Journal of Hazardous Materials 315 (2016) 52–60 Contents lists available at ScienceDirect Journal of Hazardous Materials jo ur nal ho me p ag e: www.elsevier.com/locate/jhazmat Improving the cyanide toxicity tolerance of anaerobic reactor: Microbial interactions and toxin reduction Pragya Gupta, S.Z. Ahammad, T.R. Sreekrishnan ∗ Department of Biochemical Engineering and Biotechnology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India h i g h l i g h t s • Anaerobic batch study of 110 days. • Acclimatization for cyanide biodegradation. • Understanding inhibitory effects of cyanide on methane generation and VFA production. • Identification of microorganisms tolerant to cyanide. • Community analysis using DGGE and qPCR analyses. a r t i c l e i n f o Article history: Received 24 November 2015 Received in revised form 30 March 2016 Accepted 12 April 2016 Available online 29 April 2016 Keywords: Anaerobic treatment Cyanide Acclimatization DGGE qPCR a b s t r a c t Anaerobic biological treatment of high organics containing wastewater is amongst the preferred treat- ment options but poor tolerance to toxins makes its use prohibitive. In this study, efforts have been made to understand the key parameters for developing anaerobic reactor, resilient to cyanide toxicity. A laboratory scale anaerobic batch reactor was set up to treat cyanide containing wastewater. The reactor was inoculated with anaerobic sludge obtained from a wastewater treatment plant and fresh cow dung in the ratio of 3:1. The focus was on acclimatization and development of cyanide-degrading biomass and to understand the toxic effects of cyanide on the dynamic equilibrium between various microbial groups. The sludge exposed to cyanide was found to have higher bacterial diversity than the control. It was observed that certain hydrogenotrophic methanogens and bacterial groups were able to grow and produce methane in the presence of cyanide. Also, it was found that hydrogen utilizing methanogens were more cyanide tolerant than acetate utilizing methanogens. So, effluents from various industries like electroplating, coke oven plant, petroleum refining, explosive manufacturing, and pesticides indus- tries which are having high concentrations of cyanide can be treated by favoring the growth of the tolerant microbes in the reactors. It will provide much better treatment efficiency by overcoming the inhibitory effects of cyanide to certain extent. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Cyanide is highly toxic in all forms, with hydrogen cyanide being the deadliest of all. It causes various health hazards like rapid breathing, tremors, weight loss, nerve damage and even risks to human and animal life. Many industrial wastewaters contain 0.01–10 ppm of total cyanide [1]. Wastewater from an electroplat- ing industry may contain 10,000–30,000 ppm of cyanide. However, wastewaters from coke oven plants could contain up to 50 ppm of cyanide. It is also produced as waste from other industries ∗ Corresponding author. E-mail address: sree@iitd.ac.in (T.R. Sreekrishnan). like petroleum refining, explosives manufacturing, automobile manufacturing, printed circuit board manufacturing, chemicals industries, pesticide industries and synthetic fiber production units, and many other sources. All such industrial effluents need to be treated to meet effluent disposal standards, before discharging these into the environment. The US Environmental Protection Agency (USEPA) has set a limit for cyanide contamination at 200 ppb for drinking water [2]. Similarly, in India The Central Pollution Control Board (CPCB) has set a limit for cyanide called as minimal national standard (MINAS) as 0.2 mg/L [3]. Cyanide treatment is mainly done by various chemical and physical methods, which are aerobic in nature. These methods of treatment are expensive and complicated [4]. The most com- http://dx.doi.org/10.1016/j.jhazmat.2016.04.028 0304-3894/© 2016 Elsevier B.V. All rights reserved.