Mixtures of sewage sludge and fish waste of various compositions were prepared and pyrolyzed at 950 degrees C in an inert atmosphere. On the pyrolyzed samples an activation with CO2 was carried out at 850 degrees C. The materials were used as H2S adsorbents at ambient conditions. Initial and spent samples were characterized using thermal analysis, XRD, XRF, SEM/EDX, sorption of nitrogen and surface pH measurements. An enhancement in the H2S removal capacity on the composite samples was linked to the synergistic effects of chemical composition. The adsorbents' surface reactivity was linked to the presence of Na, K, Ca, Mg and Fe in various configurations. Activation had a detrimental effect on the composites' performance as adsorbents of H2S. The sludge component provides an active iron phase, which is important for hydrogen sulfide oxidation. Potassium and sodium polysulfides and iron sulfite, sulfate, sulfide are the products of reactive adsorption. The strongest synergistic effect was found for the composite with the lowest content of the fish component. With an increase in the content of the fish waste this effect diminishes owing to the reactions of alkaline metals with silica during pyrolysis. (C) 2013 Elsevier B.V. All rights reserved.