Utilization of Effluent Water from Wastewater Treatment as a Flue Gas Scrubbing Liquid in a Sewage Sludge Incineration Plant

Compared to common, medium sized wood firing biomass power plants, sewage sludge incineration plants need quite complex systems for flue gas cleaning, as they have to deal with higher amounts of acidic gases like sulfur dioxide (SO2) and hydrochloric acid (HCl). Because of the quite high nitrogen content in the sludge as well nitrogen oxides (NOx), especially nitrogen monoxide (NO), have to be considered. During the current work, a scrubber system was developed, which fulfills the needs of such a plant, using water from the adjacent wastewater treatment plant as a scrubbing liquid. The water is taken from the effluent of the wastewater treatment plant and is returned to the bioreactor of this plant for regeneration after usage. During the extensive testing of the scrubber system, removal efficiencies of up to 99.5 % for HCl and 95 % for SO2 have been achieved. As expected, an increased liquid-to-gas ratio as well as scrubbing liquid recirculation has a positive influence on the removal efficiencies. A major finding was that the nitrite concentration of the fresh scrubbing liquid effects the NO removal efficiency. Nitrite concentrations below or above a certain range resulted in poor NO removal efficiencies, while under ideal conditions removal efficiencies of more than 50 % have been reached. Based on the gained experiences, this system can be developed further and used for flue gas treatment in similar applications. Given that the effluent water is available for free from the wastewater treatment plant, it has very low operational costs, as no additional chemicals are needed.