Degradation of phenolic contaminants in ground water by anaerobic bacteria: St. Louis Park, Minnesota. Ground Water. 20:703-710. 6. Healy, J. B., Jr., aind L. Y. ...
Vol. 48, No. 5
APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Nov. 1984, p. 1046-1048
0099-2240/84/111046-03$02.00/0 Copyright C 1984, American Society for Microbiology
NOTES Anaerobic Inhibition of Trace Organic Compound Removal During Rapid Infiltration of Wastewater STEPHEN R. HUTCHINS,* MASON B. TOMSON, JOHN T. WILSON,t AND CALVIN H. WARD Department of Environmental Science and Engineering, National Center for Ground Water Research, Rice University, Houston, Texas 77251 Received 10 February 1984/Accepted 7 August 1984
When soil columns were operated aerobically on a flooding-drying schedule in a previous study, good removals were observed for several organic compounds at concentrations ranging from 1 to 1,000 ,ug per liter in primary wastewater. In this study, fractional breakthroughs of most compounds increased substantially once operating parameters were modified and the soil became anaerobic. These results imply that microbial removal of trace organic compounds can be inhibited if anaerobic conditions develop during rapid infiltration of wastewater.
Wastewater disposal by rapid infiltration generally requires a specific flooding-drying schedule to preserve the infiltration characteristics of the soil (4). Research has shown that nitrogen removal can be optimized if the schedule is modified to develop anaerobic conditions and thus promote denitrification (3, 10). However, the effects of anaerobic conditions on the fate of trace organic compounds are unknown. Results from a field study have shown that trace organic compound removal can decrease towards the end of the flooding period during rapid infiltration of primary wastewater, and it was hypothesized that this was due to the development of anaerobic conditions (8). To study whether microorganisms were involved in trace organic compound removal, soil was transferred from the field site to laboratory columns. After the required 16-day drying period, the soil columns were operated, using design parameters from the field. The column study demonstrated that microorganisms were actively involved in trace organic compound removal (9). In brief, eight soil columns were maintained on a 6-dayflooding-16-day-drying schedule for three inundation cycles. Each set of duplicate columns had received primary wastewater at an infiltration rate of 34 cm per day, spiked with p-dichlorobenzene (PDCB), 2-methylnaphthalene (2MN), o:phenylphenol (OPP), p-(1,1,3,3-tetramethylbutyl)phenol (TMBP), 2-(methylthio)benzothiazole (2MTBT), and benzophenone (BZPN) in concentrations ranging from 1 to 1,000 ,ug/liter. In contrast to the results of the field study, trace organic compound removal was consistent throughout the flooding period. However, inorganic analyses indicated that the soil remained aerobic during flooding. We therefore induced anaerobic conditions to develop in the soil columns to evaluate the effect on trace organic compound removal. Sixteen days after the final flooding of the aerobic column study, the columns were flooded at the same infiltration rate with unfiltered primary wastewater for 6 days before beginning the subsequent 6-day flooding period with filtered primary wastewater spiked with the selected compounds. During this extended flooding period, nitrogen was delivered to the column headspace instead of air. In addition, the feed reservoirs for the columns were
modified so that nitrogen instead of air replaced the depleted feed in the reservoir during operation. Column effluents were monitored for dissolved oxygen to ensure that anaerobic conditions developed. Feed solutions and column effluents were sampled during the last 6 days of the 12-day flooding period and analyzed. During aerobic operation, microbial activity was evaluated by analyzing fractional breakthrough (mass output/mass input) of each compound at selected input concentrations. As described previously, the shape of the breakthrough
Corresponding author. t Robert S. Kerr Environmental Research Laboratory, U.S. Environmental Protection Agency, Ada, OK 74820.
FIG. 1. Breakthrough profile for OPP during aerobic (--) and
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NOTES
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FEED CONCENTRATION (pg/1) FIG. 2. Breakthrough profile for TMBP during aerobic (--) and subsequent anaerobic (-) operation of soil columns. Column effluent concentration is average + standard deviation for two replicates.
FIG. 3. Breakthrough profile for 2MTBT during aerobic (- -) and subsequent anaerobic (-) operation of soil columns. Column effluent concentration is average + standard deviation for two replicates.
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FIG. 5. Breakthrough profile for BZPN during aerobic (- -) and subsequent anaerobic (-) operation of soil columns. Column effluent concentration is average + standard deviation for two replicates.
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NOTES
profile (fractional breakthrough versus input concentration) and its consistency with successive inundation cycles can indicate whether microbial activity is a component of the removal process for that compound (9). Thus microbial activity was implicated in the fate of 2MN, TMBP, 2MTBT, and BZPN in the column study, whereas it was demonstrated for all of the compounds except 2MTBT during partial mineralization of radiolabels by the column soil microflora. In this study, the fractional breakthrough profiles for OPP, TMBP, and 2MTJ3T did not change when the soil columns became anaerobic, although the degree of breakthrough increased for each compound compared with that during aerobic operation (Fig. 1 to 3). In the previous study it was shown that mineralization accounted for only 0, 6, and 20% of the total removal observed for 2MTBT, TMBP, and OPP, respectively. Yet the increases in the fractional breakthroughs were much higher for these compounds when the system became anaerobic. This indicates that the inhibition in compound removal mediated by anaerobic conditions is not due solely to cessation of mineralization activity. In some cases, inhibition of biotransformation reactions also is not sufficient to explain the increased fractional breakthrough, as evidenced by the data for OPP (Fig. 1). At the highest input concentration, breakthrough of OPP exceeded 100%. This indicates that anaerobic conditions not only inhibited biotic removal processes but also promoted leaching of the sorbed compound as well. The mechanism of this action is unknown, although the effect has been observed in soil columns before (S. R. Hutchins, J. T. Wilson, and C. H. Ward, submitted for publication). Anaerobic conditions also promoted increased fractional breakthroughs for PDCB, although the effect was most pronounced at the lower input concentrations (Fig. 4). For BZPN, however, the effect was most pronounced at the lowest and highest input concentrations, and breakthroughs approximated 100% in both cases (Fig. 5). The general increase in column effluent concentrations of these two compounds under anaerobic conditions is consistent with the behavior observed for 2MTBT, TMBP, and OPP. This was not the case with 2MN. During the previous study, 2MN was completely removed (detection limit, 0.001 ,ug/liter), regardless of input concentration. In this study as well, 2MN was completely removed even after the columns became anaerobic. This corresponds to ca. 6 log units of removal at the highest input concentration of 680 ,ug/liter. Therefore, although the onset of anaerobic conditions can inhibit removal processes for several trace organic compounds, some compounds may not be affected. Anaerobic conditions generally increase the recalcitrance of an organic compound to biological attack (1). This is especially true for aromatic compounds. Although some aromatic compounds can be degraded or transformed even under strict anaerobic conditions, these compounds generally require the presence of an oxygenated substituent group for this to occur (6, 7, 12). Phenolic compounds would therefore be expected to be somewhat labile under anaerobic conditions (2, 5); whether this occurs with OPP and TMBP in this system is unknown. It is also difficult to assess the role of anaerobic biodegradation in the fate of 2MN, 2MTBT,
APPL. ENVIRON. MICROBIOL.
and BZPN because of the lack of data for these classes of compounds. In agreement with the data for PDCB, however, other researchers have observed marked decreases in rates of mineralization and biotransformation for halogenated benzenes under anaerobic conditions (11, 13). In summary, although several compounds can be degraded or transformed anaerobically, it appears that anaerobic processes are not as effective for trace organic compound removal during rapid infiltration. This study has demonstrated that removal of most compounds will decrease when anaerobic conditions develop in the soil during flooding. Rapid infiltration systems should therefore be operated aerobically to minimize trace organic compound contamination of associated ground waters. This work was supported by cooperative agreement CR806931-0 between the National Center for Ground Water Research and the U.S. Environmental Protection Agency. LITERATURE CITED 1. Alexander, M. 1965. Biodegradation: problems of molecular recalcitrance and microbial fallibility. Adv. Appl. Microbiol. 7:35-80. 2. Bakker, G. 1977. Anaerobic degradation of aromatic compounds in the presence of nitrate. FEMS Microbiol. Lett. 1:103-108. 3. Bouwer, H. 1974. Design and operation of land treatment systems for minimum contamination of ground water. Ground Water 12:140-147. 4. Bouwer, H., R. C. Rice, and E. D. Escarcega. 1974. High-rate land treatment. I. Infiltration and hydraulic aspects of the Flushing Meadows project. J. Water Pollut. Control. Fed. 46:834-843. 5. Ehrlich, G. G., D. F. Goerlitz, E. M. Godsy, and M. F. Hult. 1982. Degradation of phenolic contaminants in ground water by anaerobic bacteria: St. Louis Park, Minnesota. Ground Water 20:703-710. 6. Healy, J. B., Jr., aind L. Y. Young. 1979. Anaerobic biodegradation of eleven aromatic compounds to methane. Appl. Environ. Microbiol. 38:84-89. 7. Horowitz, A., J. M. Suflita, and J. M. Tiedje. 1983. Reductive dehalogenations of halobenzoates by anaerobic lake sediment microorganisms. Appl. Environ. Microbiol. 45:1459-1465. 8. Hutchins, S. R., M. B. Tomson, J. T. Wilson, and C. H. Ward. 1984. Fate of trace organics during rapid infiltration of primary wastewater at Fort Devens, Massachusetts. Water Res. 18:1025-1036. 9. Hutchins, S. R., M. B. Tomson, J. T. Wilson, and C. H. Ward. 1984. Microbial removal of wastewater organic compounds as a function of input concentration in soil columns. Appl. Environ. Microbiol. 48:1039-1045. 10. Leach, L. E., and C. G. Enfield. 1983. Nitrogen control in domestic wastewater rapid infiltration systems. J. Water Pollut. Control Fed. 55:1150-1157. 11. Marinucci, A. C., and R. Bartha. 1979. Biodegradation of 1,2,3and 1,2,4-trichlorobenzene in soil and in liquid enrichment culture. Appl. Environ. Microbiol. 38:811-817. 12. Rose, A. H. 1976. Chemical microbiology: An introduction to microbial physiology, 3rd ed, p. 187-230. Plenum Publishing Corp., New York. 13. Schwarzenbach, R. P., W. Giger, E. Hoehn, and J. K. Schneider. 1983. Behavior of organic compounds during infiltration of river water to ground water. Field studies. Environ. Sci. Technol. 17:472-479.
