H 2 S Adsorption/Oxidation on Adsorbents Obtained from Pyrolysis of Sewage-Sludge-Derived Fertilizer Using Zinc Chloride Activation Andrey Bagreev, †,‡ David C. Locke, § and Teresa J. Bandosz* ,† Department of Chemistry and The International Center for Environmental Resources and Development, City College of New York, City University of New York, New York, New York 10031, and Department of Chemistry, Queens College, City University of New York, Flushing, New York 11367 Sewage-sludge-derived fertilizer, Terrene, was used as a precursor of adsorbents tested for removal of hydrogen sulfide from moist air. The adsorbents were obtained by pyrolysis of zinc chloride-impregnated granular fertilizer at 400, 600, 800, and 950 °C in a nitrogen atmosphere. Subsamples of the materials obtained were washed with hydrochloric acid to remove the excess zinc chloride and other soluble chlorides. This treatment results in a significant increase in the sample porosity. The highest H 2 S removal capacity was obtained for the sample carbonized at 600 °C. This results from release of zinc chloride vapor during heat treatment, which acts to form micropores in the carbonaceous deposit. When inorganic oxides and salts are present in sufficient quantities, hydrogen sulfide undergoes surface reactions and is left on the surface in the form of nonvolatile sulfides and sulfates. The pores are gradually filled as the surface reaction proceeds. If catalytic metal oxides are removed, hydrogen sulfide is oxidized predominantly to sulfuric acid through the catalytic effect of the adsorption sites in the small micropores of the carbonaceous deposit. The removal of H 2 S occurs until all pore entrances are blocked with the oxidation product. Introduction Growing environmental awareness directs the atten- tion of researchers toward new and alternative methods of waste reduction and waste minimization. 1 One of the waste materials produced in abundant quantity in wastewater treatment plants is municipal sewage sludge, referred to as biosolids. Biosolids consist of organic material, mainly dead bacterial cells; inorganic compo- nents in the form of various oxides and salts (aluminum, silicon, calcium, iron, etc.); and heavy metal contami- nants such as lead and copper from plumbing. Other metals present include nickel and zinc. 2-4 Biosolids disposal methods include landfilling, incin- eration, and road paving. Biosolids can also be converted into adsorbents for wastewater pollutants or applied to soil as fertilizer. 5 Recently, the agricultural application of biosolids has been a topic of major controversy 2 because of the presence of heavy metals considered toxic to the environment. Metals such as lead, copper, and cadmium can accumulate in soils and, after extensive application of biosolids-derived fertilizer, can leave the soil permanently contaminated and not safe for the growing of food crops. It is interesting that U.S. EPA standards for heavy metals in fertilizers are up to 100 times higher than the limits allowed in any other country. 2 This could significantly increase the risk of permanent contamination and damage to ecological systems. Continuous increases in the quantity of sludge pro- duced, especially in Europe, call out for efficient and environmentally friendly approaches to its utilization. One of these is conversion of sewage sludge into adsor- bents. Since the 1970s, several patents have been issued proposing carbonization of sewage sludge 6-10 and ap- plication of the carbonized material to the removal of organics in the final stages of water cleaning 8 and to the removal of chlorinated organics. 9 Sewage-sludge- derived adsorbents have been also tested for their ability to remove acidic gases such as sulfur dioxide and hydrogen sulfide from air streams. 11,12 However, the reported capacity was not promising for their effective application. Our recent results showed that materials obtained by pyrolysis of sewage-sludge-derived organic fertilizer, Terrene, perform very well as adsorbents of hydrogen sulfide. 4 Their removal capacity is comparable to the capacity of coconut-shell-based activated carbon, which is considered as an alternative material to replace the caustic-impregnated carbons used extensively for odor control in sewage treatment plants. 13,14 The objective of this paper is to demonstrate the H 2 S removal performance of materials obtained by chemical activation of Terrene using zinc chloride. The use of zinc chloride for chemical activation was proposed by Kemmer et al. 9 and applied by Chiang and You 15 and Lu and co- workers. 11,12 Pyrolysis in the presence of a chemical agent significantly increases the microporosity, as well as the yield of carbonaceous phase. 9,11,12 These results emphasize the importance of the role of pore volume and the chemistry of the adsorbent in the process of hydro- gen sulfide removal. The data obtained support our hypothesis concerning the significance of the presence of catalytic metals and their surface dispersion to the adsorption and conversion of hydrogen sulfide to water- soluble species, which makes adsorbent regeneration feasible using simple methods, such as water washing. * To whom correspondence should be addressed. E-mail: tbandosz@scisun.sci.ccny.cuny.edu. Tel: (212) 650-6017. Fax: (212) 650-6107. † City College of New York. ‡ Permanent address: Institute for Sorption and Problems of Endoecology, Ukraine. § Queens College. 3502 Ind. Eng. Chem. Res. 2001, 40, 3502-3510 10.1021/ie010165w CCC: $20.00 © 2001 American Chemical Society Published on Web 07/13/2001