Contents lists available at ScienceDirect Environmental Research journal homepage: www.elsevier.com/locate/envres H 2 S removal from sour water in a combination system of trickling biofilter and biofilter Mojtaba Fasihi a , Mohammad Hassan Fazaelipoor a,b,* , Mashallah Rezakazemi c a Department of Chemical Engineering, Faculty of Engineering, Shahid Bahonar University of Kerman, Iran b Department of Chemical and Polymer Engineering, Faculty of Engineering, Yazd University, Yazd, Iran c Faculty of Chemical and Materials Engineering, Shahrood University of Technology, Shahrood, Iran ARTICLE INFO Keywords: Sour water Hydrogen sulfide Modeling Biological removal Trickling biofilter ABSTRACT Desulfurization of sour water was investigated in a combination system of trickling biofilter (BTF) and biofilter (BF) filled with ceramic packing materials. A critical elimination capacity (EC) of 251.93 g S m -3 h -1 was obtained for the BTF/BF system during a stepwise increase of sulfide concentration from 10 to 60 g S m -3 . This stepwise increment of loading rate also led to critical ECs of 176.21 and 478.88 g S m -3 h -1 for BTF and BF, respectively. A dynamic model describing biological H 2 S removal from sour water in the BTF/BF was developed and calibrated by a set of experimental data. The model includes the main processes occurring in the BTF/BF such as mass transfer between phases, diffusion and biological reaction inside the biofilm. The model also considers the intermediate (elemental sulfur) production/consumption and sulfate formation through the dif- ferent oxidation pathways. The model validation was performed under a starvation period and a dynamic H 2 S loading period. A sensitivity analysis was carried out to evaluate the relative importance of the key parameters on the performance of the BTF/BF system. Sensitivity analysis showed that the BTF performance is more affected by the parameters related to H 2 S mass transfer. 1. Introduction Hydrogen sulfide (H 2 S) is an extremely toxic gas with an odor threshold range of 0.5–300 ppv (Colomer et al., 2010). Exposure to a high level of H 2 S allows obstructive lung disorders and enhances the risk of ischemic heart disease; pulmonary edema can occur at 300–500 ppm, with death occurring at higher than 600–800 ppm (Yalamanchili and Smith, 2008). A high level of separation is needed to produce the drinkable water because the human can perceive in the range of 0.003–0.200 ppm (Edwards et al., 2011). H 2 S is extremely corrosive, which can cause damage to equipment used in industrial plants and also combustion engines that use biogas from anaerobic digesters. All process or waste streams in industries which contain H 2 S should be treated for use or release into the environment (Hajilary and Rezakazemi, 2018; Rezakazemi et al., 2011). H 2 S removal from sour- gas streams is commonly carried out by physicochemical methods such as the Lo-cat and Amine-Claus process. These methods are expensive because of high chemical demand and operation at high pressure and temperature (Klok et al., 2012; Rezakazemi et al., 2017). Biological removal methods offer environmental advantages due to operation at ambient temperature and pressure and low chemical consumption compared to Lo-cat process (Janssen et al., 2009). Sour water (water that contains H 2 S) is the typical waste stream in gas and oil refineries which should be treated before being reused or disposed into the en- vironment. In the refineries, H 2 S is typically removed from sour water by steam stripping in packed or tray columns. This method consumes high energy and suffers from corrosion problems. Biooxidation of H 2 S can be used to overcome the difficulties related to conventional methods of H 2 S removal. In aerobic biooxidation, dissolved H 2 S is oxidized to elemental sulfur as an intermediate product and/or sulfate as a final product (equations (1)–(3))(Mora et al., 2016). + → + HS O S HO 0.5 2 2 0 2 (1) + + → + − + S O HO SO H 1.5 2 0 2 2 4 2 (2) + → + − + HS O SO H 2 2 2 2 4 2 (3) In addition to the biological oxidation of sulfide, undesirable che- mical reactions also occur in the bioreactors (Roosta et al., 2011). + − → + − − + HS X S S H ( 1) X 0 2 (4) https://doi.org/10.1016/j.envres.2020.109380 Received 10 December 2019; Received in revised form 22 January 2020; Accepted 10 March 2020 * Corresponding author. Department of Chemical Engineering, Faculty of Engineering, Shahid Bahonar University of Kerman, Iran. E-mail addresses: fazaelipoor@yazd.ac.ir, fazaelipoor@yahoo.com (M.H. Fazaelipoor). Environmental Research 184 (2020) 109380 Available online 10 March 2020 0013-9351/ © 2020 Elsevier Inc. All rights reserved. T