The application of LDAT to the HPM2 challenge

Abstract

The challenge laid down to landfill modellers at the 4th Intercontinental Landfill Research Seminar in June 2006 was to see to what extent modellers could predict experimental results from a closely monitored anaerobic degradation laboratory experiment when given only the initial conditions. This paper presents results from the University of Southampton landfill degradation and transport (LDAT) model. The LDAT model uses chemical pathways for degradation of carbohydrates, fats and protein. When waste solids are described using the descriptors food, green waste, paper and textiles, LDAT converts these into carbohydrates, fats and protein. LDAT also accommodates pathways that proceed at different rates. The stoichiometric equations on which the LDAT degradation chemistry is currently based are used independently of LDAT to predict the gas yield that might be expected from the data that have been derived for the carbohydrate, protein and fat components. The more difficult question of estimating the timescale over which the gas emerges is also addressed. The paper gives details of the bacteria population growth rates, half-saturation constants, yield coefficients and initial bacteria masses used to obtain the reaction rates for the degradation pathways. LDAT tracks the depth of the sample which reduces with time in response to the degradation of the solids. These results are given and compared with the settlement implied by the gas yield calculations.