Working group 5: Modelling

The anaerobic digestion (AD) of biomass is a multi-stage process involving different types of microbial species. In addition to macronutrients such as carbon, nitrogen, phosphorus and sulphur, specific TM such as cobalt, nickel, tungsten or molybdenum play a crucial role in the growth and metabolism of anaerobic microorganisms where they are essential for many physiological and biochemical processes. The speciation can influence both kinetics and physics of anaerobic digestion as there is a different metal uptake rate and a different diffusivity of TM in biological biofilms depending on the TM speciation (WG1).

WG5 aims at developing an up-grading of the anaerobic digestion model N°1 (ADM1) capable to describe and simulate the effects of TM and TM speciation on AD biochemical processes.

The mathematical model will present the following peculiarities:

• Differential dynamic equations capable to describe the speciation of all TM present in the biological system taken into account. In particular these equations will give the dynamic concentrations of each TM species.

• Differential mass balance equations for substrates, products and bacterial groups involved in the anaerobic digestion process, including the biochemical reactions of the substrates conversion and the kinetics of microbial growth and decay that take into account the speciation effects.

• A redox potential modelling to determine the redox potential of the biological system, which is needed for the two above objectives.

• A differential parabolic equation able to model the diffusivity phenomena in a biofilm. system. In particular this equation will consider the different diffusivity constant of each TM species.