Enhanced biodegradation of methylhydrazine and hydrazine contaminated NASAwastewater in fixed-film bioreactor

The aerobic biodegradation of National Aeronautics and Space Administration (NASA) wastewater that contains mixtures of highly concentrated methylhydr azine/hydrazine, citric acid and their reaction product was studied on a la boratory-scale fixed film trickle-bed reactor. The degrading organisms, Ach romobacter sp., Rhodococcus B30 and Rhodococcus J10, were immobilized on co arse sand grains used as support-media in the columns. Under continuous flo w operation, Rhodococcus sp. degraded the methylhydrazine content of the wa stewater from a concentration of 10 to 2.5 mg/mL within 12 days and the hyd razine from similar to0.8 to 0.1 mg/mL in 7 days. The Achromobacter sp. was equally efficient in degrading the organics present in the wastewater, red ucing the concentration of the methylhydrazine from 10 to similar to5 mg/mL within 12 days and that of the hydrazine from similar to0.8 to 0.2 mg/mL i n 7 days. The pseudo first-order rate constants of 0.137 day(-1) and 0.232 day(-1) were obtained for the removal of methylhydrazine and hydrazine, res pectively, in wastewater in the reactor column. In the batch cultures, rate constants for the degradation were 0.046 and 0.079 day(-)1 for methylhydra zine and hydrazine respectively. These results demonstrate that the continu ous flow bioreactor afford greater degradation efficiencies than those obta ined when the wastewater was incubated with the microbes in growth-limited batch experiments. They also show that wastewater containing hydrazine is m ore amenable to microbial degradation than one that is predominant in methy lhydrazine, in spite of the longer lag period observed for hydrazine contai ning wastewater. The influence of substrate concentration and recycle rate on the degradation efficiency is reported. The major advantages of the tric kle-bed reactor over the batch system include very high substrate volumetri c rate of turnover, higher rates of degradation and tolerance of the 100% c oncentrated NASA wastewater. The results of the present laboratory scale st udy will be of great importance in the design and operation of an industria l immobilized biofilm reactor for the treatment of methylhydrazine and hydr azine contaminated NASA wastewater.