Conditions and Mechanisms in Thiocyanate Biodegradation

Abstract

Presence of thiocyanate (SCN -) is a problem of considerable interest in many industrial wastewaters, where this contaminant often appears accompanied by secondary sources of carbon, nitrogen and/or sulphur. In order to understand the effect of these compounds on the biodegradability of SCN -, this work investigates how the bacterium Pararacoccus thiocyanatus utilises the three elements that form the molecule of thiocyanate and compare this behaviour with those obtained in presence of other sources of N, S and C. Result showed that the bacterium was capable of utilizing thiocyanate as the sole substrate, achieving specific biodegradation rates of approximate 1.20 mg SCN -(mg cell·h) -1 and eliminating initial thiocyanate concentrations up to 5,000 mg L -1 . Experimental data were successfully fitted to a Teisser model, assuming the existence of substrate inhibition obtaining values of μ max of 0.059 h -1 , K s of 790 mg L -1 and K i of 6,520 mg L -1 for free mineral medium. Presence of additional carbon and nitrogen sources implied catabolic repression of the biodegradation of thiocyanate. In this case, only concentrations lower than 3,500 mg L -1 could be treated, obtaining specific degradation rates of around 0.70 mg SCN -·(h·mg cell) -1 . Tessier model values showed a higher maximum specific growth rate (0.344 h -1 ), changing also the values for affinity and inhibition constants (1,150 mg L -1 and 1,730 mg L -1 , respectively).

Understanding the simultaneous biodegradation of thiocyanate and salicylic acid by Paracoccus thiocyanatus and Pseudomonas putida

“…Similar behavior was observed by Chaudhari and Kodam (2010) with co-culture of Klebsiella pneumoniae and Ralstonia sp. and by Combarros et al (2015) with P. thiocyanatus.…”

“…Initial biodegradability tests of each pollutant by each bacterial species were carried out using the mineral medium recommended by Combarros et al (2014Combarros et al ( , 2015 (PpMM for Pseudomonas putida and PtMM for Paracoccus thiocyanatus). For co-culture experiments, a combination of both mineral media was selected (CCMM), its final composition being: 0.…”

“…For the biodegradations using an only bacterium, the culture conditions for each bacteria were chosen as recommended for an optimum growth, i.e., 200 rpm and 30°C in 250-mL Erlenmeyer flasks containing 100 mL of PpMM for P. putida and 250 rpm and 28°C in 500-mL Erlenmeyer flaks containing 100 mL of PtMM for P. thiocyanatus (Combarros et al 2014(Combarros et al , 2015. The biodegradation conditions selected for the co-culture were 30°C, 250 rpm and 100 mL of CCMM in 500-mL Erlenmeyer flasks.…”

“…So, the biological reactors in these studies were frequently considered as ''black boxes'' difficult to predict and control (Herrero and Stuckey). Others woks use model pollutants or synthetic wastewaters and pure cultures (Agarry et al 2009;Agarry and Solomon 2008;Arutchelvan et al 2005;Combarros et al 2014Combarros et al , 2015Juang and Tsai 2006;Kim and Katayama 2000;Kwon et al 2002). The aim of these studies is usually to define the capacity of the bacterium to degrade a specific compound, the biodegradation pathway and the effect of the culture conditions on the bacterial activity.…”

“…Pure cultures usually show lower resistance to stress conditions than mixed ones, amplifying the response of the system to perturbations. The removal of phenol or cyanide compounds in biological wastewaters processes using pure cultures of Pseudomonas, Klebsiella, Ralstonia, Thibacillus or Paracoccus has been analyzed (Agarry et al 2009;Agarry and Solomon 2008;Combarros et al 2014Combarros et al , 2015Juang and Tsai 2006;Kim and Katayama 2000;Kwon et al 2002). The main limitation of these studies is that they provide too simple scenarios, which usually do not reflect the complexity of the interactions.…”