9.2 Water Treatment from Lake Roine, Tampere, Finland
In the 1960s, the City of Tampere, Finland, began drawing water from Lake Roine
when the quality of water from its original lake source deteriorated. A horizontal
sedimentation basin was constructed in the early 1970s, and a laminar flotation
process was implemented in 1989. Activated carbon replaced sand filtration in 1996,
but the City was still not satisfied with its drinking water quality [33].
In 1997, a pilot dissolved air flotation (AquaDAF) system was retrofitted in one of
the conventional sedimentation basin flocculators. The DAF pilot demonstrated
much higher flotation rise rates than those previously achieved with the laminar
DAF units. In 2000, retrofitting of all laminar DAF units was completed. Today, the
plant uses only the AquaDAF for clarification. The system was retrofitted in the
original basins and sludge channels. The new structure is constructed entirely
of wood.
The AquaDAF™ system utilizes hydraulic flocculation underneath the flotation
area. Two very small unpacked saturators operate at a design recycle rate of 10%.
The only submerged moving part is the effluent weir used for desludging. Water
quality and system performance is shown in Table 7.6.
Fig. 7.18 Floating barge for algae removal from lake water
7 Lake Restoration
301
In the 1960s, the City of Tampere, Finland, began drawing water from Lake Roine
when the quality of water from its original lake source deteriorated. A horizontal
sedimentation basin was constructed in the early 1970s, and a laminar flotation
process was implemented in 1989. Activated carbon replaced sand filtration in 1996,
but the City was still not satisfied with its drinking water quality [33].
In 1997, a pilot dissolved air flotation (AquaDAF) system was retrofitted in one of
the conventional sedimentation basin flocculators. The DAF pilot demonstrated
much higher flotation rise rates than those previously achieved with the laminar
DAF units. In 2000, retrofitting of all laminar DAF units was completed. Today, the
plant uses only the AquaDAF for clarification. The system was retrofitted in the
original basins and sludge channels. The new structure is constructed entirely
of wood.
The AquaDAF™ system utilizes hydraulic flocculation underneath the flotation
area. Two very small unpacked saturators operate at a design recycle rate of 10%.
The only submerged moving part is the effluent weir used for desludging. Water
quality and system performance is shown in Table 7.6.
Fig. 7.18 Floating barge for algae removal from lake water
7 Lake Restoration
301