Treatment of simulated wastewater containing toxic amides by immobilized Rhodococcus rhodochrous NHB-2 using a highly compact 5-stage plug flow reactor

Biodegradation of toxic amides by immobilized Rhodococcus rhodochrous NHB-2 has been studied to generate data for future development of reactors for the treatment of simulated wastewater containing various toxic amides. The whole resting cells were immobilized in different matrices like agar, polyacrylamide and alginate. Agar gel beads were selected for the treatment of simulated wastewater containing 100 mM each acetamide, propionamide, and 10 mM of acrylamide and packed in a highly compact five-stage plug flow reactor. The immobilized bacterium worked well in a broad pH range from 5 to 10, with an optimum at 8.7. The apparent Km-value for the turnover of acetamide for the resting cells was determined to be around 40 mM at pH 8.5 and 55 degreesC, whereas the Km-value of the purified amidase was predicted to be about 20 mM. This organism exhibited greater turnover of aliphatic amides as compared to aromatic amides. Although these cells showed maximal amide-degrading activity at 55 degreesC, simulated wastewater treatment was carried out at 45 degreesC, because of the greater stability of the amidase activity at that temperature. Of note, indices for overall temperature stability, based on the temperature dependence of apparent first order kinetic temperature denaturation constants, were determined to be) 7.9 +/- 1.1 x 10(-4), and -13.7 +/- 1.3 x 10(-4), -14.5 +/- 0.7 x 10(-4), and -13.7 +/- 0.8 x 10(-4) degreesC min, for free cells and cells immobilized in alginate, agar and polyacrylamide respectively. After 250 min the reactor showed maximum degradation of acetamide, propionamide and acrylamide of about 97, 100 and 90%, respectively by using 883 enzyme activity units per reactor stage. The results of this investigation showed that R. rhodochrous NHB-2 expressing thermostable amidase could be used for the efficient treatment of wastewater containing toxic amides. Therefore, we suggest that this microbe has a very high potential for the detoxification of toxic amides from industrial effluents and other wastewaters.