OSAKA -- "Natto," the infamous fermented soybean dish with its characteristic pungent smell and stickiness, may not exactly be the food of choice for many people. But an Osaka firm, in cooperation with Osaka City University, has begun an experiment to use polyglutamates -- the main component of the natto bacillus that turns soybeans to natto -- to help clean up the water in Osaka Castle's inner moat.

It is well known among researchers that high molecule polyglutamates that have been exposed to gamma rays absorb 1,000 times their mass in water, according to Dr. Tsutomu Okada, a researcher at Biseibutsukagakukenkyusho (microorganism science laboratory) Co., which started work on purifying the water in Osaka Castle Park last week.

"I have tried to utilize this substance in meaningful ways and found out that when put in dirty water, the substance somehow congeals mud and other dirt and pollutants, turning them into a gel," said the 61-year-old Okada, who is also a visiting professor at Osaka City University.

Why this happens is still unclear, but Okada said this new type of coagulating agent has three distinctive features when compared to conventional ones.

"The agent itself is harmless to humans. It congeals dirt in water at normal temperature, so it is not necessary to heat or cool the liquid," he said. "And after it takes in the dirt, the gel can be dissolved by microorganisms into water and carbonic acid gas.

"Thus, the whole system is environmentally friendly, which should be a great advantage as consumers' environmental awareness is high," he said, adding that the agent potentially has a wide range of uses other than just cleaning up castle moats.

The water-purifying device, set up last week, pumps 40 tons of water at a time from the inner moat into a water tank. Between 20 grams and 40 grams of coagulant is then poured into the tank and the dirt is sucked into the polyglutamate gel, which in turn sinks to the bottom within 30 minutes to 60 minutes.

The sediment is pumped to a different tank where the deposit is broken down in a few days by microorganisms.

The supernatant water is then pumped into another tank where it will sit for another three to four hours to allow more dirt to settle to the bottom.

The water is filtered three times a day and the clean-up work is scheduled to last for six months on a trial basis, processing about 21,000 tons of water in that time.

Because that is less than 10 percent of the estimated 240,000 tons of water in the moat, Okada predicts there will not be a dramatic change in the water's appearance.

Still, the visibility in the water would be improved from the current level of 60 cm to a maximum of 150 cm, he said.

According to park officials, the deterioration in the quality of the moat's water has been stemmed somewhat since 1995, when the city began allowing water from outside to be funneled into the moat when circumstances required.

The moat can also become dirty and smelly depending on factors such as temperature and sunlight, although the main causes of impurities in the water are duckweed and fish corpses, they said.

Okada said he is confident of the effectiveness of the purification device, as he and the laboratory successfully conducted a similar clean-up of the moat surrounding Kishiwada Castle in the city of Kishiwada, Osaka Prefecture, in November using a device about one-fifth the size of the one currently in operation at Osaka Castle.

One of the more difficult aspects of this purification method is manufacturing polyglutamates at a low cost. Although natto bacilli are found naturally in the environment, those used to make natto are of high quality and very expensive.

Okada's lab is able to produce polyglutamates cost-effectively, but he refused to divulge what made this possible -- saying it was a secret.

"The significance of this attempt is that we can apply biotechnology developed at the university to our everyday lives. This agent can be used in many other ways in the future, such as a material for diapers," he said.