Recovery of microbial diversity and activity during bioremediation following chemical oxidation of diesel contaminated soils

Abstract

To improve the coupling of in situ chemical oxidation and in situ bioremediation, a systematic analysis was performed of the effect of chemical oxidation with Fenton's reagent, modified Fenton's reagent, permanganate, or persulfate, on microbial diversity and activity during 8 weeks of incubation in two diesel-contaminated soils (peat and fill). Chemical oxidant and soil type affected the microbial community diversity and biodegradation activity; however, this was only observed following treatment with Fenton's reagent and modified Fenton's reagent, and in the biotic control without oxidation. Differences in the highest overall removal efficiencies of 69 % for peat (biotic control) and 59 % for fill (Fenton's reagent) were partially explained by changes in contaminant soil properties upon oxidation. Molecular analysis of 16S rRNA and alkane monooxygenase (alkB) gene abundances indicated that oxidation with Fenton's reagent and modified Fenton's reagent negatively affected microbial abundance. However, regeneration occurred, and final relative alkB abundances were 1-2 orders of magnitude higher in chemically treated microcosms than in the biotic control. 16S rRNA gene fragment fingerprinting with DGGE and prominent band sequencing illuminated microbial community composition and diversity differences between treatments and identified a variety of phylotypes within Alpha-, Beta-, and Gammaproteobacteria. Understanding microbial community dynamics during coupled chemical oxidation and bioremediation is integral to improved biphasic field application.

Coupling chemical oxidation and biostimulation: Effects on the natural attenuation capacity and resilience of the native microbial community in alkylbenzene-polluted soil

“…A recovery of the hydrocarbon-degrading populations was revealed in microcosms after MFR treatments, because of either the better resistance of this population against chemical oxidation or a competitive advantage in this population following chemical oxidation. This effect has also been observed in recent studies; after the microbial communities were adversely affected in the first weeks by MFR application, a rebound of bacterial communities can be expected during longer-term periods [14], and Fenton's reagent can stimulate bioremediation in pilot-scale experiments [56].…”

“…Subsequent H 2 O 2 additions were conducted when H 2 O 2 was not detected. was quantified by spectrophotometric analysis at 525 nm as described elsewhere [14].…”

“…Abiotic and biotic controls (that did not receive chemical oxidation treatment) also received this treatment. The nutrients were added by using 1 mL of ten-fold concentrated medium in phosphate buffer (pH 7) as described previously [14]. The bottles were incubated four weeks at 20°C, shaken horizontally and sheltered from the light.…”

“…The combination of these two technologies can provide a more efficient remediation of the contaminated subsurface. Although few studies have demonstrated the feasibility and efficiency of the treatment combination [7,[11][12][13][14], their overall effect on native microbial communities and its degradation capabilities is still poorly understood. The use of chemical oxidants at certain concentrations to degrade pollutants can hamper further biodegradation processes [7].…”

Geochemical and Microbiological Characteristics during in Situ Chemical Oxidation and in Situ Bioremediation at a Diesel Contaminated Site

“…It is noteworthy that in general total bacterial abundance showed a greater absolute decrease than alkB gene copy number, indicating a relative enrichment of microorganisms able to degrade alkanes, as has been observed previously. 37 Wells where the largest impacts on microbial communities were observed correlated with those having more significant or prolonged decreases in pH (C1, C6, C9; Figures 2 and3). The effect on the microbial community was moderated in wells with less pronounced pH decrease, such as C7.…”