Dan Cassidy and Andrew Hudak, Western Michigan University

A continuous-flow reactor (CSTR) and a soil slurry-sequencing batch reactor (SS-SBR) were maintained in 8-L vessels for 200 days to treat a soil contaminated with polycyclic aromatic hydrocarbons (PAH). Concentrations of Corynebacterium aquaticum, Pseudomonas aeruginosa, Pseudomonas putida, and Pseudomonas stutzeri were determined using fatty acid methyl ester (FAME) analysis. Biosurfactant concentrations in filtered slurry were measured. The two modes of operation resulted in the selection of significantly different microbial consortia with different biosurfactant-producing and PAH-degrading abilities. Biosurfactants were produced in the SS-SBR to levels of nearly 40 times the critical micelle concentration (CMC) early in the cycle, but were completely degraded by the end of each cycle. Some biosurfactant production was observed in the CSTR but levels did not exceed the CMC. Total PAH removal efficiency was 93% in the SS-SBR, compared with only 67% in the CSTR. Considerable foaming occurred in the SS-SBR as a result of the biosurfactant concentrations above the CMC. Reversing the mode of operation in the reactors on day 100 caused a complete reversal in microbial consortia and in reactor performance by day 120. These results show that bioslurry reactor operation can be manipulated to control overall reactor performance.

Valentine A. Nzengung, K.C. Das, J. Kastner and Alicia G. Browder, University of Georgia

Contamination of soils, surface, and ground water has occurred at military and industrial facilities involved in the manufacture, testing and use of ammonium perchlorate. A 1998 Remedial Investigation/Feasibility Study (RI/FS) for the Longhorn Army Ammunition Plant (LHAAP) in Karnack, Texas, indicated that perchlorate has seriously impacted surface, groundwater and soils at the site. Laboratory screen tests identified chicken manure, cow manure, and ethanol as suitable carbon sources for the enhancement of in-situ bioremediation of perchlorate in contaminated LHAAP soils. Optimum doses and efficient modes of application of each amendment to achieve desired treatment endpoints at different depths in the subsurface (vadose zone) were determined using column tests. In October 2000, an in-situ bioremediation study for perchlorate-contaminated soils was initiated at the LHAAP. Six identical treatment cells (4.57 x 2.74 m) and one control cell (5.5 x 5.5 m) were sectioned off (isolated) using plastic liners. Tensiometers were installed to monitor moisture at depth. Duplicate cells were treated with the same predetermined concentration of each nutrient amendment. No amendment was added to the control cell. Water was added to all 7 cells to achieve complete saturation to desired treatment depths below ground surface. The maximum concentration of perchlorate in the selected treatment plots at the start of the pilot study was 400 mg/kg. After three winter months, we have observed 60 - 90% reduction of perchlorate in the treated cells and no reduction in the control cell. The results of this pilot study demonstrate that perchlorate contaminated soils can be treated in-situ by applying the cost-effective techniques we have developed to deliver nutrients amendments to desired depths. We will compare the costs of our in-situ soil treatment process with the costs of conventional dig-and-treat approaches and discuss the many lessons learned.

Herbert E. Woike, Timothy F. Keane, and Jonathan K. Child, Fuss & O’Neill, Inc; Sam Fogel and Margaret Findlay, Bioremediation Consulting, Inc.

This project involved the assessment and remediation of petroleum hydrocarbon contaminated soil at an approximate two-acre former heating oil storage and distribution facility located in north-central Massachusetts. No. 2 heating fuel was stored in two 10,000 gallon above ground storage tanks (ASTs). During the early summer of 1998, contaminated soil was excavated in the vicinity of the former ASTs and staged on-site in an approximate 12,000 square-foot, poly-vinyl chloride (PVC) lined containment cell. Approximately 650 cubic yards of soil was placed within the bioremediation cell (landfarm) to a maximum thickness of 24 inches. Remedial activities were performed in accordance with the Massachusetts Contingency Plan.

Operation and maintenance (O&M) of the landfarm continued through two summer seasons until remedial target levels were achieved in the fall of 1999. O&M activities included the periodic application of commercially available fertilizers (nitrogen and phosphorus) and soil aeration to stimulate the growth of petroleum degrading bacteria. The presence of an indigenous petroleum degrading bacterial population was confirmed and evaluated by Bioremediation Consulting, Inc.

Oxygen was introduced into the landfarm soil matrix by mechanical mixing which was conducted approximately monthly, except during cooler fall and winter months when bacteria are expected to be less metabolically active. Due to the thickness of soil within the landfarm and the presence of cobbles within the soil matrix, mixing of the landfarm could not be achieved by typical tilling operations and was instead conducted by backhoe.

The progressive reduction in petroleum hydrocarbon compounds within the landfarm was documented through monitoring of landfarm soil during six sampling events. Following the final round of landfarm sampling, soil within the containment cell was backfilled in the excavation and the site was closed without the need for an Activity and Use Limitation.