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Abstract

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 approximately 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 approximately 5 mg/mL within 12 days and that of the hydrazine from approximately 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.

Advanced Rhodococcus Biocatalysts for Environmental Biotechnologies

“…Inorganic adsorbents include minerals (macrostructured foam ceramics, ceramic beads, corund, foamed vermiculite, diatomaceous earth, and coarse sand grains), as well as coconut shell-based granular activated carbon. There are also synthetic polymers (nonwoven fibers, polyurethane foam, and polycaproamide fiber), which are chemically inert and easily regenerated [13,89,92,97,98,100,118]. Selectivity of synthetic polymers towards hydrophobic compounds and rhodococcal cells could be improved using various modifications like saturation of surface with functional (alkyl, nitryl, and carbonyl) groups, thickness variations, and changes in the fiber packaging density [97].…”

“…For example, exponentially-growing Rhodococcus erythropolis cells were adsorbed faster on Biolite than their stationary-phase counterparts [13]. It should be noted that resting cells, i.e., washed from the growth medium and resuspended in the buffer, are more frequently used [70,83,85,90,91,96,118] than growing cells [13,67,93,102] due to easy control of their adhesion efficacy and catalytic activities. However, growing R. ruber cells were used, for example, in the propane-fed membrane bioreactor since its construction promoted the biofilm growth and a pollutant (N-nitrosodimethylamine) was degraded as a cometabolite [102].…”

“…A disadvantage of this procedure is the long time required. For Rhodococcus, acclimation time varied between 2.5 and 13.0 days [13,40,67,85,91,100,118,130]. At the same time, acclimation guarantees higher initial rates of biodegradation with or without a shortened lag-phase.…”

“…Two methods are currently used to obtain acclimated Rhodococcus cells: single batch cultivation in the presence of a pollutant, often at concentrations lower than working ones [40,100,130], or sequenced cultivation with a gradual increase of the pollutant concentration [13,67,91,118]. For example, R. rhodochrous IEGM 608 cells were pre-grown in the presence of 0.0007% isoquinoline during 3 days prior to biodegradation of a pharma pollutant, drotaverine hydrochloride [40].…”

“…Prieto et al [13,67] cultivated R. erythropolis UPV-1 cells at increased phenol concentrations (0.2 and then 0.4 g/L) to obtain an acclimated culture. Rhodococcus bacteria used for detoxification of the NASA scrubber water rich in hydrazine, methylhydrazine (major constituents in a variety of rocket fuels and missile propellants), and citric acid, were serially conditioned with 5, 10 and 15% (v/v) scrubber water before the commencement of experiments involving full strength wastewater [118]. In reference [91], ten cultivation passages were carried out with increasing concentrations of the xenobiotic (phenol) to obtain an adapted Rhodococcus wratislaviensis culture.…”