Journal of Water Process Engineering 7 (2015) 203–209 Contents lists available at ScienceDirect Journal of Water Process Engineering journal h om epage: www.elsevier.com/locate/jwpe Resilience of methanogenesis in an anaerobic reactor subjected to increasing sulfate and sodium concentrations N. Callado a , M.H.R.Z. Damianovic b , E. Foresti b,∗ a Center for Technology, Federal Univesity of Alagoas (UFAL), Campus A.C. Simões – BR 101 Norte – Km. 14 – Tabuleiro do Martins, 57.072-970 Maceió/AL, Brazil b Biological Process Laboratory, Department of Hydraulic and Sanitation, Sao Carlos School of Engineering, University of Sao Paulo (EESC/USP), Av. Joao Dagnone, 1100–Santa Angelina, 13.563-120 Sao Carlos, SP, Brazil a r t i c l e i n f o Article history: Received 16 July 2014 Received in revised form 4 May 2015 Accepted 16 June 2015 Available online 20 July 2015 Keywords: Sulfate reduction Methanogenesis COD/Sulfate ratio UASB inhibition a b s t r a c t Various types of industrial activities produce saline and/or sulfate-rich effluents and could use the anaer- obic treatment process as the core technology. However, both salinity and sulfate can interfere with the process. This study investigated the performance of a UASB reactor in the treatment of synthetic wastewater containing glucose, acetate,methanol and sodium sulfate. The reactor had a useful volume of 10.5 L and was operated for 266 days at the hydraulic detention time of 15.6 h. The influent chemical oxygen demand (COD) was kept at 2000 mg L -1 whereas sodium sulfate concentrations increased along eighteen experimental phases, defined by the applied COD/[SO 4 2- ] ratio. Influent sulfate and sodium concentrations ranged from 25 to 10,000 mg L -1 and from 750 to 5350 mg L -1 , respectively. The progres- sive increase of sodium and sulfate concentration and the consequent decrease of the COD/[SO 4 2- ] ratios affected the reactor’s performance, but the average COD removal efficiency remained above 80%. The observed partial process inhibition can be attributed to the synergistic effect resulting from the sulfide generated and the presence of sodium cations. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Anaerobic systems have been employed in various industrial wastewater treatment processes, including those containing saline and sulfurous compounds – however, both cations and sulfates can interfere with the treatment process. Residues from food pro- cessing industries (salt refineries, fish processing and dairy), from petrochemical and chlorine chemical industries, tannery compa- nies and pharmaceutical industries are some examples of residues with these characteristics. Sulfate-reducing bacteria (SBR) promote competitive interac- tions with the consortium of methanogenic archaea (MA). The greater affinity for hydrogen causes the SBR to outcompete the hydrogenotrophic methanogens. The BRS can use acetate that also may compete with acetoclastic methanogenic [14,12]. Notwith- standing, Damianovic and Foresti [3], have shown that efficient treatment of sulfate-rich wastewater is feasible, since the associ- ation of methanogenesis and sulfidogenesis is possible depending on the electron donor availability. ∗ Corresponding author. E-mail address: eforesti@sc.usp.br (E. Foresti). According to O’Reilly and Colleran [15], the main parameter that controls the interactions between SRB and MA is the rela- tionship between the amount of available organic substrates and sulfate. As organic matter is expressed as chemical oxygen demand (COD), the COD/[SO 4 2- ] ratio is usually considered the process con- trol parameter. Theoretically, when the COD/[SO 4 2- ] ratio is equal to 0.67, there is enough sulfate to drive the electron flow to sul- fidogenesis and not to methanogenesis. In situations where the COD/[SO 4 2- ] ratio is above 0.67, the sulfidogeniesis and methano- genesis can occur simultaneously. Below this value, sulfidogenesis tends to be predominant, given that sulfide generation can partially inhibit methanogenesis, thus affecting the overall organic matter removal. However, there are contradictory results in the literature regarding the effects of sulfate reduction on the anaerobic process. While some authors have reported competition between SRB and MA by acetate and hydrogen, others have reported on a syntrophic relationship between these two bacterial groups. SRB microorganisms are a very heterogeneous group that com- prises representatives of the domains bacteria and Archaea, which use sulfate as the final electron aceptor. These microorganisms have been found in psychrophilic and hyperthermophilic envi- ronments, as well as in freshwater and hypersaline environments [8]. They have the ability to metabolize a variety of compounds, http://dx.doi.org/10.1016/j.jwpe.2015.06.011 2214-7144/© 2015 Elsevier Ltd. All rights reserved.