Information of slow sand and alternative biological filtration in Japan

(1)Information of slow sand filtration in Japan

The History of Slow Sand Filtration in Japan

In 1887 the first modern water supply facility in Japan was set up in Yokohama, and a water purification plant by slow sand filtration, whose design population served was 70000, was made in Nogeyama.
Here is an outline after that time.

Introduction of slow sand filter facilities in Japan

Water purification plants by slow sand filtration are now working all over the country.
Even though the number and the scale are getting smaller, the number of Water supply system (population supplied is over 5000) is 541 and the number of Private water supply facilities (population supplied is less than 5001) is around 2000. (Data as of 2003)

Water purification mechanism of slow sand filter

Slow sand filtration is a way of purifying water by microbial action. On the sand layer of slow sand filter, biofilm, which has a thickness of a few millimeters, is made by algae and microorganism.
When water goes through the layer, turbidity is removed by the sticky biofilm and dissolved organic substances are used to metabolize of microorganisms, such as bacteria, fungi and protozoans. Water made through well-controlled slow sand filter is really good quality, which means 90 to 99% of bacteria is removed.

History of waterworks in Nagoya

Some facilities, such as Nabeyaueno Water Purification Plant, in Nagoya were established in 1914, and after that they have been working for supplying people with safe and pleasant tasting water for over 100 years. Here is the history of waterworks in Nagoya.

Slow Sand Filtration as an effective way for International Contribution

Slow sand filtrations need less energy and no chemicals, so they are relatively low in cost and easy to be controlled. That is why this technology is suitable for environmental conditions in developing countries. International contribution projects with the technology of slow sand filtration are in progress.

(2)Information of alternative biological filtration in Japan

Below is biological filtration in Japan without slow sand filtration.

1.Biological activated carbon

Biological activated carbon is an activated carbon which has bacteria that purifies water. It purifies water by 2 actions, adsorption by activated carbon and disassimilation by bacteria. Activated carbon has small countless holes and the surface area is large, so it can absorb organic substances which cause unpleasant smell. Bacteria on an activated carbon disassimilate ammonia and organic carbons. The organic carbons, which were changed by ozone-treatment, can be easily used by bacteria.

Mechanism of advanced water treatment

Advanced water treatment means water purification uses ozone and biological activated carbon. Organic substances are chemically disassimilated by ozone, and the changed substances are able to be used by bacteria easily. Bacteria on an activated carbon biologically disassimilate the changed substances. This way of treatment is the same as natural purification, and makes safe and pleasant tasting water.

2.Contact oxidation process

During the 70’s, water quality was getting worse. That is why some kinds of equipment were developed to improve the quality of raw water. One is the honeycombed equipment which has an air lift. This was developed under the idea “fold the river and pack it into a tank.” There are also Rotating Disk Biological Contactor Process, which is a rotating disk organisms attach to, and biological contact filtration process, which uses functions of slow sand filtration more effectively, such as the filtration and disassimilation by bacteria.
Biological slime process, such as Rotating Disk Biological Contactor Process and Contact Oxidation Process was developed for treatment of sewage and wastewater in Europe. In Japan, it had been researched for purifying drinking water in the 60’s, and was put to practical use in the 70’s.