Evaluation of oxygen injection as a means of controlling sulfide production in a sewer system Oriol Gutierrez a,1 , Janani Mohanakrishnan a,1 , Keshab Raj Sharma a , Rikke Louise Meyer b , Ju ¨ rg Keller a , Zhiguo Yuan a, * a Advanced Water Management Centre, Building 60, Research Road, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia b Department of Biological Sciences and Interdisciplinary Nanoscience Centre, Building 1540, Ny Mungekade 8000, University of Aarhus, Aarhus C 8000, Denmark article info Article history: Received 19 March 2008 Received in revised form 11 July 2008 Accepted 31 July 2008 Published online 9 August 2008 Keywords: Sulfide Oxygen Sulfate reducing bacteria Biofilm Rising main sewer abstract Oxygen injection is often used to control biogenic production of hydrogen sulfide in sewers. Experiments were carried out on a laboratory system mimicking a rising main to investi- gate the impact of oxygen injection on anaerobic sewer biofilm activities. Oxygen injection (15–25 mg O 2 /L per pump event) to the inlet of the system decreased the overall sulfide discharge levels by 65%. Oxygen was an effective chemical and biological oxidant of sulfide but did not cause a cessation in sulfide production, which continued in the deeper layers of the biofilm irrespective of the oxygen concentration in the bulk. Sulfide accumulation resumed instantaneously on depletion of the oxygen. Oxygen did not exhibit any toxic effect on sulfate reducing bacteria (SRB) in the biofilm. It further stimulated SRB growth and increased SRB activity in downstream biofilms due to increased availability of sulfate at these locations as the result of oxic conditions upstream. The oxygen uptake rate of the system increased with repeated exposure to oxygen, with concomitant consumption of organic carbon in the wastewater. These results suggest that optimization of oxygen injection is necessary for maximum effectiveness in controlling sulfide concentrations in sewers. ª 2008 Elsevier Ltd. All rights reserved. 1. Introduction Sewers have long been recognized as sites of biological and chemical transformations (Thistlethwayte, 1972; Hvitved- Jacobsen, 2002a; Zhang et al., 2008). One biotransformation with serious implications for wastewater authorities is the reduction of oxidized sulfur species, leading to the formation and release of hydrogen sulfide gas. The bacteria responsible for sulfide generation, the sulfate reducing bacteria (SRB), are located in biofilms of anaerobic sewer sections. The avail- ability of sulfate and organic substrates in domestic sewage provides SRB with optimal conditions for growth and respi- ration (Hvitved-Jacobsen, 2002a). Emission of sulfide from the liquid to the gas phase in subsequent gravity sewers results in corrosion and damage to sewer infrastructure and is also the cause of odour and health problems (US EPA, 1974). A number of operational strategies have been employed to control sulfide production in sewer networks (Boon, 1995; Boon * Corresponding author. Tel.: þ61 7 3365 4374; fax: þ61 7 3365 4726. E-mail addresses: oriol@awmc.uq.edu.au (O. Gutierrez), janani@awmc.uq.edu.au (J. Mohanakrishnan), keshab@awmc.uq.edu.au (K.R. Sharma), rikke.meyer@biology.au.dk (R.L. Meyer), j.keller@awmc.uq.edu.au (J. Keller), zhiguo@awmc.uq.edu.au (Z. Yuan). 1 Joint first authors in this publication. Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres 0043-1354/$ – see front matter ª 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2008.07.042 water research 42 (2008) 4549–4561