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Home > Outline of Japan's Industrial Pollution Abatement > Preventative Measures Against Water Pollution Jinzu River, Toyama Prefecture > 2) Countermeasures against pollution from waste water

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Update:April 1, 2010

2) Countermeasures against pollution from waste water


Waste Water was roughly divided into 4 types: abandoned well water, benefication process water, sedimentation basin water and refining process water.
Countermeasures taken against each of these were as follows.

  • (1)Abandoned well water
    In the mining process, some 10,000 cubic meters of well water gushes out of the ground per day. The mining floor and wall rock of the Kamioka Mines is laden with limestone which gives well water a weak basicity somewhere around pH 8. Therefore, a 1 ppb level of heavy metal dissolved in fresh water should not create any problems of cadmium contamination. Consequently, well water was divided into fresh water and brackish water, with approximately 8,000 cubic meters of fresh water being used as cooling water and process water per day. The roughly 2,000 cubic meters per day of brackish water was run through. a thickener and solids were separated out, bringing cadmium concentration to 1ppb.
  • (2)Benefication process water
    The benefication process requires about 10,000 cubic meters of water per day. About half of the water is contained in waste products and is sent to sedimentation basins, while the other half is recycled in a closed system.
    As a result, not onTy1 has cadmium discharge been prevented, but economical benefits have also be achieved such as increasing benefication recovery and minimizing the volume of required chemical reagents.
  • (3)Sedimentation basin water
    Every day, abut 5,000 cubic meters of water contained in benefication waste, 5,000 cubic meters of waste conveyance water, 10,000 cubic meters or rain water collected around the sedimentation basin and 20,000 cubic meters of contaminated retention water, from into the sedimentation basin. After treating the some 40,000 cubic meters or waste per day, 20,000 cubic meters are used as industrial water and the remaining 20,000 cubic meters are discharged into the river system.
    Sedimentation is done using a cyclone to separate particles in benefication waste that are 75Um and larger in size from those that are smaller. The larger particles are deposited on a dam-like embankment whereas the smaller particles are deposited in the center of the pond. The pond functions as a sedimentation basin for solid-liquid separation (A large volume or particles is contained in the water), The particle embankment functions as a earthen dam. The pond is treated with limemilk to keep pH to that of a weak base. The supernatant, rain water inside the site and permeated water inside the site is collected by an underdrain and discharged. Cadmium concentration is between 1 and 2 ppb (Fig.4-l).
  • (4)Refining process water
    The refining process uses approximately 10,000 cubic meters of industrial water and 30,000 cubic meters of cooling water per day. Like benefication process water, process water contains a high concentration of heavy metals, therefore water is recycled, neutralized and subjected to rapid filtration.
    Owing to these countermeasures, the 8 ppb concentration of cadmium found in waste water and the 35 kg per day discharge volume of 1972, were reduced to one seventh by 1992, at 1.4 ppb and 5 kg per day respectively. These results show the efforts of taking countermeasures against waste water and brought down the concentration of cadmium in the water to roughly that of natural water (Fig.4-2).