Most DAF equipment can not make enough adequate microbubbles.
The most important and difficult part of DAF (dissolved air flotation) system is microbubble generation. Almost all
microbubble generation is done by “pressure tank method” using a pressure tank. However, it is very difficult to
adjust / keep the optimal pressure in the pressure tank, so there are sites where microbubbles are not generated at all.
In addition, microbubbles generated by the pressure tank method inevitably use a large amount of flocculants because
the size of the microbubbles is large and the number of microbubbles is small meaning the ability to separate SS
(suspended solids) from water is low.
Many water treatment companies have DAF systems but most of them use crude methods. So there are many sites where
the DAF system is not working sufficiently.
Why we cannot make sufficient quality microbubbles using a pressure tank?
Air is not easily dissolved in water.
According to “Henry’s law” the amount of air dissolved in water is in
proportion to the amount of pressure so five times air will dissolve
in water when the pressure is increased five times more than the
The pressure tank method relies on this law to generate microbubbles.
The theory is to dissolve air in water at several times the atmospheric
pressure in the pressure tank, and then release it under atmospheric
pressure so that saturation point decreases and dissolved air can not
stay in a dissolved state and becomes fine bubbbles (microbubbles).
However, in reality, in the pressure tank, air does not dissolve
according to Henry’s law. The reason is that even if compressed
air is blown into the pressurized tank, most of the air will change
into coarse bubbles in an instant so that most of the air will come out
of the water quickly in the pressure tank, and undissolved air will be
generated in large quantities.
Undissolved air is released from the "air vent valve" at the top of the
pressure tank or the outlet of the pressure tank". (*Please see the
illustration on the right.)
The pressure tank method has two fundamental flaws. The first one is
that not all of the blown air (raw material) converts to microbubbles.
A lot of the blown air is “discarded” as coarse bubbles. Even if the
amount of blown air is increased, the amount of microbubbles will not increase because it is only increasing coarse bubbles.
The second fundamental flaw is that it is very difficult to fine the optimum operating conditions because of the difficulties of
controlling the internal pressure in the tank which change every day and if there is a change however small it can affect the
ratio of dissolved / undissolved air so microbubbles can not be generated consistently.
OHR microbubble generation mechanism is completely different from the others.
No pressure tank and daily adjustment required.
The advantage of OHR flotation separation is that pressure tank and daily adjustment are completely unnecessary. It requires only the initial operation adjustment. After that it can be consistently operated over a long period. The configuration of the equipment is very simple with one OHR MIXER and one pump, and it can generate very large amounts of microbubbled water up to 15,000L/min (900m3/h).
For details, please contact us.
The fineness of OHR’s microbubbles have been proven.
It was revealed in a comparative test conducted by a water treatment company.
Company X the biggest water treatment engineering company in
Japan analysed and collected data from three companies; company K,
company N and OHR. Microbubbled water generated by the equipment
of these three companies were collected in 1L measuring cylinders
respectively to observe how long it took for all microbubbles to
disappear. See the table on the right for the results.
You can see that the OHR has a much longer staying time than other
companies’ products. (*This test report can be provided on request.)
In flotation separation, the finer the microbubble the better because they are more likely to attach to the finer SS (suspended
solids) and raise them to the water surface. Depending on the manufacturer / type of microbubble generator, there is a big
difference in the ability to float and separate SS.