Ultrasonic and Electrokinetic Remediation of Low Permeability Soil Contaminated with Persistent Organic Pollutants

摘要

Electrokinetics has emerged as a potential technique for in situ soilremediation and especially unique because of the ability to work in lowpermeability soil. In electrokinetic remediation, non-polar contaminants likemost organic compounds are transported primarily by electroosmosis, thusthe process is effective only if the contaminants are soluble in pore fluid.Therefore, enhancement is needed to improve mobility of these hydrophobiccompounds, which tend to adsorb strongly to the soil.On the other hand, as a novel and rapidly growing science, the applicationsof ultrasound in environmental technology hold a promising future.Compared to conventional methods, ultrasonication can bring severalbenefits such as environmental friendliness (no toxic chemical are used orproduced), low cost, and compact instrumentation. It also can be applied onsite.Ultrasonic energy applied into contaminated soils can increasedesorption and mobilization of contaminants and porosity and permeabilityof soil through developing of cavitation. The research investigated the coupling effect of the combination of these twotechniques, electrokinetics and ultrasonication, in persistent organic pollutantremoval from contaminated low permeability clayey soil (with kaolin as amodel medium). The preliminary study checked feasibility of ultrasonictreatment of kaolin highly contaminated by persistent organic pollutants(POPs). The laboratory experiments were conducted in various conditions(moisture, frequency, power, duration time, initial concentration) to examinethe effects of these parameters on the treatment process. Experimental resultsshowed that ultrasonication has a potential to remove POPs, although theremoval efficiencies were not high with short duration time. The study alsosuggested intermittent ultrasonication over longer time as an effective meansto increase the removal efficiencies.Then, experiments were conducted to compare the performances amongelectrokinetic process alone and electrokinetic processes combined withsurfactant addition and mainly with ultrasonication, in designed cylinders(with filtercloth separating central part and electrolyte parts) and in openpans. Combined electrokinetic and ultrasonic treatment did prove positivecoupling effect compared to each single process alone, though the level ofenhancement is not very significant. The assistance of ultrasound inelectrokinetic remediation can help reduce POPs from clayey soil byimproving the mobility of hydrophobic organic compounds and degradingthese contaminants through pyrolysis and oxidation. Ultrasonication alsosustains higher current and increases electroosmotic flow. Initial contaminantconcentration is an essential input parameter that can affect the removaleffectiveness.