Οξείδωση της φαινανθρίνης στα εδάφη μέσω των θερμικά ενεργοποιημένων οξειδωτικών: υπερθειικό και υπεροξυμονοθειικό κάλλιο

Abstract

The present bachelor thesis was conducted in order to study the removal of phenanthrene (a polycyclic aromatic hydrocarbon-PAH) from two different types of soil, through thermal activation of the oxidants potassium persulfate and potassium peroxymonosulfate. The concentration of the oxidants used had the same molarity of 0.052, 0.0052, and 0.00052 mol/L. A series of experiments was performed in order to determine the effect of temperature (T= 20μC and 45μC) and oxidant concentration on the removal of phenanthrene (1000 ιg/g of dry soil) from the two different types of soil. Prior to the experiments the physical characteristic of each soil and its composition were determined. For experiments on the effect of temperature on the activation of oxidants, the samples were placed a temperature controlled room (T= 20μC) and a laboratory oven (T= 45μC). The residence time of the samples in both cases was 24 hours. Each experiment was carried out in triplicates for each sample. In addition four control samples (oxidant free) were analyzed (two containing soil spiked with phenanthrene and two containing only soil). After the elapse of the 24 hours the samples were collected and analyzed in order to measure the remaining concentration of phenathrene, oxidant as well as the concentration of the humic and fulvic acids. Determination of the residual oxidant concentration was conducted through volumetric titration with sodium thiosulfate following the reaction with potassium iodide. Phenanthrene was first extracted with an organic solvent (ethyl acetate) in order to determine its remaining concentration and was analyzed with a gas chromatography (GC-FID). The results showed that in soils with high concentration of organic matter the pollutant is not sufficiently removed. For instance the content of organic matter was 11.1±0.1 % for soil A and respectively 24.9±0.1 % for soil B. The highest observed removal of the organic pollutant was 17±2% at 20μC with the use of potassium persulfate for soil A, while for soil B the highest measured removal value was 13±2.8 % at 45μC with the use of potassium peroxymonosulfate. This occurs because the free radicals formed from the thermal activation of the oxidants, oxidize the organic content of the soil, instead of the pollutant since it is found in higher concentration than the later. This was proven from the analysis of the humic and fulvic acids that their concentration increased with increasing oxidant concentration, irrespective of the soil and temperature used for activation.