Stable carbon isotope analysis: a tool to monitor bioremediation status and achieve site closure

摘要

Bioremediation, including bioventing, biopiling, and landfarming, was used to remediate deep and surficial soil, respectively, impacted with crude oil as the result of an oil well blowout in Trecate, northern Italy in 1994. The bioventing system and the biopiles were engineered and key process control parameters were strictly controlled to achieve maximum mass removal efficiency and the very low numerical endopints established by Italian regulatory authorities at the outset of the project. Further, the bioventing system and the biopiles were monitored using both in situ respirometry and mass removal calculations and plotting. After approximately 12 months of operation, the mass removal plots showed that mass removal in the biopiles had achieved its asymptotes - an indication of biodegradation rate decline and a strong suggestion of substrate limitation. However, in situ respirometry test results showed that the microbial community continued to mineralize carbon of unknown character at a significant rate, which suggested that the biodegradation process was ongoing. Stable carbon isotope analysis of the expelled crude oil, contaminated soil, background soil, wood chips, soil vapor, and ambient air was used to determine whether the carbon being oxidized by the microbial consortium was from naturally occurring material in the soil (i.e.,, humus) and wood chips used to bulk the biopile soils or from residual crude oil. This discrimination, along with the asymptotic mass removal plots, served as the basis to conclude that bioremediation had proceeded to its logical endpoint, and that continued biopile operation would not appreciably reduce the hydrocarbon mass.