Is the filtering tank working well to clean the waste water?

Through the laboratory test, it is confirmed the tank is surely reduce the pollution.

At the site, we checked the value of COD, Chemical Oxygen Demand. The values of both, before and after the filtering, were the same around 120 mg per little. A bit strange result.

So Jun brought back the sample water to Japan and asked the laboratory test.

Sample A before the filtering.
Sample B after the filtering.

The result was the value of COD reduced from 200 to 130 mg/l. BOD, Biological Oxygen Demand, was also reduced from 370 to 200. (Correction: I am sorry that I was saying the values were reduced more than half. It was wrong.)

Somehow the value of surfactant which is harmful specially within some weeks after discharging into the nature, was increased from 54 to 290 mg/l. It was considered as the result of maintenance work of the tank. Oily layer at the top of sand filter might be catching surfactant and was released after the maintenance work, Prof. Nakano suggested.

In other words, surfactant was well trapped inside of the tank, not released into the ecosystem.

We may keep monitoring the water quality continuously. New test kit for COD was already sent to Yap from Japan. So let us see the result…