Graded Modified Fenton Oxidation Of Highly Oil Contaminated Soil

In the process of high concentration oil contaminated soil oxidized by gradedmodified Fenton reagent, high-dose of H₂O₂was added by one-time. It will decrease thestability of H₂O₂and kill native bacteria due to high temperature of soil. Therefore, thispaper mainly studies the properties of high concentration oil contaminated soil bygraded modified Fenton oxidation under low-dose of H₂O₂in many times. The effectand their factors on contaminated soil remediation using three different high oilcontaminated soil were invesigated. In addition, the characteristics of oxidized TPH andSOM, the characteristics of H₂O₂consumption and soluble ferric ion consumption, andthe influence of these factors mentioned above in Fenton oxidation of petroleumhydrocarbon were investgated. These will provide the theoretical basis for remediationof petroleum contaminated soil in the field.The experiment of conclusions as below:（1） The results show that removal efficiency of TPH reached to30%to60%for soilS1and S2when H₂O₂was added2⁶times in stepwise addition. In addition, whenH₂O₂was stepwise addition, H₂O₂consumption per gam TPH oxidized significantlydecreased, the value were40g⁷0g,25g⁴5g and40g⁷0g, which were lower than thatof H₂O₂consumption （77g,55g and158g） at single addition. So, stepwise addition ofH₂O₂can save48%⁷5%of H₂O₂.（2） Three oil contaminated soils such as S1, S2and S3（initial TPH concentrationare14.4g/kg,23.2g/kg,95.6g/kg, respectively） were oxidized by graded modifiedFenton. For soil S1and S2when the mole ratio of Fe2+and H₂O₂was1:129, and H₂O₂ was added at four times, the highest removal efficiency of TPH reached58%. However,the removal efficiency of TPH is only32%by single dosing of H₂O₂or so, improvedtwo times nearly. Under the same condition the highest removal rate of TPH reached9%for soil S3. However, the removal efficiency of TPH is only2³%by single dosingof H₂O₂.The effect of soil S1and S2are better than soil S3.（3） The soils S1, S2and S3were oxidized by graded modified Fenton, oxidationefficiency of SOM were2.11%³.82%,6.48%⁹.39%and0.75%².02%, all lessthan that of under single addition（3.4%⁴.02%,8.42%⁹.6%and2.15%².71%）.So, the oxidation of SOM decrease in graded modified Fenton process.（4） In the experiments of different iron dosing quantity, when H₂O₂was addedmore than four times, the maximum removal rate of TPH in soil S1, S2and S3reachedin the mole ratio of Fe2+and H₂O₂was1:129. The maximum removal rates of TPH were59.78%,58.82%and9.16%. When Fe2+concentration continues to rise to9.28mmol/L,removal efficiency of TPH will reduce to57.00%,55.85%and7.27%. The soil organicmatter （SOM） affected by different iron dosing quantity slightly. When H₂O₂was addedfour times, the SOM value of soil S1, S2and S3were14.43%,12.98%and14.83%asFe2+concentration was5.8mmol/L. When Fe2+concentration continues to rise to9.28mmol/L, the SOM value of soil S1, S2and S3were14.67%,12.79%and14.67%.（5） The Dosing frequency of H₂O₂is the most important factor for thedecomposition of H₂O₂. In the same dose of H₂O₂, the less dosing times, H₂O₂decomposed faster. When H₂O₂was added by one-time in4hours, H₂O₂decompositionrate is as high as182.63mmol/（L h）, and H₂O₂decomposition rate gradually slow downwith the more times. When H₂O₂was added at six times, the decomposition rate wasonly30mmol/（L h）.（6） Soil properties will also affect the decomposition of H₂O₂. When Fe2+concentration was8.12mmol/L, the decomposition rate of soil S1and S2were at therange of from37.22mmol/（L h） to182.63mmol/（L h） and from35.81mmol/（L h） to177.82mmol/（L h）, which is larger than that of in soil S3（26.61mmol/（L h）¹31.64mmol/（L h））.（7） Ferrous ion concentration have the influence in the decomposition of H₂O₂. Italso affected by soil properties. When same addition times of H₂O₂was set and Fe2+ concentration was8.12mmol/L, the maximum decomposition rate of H₂O₂in soil S1and S2were182.63mmol/（L h） and177.82mmol/（L h）, respectively. For soil S3H₂O₂decomposition rate increased with increasing ferrous ion dosage. The maximum valuewas143.61mmol/（L h） when Fe2+concentration is9.28mmol/L.（8） In the study of dissolve iron ion transformed by graded modified Fenton reagent,the soluble total iron concentration will continue to decline, when Fe2+concentrationwas5.8mmol/L and6.96mmol/L, the consumption of soluble total iron concentrationwas from2.84mmo/L to6.18mmo/L, and when Fe2+concentration was8.12mmol/L and9.28mmol/L, the consumption was from0.83mmo/L to2.70mmo/L, so it suggest thatdosing quantity of Fe2+is conducive to the reduction of iron ion.（9） H₂O₂stability and TPH absolute remove quantity affected by soil property,they increased with increasing added times of H₂O₂, but not as useful as more times.The best H₂O₂decomposition rate of soil S1, S2and S3were42.41mmol/（L·h）,44.67mmol/（L·h） and24.61mmol/（L·h）, respectively.（10） In H₂O₂stability of the influence of soil organic matter oxidation study,increasing the stability of H₂O₂can decrease slightly SOM removal efficiency, about1²%.