Cyanide (CN-) is used in mining, steel, electroplating, and chemical industries, and in recovering gold and silver from ores (Dash et al. 2009) and as a result it enters wastewater treatment plants (WWTPs) through industrial discharges. Most cyanides are highly toxic and can inhibit nitrification in activated sludge systems (Neufeld et al. 1986). Most cyanide nitrification inhibition studies have been conducted using physiological responses, such as those based on ammonia-dependent specific oxygen uptake rate (SOUR), and nitrifying pure cultures. For example, N. europaea cells exposed for 3 h to 1 or 2 µM NaCN showed 39% or 67% inhibition in ammonia dependent SOUR (Park and Ely 2009). In respirometry-based studies using nitrifying sludge cultures it was observed that free cyanide concentrations greater than 0.2 mg/L must be avoided for stable operation of biological nitrification processes (Neufeld et al. 1986). None of these types of studies have simultaneously evaluated the impact of cyanide on mixed cultures using SOUR and gene transcript concentrations. Our objective was to perform such a comparison in nitrifying mixed cultures exposed to cyanide. In this study, the transcriptional responses of genes amoA and hao in autotrophic AOB present in nitrifying enrichments were examined for environmentally relevant concentrations of cyanide. Specifically, we applied reverse transcriptase-qPCR (RT-qPCR) assays targeting function-specific genes linked to nitrifying bacteria to measure the relative expression of AOB in response to acute exposure (12 h) of nitrifying enrichments to varying concentrations of cyanide. We compared the transcriptional responses to respirometry-based measurements for the same set of samples to evaluate the efficacy of using functional gene transcript levels as indicators of nitrification activity.

Inhibition and gene expression of wastewater nitrifying enrichments exposed to cyanide

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.