Programme  Poster session 2  abstract 777

Impact of filter operation on filtrate quality

Author(s): Zielina Michal, Wojciech Dabrowski
Cracow University of Technology 24 Warszawska Street, 31-155 Krakow, Poland tel. +48-12-6282551, fax. +48-12-6282042 email:

Keyword(s): water treatment, water filtration, variable declining rate filtration, filter operation

Article: abs777_article.doc
Poster: abs777_poster.pdf
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Session: Poster session 2
AbstractUsually, rapid filters are operated under constant flow rate, eventually

constant head loss. In practice, filters cooperate one with each other and the filtration rate in time. Variable Declining

Rate Filters operate with orifices installed at outflows instead of flow rate controllers. Appropriate relations between

laminar head loss of flow through filter media and turbulent head loss of flow through orifices let to keep declining

filtration velocity between limited values. Lower hydraulic load at the end of filter runs under Variable Declining Rate

control system results in rarer backwashes of the filters and give financial profits. Smooth change of declining

filtration velocity during the run and low value at the end of filtration cause that quality of total outflow from Variable

Declining Rate Filtration plants should not be poorer than from traditionally operated filter plants. Experimental

research has confirmed that theory. Poorer filtrate quality do not follow economic profits of Variable Declining Rate

Filters. Results, even revealed that quality of filtrate produced under Variable Declining Rate Filtration was better for

higher ratio of maximum to average rate filtration. Similar conclusions were received from numerical simulation

realized based on dynamic model connecting equations describing hydraulic work of declining rate filters and

filtration kinetic equations compiled from theory of limited trajectory. The computer simulation considered particle

size distribution analysis, for Variable Declining Rate operation led to improved removal of smaller particles, but also

a decrease in removal efficiency for larger particles was noticed.

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