Methane yeilds from anaerobic digestion of food waste : Variation of load, retention time and waste composition in simulating methane yeilds, using the "Anaerobic digestion model no.1" (ADM1)

Sammanfattning: High demands for renewable energy sources are increasingly making methane gas from biogas facilities more interesting and profitable.When designing biogas facilities, engineers often have a limited set of data to work with. It is often too expensive and time consuming to examine the behavior of the anaerobic processes depending on some key operational parameters, such as the organic loading rate the reactor retention time and the waste composition. The purpose of this thesis is to use the “Anaerobic Digestion Model no.1”, a well-known mathematical description of the biogas process describing the 24 most important biochemical reactions in the anaerobic process, to investigate how different parameters in the model affect methane production. The focus of this thesis is methane production from food waste. The thesis also aims to describe if, and how, researchers can use relatively simple methods and data from literature in calibrating the model and if such a calibration can correlate with production data from a large scale biogas facility, which digests food waste. The biogas reactors which are investigated operate under mesophilic temperatures (≈35⁰C). A model was implemented in Matlab® code and a mathematical extension was also brought to the default model to take into account the detrimental effects on methane production from volatile fatty acids. The model used correlates well with lab scale data. Steady state comparisons between the production data from a large scale food waste degrading reactor was also made, and model predictions were very close to those of the acquired values.Results also show a potential in increasing the reactor load and allowing a shorter retention time without much loss in methane production. This may show that important cost reductions relating to reactor size can be achieved. This, however, needs to be investigated further since the model has been calibrated for loads that are unreasonably high for industrial applications.