Pilot-Scale demonstration on soil containing phenoxy-acid herbicides (2,4-D, and 2,4,5-T), and other chlorinated pesticides (DDT, DDD, and DDE)
The application of DARAMEND® served to reductively de-chlorinate, and subsequently mineralize the chlorinated herbicides and pesticides.
Treatment of 350 tons of soil impacted by phenoxy-acid herbicides (2,4-D, and 2,4,5-T), and other chlorinated pesticides (DDT, DDD, and DDE).
The treatment process involved the application of DARAMEND® to a 60 cm thick layer of soil within a treatment cell. Due to the volatile and highly toxic nature of the phenoxy-acid herbicides the treatment cell was covered with a polyethylene clad greenhouse. Negative pressure was maintained within the greenhouse by continuously drawing air from the greenhouse and discharging it through a granular activated carbon filter. Soil undergoing treatment was subjected to several treatment cycles and was irrigated to 90% of the soil water holding content at the start of each treatment cycle.
The concentrations of the target contaminants, 2,4-D, 2,4,5-T, and DDT, were reduced by over 96%, 84%, and 91% respectively (Figure 1). Initial mean concentrations of 97.7 mg/kg, 8.1 mg/kg, and 54 mg/kg, were reduced to 3.6 mg/kg, 1.3mg/kg, and 4.7mg/kg, respectively.
The estimated treatment cost for the full-scale application of DARAMEND® bioremediation at this site, which would have involved the treatment of 35,000 tons of similarly contaminated material, was approximately US$127.00/ton. The cost associated with this project is slightly elevated when compared with most similarly sized projects due to the extremely toxic and semi-volatile nature of the contaminants, and consequently, the extraordinary steps required to ensure workplace safety and to prevent any environmental impacts during treatment.
Treatment of this material to the above levels required the application of nine treatment cycles. At this site, each treatment cycled required approximately one month, for a total active treatment period of approximately 9 months. Although one month was required per cycle during this pilot-application, improvements made in the application procedures for this technology have reduced the time required per cycle to an average of about 10 days. Using improved techniques Adventus estimates that the same level of treatment could now be accomplished in 3 to 4 months.