Sewage Sludge-derived Adsorbents for H2s Removal

Various methods have been used to dispose of or utilize municipal sewage sludge (1), including incineration, landfilling, road surfacing, conversion to fertilizer, compression into building blocks, and carbonization (1-4). Since 1976 several patents have been issued on carbonization of sewage sludge and various applications of the final materials (4-7). Carbonization of sludge in the presence of chemical activating agents such as zinc chloride and sulfuric acid produces new sorbents, with patented applications in such processes as removal of organics in the final stages of water cleaning (5) and removal of chlorinated organics (6). The process of carbonization of biosolids has been studied in detail using different chemical agents and various conditions (8-11). Materials obtained as a result of the treatment have surface areas between 100 and 500 m/g, but their performance as adsorbents has been demonstrated to be much worse than that of activated carbons. The ability of these adsorbents to remove organics such as phenols, or sulfur dioxide and hydrogen sulfide (10, 11) have been tested so far; their capacity for the adsorption of SO2 reported by Lu was less than 10% of the capacity of Ajax activated carbon (11). When the performance for H2S adsorption was compared, the capacity of sludge-derived adsorbents was only 25% of the capacity of Calgon carbon, IVP 4x6 (10). The objective of this paper is to demonstrate the superior performance of materials obtained by simple carbonization of the New York City municipal sewage sludge-derived product, Terrene, as adsorbents for hydrogen sulfide. As indicated elsewhere (12), this sludge-derived material is expected to work well as a hydrogen sulfide adsorbent because of the presence of either iron and other catalytic metals, or organic nitrogen in the matrix of the carbonaceous components. The results obtained show that the capacity of these adsorbents exceeds that of coconut shell-based activated carbon, which is considered as one of the alternative sorbents to replace the caustic-impregnated carbons commonly used as hydrogen sulfide adsorbents in municipal sewage treatment plants (13, 14). Experimental