Techno-economic assessment of biogas plant upgrading by adsorption of hydrogen sulfide on treated sewage–sludge P.G. Aguilera, F.J. Gutiérrez Ortiz ⇑ Departamento de Ingeniería Química y Ambiental, Universidad de Sevilla, Camino de los Descubrimientos, s/n, 41092 Sevilla, Spain article info Article history: Received 2 June 2016 Received in revised form 17 July 2016 Accepted 5 August 2016 Keywords: Desulfurization Biogas Sewage-sludge based adsorbent Hydrogen sulfide Techno-economic assessment abstract Biogas plant upgrading by adsorption of hydrogen sulfide on treated sewage–sludge was techno- economically assessed. Three different processes were included in the study: the desulfurization of bio- gas by adsorption, the in-situ regeneration of the adsorbent and its production from sewage-sludge. Biogas plant upgrading was performed for a flow rate of 1000 Nm 3 /h of biogas with a H 2 S concentration of 2000 ppmv and a breakthrough concentration of 200 ppmv, which is the technical limit value for inter- nal combustion engines. The cost due to the steam required for the in-situ regeneration was evaluated in two different scenarios: as a bought external utility and as an in-situ produced utility, installing an elec- tric or a biogas steam boiler. According to the cash flow analysis carried out, all the options require a sim- ilar minimum selling price for the upgraded biogas (about 0.27–0.29 €/Nm 3 ), with a cost of the overall desulfurization process between 2.5 and 4.0 c€/Nm 3 . Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Anaerobic digestion is a biochemical degradation process that is widely performed from organic matter present in municipal solid waste (MSW) deposited in a landfill. Previous results of life cycle assessment have shown that anaerobic digestion is always favor- able with respect to the scenario in which organic wastes from MSW are aerobically processed [1]. Four main stages are normally involved in the process, including hydrolysis, fermentation, anaer- obic oxidation and methanogenesis. Landfill gas (LFG) or biogas is produced by anaerobic digestion process. It is mainly composed of methane, carbon dioxide, moisture, and minor components such as H 2 S. By using biogas as energy resource, greenhouse gas emissions are reduced by the substitution of fossil fuels [2,3]. Nevertheless, biogas also contains hydrogen sulfide, which is highly corrosive, so it has to be removed before entering the biogas in an internal combustion engine. For H 2 S biogas removal, one of the most utilized methods is adsorption on activated carbon [4]. In recent years, the search for low-cost adsorbents has been promoted to reduce the high operat- ing costs. Locally available precursors such as natural materials, wastes from agriculture, industry or domestic, as well as some of their by-products (slag, sludge, fly-ash, bagasse or red mud) can be utilized as low-cost adsorbents. Activated carbon produced from sewage-sludge by thermal treatment to remove hydrogen sulfide from biogas has been previously tested, characterized and regenerated after being used, and the adsorption process has been modeled [5–8]. In some cases, capacities of adsorption doubled that of the commercial unimpregnated activated carbon tested and used as reference [5]. Moreover, the design of the regeneration process was performed with the aim of minimizing the use of resources such as water consumption, time and energy (tempera- ture) demand while achieving a high rate of regeneration. The selected in-situ regeneration consists of entering firstly steam at 250 °C, and then air at ambient temperature, in a second step. At lab-scale, it could be performed in a short period (20 min) and the adsorption capacity decreased only 2.6% on average in each adsorption/regeneration cycle [6] (calculated for a breakthrough concentration of 200 ppmv). Scientific literature contains some studies on production of low- cost adsorbents from different materials, where the treatment of activation and its applications are described [5,9]. In a recent review, the production cost of adsorbents from alternative precur- sors from wastes was estimated to be less than 0.1 US$ per kg, and usually between 0.01 and 0.05 US $ per kg [9]. However, to our knowledge, no other studies exist on techno-economic assessment of the biogas upgrading process using adsorbents produced from sewage-sludge for H 2 S removal. On the contrary, there are studies that compare upgrading technologies [10–12], as well as techno- economic evaluations focused on the MSW energy recovery through gasification [13]. Thus, this work is aimed at carrying http://dx.doi.org/10.1016/j.enconman.2016.08.005 0196-8904/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: frajagutor@us.es (F.J. Gutiérrez Ortiz). Energy Conversion and Management 126 (2016) 411–420 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman