Abstract
Waste drill cuttings (WDCs), produced during gas and oil drilling consisting of 80% rock cuttings and 20% drilling muds, are an increasingly potent source of environmental pollution. We studied the efficiency of bioaugmentation and phytoremediation to remediate WDCs in an experiment where WDCs were incubated in a greenhouse for 120 days with and without black locust (Robinia pseudoacacia) plant and with or without bacterial and fungal consortium inoculant. The pollutant removal rates were highest in inoculated and planted treatment, followed by inoculated treatment and planted treatment. The small decrease in contaminant level in the control treatment suggested that indigenous microorganisms in WDCs had little pollutant degradation capability. In the inoculated and planted treatments, after 120 days, the germination rate of red clover seeds was on the same level as in the natural soil, showing a marked decrease in the ecotoxicity of WDC. Both the bacterial and fungal richness and bacterial diversity increased in all the treatments over time, whereas fungal diversity increased only in the not-inoculated treatments. The activity of laccase enzyme played a key role in the bioremediation process. The enzyme activities were mostly governed by inoculated consortium and soil bacterial community, and black locust affected the bioremediation mainly through its effect on N content that further affected bacterial and fungal communities.
Highlights
Waste drill cutting (WDC) produced during gas and oil drilling consists of 80% rock cuttings and 20% drilling muds
We studied the efficiency of bioaugmentation and phytoremediation to remediate WDCs in an experiment where WDCs were incubated in a greenhouse for 120 days with and without black locust (Robinia pseudoacacia) plant and with or without bacterial and fungal consortium inoculant
WDC + M + P than in the not-inoculated treatments WDC and WDC + P (P < 0.05) (Figure 1), suggesting that inoculation with fungal and bacterial consortium enhanced the removal of Total petroleum hydrocarbon (TPH)
Summary
Waste drill cutting (WDC) produced during gas and oil drilling consists of 80% rock cuttings and 20% drilling muds. Vegetated soils are capable of supporting high microbial numbers and diversity, combining bioaugmentation with plants that provide nutrients for bacterial growth may affect the establishment of the inoculum (Gkorezis et al, 2016). To our knowledge, combined phytoremediation and bioaugmentation in WDC bioremediation has not been studied to date, and the relative contribution of changes in microbial communities to WDC bioremediation efficiency has not received attention. The objectives of this research were (1) to evaluate the efficiency of combined bioaugmentation and phytoremediation in organic pollutant degradation using a fungal and bacterial consortium as microbial inoculant and Robinia pseudoacacia (black locust), (2) to determine changes in microbial communities during the WDC bioremediation, and (3) to estimate the relative contributions of treatments and microbial communities on WDC bioremediation efficiency
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