Kinetics of nitrate- and nitrite-removal by Rhodotorula Glutinis: determination of a reaction mechanism

Nitrate- and nitrite-removals represent a fundamental step in the water treatment industry. Denitrification is typically obtained through a biological process where specialized microorganisms are able to reduce nitrate and nitrite to ammonium ion or molecular nitrogen. In this context, the continuous search for a more sustainable economy demands for alternative microorganisms capable to assimilate nitrate and nitrite in a more convenient way. For this reason, in this work the attention is focused on “Rhodotorula Glutinis”, a yeast with acknowledged capability of NOx assimilation (Hipkin, 1989; Smith, 1992). More specifically, five different reaction mechanisms are defined as possible candidates to describe the system behavior at the scale of the industrial process i.e. unstructured modelling of transients biomass and nutrient concentrations in the pseudo-homogeneous liquid phase. The hypothesized mechanisms differ in the source of nitrogen used as nutrient for biomass culture (being nitrate, nitrite or ammonium ion), and in considering or not the nitrate- and nitrite-reduction as growth-associated reactions. However, the general reduction pathway proposed for yeasts (Siverio, 2002), i.e. from nitrate to nitrite, and then ammonium ion by means of nitrate- and nitrite-reductase, is always respected. System behavior in a isothermal Batch reactor is simulated by varying initial composition of nitrate and nitrite concentrations while keeping an excess of dissolved oxygen and substrate. The value of the model parameters used in the simulations is taken from the literature and related to similar microorganisms, when available. On the other hand, the stoichiometry is determined by following the fundamental approach proposed by Rittmann and McCarty (1998), based on the selection of an empirical, chemical formula of the cell, and the partitioning of substrate between energy generation and microbial synthesis. In conclusion, a sequence of experimental runs to discriminate the reaction mechanism more capable to follow system behavior among the five proposed maybe defined. Bibliografia B.E.Rittmann, P.L.McCarty. "Stoichiometry and Bacterial Energetics ." Environmental Biotechnology: Principles and Applications, 1998: 126-164. C.R. Hipkin. "Nitrate assimilation in yeasts." Oxford Science Publications, 1989: 51-68. N.A.Smith. "Nitrate Reduction and ATNC Formation By Brewery Wild Yeasts ." Journal Insitute Brewery, 1992: 415-420. J.M.Siverio. "Assimilation of nitrate by yeast." FEMS MICROBIOLOGY Reviews, 2002: 277-284.