INFLUENCE OF CARBON SOURCE ON NITRATE REMOVAL BY NITRATE-TOLERANT KLEBSIELLA-OXYTOCA CECT-4460 IN BATCH AND CHEMOSTAT CULTURES

The nitrate-tolerant organism Klebsiella oxytoca CECT 4460 tolerates n itrate at concentrations up to 1 M and is used to treat wastewater wit h high nitrate loads in industrial wastewater treatment plants, We stu died the influence of the C source (glycerol or sucrose or both) on th e growth rate and the efficiency of nitrate removal under laboratory c onditions. With sucrose as the sole C source the maximum specific grow th rate was 0.3 h(-1), whereas with glycerol it was 0.45 h(-1). In bat ch cultures K. oxytoca cells grown on sucrose or glycerol were able to immediately use sucrose as a sole C source, suggesting that sucrose u ptake and metabolism were constitutive. In contrast, glycerol uptake o ccurred preferentially in glycerol-grown cells. Independent of the pre culture conditions, when sucrose and glycerol were added simultaneousl y to batch cultures, the sucrose was used first, and once the supply o f sucrose was exhausted, the glycerol was consumed. Utilization of nit rate as an N source occurred without nitrite or ammonium accumulation when glycerol was used, but nitrite accumulated when sucrose was used. In chemostat cultures K. oxytoca CECT 4460 efficiently removed nitrat e without accumulation of nitrate or ammonium when sucrose, glycerol, or mixtures of these two C sources were used. The growth yields and th e efficiencies of C and N utilization were determined at different gro wth rates in chemostat cultures. Regardless of the C source, yield car bon (Y-C) ranged between 1.3 and 1.0 g (dry weight) per g of sucrose C or glycerol C consumed. Regardless of the specific growth rate and th e C source, yield nitrogen (Y-N) ranged from 17.2 to 12.5 g (dry weigh t) per g of nitrate N consumed. In contrast to batch cultures, in cont inuous cultures glycerol and sucrose were utilized simultaneously, alt hough the specific rate of sucrose consumption was higher than the spe cific rate of glycerol consumption. In continuous cultures double-nutr ient-limited growth appeared with respect to the C/N ratio of the feed medium and the dilution rate, so that for a C/N ratio between 10 and 30 and a growth rate of 0.1 h(-1) the process led to simultaneous and efficient removal of the C and N sources used. At a growth rate of 0.2 h(-1) the zone of double limitation was between 8 and 11. This sugges ts that the regimen of double limitation is influenced by the C/N rati o and the growth rate. The results of these experiments were validated by pulse assays.