A respirometric method to study biodegradation kinetics of solid organic wastes

Composting may be an important way to reduce wastes and to re-use organic matter because its products may be used as soil conditioners and/or organic fertilizers. Nevertheless, the composting treatment development depends on the quality of its end products which have to be safe for the environment and to be interesting in an agronomic point of view. However, such a quality can only be assured by a strict control of the applied composting treatment. Thus it implies a good understanding of its reactional phenomena. This aerobic treatment is mainly governed by three complex and interdependent phenomena : mass transfers, heat transfers and microbiological degradations. In this work the biological phenomena are specifically studied because they are linked to the intrinsic characteristics of the substrate : for example its organic matter fractionation. Indeed, the knowledge of biological kinetics and substrate characteristics may allow to estimate the biodegradability potential and the stabilisation state of the organic matter. This may be very useful to control the composting treatment. In this objective, a respirometric device has been set up to measure the oxygen consumption rate evolution during the degradation of organic matter samples. In order to study the influence of environmental conditions (temperature, aeration, moisture and free air space) on the biological reactions, the respirometric apparatus has to be designed to control these parameters. In this context, experiments are realised to check if the temperature and moisture are constant during the respirometric test. Moreover, a study is driven to control that the selected aeration system provides a sufficient oxygen quantity with an homogenous concentration in the whole sample. In the same way a new apparatus called air pycnometer has been set up and calibrated to measure the free air space at the beginning and the end of the respirometric test. After having checked all these controls, the respirometric method will be used to study the biological behaviour of an organic solid medium and find the optimum environmental conditions of biological degradation. Then the results will be compared with a mathematical model to determine the kinetic parameters of the biodegradation model. Modelling would allow to predict the biodegradability potential and the stabilisation state of the organic matter.