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

Abstract

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 solidswere 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. Forthis particulartype 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.

H2S removal from syngas using wastes pyrolysis chars

“…Few studies compared the H 2 S removal efficiency of activated carbon in moist and dry conditions and revealed that humidity strongly promoted the adsorption efficiency of activated carbon [5,24,36]. The reaction mechanism in dry atmosphere with zeolite has recently been investigated [12], but still remains unclear with activated carbons.…”

Removal of copper on composite sewage sludge/industrial sludge-based adsorbents: The role of surface chemistry

“…The efficient method of their industrial "recycling" and thus waste minimization is via pyrolysis, in which adsorbents are produced. It was recently demonstrated that such adsorbents can effectively remove dyes [13,19,20], heavy metals [13][14][15], phenols [13], or hydrogen sulfide [21][22][23][24][25][26][27]. Their high removal capacity is a result of complexity of surface chemistry, specific porosity, and high volume of mesopores.…”

“…That surface chemistry includes basic pH and presence of catalytic centers based on iron and other transition metals. These entities are formed as a result of solid state reactions during pyrolysis of complex inorganic/organic matrices [24,25,27]. Moreover, there is an indication that the pyrolysis conditions can be adjusted toward obtaining the most effective adsorbents for a desired application [28,29].…”

Use of sewage sludge combustion ash and gasification ash for high-temperature desulphurization of different gas streams

“…As a result of surface reactions, H 2 S can be oxidized to either sulphur or SO 2 [8]. Activated carbons of different characteristics have also been prepared from sewage sludge pyrolysis or carbonization [10][11][12][13], obtaining pollutant removal results comparable to those corresponding to commercial catalytic activated carbons [13].…”