Clearly misrepresentation of Oxygen Transfer Rate efficiency.
There is no official standard of measuring OTR in industrial wastewater in Japan.
For example, because the fuel consumption performance of a car is measured based on strict standard criteria, the user can judge
the superiority or inferiority of performance fairly, but there is no official Oxygen Transfer Rate (OTR) measurement standard for
air diffusers in industrial wastewater treatment in Japan.
(*There is a standard determined by the Japan Sewage Works Agency for sewage treatment which air diffusers in the sewage
treatment industry must comply with. However for industrial wastewater there is no official standard to measure OTR.)
As a result some air diffuser manufacturers advertise a high OTR based on non-scientific principles when in fact if based on
scientific principles their OTR would be very low.
For details, see the followings.
How to correctly measure OTR.
1) Water depth
The deeper the water, the stronger the water pressure, so the OTR increases.
The difference in water is an important factor to increase / decrease OTR. Therefore when measuring OTR it is necessary to obtain
data at every water depth. (e.g. 3.0m / 3.5m / 4.0m / 4.5m / 5.0m / 5.5m …)
For example, after obtaining the OTR data at the 3.0m water depth, drain the water and fill the water up to 3.5m water depth and
take the data at 3.5m water depth, then drain the water and fill the water up to 4.0m water depth and take the data at 4.0m water
depth, and then 4.5m, 5.0m, 5.5m and so on. Set one DO (dissolved oxygen) meter in the tank each time and record the temporal
change in DO concentration. See the following fig-1. This is the basic method to obtain OTR data which requires time and effort.
However, there is a company that takes shortcuts and sets DO
meters at 1.0m, 2.0m, 3.0m and 4.0m from the surface in one tank
filled with water up to 5.0m depth, and obtains DO data for each
water level at the same time. Then based on this data, OTRs for
each depth are calculated. See the fig-2 on the right.
This testing method is scientifically incorrect. Regardless of the
drop point of the DO meter, it is impossible to accurately obtain
OTR at lower than 5.0m water depth.
Due to the impossibly high OTR obtained by this incorrect
method, the company have been advertising their air diffuser as
a ”highly efficient air diffuser”.
2) Position and direction of DO meter’s electrode tip
When measuring the OTR, it is necessary to remove all DO from water (e.g. tap water) in the tank to zero by adding sodium
sulfite firstly, and then discharge air from the air diffuser and measure the increase in DO value using a DO meter. How to use the
DO meter is important. See the following points.
(1) When the bubbles discharged from an air diffuser directly touch the DO meter’s electrode tip, the correct DO value can
not be measured accurately because it measures undissolved oxygen (oxygen gas in the bubbles) as if it is DO. This is
especially relevant in the fig-2 case above where the electrode tip is set above the air diffuser as shown. To prevent this,
it is necessary to set the electrode tip in a position where the rising bubbles do not hit it directly.
(2) When you set the DO meter in water normally,
the electrode tip will face downwards. To avoid
this, bend the cable and fix the electrode with
the cable using vinyl tape, then the electrode
tip will face upwards as shown in the picture
on the right.
This improvised method prevents air bubbles
discharged from air diffusers directly hitting
the electrode tip and measuring undissolved
oxygen (oxygen gas in the bubbles) as if it is
DO. When the electrode is facing upwards,
discharged bubbles from the air diffusers do
not attach directly to the electrode tip. Only
following this improvised method can the DO
be accurately measured.
*This method is very important, but in most
cases it is measured with the electrode tip
facing downwards. This means there are many cases where DO is not measured correctly and undissolved oxygen is measured
as if it is DO.
3) Water temperature
Due to the law of nature, the saturation value of DO depends greatly on the water temperature. When aerated with an air diffuser,
the water temperature increases due to the hot air discharged by the air blower, so both the water temperature and the DO value
at the time of the OTR test must be recorded and that data should be included in the test report. This is a questionable OTR test
report that has no water temperature data at all, so be careful.
You need to check the OTR test report.
You have to check the OTR test report of the air diffuser before purchasing it whether the advertised OTR is obtained based on
correct scientific methods. (*Particular attention is required for air diffusers advertised with a much higher OTR than the other air
There is a manufacturer that advertises false OTR in their brochure even though they did not obtain OTR data at all.
OHR will clearly show the OTR test report.
OHR obtained OTR data of OHR AERATOR by a scientifically proven method.
In addition, there is an OHR AERATOR OTR evaluation report conducted by another company. Please request these reports from us.