Model-based control for a demand-driven biogas production to cover residual load rises.

The development of systems for energy storage and demand-driven energy production will be essential to enable the switch from fossil to renewable energy sources in future. To cover the residual load rises, a rigorous dynamic process model based on the Anaerobic Digestion Model No. 1 (ADM1) was applied to analyse the flexible operation of biogas plants. For this, the model was optimised and an operational concept for a demand-driven energy production was worked out. Different substrates were analysed, both by batch fermentation and Weende analysis with van Soest method, to determine the input data of the model. The lab results show that the substrates have got different degradation kinetics and biogas potentials. Finally, the ADM1 was extended with a feeding algorithm which is based on a PI controller. Essential feeding times and quantities of available substrates were calculated so that a biogas plant can cover a defined energy demand. The results prove that a flexible operation of biogas plants with a feeding strategy is possible.

Modelling anaerobic digestion in a biogas reactor: ADM1 model development with lactate as an intermediate (Part I).

The Anaerobic Digestion Model No. 1 (ADM1) was extended to include lactate, a crucial metabolic product during sugar fermentation. This study tests the validity of the modified ADM1 model in improving the predictions of a standard biogas reactor. This reactor was prepared in the laboratory with simple organic substrates with an intention to represent an 'average biogas plant'. Kinetic parameters were determined from a lactic acid enriched steady-state reactor. The parameters were adjusted further in order to acquire satisfying simulation results systematically with the batch experiments and then against the standard biogas reactor. Arresting methanogenesis revealed that lactate degradation occurred majorly via acetate followed by propionate, and a non-negligible proportion of butyrate too was found, which were further updated in the model. The modified ADM1 provided a successful correlation with the experimental results for the batch and continuous experiments. We justified that inclusion of lactate in the model resulted in optimized simulation for both biogas and methane content in the standard biogas reactor.

Wet biowaste digestion: ADM1 model improvement by implementation of known genera and activity of propionate oxidizing bacteria.

Anaerobic digestion of biowaste not only reduces environmental burden but also plays an important role for sustainable energy supply. For process optimization simulation based on the Anaerobic Digestion Model No. 1 (ADM1) is commonly used. The ADM1 was extended to include the known three genera of propionate oxidizing bacteria (POB) and the two routes of propionate degradation (methyl-malonyl CoA and C6-dismutation pathway). Kinetic parameters for anaerobic propionate oxidation by single strains of the three propionate oxidizing genera were determined from defined tri-cultures of the POB with hydrogenotrophic and acetotrophic methanogens and implemented into ADM1. The such improved model ADM1xpro was evaluated with operational data from a full scale wet biowaste digestion plant. Predicted amounts of biogas and composition with ADM1xpro (2201 m³ d-1, 68.1 % CH4 and 31.9 % CO2) correlated well with full-scale process data (2171 m³ d-1, 67.5 % CH4 and 31.9 % CO2).

Application of Anaerobic Digestion Model No. 1 for describing anaerobic digestion of grass, maize, green weed silage, and industrial glycerine.

Anaerobic digestion of organic waste plays an important role for the development of sustainable energy supply based on renewable resources. For further process optimization of anaerobic digestion, biogas production with the commonly used substrates, grass, maize, and green weed silage, together with industrial glycerine, were analyzed by the Weender analysis/van Soest method, and a simulation study was performed, based on the International Water Association's (IWA) Anaerobic Digestion Model No. 1 (ADM1). The simplex algorithm was applied to optimize kinetic constants for disintegration and hydrolysis steps for all examined substrates. Consequently, new parameters were determined for each evaluated substrate, tested against experimental cumulative biogas production results, and assessed against ADM1 default values for disintegration and hydrolysis kinetic constants, where the ADM1 values for mesophilic high rate and ADM1 values for solids were used. Results of the optimization lead to a precise prediction of the kinetics of anaerobic degradation of complex substrates.