Estimating In Situ Biodegradation Rates of Petroleum Hydrocarbons and Microbial Population Dynamics by Performing Single-Well Push–Pull Tests in a Fractured Bedrock Aquifer

Abstract

The single-well push–pull test (SWPPT) was adapted to quantify in situ aerobic respiration and denitrification rates and to assess microbial population dynamics in a petroleum-contaminated fractured bedrock aquifer. Among three test wells, significant dissolved oxygen (DO) consumption was observed only in one well, with average zero- and first-order rate coefficients of 0.32 ± 0.63 and 7.07 ± 13.85 mmol L−1 day−1, respectively. Of the four test wells, significant NO3 − consumption was noted in three wells. The average zero- and first-order rate coefficients were 2.87 ± 2.21 and 11.83 ± 7.99 mmol L−1 day−1, respectively. These results indicate that NO3 − was more effectively consumed within this fractured bedrock aquifer. Significant DO or NO3 − (electron acceptors (EAs)) consumption, the limited contribution of Fe(II) to overall EAs consumption, the production of dissolved CO2 during aerobic respiration and denitrification tests, and N2O production strongly suggest that the EAs consumption was largely due to microbial activity. Detection of Variovorax paradox, benzene-degrading culture, and 28 novel microbial species after the addition of O2 or NO3 − suggests that EA injection into a fractured rock aquifer may stimulate aerobic or denitrifying petroleum-degrading microbes. Therefore, SWPPT may be useful for quantifying in situ aerobic respiration and denitrification rates and for assessing microbial population dynamics in petroleum-contaminated fractured bedrock aquifers.