Dried Sludges and Sludge-Based Chars for H2S Removal at Low Temperature: Influence of Sewage Sludge Characteristics

The use of sewage sludge as a precursor of adsorbent/catalyst materials for environmental applications has been encouraged during the past few years. Due to the heterogeneous nature of sludges, there exists a lack of information regarding the characteristics of these low-cost precursors and how their physicochemical properties affect the final performance of materials prepared from them. In this work, three sewage-sludges collected at WWTPs with assorted sludge/wastewater treatment schemes were used as precursors of adsorbents/catalysts for H2S removal at room temperature. All the solids were characterized to establish their textural properties and chemical composition, including the speciation of the adsorbents/catalysts inorganic fraction. Thermal treatment (gasification) of the raw (dried) sludges increased the H2S removal ability in all cases. For these thermally treated materials, catalytic conversion to elemental sulfur and sulfate moieties was found to be the main route of H2S removal. Results indicate that adsorbents based on an iron/calcium-containing sludge were the most reactive and exhibited the highest capacities for H2S retention. For this particular type of sludge, a reasonably good performance was observed even when the dried (raw) sludge was used as adsorbent/catalyst. Alternatively, the oxidation of H2S by chars obtained from the other two sludges under study was related to their textural properties.