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Minimizing bacterial biofilm in water using froth flotation and shock chlorination

Hassan, Ghanim (2015) Minimizing bacterial biofilm in water using froth flotation and shock chlorination. PhD thesis, University of Sheffield.

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Abstract

Microorganisms in potable water systems are either present in the planktonic “floating stage”, or attached to surfaces, usually as biofilm. Many hygienic and economic problems are attributed to this phenomenon. Through the last seven or so decades many trials were made to overcome biofilm problems. Unfortunately, biofilm prevention stills a premature field of science. Therefore, serious solutions with new horizons are needed. The objective of this study is to provide a water distribution system which is free of microorganisms, both in the planktonic and biofilm stages, and biocides. The two components are interactive; biofilm formation is stimulated by the presence of low (residual) levels of biocides whereas removing the bacteria results in less or no biocide being needed. The first part of the research investigates the use of chemical free froth flotation to remove microorganisms. Bacteria are hydrophobic and thus should be able to be separated by froths. A method for producing froth without using chemicals has been developed to avoid water quality deterioration and this froth is shown to hold bacteria without the need for biocide treatment or frothing chemicals. Experiments were undertaken to explore how far this process can purify a water stream. The froths formed were found to hold up to 2×108 cfu ml-1 of bacteria without chemical collectors, and made a cfu/ml drop of 55% between the inlet and outlet streams. The second area of research investigated shock chlorination and dechlorination to kill the microorganisms but almost immediately remove the biocide. Among all the dechlorination techniques, aeration was found to be the most suitable method. Investigations were undertaken to determine how fast and how practically acceptable the method of dechlorination by aeration is. Dechlorination design demand was found to be (9×10-4 lair/(lwater . ppm )). Around these two main areas of research supporting researches were undertaken. Studies found that dead bacteria were able to be removed by froth flotation as well as, or even better than live bacteria. Chlorination was faster than dechlorination under the same conditions by a factor of 25%. At low bacterial content, chlorine demand is directly proportional to cfu/ml. Zero bacterial content can be obtained through shock chlorination. The newly developed iPhone and iPad colony counting applications were investigated as a rapid way of measuring bacterial count. These were found to be reliable and accurate and, with additional manual manipulation proved very suitable to use for counting bacteria.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Chemical and Biological Engineering (Sheffield)
Identification Number/EthosID: uk.bl.ethos.665037
Depositing User: Mr Ghanim Hassan
Date Deposited: 02 Sep 2015 10:10
Last Modified: 03 Oct 2016 12:18
URI: http://etheses.whiterose.ac.uk/id/eprint/9723

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