Ex-situ soil washing of diesel contaminated soil using impinging stream reactors and selective soft self attrition

[摘要] ENGLISH SUMMARY: When considering oil spills, the focus has usually been on the pollution of water andthe corresponding impact on the animals and habitat concerned. There is, however,another important aspect that has largely been neglected - soil contamination. Theremediation of diesel contaminated soil, making use of soil washing techniquesconsisting of two technologies i.e., Impinging Stream Reactors and Selective Soft SelfAttrition was studied in this project. The primary aim of these processes will be as apre-treatment step for bioremediation in a complete treatment system, capable ofreducing total remediation times considerably.The Impinging Stream Reactor (ISR) process uses a high pressure water jet to removethe diesel from the soil particles. The Selective Soft Self Attrition (SSSA) processuses a novel stirrer to stir a high density slurry (consisting of contaminated soil andwater) resulting in interparticle scrubbing that removes the contaminant. Bothprocesses were optimised with respect to all operating variables.The most important variable in soil remediation is the particle size distribution to betreated. Four samples of silica sand differing only in particle size fraction were usedto represent the range from fine silty soils (42% -10 μm) to coarse sandy soils (+500μm). The Impinging Stream process was able to reduce diesel contamination levels insandy soils by 96% (this corresponds to 2000 ppm, the most sensitive sites requiringlevels below 200 ppm) but was not effective in treating silty soils. The Selective SoftSelf Attrition process was able to reduce diesel contamination on sandy soils by 96%(to 2000 ppm) and silty soils by 94% (to 3000 ppm). Adding coarser sand as grindingagent to silty soils, reduces this value a further 2% (to below 2000 ppm).Analyses of the sand (after washing) were done by extracting the diesel withMethylene Chloride in a Soxhlet Extraction Unit, after which the solvent wasevaporated and the residual diesel determined gravimetrically. Altering theevaporation part by slowing it down considerably, resulted in improved accuracy andrepeatability. Gas chromatographic analyses of the diesel extracted from the sand wasalso done and showed that the components in diesel lighter than C 15 are beingpredominantly removed during these processes.

[发布机构] Stellenbosch University