Remediation of hydrocarbon chronically contaminated soil: combination of oxidation by persulfate addition and bioremediation

ROSSO, JANINA A.; DAVID GARA, PEDRO M.; MEDINA, ROCIO; DEL PANNO, MARÍA TERESA

Lyon

Conferencia; 14th International Conference on Sustainable Use and Management of Soil, Sediment and Water Resources; 2017

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous compounds in the environment generated by natural andanthropogenic activities. Because their hydrophobicity and low water solubility they are highly persistent in soil.Although the use of chemical oxidants can overcome the limitations of bioremediation, it is known that it damages thecommunity and soil structures. We studied the effect of combined technologies, chemical oxidation followed bybioremediation, on chronically hydrocarbon contaminated 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% moisture content), for 1 year as bioremediationprocess, BOxS. Soil microcosms without oxidation were used as bioremediation control, BS.The PAH concentration, PAH bioavailability (%), dissolved total carbon (% DTC), absorption and fluorescence of organicmatter (OM), total nitrogen (N), sulphate (SO42-), phosphorous (P) and bacterial diversity were analysed. Hill?s numberswere used as diversity measures. The results were analysed using methods from the multivariate statistic.The PS application produced 30% of PAHs elimination and an increase of DTC and PAH bioavailability. The aqueousextract fluorescence attributed to the organic matter was higher than S0, but the relative emission from PAHs waslower. The corresponding spectroscopic analysis (E4/E6) did not show changes.Before the oxidation, S0 showed a very high diversity being an equal community. A dramatic decline in the richnesswas observed after PS oxidation. The OxS community showed an uneven assemblage with a few dominant species. TheActinomycetales (57%) and Bacillales (20%) were the predominant orders. By analysis of 16SrDNA hypervariable region,we found successional changes in the community along the treatment. The low richness and uneven assemblageremained until the fifth month but with Pseudomonadales as predominant order (71%). Slowly, the bioremediationallowed 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 elimination was observed, leaving a lower DTC value in BOxS. Thefluorescence intensity from OM was similar to S0 but principally as consequence of humic-like substances contribution,suggesting that the bacterial successional changes were principally to expenses of the available compound from theoxidized OM. The increment on P also suggested the effective bacterial involvement in the soil P cycle. The significantlyhigher SO42- concentration seemed to no exert much effect on the soil bacterial diversity.The bioremediation in BS after one year also showed a low richness. Although a reduced fluorescence was detected inthis microcosms, the relative PAH and OM fluorescence contribution did not change.The coupled technology studied was suitable for elimination of PAHs with the recovery of microbial diversityassociated to the metabolism of oxidized OM. The multifaceted approach were useful for understanding the globalprocess in a chronical-contaminated soil.