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Тhe paper describes a new pilot-scale biogas plant of the Institute of Microbiology - Bulgarian Academy of Sciences. The equipment includes: a 100 L pilot bioreactor, a 200 L metal gasholder, sensors, actuators, a two-level automatic process monitoring and control system, a fire and explosion protection system and two web cameras. The monitoring and control system is composed on the lower level of a controller Beckhoff, and on the higher level - of a PC with specialized software (under development). The pilot biogas plant is designed to work out and scale up various anaerobic digestion (AD) technologies based on different types of feedstock. All the data will be stored on the PC for quick reference and possibly data mining, parameter identification and verification of different AD mathematical models.

The paper deals with the state estimation of a second-order model of anaerobic digestion. This estimation is necessary to implement the sophisticated control algorithms that have already been developed for this process. Hereby design and performance of a classical Kalman filter (compared with other two deterministic estimation approaches) for the main variables of this model have been discussed and analysed by simulations. The performance analysis has been conducted at realistic random perturbations, comparable with experimental data, on the one hand, and on the other – with and without parameter perturbations. Although at random perturbations alone the Kalman filter has a clear advantage over the two equipollent deterministic estimators, at the presence also of parameter perturbations, to which the Kalman filter is more sensitive, no such advantage is guaranteed.

The principle of extremum seeking control has been applied on a cascade of two anaerobic bioreactors using the dilution rate as control action and the biogas flow rates as measured outputs to be maximized. In all cases maximum biogas flow rate with sensible decrease of the general output depollution parameter (compared to the case of one single bioreactor) has been obtained, starting from different initial conditions. With the same algorithm, good performances have been obtained in the presence of variations of the inlet organics. Its implication for biotechnology may result in substantial economic benefits.

Abstract: The paper deals with local asymptotic stability analysis of some mass balance dynamic models (based on one and on two-stage reaction schemes) of the anaerobic digestion (AD) in CSTR. The equilibrium states for models based on one (with Monod, Contois and Haldane shapes for the specific growth rate) and on two-stage (only with Monod shapes for both the specific growth rate of acidogenic and methanogenic bacterial populations) reaction schemes have been determined solving sets of nonlinear algebraic equations using Maples. Their stability has been analyzed systematically, which provides insight and guidance for AD bioreactors design, operation and control.

Anaerobic digestion is an effective biotechnological process for treatment of different agricultural, municipal and industrial wastes. Use of mathematical models is a powerful tool for investigations and optimisation of the anaerobic digestion. In this paper a simple mathematical model of the anaerobic digestion of wasted fruits and vegetables was developed and verified experimentally and by computer simulations using Simulink. A three-step mass-balance model was considered including the gas phase. The parameter identification was based on a set of 150 days of dynamical experiments in a laboratory bioreactor. Two step identification procedure to estimate 4 model parameters is presented. The results of 15 days of experiment in a pilot-scale bioreactor were then used to validate the model.