Are "water quality" and "smell" improved? Sand at Kozushima February 13 20:05

Smooth, clean white sand.
It was brought to Odaiba, Tokyo from Kozushima in the Izu Islands.
This sand has begun to purify the sea water, which is the venue for the Tokyo Olympic and Paralympic Games.
How is that effect?
(Yuki Uchiyama, Social Affairs Reporter)

Sand injection into the sea of ​​Odaiba

The sea of ​​Tokyo Odaiba looking into Rainbow Bridge in front of you.
The venue for the Tokyo Olympics and Paralympics triathlon.

Here, the work to cover the seabed with sand from Kozushima began on February 8. A large amount of sand carried by boat from the island was thrown into the sea one after another by shovel cars.

What is the water quality problem in Odaiba?

The trigger for this measure was the test tournament held last August.
During the water test, Escherichia coli exceeding twice the standard value set by the international sports organization was detected from the venue.
Players also pointed out the turbidity and smell of water, and the "swimming" swimming in the sea at the venue was suspended.

When I dive ...

This video was taken by an NHK news crew last month while diving into the local sea.

The sea was muddy, and in some places, it became invisible for several tens of centimeters.

When you reach the bottom of the sea, you see something like dark mud.
Several dead shellfish were found.

E. coli exceeding the standard

In a water quality survey conducted around the venue in 2017 by Tokyo Metropolitan Government, up to 21 times the number of coliform bacteria and up to 7 times the number of fecal coliform bacteria detected by international sports organizations were detected.
In particular, it is said that the risk of occurrence increases in summer when the water temperature is high and there are many sudden heavy rains.

Why E. coli?

Why was E. coli detected in the first place?
According to the capital, the sewage treatment system in Tokyo is partly responsible.
The mechanism is a "merging system" that collects domestic wastewater and factory wastewater using the same sewer pipe as "rainwater".

As shown in this figure, when heavy rain falls and the sewer pipe exceeds its capacity, untreated sewage is discharged to the sea together with rainwater.

Approximately 80% of the 23 wards of Tokyo have this "joining type".
When it rains, sewage from this area flows into Tokyo Bay, where Odaiba is located.

The Tokyo Metropolitan Government has implemented various measures to improve the water quality and remove odors, in addition to improving the sewage storage facilities, etc., for the Games.
One is to set up "triple screens" to prevent the inflow of sewage, and the other is to cover the sea floor with "sand on Kozushima".

Measure 1: Screen

The first is a screen measure.
In the summer of Tokyo, the city and the Organizing Committee conducted an experiment to screen some areas of the venue with screens to prevent inflow of sewage.

As a result, in the 27 days of the experiment, E. coli exceeded the water quality standard for 12 days in the area without a screen, while the inside of a single screen was 2 days. The inside of the triple screen was below standard all day.

Based on these results, we set up a single screen at the test tournament last August.
However, since E. coli has exceeded the standard value, it means that the production will be done with three screens.

Measure 2: Sand on Kozushima

In addition, in anticipation of water purification, we decided to cover the seabed with sand from Kozushima.

When asked to the Tokyo Metropolitan Government Port and Harbor Bureau, "Why is sand on Kozushima?", It is expected that shellfish will settle in the sandy area, thereby ingesting nutrients from the sea and purifying water. .
In addition, the sand of Kozushima was originally used for the artificial sand beach of Odaiba, and there was also know-how in transportation.

The budget for inputting this sand is 60 million yen. The amount of sand is equivalent to 1980 cups on a 10-ton truck.

Ask the person in charge in Tokyo and experts-What are the effects of the measures?

Will these two measures improve the water quality of the competition venue?
We spoke with a person in charge of the Tokyo Metropolitan Olympic and Paralympic Games Prep Bureau and an expert on water quality.

Koichi Yajima, Chief of the Competition and Public Affairs Section “The management side welcomes sand covering and expects a purification function, but even if it is sanded, it cannot shut out sewage completely. We believe that this is not a measure that has a direct effect on the reduction of Escherichia coli, which is a challenge in the operation of the Games, but a measure that can be expected from a long-term perspective. By making it "triple," I want to clear the issues. "

Specialist in coastal environmental science Yukio Koibuchi, Associate Professor at the University of Tokyo "These measures cannot prevent the inflow of pollutants from treatment facilities, and it is impossible to determine whether sand is actually purified without measuring its effectiveness. Regarding screens, Tokyo Bay has a large tidal range of 2 meters, making it difficult to completely prevent sewage from entering through the screens. Need to be verified. ''

When you go to the site, the surroundings of the venue are certainly wonderful views overlooking the rainbow bridge and skyscrapers lining the city center.

However, if the important water quality remains as it is, it cannot be said that it is very athlete first.
In the remaining period until the tournament, I hope that you will continue to make the best efforts to create a competitive environment.

Social Affairs Reporter Yuki Uchiyama