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Impact of transient change of filter operating parameters on filtrate quality

Congress: 2008
Author(s): Zielina Michał, Dąbrowski Wojciech, Piątkiewicz Dominik
Cracow University of Technology 24 Warszawska Street, 31-155 Krakow, Poland tel. +48-12-6282551, fax. +48-12-6282042 email: mziel@vistula.wis.pk.edu.pl

Keyword(s): water filtration, flow rate control, variable declining rate filtration, filtration velocity
AbstractImpact of transient change of filter operating parameters on filtrate quality Zielina M., Dąbrowski W., Piątkiewicz D. Cracow University of Technology 24 Warszawska Street, 31-155 Krakow, Poland tel. +48-12-6282551, fax. +48-12-6282042 email: mziel@vistula.wis.pk.edu.pl Oral Congress Sub-themes 1. Development of water resources and infrastructure - Data, monitoring and information technology 2. Water availability, use and management - Water quality management: surface and ground water Abstract Rapid filtration is still one of the base processes in municipal water treatment plants. Several different kinds of filter operating systems are commonly known. Constant Rate filtration is traditionally the most popular. This system is characterized by installing flow rate controllers too keep an almost constant flow rate through all the filters. Operating regulator creates transient changes of head-loss to hold hydraulic load being constant in time and the same for all the filters in a plant. This changes of head loss may result sudden temporal changes of filtration velocity so in consequence, particles collected in the media may be partially detached and the quality of filtrate deteriorates. This quality is measured by particles counter, or less precisely by measuring the turbidity. Variable Declining Rate systems do not require flow rate controllers and probably no significant surge effect usually exists. Observation of twelve filters cooperating each other in an existing water treatment plant show significant effect of one filter backwashing on flow-rates through the rest of them. For poor raw water quality the filters of the plant are used to be backwashed once per several hours. Sometimes, several of the filers are backwashed simultaneously at the same period of time, when energy supply is cheaper than through the rest of a day. It results in a frequently occurring sudden increase of flow through the filters remaining in operation, in spite of the flow rate controllers. At such moments, almost three times higher values of nephelometer turbidity and suspension concentrations were observed. Experiments conducted for similar conditions were carried out in a laboratory. A significant effect of sudden change of filtration velocity on filtrate quality was observed.
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