Abstract: A novel method for control of biodegradation is disclosed, said biodegradation being performed by mixed cultures of microorganisms. Measurements and adjustment (preferably on-line) of process parameters which relate to metabolic activity of the microorganisms are performed in such a manner that simultaneous nitrification and denitrification is effected in the same environment while keeping the oxygenconcentration below 1 ppm. The method allows the use of high biomass concentrations (up to 20 kg/m.sup.3) and reduces energy consumption and process volume of e.g. activated sludge processes, thereby saving costs for waste water purification. Generally, the process ensures optimized conditions for microorganisms in the process. Also disclosed is a method for waste water purification and a waste water purification plant which both employ the method for control of biodegradation. Finally, a method for determining set-point values allowing the control is also disclosed.

Abstract: A waste water purification plant for biological treatment, and optionally mechanical and/or chemical treatment, of biodegradable material present in an aqueous environment is provided. The plant in a biological treatment part contains at least one sensor which measures fluorescent emission and/or variation therein of at least one characteristic biogenic fluorophore present in the biological treatment part which comprises a mixed culture of microorganisms, and which plant further includes a data processing device connected to the at least one sensor and a control device connected to the data processing device. The plant also contains a portion for determining quality and/or quantity of the material to be treated including an additional mixed culture of microorganisms, a sample of the biodegradable material and a further sensor or sensors for measuring fluorescent emission.

Abstract: A method for controlling and/or optimising a process in which a biological system comprising mixed cultures of microorganisms, biodegradable material, one or more biogenic fluorophores and optionally other soluble and/or insoluble and/or suspended substances in an aqueous environment is subjected to one or several separation processes and/or to chemical reactions and/or to biological treatment so as to obtain as a final product purified water which has a substantially lower content of biodegradable matter than the biological system, which method comprises monitoring the microbiological activity of the biological system and/or fluctuations thereof by on-line measurement of fluorescent emission and/or variations therein for at least one of the fluorophores in the system when irradiated with light and controlling one or several parameters of the process by using results from the measurement as measured variable(s) in an on-line automatisation system.