Effect of adsorbent composition on H2S removal on sewage sludge-based materials enriched with carbonaceous phase

In order to improve the carbonaceous phase content in sewage sludge derived adsorbents, dewatered sludge was physically mixed with polystyrene sulfonic acid-co maleic acid sodium salt with the following ratios of polymer to sludge: 10:90, 30:70, 50:50 and 70:30. The samples, along with the pure precursors, were carbonized at 950 °C and then washed in water to remove the excess of sodium salt/hydroxide. The performance of materials as H₂S adsorbents was tested using a home-developed dynamic breakthrough test. The samples, before and after adsorption process, were characterized by adsorption of nitrogen, potentiometric titration, thermal analysis and SEM. Differences in the performance were linked to the surface properties. It was found that mixing polymer with sludge increases the amount of H₂S adsorbed/oxidized in comparison with the adsorbents obtained from pure precursors (sludge or polymer). Sewage sludge provides the catalytic centers for hydrogen sulfide oxidation whereas a carbonaceous phase contributes to an increase in the dispersion of catalytic centers and provides more “storage space” in its micropores. There is an optimal ratio in the composition of the precursors for which the best performance is achieved. When the content of the polymer is too high, the “buffering capacity” of the sludge-derived phase is not enough to neutralize the suppressing effect of acidic surface groups of a carbonaceous phase.