INFLUENCE OF ABIOTIC PARAMETERS ON THE EFFICIENCY OF CHEMICAL OXIDATION OF PAHCONTAMINATED SOIL AND ITS IMPACT ON SOIL MICROBIAL COMMUNITY.

MARINA PELUFFO; NADIA VILLALBA VILLALBA,; VERÓNICA C. MORA; JANINA A. ROSSO; IRMA S. MORELLI

Barcelona

Congreso; 12th International UFZ-Deltares Conferenceon Groundwater-Soil-Systems and Water Resource Manangment; 2013

Polycyclic aromatic hydrocarbons (PAH) are ubiquitous compounds of particular concern because of their widespread occurrence in the environment and their carcinogenic potential. Bioremediation is a low-cost and low-disturbance solution for the cleaning of contaminated sites. However, a general problem of bioremediation of PAH-contaminated soil is the slow degradation rate. On the other hand, in situ chemical oxidation has been increasingly regarded as a relevant technology for remediation of soils contaminated by recalcitrant organic contaminants, including PAH. However, the efficiency of chemical oxidation is dependent of PAH properties and soil characteristics and its potential effect on soil physical, chemical and biological properties is relevant. To address the limitations of individual remediation techniques and to achieve better PAH removal efficiencies, the combination of chemical and biological treatments can be used.In a previous work we evaluated the feasibility of using a surface application of an oxidative treatment with Persulfate (PS) in soil microcosms contaminated with phenanthrene, looking on soil physicochemical and biological parameters. In these microcosms, residual concentration of PS declined after 7 days of treatment, and at this time the PS concentration of 21.0 g/kgDRY SOIL achieved a 30% of phenanthrene elimination but with an important impact on soil pH, soil electrical conductivity, heterotrophic bacteria counts and bacterial community composition, inhibiting the biodegradation process. The addition of a PS concentration of 8.61 g/kgDRY SOIL reached only a 20% of phenanthrene elimination during the first 7 days of treatment, without negatives effects on the studied physicochemical and biological soil properties. The aim of this study was optimized the abiotic parameters (salt and applications way, and soil moisture) to enhanced the oxidation process and its impact on soil physicochemical and biological properties. Six different treatments were tested in soil microcosms freshly contaminated with phenanthrene (100 mg/kgDRY SOIL). In two treatments the microcosms were maintained to a 44.5% of soil water-holding capacity (SWHC) and sodium PS was added, in once application, at 8.60 and 43.01 g/kgDRY SOIL, (NaPS1 and NaPS2, respectively). In treatments NaPS3 and NaPS4 the same application of sodium PS was performed, but the microcosms were keeping to a 65% of SWHC. The last two treatments (with 44.5% of SWHC) were prepared with ammonium PS, added in a single addition of 41.7 g/kgDRY SOIL (NH4PS1) and in successive additions of 5 g/kgDRY SOIL reaching a concentration of 20 g/kgDRY SOIL (NH4PS2) at 7 days. Control microcosm contaminated with phenanthrene but without oxidant addition was prepared for each experimental condition. All microcosms were carried out in triplicate trays and incubated in controlled conditions to support a simultaneous biological process (temperature and oxygen availability). Analyses of phenanthrene and PS concentration, soil characteristics (pH, conductivity) and microbial density were performed.After 7 days of treatment the microcosms NaPS1 and NaPS2 showed 20 and 30% of phenanthrene elimination, respectively, while NaPS3 and NaPS4 were less efficient (only 1 and 10%, respectively), indicating that the increment in percentage of SWHC did not improve the oxidation process. Treatments NaPS2 and NH4PS1 reached the same percentage of degradation (30%), showing that the cation (Na+ or NH4+) did not have any influence on the process. The phenanthrene elimination in the microcosm NH4PS2 (successive additions) was coincident with the found in the NaPS2 and NH4PS1 microcosms, although a lower amount of PS was added, and with a lower impact on soil physicochemical and biological properties. This behavior suggests that addition of PS in small doses would be more efficient, improving the oxidation process with a lower impact on soil microbial community.