Continuous denitrification by external electron-donor supply utilizing an algorithm-based software controller

This paper presents the development and application of a knowledge-based software controller for the external electron-donor supply in the anaerobic denitrification stage. The basic principle of the control concept is based on the continuous measurement of the methane concentration in the off-gas. Since under anoxic conditions and incomplete NOx− removal the denitrifying species out-compete efficiently the methanogens for the carbon source, the appearance of methane at a significant concentration (≥0.3%) in the gas phase indicates the complete denitrification and the increasing consumption of the C-source by the methanogens. Thus, a software controller that uses the methane concentration as variable was designed for process control and tested in different reactor types (CSTR, Fluidized bed). The necessary amount of the external electron-donor can be kept at the optimal level without any undesired accumulation of nitrite or nitrate.