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

The aerobic biodegradation of National Aeronautics and Space Administration (NASA) wastewater that contains mixtures of highly concentrated methylhydrazine/hydrazine, citric acid and their reaction product was studied on a laboratory-scale fixed film trickle-bed reactor. The degrading organisms, Achromobacter sp., Rhodococcus B30 and Rhodococcus J10, were immobilized on coarse sand grains used as support-media in the columns. Under continuous flow operation, Rhodococcus sp. degraded the methylhydrazine content of the wastewater from a concentration of 10 to 2.5 mg/mL within 12 days and the hydrazine from 0.8 to 0.1 mg/mL in 7 days. The Achromobacter sp. was equally efficient in degrading the organics present in the wastewater, reducing the concentration of the methylhydrazine from 10 to 5 mg/mL within 12 days and that of the hydrazine from 0.8 to 0.2 mg/mL in 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, respectively, in wastewater in the reactor column. In the batch cultures, rate constants for the degradation were 0.046 and 0.079 day^-1 for methylhydrazine and hydrazine respectively. These results demonstrate that the continuous flow bioreactor afford greater degradation efficiencies than those obtained when the wastewater was incubated with the microbes in growth-limited batch experiments. They also show that wastewater containing hydrazine is more amenable to microbial degradation than one that is predominant in methylhydrazine, in spite of the longer lag period observed for hydrazine containing wastewater. The influence of substrate concentration and recycle rate on the degradation efficiency is reported. The major advantages of the trickle-bed reactor over the batch system include very high substrate volumetric rate of turnover, higher rates of degradation and tolerance of the 100% concentrated NASA wastewater. The results of the present laboratory scale study will be of great importance in the design and operation of an industrial immobilized biofilm reactor for the treatment of methylhydrazine and hydrazine contaminated NASA wastewater.     

Subsampling Variance for 2,4-DNT in Firing Point Soils

At 105-mm howitzer firing points, 2,4-DNT is detectable in the surface soils, but field sampling and laboratory subsampling uncertainty can be large during quantitation. The 2,4-DNT is in particulate form, within fibers or slivers of the nitrocellulose-based propellant. The slender fibers range up to 7.5 mm in length with masses of several 100 μ g. Size fractionation of a firing point soil revealed that most of the 2,4-DNT was in the 0.595- to 2.00-mm size range, although the bulk of the soil was less than 0.6 mm prior to grinding. Machine grinding for five minutes was needed to pulverize the propellant fibers sufficiently so that estimates of 2,4-DNT were reproducible in replicate analytical subsamples. To determine 2,4-DNT, we have adopted the practice of grinding firing point soils for five one-minute intervals, with time for heat dissipation between grinds, prior to obtaining individual or replicate 10-g subsamples.