Helen L. Duckhouse's research while affiliated with Coventry University and other places

Ultrasound can be used to improve the efficiency of a biocide. Previous studies have shown a dramatic frequency effect, depending on the timing of the sonication with respect to biocidal treatment i.e. whether it is sequential or simultaneous. In this study we have investigated the effect of ultrasonic power on the inactivation of suspensions of E. coli using two different frequencies and pre and simultaneous treatment with sodium hyperchlorite. Power does affect the kill rate but the frequency appears to be the major factor in terms of the timing of the ultrasonic treatment.

Ultrasound alone is capable of killing bacteria when sufficient power is applied but ultrasound at low powers can also be used to improve the effectiveness biocides. In this paper, we explore the effect of the timing of the ultrasonic treatment at 20 and 850 kHz on the biocidal efficiency of sodium hypochlorite solution towards Escherchia coli suspensions. A remarkable frequency effect has been noted. At the lower frequency of 20 kHz the improvement in biocidal activity is greatest when the ultrasound is applied at the same time as the hypochlorite. At the higher frequency of 850 kHz the improvement is best when ultrasound is used as a pre-treatment immediately followed by hypochlorite addition under normal (silent) conditions. The kill rate achieved for pre-treatment using 850 kHz and simultaneous treatment using 20 kHz are very similar. However the former involves less acoustic energy and so is considered to be the more efficient.

ABSTRACT: The disinfection stage in water treatment is very important in that it is here that disease causing micro-organisms (bacteria, fungi and viruses) can be killed. Traditionally chlorine has been used as the biocide of choice but there are problems with the use of chlorine in that organic pollutants present in wastewater can react with the chlorine to produce toxic products. There are two ways in which such problems can be overcome either (a) by finding an alternative biocide that does not generate toxic bi-products or (b) by reducing the concentration of chlorine used while maintaining its effectiveness. It has been reported that it is possible to use ultrasound to achieve the same biocidal effects but at a lower concentrations of chlorine [1]. Other studies have shown that ultrasound at high powers can kill bacteria directly and that low powers can disperse bacterial clumps making individual bacteria more susceptible to external influences [2]. Here we report a systematic study of the influence of ultrasonic pre-treatment at different frequencies and powers on the destruction of micro-organisms by subsequent chlorination. The micro-organism studied was Escherichia coli (strain B) and the standard disinfection conditions involved chlorine (1ppm using NaOCl) and a contact time of 15 minutes. Ultrasound was applied before the addition of chlorine using a range of frequencies (1.2MHz, 850kHz, 512kHz, 38kHz, and 20kHz) and at different irradiation times (0.5, 1.0, 2.0 and 5 minutes). Viable plate counts were used as the method of estimation of bacterial kill and calorimetry was used to estimate ultrasonic power. Compared to the control reaction (exposure of the micro-organism for 15 minutes to chlorine at a concentration 1ppm) it was found that a short period of sonication before chlorination (<5 minutes) improved the kill at all frequencies. Somewhat surprisingly a 5 minute sonication period appeared to reduce the effect of chlorination. We have demonstrated that the use of ultrasound before chlorination can improve the kill rate by up to a 2-log reduction in bacteria. The ultrasonic effects follow the trend of 850kHz (1.22W) > 1.2MHz (7.86W), 512kHz (11.64W), 38kHz (10.37W) > 20kHz (22.34W) and that a shorter ultrasonic time is better than longer ultrasonic times. In other words shorter times at 850kHz (1.22W) proved to be much more effective as a pre-treatment. 1. T.J.Mason, A.P.Newman, S.S.Phull and C.Charter, Sonochemistry in Water Treatment - a Sound Solution to Traditional Problems, World Water and Environmental Engineering, p 16, April 1994. 2. E.Joyce, S.S.Phull, J.P.Lorimer and T.J.Mason, The development and evaluation of ultrasound for the treatment of bacterial suspensions, Proceedings of the Third Conference on Applications of Power Ultrasound in Physical and Chemical Processing (Usound3), Progep, Toulouse, 87-92, 2001.

The structures of the title compounds, [PtCl(2)(C(7)H(5)N(3)O(2)S)(2)].4C(3)H(7)NO, (I), and [Pt(C(3)H(5)N(3)S)(4)][PtCl(6)].2C(3)H(7)NO, (II), respectively, comprise square-planar Pt(II) centres. In the cation and anion of (II), the Pt atoms lie on independent inversion centres. For (I), the metal atom is N-bonded to two trans organic ligands and also bonded to two Cl atoms, whereas in (II), the Pt atom is N-bonded to four organic ligands, the charge being balanced by the presence of an additional [PtCl(6)](2-) species (from the starting material). Both structures contain dimethylformamide solvate molecules, four in the asymmetric unit of (I) and one in (II), which are involved in the hydrogen-bonding network via N-H.X and C-H.X associations.

The structure of the title compound, [Cu2(C8H6NO4)4(C4H5N3)2], comprises individual units of tetra-μ-carboxyl­ato-O:O′-dicopper(II) end-capped with two 2-amino­pyrimidine mol­ecules. These pyrimidines then form dimers across a typical N—H⃛N association, thus producing linear hydrogen-bonded polymer chains.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The structure of the title compound, [Cu2(C9H9O3)4(C4H5N3)], comprises a zigzag polymer of alternating tetrakis­(carboxyl­ato-O:O′)­dicopper(II) and 2-amino­pyrimidine units linked by axial Cu—N bonds, and the non-centrosymmetric structure has four unique (3-methoxy­phenyl)­acetate moieties.