Bioremediation of Nitrochlorobenzene, Nitroaniline, Chloroaniline, and Other Organics in Groundwater.



The uppermost aquifer beneath a chemical plant contains residual concentrations of o-nitrochlorobenzene from a tank car spill, as well as other plant-related organic compounds of concern (COC), including 2-nitroaniline and o-chloroaniline. The aquifer consists of low permeability clays and silts, and produces only a few gallons of groundwater per day from a shallow recovery well previously installed for remediation. Soil removal was the principal mechanism to treat the tank car spill. Subsequent recovery of residual groundwater contamination has been ineffective for more than 10 years due to low aquifer yield, and the recalcitrant nature of the COC. Aerobic treatment was facilitated using the Oxygen Release Compound (ORCâ). The treatment area was approximately 80 square meters and the depth of treatment was approximately 6 meters of aquifer profile. The DO and ORP measurements were highly variable, but trended up for the first three months following ORC injection. The DO and ORP trends began to decrease approximately six months following injection. The DO ranged between 3.5 mg/l and 10.7 mg/l, and the ORP ranged between 291 mV and 367 mV during this six month period. Maximum contaminant concentration reductions observer during the pilot test varied from 28% to 83%, and rebound was detected following the effective life of the ORC. The relatively low sorption of the compounds to soil, and the influx of contaminated groundwater into the pilot test area indicate that a permeable bioremediation-barrier represents the most effective remedial option for this site.


A field-scale pilot study to evaluate in-situ treatment of the compounds of concern (COC) was performed. Aerobic treatment of various COC in soil systems has been reported to be highly variable (Abou-Rizk et al., 1995; Myers et al., 1995; Zappi et al., 1995), and the goal of the pilot test was to establish that aerobic bioremediation of the COC was a viable option at this site. Oxygen Release Compound (ORCâ), manufactured by Regenesis Bioremediation Products in San Juan Capistrano, California, is a patented formulation of magnesium peroxide that slowly releases molecular oxygen when hydrated, thereby facilitating aerobic bioremediation of the COC. Numerous remedial options were evaluated, and ORC was identified as the preferred method to oxygenate the aquifer. The ORC releases oxygen slowly over a period of 6 to 9 months, which corresponded to the scheduled testing period.


The ORC design/loading rates were based on dissolved organic compound mass in the treatment area, as well as dissolved oxygen (DO) concentrations and oxidation-reduction potential (ORP) measurements. The ORC was injected in a grid pattern around the recovery well which continued to extract groundwater, thereby enhancing the rate of oxygen movement through the treatment area.

Baseline COC sampling was performed prior to ORC injection, and the post-treatment monitoring protocol included DO and ORP in addition to the COC. A supplementary investigation is planned to measure the potential for the contaminants to partition from the adsorbed phase into the dissolved phase. A soil core will be obtained from the site during pending investigation efforts to facilitate this analysis.


Table 1 depicts the efficacy of the six month bioremediation process at this site for the COCs. Figures 1 to 3 illustrate the reductions over time in the COCs as measured in monitoring well F-2, which is located in the central portion of the pilot test area. Figure 4 illustrates the changes in dissolved oxygen (DO) and Figure 5 describes the oxidation-reduction potential (ORP) at the site during the pilot test.


The bioremediation process effectively reduced dissolved masses of o-nitrochlorobenzene, 2-nitroaniline and o-chloroaniline, and also reduced dissolved mass of other COCs. Rebound of the COC concentrations were observed after the oxygen from the initial ORC treatment was spent. The project will be expanded to include a long-term barrier design using ORC to continuously deliver oxygen to the aquifer, and eliminate the potential for off-site migration of dissolved COC.

TABLE 1. Maximum decrease in dissolved compounds of concern concentrations following ORC treatment.


% Concentration Reduction

















FIGURE 1. Change in 1,2-DCA and 1,2-DCP concentrations following ORC application.


FIGURE 2. Change in 2-nitroaniline and o-chloroaniline concentrations following ORC application.


FIGURE 3. Change in chlorobenzne, nitrobenzene, o-nitrochlorobenzene, naphthalene and 2-chlorophenol concentrations following ORC application.


FIGURE 4. Change in dissolved oxygen following ORC application.


FIGURE 5. Change in ORP following ORC application.


Abou-Rizk, J.A.M., M.E. Leavitt and D.A. Graves. 1995. In Situ Aquifer Bioremediation of Organics Including Cyanide and Carbon Disulfide. Applied Bioremediation of Petroleum Hydrocarbons. Vol. 3(6): 175-183. Battelle 1995.

Myers, J.M., B.S. Banipal and C.W. Fisher. 1995. Biodedgradation of Oil Refinery Wastes. Applied Bioremediation of Petroleum Hydrocarbons. Vol. 3(6): 445-451. Battelle 1995.

Zappi, M.E., D. Gunnison and H. Fredrickson. 1995. Aerobic Treatment of Explosives-Contaminated Soils Using Two Engineering Approaches. Bioremdiation of Recalcitrant Organics. Vol. 3(7): 281-288. Battelle 1995.

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