Remediation of a hydrocarbons chronically contaminated soil by combination of persulfate oxidation and bioremediation

ANTONIO JOSÉ FERNÁNDEZ-GONZÁLEZ; PEDRO DAVID GARA; DEL PANNO M.T.; MEDINA R.; ROSSO J. A.

Lyon

Conferencia; AquaConSoil - 14th International Conference; 2017

Title: Remediationof a hydrocarbon chronically contaminated soil by combination of persulfate oxidationand bioremediation.Polycyclic aromatic hydrocarbons(PAHs) are ubiquitous compounds in the environment generated by natural andanthropogenic activities. Because their hydrophobicity and low water solubilitythey are highly persistent in soil. Although the use of chemical oxidants canovercome the limitations of bioremediation, it is known that it damages thecommunity and soil structures. We studied the effect of combined technologies,chemical oxidation followed by bioremediation, on chronically hydrocarboncontaminated soil.A chronically contaminated soil (S0)with 214 ppm of PAHs was treated with ammonium persulfate (PS) (3.3 g PS/ kgdry soil), OxS. Microcosms of oxidized soil were incubated (25°C, 25% moisturecontent), for 1 year as bioremediation process, BOxS. Soil microcosms withoutoxidation were used as bioremediation control, BS. The PAH concentration, PAHbioavailability (%), dissolved total carbon (% DTC), absorption and fluorescenceof organic matter (OM), total nitrogen (N), sulphate (SO42-),phosphorous (P) and bacterial diversity were analysed. Hill?s numbers were usedas diversity measures. The results were analysed using methods from themultivariate statistic.  The PS application produced 30% of PAHs eliminationand an increase of DTC and PAH bioavailability. The aqueous extract fluorescenceattributed to the organic matter was higher than S0, but therelative emission from PAHs was lower. The corresponding spectroscopic analysis(E4/E6) did not show changes.Beforethe oxidation, S0 showed a very high diversity being an equalcommunity. A dramatic decline in the richness was observed after PS oxidation. TheOxS community showed an uneven assemblage with a few dominant species. The Actinomycetales (57%) and Bacillales (20%) were the predominant orders.By analysis of 16SrDNA hypervariableregion, we found successional changes in the community along the treatment. Thelow richness and uneven assemblage remained until the fifth month but with Pseudomonadales as predominant order(71%). Slowly, the bioremediation allowed that the diversity was recovery(BOxS); despite of the richness was still low in compare with S0. At the end of the treatment, 47.5% of total PHA eliminationwas observed, leaving a lower DTC value in BOxS. The fluorescence intensity fromOM was similar to S0 but principally as consequence of humic-like substancescontribution, suggesting that the bacterial successional changes wereprincipally to expenses of the available compound from the oxidized OM. The incrementon P also suggested the effectivebacterial involvement in the soil P cycle. The significantly higher SO42- concentrationseemedto no exert much effect on the soil bacterial diversity. The bioremediation in BS after one year also showed alow richness. Although a reduced fluorescence was detected in this microcosms, the relative PAH andOM fluorescence contribution did not change. The coupled technology studied wassuitable for elimination of PAHs with the recovery of microbial diversityassociated to the metabolism of oxidized OM. The multifaceted approach wereuseful for understanding the global process in a chronically-contaminated soil.