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THE SONOCHEMISTRY CENTRE AT COVENTRY UNIVERSITY ‘The Home of Sound Science’
ULTRASOUND IN ENVIRONMENTAL PROTECTION AND WASTE CONTROL
Research into the use of ultrasound in environmental protection has received a considerable amount of attention with the majority of investigations focusing on the harnessing of cavitational effects for the destruction of biological or chemical pollutants in water and the processing of sewage. The field is much broader than this however and a summary of topics is given in the Table.
Air Cleaning >
The inhalation of airborne particles is now recognized as a serious public Using this type of device airborne ultrasound has been used for both the precipitation of airborne powders and defoaming.
Land Remediation
For contaminated soil wastes the currently available options for management and disposal are principally:
· Permanent storage in a secure landfill. This will result in a permanent retained liability by the waste generator. · Incineration in a permitted waste incinerator. This is costly and entails the risk of atmospheric emissions. · Soil washing to produce bulk soil with low-level contamination. However the washing process itself will produce a volume of solvent that must be treated before disposal.
For many years ultrasound has been considered as a technology to promote the process of soil washing and if subsequent disposal of the washings was considered at all this was perhaps to be a separate treatment. An integrated system has been developed in Canada (by Sonic Environmental Solutions Inc.) for large scale continuous processing using acoustic frequencies in the audible range that incorporates the clean-up of the washings and recycling of the solvent. The equipment itself affords vibrational amplitudes considerably larger than those available using ultrasound and it has proved to be particularly efficient for the removal and destruction of PCB contaminants in soils. The equipment generates vibrational energy through the use of resonant bending modes in a large cylindrical steel bar. The bar is driven into a cloverleaf type of motion by firing six powerful magnets (three at each end of the bar) in sequence. The bar is supported by air springs so that the ends and the centre are then caused to rotate at a resonance frequency depending on its size.
One such unit, operating at a power of 75kW, drives a bar that is 4.1 metre long and 34 cm in diameter at its resonance frequency of 100 Hz. The bar weighs 3 tonnes and produces an amplitude of vibration at each end of 6 mm. For the washing of soils a mixing chamber is rigidly mounted on each end of the bar and these are used in three process areas: PCB extraction, PCB destruction and solvent recovery. The use of this generator for pilot testing has proved that processing can be achieved at a commercial scale of around 3 to 4 tonnes of soil/hour.
Water Remediation
Removal of biological contamination
Some species of bacteria produce colonies and spores, which agglomerate in spherical clusters (e.g. Bacillus subtilis). The use of a biocide can destroy microorganisms on the surface of such clusters but often leaves the innermost bacteria intact. Flocs of fine particles e.g. clay can entrap bacteria which can also protect them against disinfection [Mir, 1997]. Due to these problems alternative methods of purifying water are being investigated and amongst these the application of ultrasound is proving to be of considerable interest. Ultrasound is able to inactivate bacteria, make them more susceptible to biocides and/or deagglomerate bacterial clusters or flocs depending upon the power and frequency applied through a number of physical, mechanical and chemical effects arising from acoustic cavitation.
Removal of Chemical contamination
The mechanical effects of cavitational collapse together with the production of radical species combine to provide the essential elements for water decontamination. The primary radicals produced during the sonication of water are OH. and H. and the fate of these is quite complex (Scheme 18). The HO. radical is extremely reactive and is capable of oxidising most chemical compounds dissolved in the water. This oxidation is mainly responsible for the degradation of organic pollutants in sonicated aqueous media. The efficient generation of HO. is therefore an important goal in waste treatment.
1. Degradation of dye effluent, J.P.Lorimer, T.J.Mason, M.Plattes, S.S.Phull, and D.J.Walton, Pure and Applied Chemistry, 73, 1957-1968 (2001). 2. Potential uses of ultrasound in the biological decontamination of water, T.J.Mason, E.Joyce, S.S.Phull, and J.P.Lorimer, Ultrasonics Sonochemistry 10, pp 319-324 (2003). 3. Ultrasound in Advanced Oxidation Processes, T.J.Mason and C.Petrier, Chapter 8 in Advanced Oxidation Processes for Water and Wastewater Treatment, pp 185-208, ed S Parsons, IWA Publishing (2004). 4. Application of UV radiation or electrochemistry in conjunction with power ultrasound for the disinfection of water Eadaoin M. Joyce, Timothy J. Mason and John P. Lorimer , Int. J. Environment and Pollution 27, 222-230 (2006) 5. Oxygen-induced concurrent ultrasonic degradation of volatile and non-volatile aromatic compounds Christian Pétrier, Evelyne Combet and T.J.Mason, Ultrasonics Sonochemistry 14, (2007) in press.
Examples of projects
Water purification:
Advanced oxidation methods involving sonochemistry“Degradation of water pollutants using ultrasound”
Biological decontamination“The effect of ultrasound in combination with uv radiation and/or electrolysis for the biological decontamination of potable water” “The effect of sonication at different frequencies on microbial disinfection usinghypochlorite”
“Controlling algae in reservoirs with ultrasound”
“Assessment of hydrodynamic cavitation methods compared with sonochemistry for the decontamination of water”. Soil remediation
“Sonic and ultrasonic removal of chemical contaminants from soil in the laboratory and on a large scale”
Airborne pollution
“Ultrasound for the removal of dust, suppression of foam”
Surface Cleaning
“Membrane fouling and integrity in the municipal sector: a multi-faceted approach to their amelioration” “Surface decontamination in the food industry”
MICROBIOLOGY
The effect of ultrasound on biological systems and biotechnological processes depends strongly on frequency, intensity and sonication time.
Low intensity effects (i.e. under conditions which occur below the cavitation threshold) are the result of microstreaming and acoustic streaming. At these intensities, where no cavitation damage will occur, the beneficial effects are:
· activation of enzymes in enzymatic reactions · improvements in microbial reactions (e.g. fermentation) · improvement of the bioavailability of contaminants in environmental remediation using microorganisms
Higher intensity effects are the result of cavitational damage and may be summarised as follows:
· destruction of cell walls and release of cell components into the surrounding solution (damage to cell components e.g. DNA, proteins is limited if sonication time is short) · extraction of organic substances from plants · emulsification of food (see Food section) · damage of cell walls and cell components at very high intensity · killing of microorganisms (see Environmental Remediation) · improvement of the conventional bacterial decontamination (disinfection) of water · destruction of biological tissue e.g. tumours or kidney stones (see Therapeutic Ultrasound)
1. The use of ultrasound in microbiology - Sonomicrobiology. S.S.Phull and T.J.Mason, Advances in Sonochemistry, Vol 5, ed. T.J.Mason, JAI Press, 175-208 (1999) 2. Potential uses of ultrasound in the biological decontamination of water, Mason, T.J., Joyce, E., Phull, S.S. and Lorimer, J.P., Ultrasonics Sonochemistry 10, pp 319-324 (2003). 3. The effect of sonication on microbial disinfection using hypochlorite, H. Duckhouse, T.J. Mason, S.S. Phull, and J.P. Lorimer, Ultrasonics Sonochemistry 11, 173-176 (2004). 4. A review of research into the uses of low level ultrasound in cancer therapy, Tinghe Yu, Zhibiao Wang and T.J.Mason, Ultrasonics Sonochemistry 11, 95-103 (2004).
Examples of Projects
“The effect of ultrasound and ultraviolet radiation on bacterial suspensions”
“The effect of ultrasound and ultraviolet radiation on gram positive and gram negative bacteria”
“The influence of ultrasound on the uptake of chemotherapeutic agents into cells”
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