EarthFax Engineering, Inc. and its affiliate EarthFax Development Corp. have demonstrated the degradation of pentachlorophenol ("PCP") and Lindane in soil under full-scale conditions through the use of white-rot fungi ("WRF"). The work was performed at the site of a former wood treatment facility located in North Carolina.
Initial bench-scale testing with two fungal strains indicated that inoculation with the WRF Pleurotus ostreatus would result in optimal degradation of lindane. Concentrations of Lindane decreased from about 345 ppm to 30 ppm within 45 days. Inoculation rates of 20 to 40% (w/w) substrate to soil were found to be most effective.
Subsequent pilot-scale tests were conducted utilizing treatment cells with capacities of about two cubic yards each. During the 274-day test, PCP concentrations were found to degrade from 447 ppm to 41 ppm with 20% substrate, and from 242 ppm to 15 ppm with 40% substrate. Lindane concentrations degraded from 558 ppm to 37 ppm with 20% substrate, and from 387 ppm to 10 ppm with 40% substrate during the 274-day test. With similar percentages of degradation, no advantage was seen to the use of the higher inoculation rate.
Following performance of the pilot-scale tests, approximately 750 tons of contaminated soil were excavated, with field verification sampling to ensure an appropriate extent of excavation. The contaminated soil was mixed with 16% (w/w) fungal inoculum (i.e., sawdust and cottonseed hulls thoroughly colonized with the WRF Pleurotus ostreatus) and placed in a biocell (50'Wx 100'Lx7'D) for on-site treatment. The biocell included a bottom liner on which perforated ventilation piping was laid and covered with pea-gravel. The cell was then loaded with the soil/inoculum mixture and additional perforated piping was installed on top of the mix. The loaded cell was covered with an additional liner and a regenerative air blower was attached to the piping to inject air into the bottom of the cell and withdraw it from the top. To reduce heat being introduced into the pile, the blower pattern was later modified to pull air from the bottom of the pile and discharge that air to the atmosphere.
Biocell construction was completed in February 1997, and samples of the soil/inoculum mix were collected at that time and periodically thereafter. These samples were analyzed by EPA Methods 8270 (for PCP) and 8080 (for Lindane). During each sampling round, a minimum of four samples were collected from the cell (one each from the upper and lower half of the north and south ends of the cell), with each sample consisting of three randomly-selected subsamples.
Results of PCP and Lindane analyses are presented in Figure 1. Prior to excavation, PCP concentrations in the soil varied up to 2,300 ppm. Following mixing, initial PCP concentrations ranged from 33 to 70 ppm, averaging 51 ppm. Within 31 days, the average PCP concentration had decreased 61% to 20 ppm, with all samples below the industrial treatment goal of 48 ppm. After 24 months of treatment, the average PCP concentration had decreased 94% to 3.0 ppm, thus also achieving the residential risk-based concentration of 5.3 ppm.
Lindane concentrations in the pre-excavation soil varied up to 13,000 ppm. Following mixing, initial Lindane concentrations ranged from 7.1 to 37 ppm, averaging 21 ppm. After 24 months of treatment, the average Lindane concentration had decreased 97% to 0.57 ppm, achieving the industrial treatment goal of 4.4 ppm and nearly also reaching the residential risk-based concentration of 0.49 ppm.
This project verifies the previous bench-scale work of Kennedy et al. (1990), who demonstrated the ability of a WRF to degrade Lindane in liquid and solid cultures. It further verifies the bench-scale findings of Mileski et al. (1988) and the pilot-scale work of Lamar et al. (1993) with respect to PCP degradation.