Water Science & Technology: Water Supply Vol 1 No 2 pp 115–122 © IWA Publishing 2001
Pre-treatment with dissolved air flotation considering an integrated
process design
J Dahlquist* and M Kulesza**
*
PURAC AB, Box 1146 SE-2221 05 Lund, Sweden
**
Zakład Wodociągu Pół/nocnego MPWiK, Warsaw, Poland
ABSTRACT
The raw water from Lake Zegrzynski is difficult to treat and requires a
high chemical dosing rate of coagulant for the reduction of organic matter
in order to comply with EU standards. The high degree of reduction calls
for an efficient coagulant, but also an optimal chemistry such as correct
dosing amount and an optimal flocculation-pH. The paper describes different
removal efficiencies of organic matter, particularly with respect to pH in
flocculation.
During the warm season, the raw water can also suffer from large amounts
of plankton that are difficult to remove to a satisfactory degree. In a
two-step chemical treatment concept, with Dissolved Air Flotation (DAF)
and the pulsator process, the plankton content in the final outlet water
is reduced to very low levels. It follows that eventual peaks of plankton
in the raw water cannot be detected in the final outlet water.
Ozone is added for removal of taste and odour originating from the presence
of plankton. In the pre-treatment step prior to the ozonation, a great deal
of the organic matter is removed, which reduces the necessary ozone dosage.
The Municipal Water Company of Warsaw City has decided to consider an
additional pre-treatment step to the existing water treatment plant at
Wieliszew. For that purpose, and bearing in mind an integrated process
design, the company has performed pilot-scale experiments with DAF
installed prior to a process line identical with the existing full-scale
plant. The experimental flow is about 10 m3/h.
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