Resources from sewage sludge ashes can be re-utilized for the recycling economy and pollutants can be removed by using a thermochemical process. An online analysis method has been developed for the determination of element mass fractions in the ashes and their products originating from the process. The applied analysis system is a method combination of laser-induced breakdown spectroscopy (LIBS) and X-ray fluorescence (XRF) spectroscopy. Robustness and a modular construction are important demands for successful future applications.