The effect of ultrasound in combination with UV radiation or electrolysis on the biological decontamination of potable water

Abstract

There is an increasing incidence in health problems related to environmental issues, which originate from inadequate treatment of potable ,waters. This has compelled scientists and engineers to engage in innovative technologies to achieve a maximum disinfection at affordable costs. Some species of bacteria produce colonies and spores, which agglomerate in spherical clusters and this protects organisms on the inside against biocidal attack. Floes of fine particles e.g. clay can entrap bacteria which can also protect them against the biocides. Other bacteria have the ability to mutate thus building up resistance to conventional biocides ( e.g. chlorine). Ultrasound has been shown to be effective in improving the effectiveness of biocides such as chlorine and ozone. The aim of this present study was to investigate the effect of (a) power ultrasound using different frequencies and power settings (20kHz, 40kHz and 1.2MHz) (b) UV radiation (254nm) on static and circulating systems( c) electrolysis (150mA applied current) ( d) power ultrasound ( 40kHz) in combination with UV radiation (254nm) or electrolysis (1 00mA applied current) on aqueous suspensions of coliform bacteria. This involved building and testing novel disinfection systems to determine their effect on coliform bacteria. Electrolysis experiments incorporated a number of different applied currents and electrode material (carbon (graphite and felt), copper, stainless steel, brass, and titanium) to determine the effect of each treatment system and to provide a greater knowledge of the fundamentals of disinfection through the production of hypochlorite in situ from saline solution via electrolysis. Results indicate the most efficient conditions for disinfection employing 150mA electrolysis or 1 00mA electrolysis in conjunction with 40kHx ultrasound using the same electrode material for the anode and cathode was brass with an 8-log reduction after 5 minutes, however dispersion of copper particles into solution occurred. The most efficient system, which did not result in subsequent pollution, was electrolysis at 150mA using carbon felt as anode and copper as cathodes resulting in 100% kill following 10 minutes treatment. Results indicate ultrasound alone has only a moderate effect on bacterial suspensions with less than a 1-log reduction following 60 minutes treatment. The effect of UV radiation is minimal unless there is adequate mixing of suspensions. UV static systems achieved less than a I-log reduction after 60 minutes treatment compared with UV circulating systems achieving an 8-log ( I 00% kill) reduction after 40 minutes. When UV was used in conjunction with power ultrasound ( 40kHz) there was improvement in the overall treatment time, UV static systems achieved an 8-log reduction after 50 minutes and UV circulating systems after 30 minutes. The results show that combined electrolysis at 1 00mA and 40kHz ultrasound appears to amplify the effect of electrolysis at 150mA. A combination of both treatments is significantly better than sonication or electrolysis alone.

Date of Award	2003
Original language	English
Awarding Institution	Coventry University
Supervisor	Timothy Mason (Supervisor), S S Phull (Supervisor) & J.P. Lorimer (Supervisor)