NOVELTY - The method of monitoring anaerobic reactor (2) for bacteriological treatment of a substrate, comprises measuring a condition of reactor, and monitoring optimization for maximizing result to select modifying action statistically according to measured condition. The substrate produces a recoverable by-product having methane, hydrogen and ethanol. The reactor comprises an actuator (18) to control an admission of- the substrate, a pH regulating agent and nutrients in the reactor.    USE - Useful for bacteriological treatment of a substrate.    ADVANTAGE - The method of monitoring reactor is autonomous, reliable and cost effective.    DETAILED DESCRIPTION - The method of monitoring anaerobic reactor (2) for bacteriological treatment of a substrate, comprises measuring a condition of reactor, and monitoring optimization for maximizing result to select modifying action statistically according to measured condition. The substrate produces a recoverable by-product having methane, hydrogen and ethanol. The reactor comprises an actuator (18) to control an admission of- the substrate, a pH regulating agent and nutrients in the reactor. The condition of the reactor has an outflow measurement, which is carried out by using an outflow sensor of reaction product. The modifying action is selected statistically to maximize the monitoring optimization with an algorithm. The condition of the reactor has a pH measurement, which is carried out using a pH sensor. The step of monitoring optimization comprises evaluating a modifying action of the reactor condition and predicting an evolution of the monitoring optimization in response to the modifying action. The evolution of the modifying action is repeated for a predetermined set of modifying actions in which the modifying action having a substrate inflow modification operation. The evolution of the monitoring optimization comprises a statistical expectancy of a balanced sum of values of the monitoring optimization. The substrate inflow modification comprises maintaining operation of the inflow to increase and decrease the inflow. The pH modification has a pH- augmentation operation, maintenance operation and reduction operation. The predetermined set of modifying actions includes the modifying action having an operation of the modification of nutrients. The modification of nutrients includes an additional nutrients operation and a neutral operation. Each modification action includes a combination of operations, which is selected from a predetermined operation. The step of measuring the condition of reactor comprises a sub stage of treating the measurements, which is carried out using pattern recognition to produce pretreated measurement data. The pretreated measurement data is taken into account at the step of monitoring optimization to choose the modifying action in which the monitoring optimization is carried out by a prediction module with a neutral network. Selecting a modifying action in the predetermined unit of modifying actions comprises calculating a probability associated with each modifying action from the evolutions of the monitoring optimization and choosing the modifying action by random pulling according to calculated probabilities. The probability calculations are carried out by a Gibbs formula. The condition of the reactor is measured at a given time to determine a parameter of veracity and to calculate the probability associated with each modifying action according to the parameter of veracity. The probabilities are determined according to the parameter of veracity to amplify a difference between the probabilities when the veracity parameter is high, and to decrease a variation between the probabilities when the veracity parameter is low. A simulation module has a learning rate lower than or equal to a learning speed of the prediction module. The monitoring optimization is a variable function of a reaction output, outflow of reaction product, a capacity storage for the reaction product and a quantity of substrate. The reactor is useful for digesting organic substrate. An INDEPENDENT CLAIM is included for a monitoring device.    DESCRIPTION OF DRAWING(S) - The diagram shows a device for monitoring anaerobic reactor:    Reactor; (2)    Pipe; (12)    Actuator; (18)    Boiler; (21)    Heat exchanger. (32)