Author's personal copy Process Safety and Environmental Protection 9 2 ( 2 0 1 4 ) 261–268 Contents lists available at ScienceDirect Process Safety and Environmental Protection journal h om ep age: www.elsevier.com/locate/ps ep Biotrickling filters for biogas sweetening: Oxygen transfer improvement for a reliable operation Ginesta Rodriguez a , Antonio D. Dorado a , Marc Fortuny b , David Gabriel c , Xavier Gamisans a,∗ a Department of Mining Engineering and Natural Resources, Universitat Politècnica de Catalunya, Bases de Manresa 61-73, 08240 Manresa, Spain b Aeris Tecnologías Ambientales, Parc de Recerca, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain c Department of Chemical Engineering, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain a b s t r a c t An industrial-scale biotrickling filter for the removal of high concentrations of H 2 S is described in this work. The system has been operating at H 2 S inlet concentrations between 1000 and 3000 ppm v at acidic conditions. A decrease of pH from 2.6 to 1.8 did not affect the biological activity inside the biofilter while reducing the water make-up con- sumption up to 75%. The current oxygen supply system, based on direct injection of air to the liquid phase, has demonstrated to be inefficient for a long-term operation leading to elemental sulfur accumulation in the packing material (i.e. promoting clogging episodes). The present study demonstrates it is possible to partially remove (40.3%) the deposited elemental sulfur by bio-oxidation when biogas is not fed. In normal operation conditions, the imple- mentation of an aeration system based on jet-venturi devices has shown quite promising results in terms of oxygen transfer efficiency and robustness. Such improvement of oxygen transfer was translated in a better conversion of H 2 S to sulfate, which increased around 17%, prolonging the lifespan operation at low-pressure drop. © 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Keywords: Biotrickling filter; Hydrogen sulfide; Mass transfer; Jet-venturi; Elemental sulfur; Acidic pH 1. Introduction The use of renewable and alternative energy sources is an effort to reduce the greenhouse gas emissions and global warming. In this sense, the biogas produced in the anaerobic digestion in both municipal solid wastes (MSW) and wastewa- ter treatment plants (WWTP) is a prominent, renewable energy source. Burning biogas in a combined heat and power (CHP) plant is an interesting option to reduce the emissions and the operational cost of a WWTP. However, prior to biogas burning it is necessary to remove the hydrogen sulfide (H 2 S) pro- duced during anaerobic digestion process. This will eventually avoid facility corrosion, unnecessary production of byprod- ucts, and SO 2 emissions. The specifications for the maximum content of H 2 S for CHP are in the range of 0.02–0.05% (v/v) (200–500 ppm v ). The biogas generated in anaerobic digestion facilities in WWTPs contains average concentrations of H 2 S in ∗ Corresponding author. E-mail address: xavierg@emrn.upc.edu (X. Gamisans). Received 2 July 2012; Received in revised form 28 January 2013; Accepted 15 February 2013 the range from 0.1 to 0.5 vol.% (1000–5000 ppm v ) (Walsh et al., 1998). Biological removal of H 2 S in biotrickling filters (BTF) has been successfully tested in applications at moderate-low pol- lutant loads containing H 2 S concentrations up to 12,000 ppm v (Fortuny et al., 2008). The technology has proved to be a good alternative to the more expensive physical–chemical systems (Kim and Deshusses, 2005). In recent years, the use of the biofiltration technology for the removal of H 2 S at high con- centrations have been developed and tested at industrial-scale (Tomás et al., 2009). However some issues concerning the pro- duction of by-products such as elemental sulfur, which has been related to clogging episodes, hinders the robustness and reliability of the technology. In the previous studies of Tomás et al. (2009), performed in the same BTF at similar operation conditions, an elementary analysis denoted that the 95% of the solid deposited on the packing material was elemental sulfur. 0957-5820/$ – see front matter © 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.psep.2013.02.002