• Grönroos, Antti

Abstract

There are a great variety of potential applications ofhigh-intensity ultrasonic energy. Of these, cleaning,plastic pounding, and at present also sludgedisintegration and the remediation of contaminated soilare probably the best known and offer the most generalmarket for high-intensity ultrasonics. All developmentswithin the area of ultrasound applications lead to thecreation of environmentally friendly processes andcompounds, emphasizing the role of ultrasound in "greenchemistry". Ultrasound technology is considered not easyto use in industrial processes, since devices providinghigh sonic energy are not easy to construct. This thesisinvestigates on a semi-pilot scale if it is possible toenhance the disintegration of three quite differentsamples: polymers, sludge, and contaminated soil by usingultrasound.The results indicate that it is possible to enhance thedisintegration of polymers by means of ultrasonic poweronly when the cavitation threshold is exceeded. Above thecavitation threshold, the most extensive degradation tookplace at the lowest ultrasonic frequency used. Thebiggest decrease (from 115,000 g/mol to 30,000 g/mol) inrelative molecular mass (RMM) was observed when theconcentration of polyvinyl alcohol (PVA) was the lowest(1.0%). However, in the case of carboxymethylcellulose(CMC) it was observed that there is an optimum polymerconcentration (1.5-2.0%) where degradation is mostefficient. The thesis shows that the extent of ultrasonicdepolymerization decreases with decreasing molecular massof the cmC polymer. The study also reveals thatultrasonic irradiation causes narrowing of the molecularmass distribution. The degradation of cmC polymerproceeded linearly and the rate of ultrasonicdepolymerization decreased with decreasing molecularmass. In cases where the initial dynamic viscosities ofpolymer solutions were not the same, the sonolyticdegradation of cmC polymer mainly depended on the initialdynamic viscosity. The higher the initial dynamicviscosity, the faster the degradation. This work confirmsthe general assumption that the shear forces generated bythe rapid motion of the solvent following cavitationalcollapse are responsible for the breakage of the chemicalbonds within the polymer. The effect of polymerconcentration could be interpreted in terms of theincrease in viscosity with concentration, causing themolecules to become less mobile in solution with smallervelocity gradients around collapsing bubbles.Ultrasonic disintegration of sludge increased the amountof soluble chemical oxygen demand (SCOD) and theproduction of methane. Multivariate data analysissuggested that ultrasonic power, sludge dry solids (DS),sludge temperature, and ultrasonic treatment timesignificantly affect sludge disintegration. It was alsofound that high ultrasound power together with a shorttreatment time is more efficient than low ultrasoundpower with a long treatment time. When using highultrasound power, the ultrasound propagation is animportant factor both in cavitation erosion preventionand reactor scale-up. Ultrasound efficiency rose linearlywith input power in sludge at small distances from thetransducer. On the other hand, ultrasound efficiencystarted even to decrease with input power at longdistances from the transducer. When using oxidizingagents together with ultrasonic disintegration there wasno increase in SCOD and only a slight increase in totalorganic carbon (TOC) compared to ultrasonic treatmentalone. However, when using oxidizing agents together withultrasound, no enhancement in methane production wasobserved.Ultrasound improved the remediation results of bothproducts (sink and float products) in heavy mediumseparation. This phenomenom was based on the fact thatthe amount of ultrafine metal fraction was diminishedwhen attrition conditioning was replaced by ultrasound.The remediation process produced float product (cleanedsoil) that could be left where it was. This would makefor lower process costs since there is no need to movelarge quantities of soil material.

Topics

• impedance spectroscopy
• polymer
• Carbon
• Oxygen
• laser emission spectroscopy
• viscosity
• ultrasonic
• alcohol
• molecular mass