OFUNATO, Iwate Prefecture--Scientists are coming to the assistance of a coastal city ravaged by tsunami, with two experimental projects aimed at cleaning contaminated seawater so that farming of oysters and marine produce can be restored.
OFUNATO, Iwate Prefecture--Scientists are coming to the assistance of a coastal city ravaged by tsunami, with two experimental projects aimed at cleaning contaminated seawater so that farming of oysters and marine produce can be restored.
The projects are trying to decontaminate seawater using cedar tree bark and "micro bubbles."
The waters off Ofunato have been polluted by the massive leakage of heavy oil from a large number of fishing boats and their fuel tanks after tsunami spawned by the March 11 Great East Japan Earthquake struck northeastern Japan.
Debris washed into the sea was soaked with the oil, which is deadly to sea life, and poses a great challenge in the recovery work.
Local officials complained that repeatedly scooping oil from the surface of the water did not remove the toxic substance.
In response, the Oita Industrial Research Institute in Oita Prefecture came to their assistance using common cedar bark as an absorbant.
The institute has been developing oil absorption mats made of cedar tree bark for more than 10 years. Cedar contains lignin, a high molecular weight polymer, which repels water and absorbs oil.
Institute researchers have also devised a method to dissolve oil with the use of farmland manure created by fermented bark.
With dung mixed in, the bark manure emits heat and increases the growth of microorganisms that absorb oil.
When an oil-soaked mat is placed in the bark manure, oil will be eliminated in about 200 days.
In fact, a heavy oil-slicked cedar bark mat was dissolved to the point that its shape was no longer recognizable after it was placed in bark manure at a factory in Ofunato in September.
Another project under way is aimed at facilitating the growth of oysters through so-called “micro bubbles,” which purifies the water.
The method was developed by Hirofumi Onari, instructor of civil engineering at the Tokuyama College of Technology in Yamaguchi Prefecture.
A device placed underwater about eight meters below the surface produces a white veil of air bubbles--each bubble 0.02 millimeters in diameter--spewing oxygen and nitrogen that help purify the water.
In August, 104 micro-bubble devices were placed under water near farming rafts owned by Kenshi Shida, 59, and other farmers.
The devices together produce 104 liters of fine bubbles per minute.
“Oysters and scallops grow faster as a result of accelerated metabolism with purified water,” Onari said. “That will shorten the period for farming and bolster the output.”