Water Science & Technology: Water Supply Vol 1 No 1 pp 17–23 © IWA Publishing 2001
Artificial mixing to reduce growth of the blue-green alga Microcystis in
Lake Nieuwe Meer, Amsterdam: an evaluation of 7 years of experience
E Jungo*, PM Visser**, J Stroom*** and LR Mur****
*
Jungo Engineering Ltd., Schaffhauserstrasse 331, CH-8050 Zurich, Switzerland
Email: jungo_eng@bluewin.ch
**
Jungo Engineering Ltd., Schaffhauserstrasse 331, CH-8050 Zurich, Switzerland
***
ARISE/MB, University of Amsterdam, Nieuwe Achtergracht 127,
1018 WS Amsterdam, The Netherlands
****
Water Authority Rijnland, P.O.Box 156, 2300 AD Leiden, The Netherlands
ABSTRACT
The problem of Lake Nieuwe Meer (area = 1.3 km2, max.
depth 30 m, Ptot = 500 mg/m3) was extensive growth
of Microcystis with disturbing scum forming. Since 1993 the lake has been
artificially mixed in summer by a bubble plume installation. The result
is quite successful since the mass of Microcystis is up to 20 times lower
than in the years before mixing and no scum is present any more. The study
in Lake Nieuwe Meer showed a shift from cyanobacterial dominance (mainly
Microcystis) to flagellates, green-algae and diatoms when artificial mixing
was applied. Total phosphorus and nitrogen concentrations did not change as
a result of mixing and had apparently no effect on the shift in the
phytoplankton composition. The chlorophyll-a concentration was much lower
in the mixed lake as a result of dilution. The total algae biomass decreased.
The transparency did not improve. The total heat energy of the lake is
slightly higher than before mixing but still remains in the range of annual
fluctuation. The temperature on the surface is approximately 2°C lower. In the whole water-body oxygen was always higher than
5 mg/l. Living space for fish is therefore wider.
The installation in Lake Nieuwe Meer consists of flexible pipes near the
sediment, built in a way to prevent sediment erosion and transport into the
water. There are no constructions in the water-body. All mechanical parts
are on land. The layout of the installation is shown in Fig. 1. Installed
compressor energy is 85 kW. This is equivalent to an upper middle-class
motor-car. The design was made specifically for this problem. It is
based on the physical data of the algae and the plant.
It would be beneficial to use this 7 year's experience for further
applications e.g. elimination of toxic algae in drinking-water reservoirs.
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