pile height.<p>The air permeability κdecreased with increasing air velocity. For raw material, κdecreased with the wetness at comparable air-filled volume fractions θ <sub><font size="-2">g</font></sub> . The oxygen diffusion coefficient D <sub><font size="-2">O2</font></sub> was proportional to θ<font size="-2"><sub>g</sub><sup>1.5</SUP></font>. There was no effect of the age of the material on D <sub><font size="-2">O2</font></sub> . The thermal conductivity coefficient λincreased with the temperature. At constant temperature and for solid phase fractions less than 0.3, λincreased linearly with the liquid phase fraction.<p>The biochemical properties, such as the rates of heat production and oxygen consumption, were estimated from theoretical considerations and were determined experimentally in an isothermal calorimeter. The time course of the expermental production/consumption rates showed a characteristic pattern consisting of a peak activity during the first 4 to 5 days followed by a gradually decreasing pseudo-steady state.<p>Finally, experimental results of compost piles on a semi-practical scale were interpreted in terms of the identified processes and experimental values of material properties.
|Qualification||Doctor of Philosophy|
|Award date||10 Sep 1996|
|Place of Publication||S.l.|
|Publication status||Published - 1996|