In the previous report, the improved sludge produced by slurry shield tunneling using the neutral inorganic material composed Liquid-A, Liquid-B and Powder (referred to as“3-kinds-type improved material”), could satisfy the conditions for the provision of the individual governmental system, and the technique of the quality control of the improved sludge production was described. This report is described on the environmental influence assessment of the improved sludge and the improved neutral inorganic material (referred to as“2-kinds-type improved material”) . The environmental influence assessment of the improved sludge was carried out by the water quality test and the fish toxicity test using the improved sludge-dissolved water and the plant growth inhibition test using the improved sludge. The results are summarized as follows.
(1) As for the concentration of the ingredients of the improved sludge-dissolved water of the improved sludge using the 3-kinds-type, if the concentration is 10 times diluted by the rainfall is acceptable, pH, EC, Na
+, Al
3+, SiO
2and K
+are lower, but Ca
2+, SO
42-, and PO
43-are higher than the concentration of the river water.
(2) As for the fish toxicity of the improved sludge, in the acute toxicity test using the undiluted dissolved water, the local gill disorder is observed locally when much addition quantity of material is used. However in the subacute toxicity test using 10 times diluted dissolved water, a abnormality isn't observed.
(3) The plant growth inhibition of the improved sludge is exhibited when a large quantity of material is added. However it is seen that there is hardly any difference in the inhibition between the improved sludge and the control (field's soil) when the improved sludge is added in a low quantity.
In condition of these results, the 2-kinds-type improved material was developed and the water quality test of the dissolved water of the improved sludge using this material was carried out. As a result, in case of 10 times diluted, although only PO
43+is slightly higher than the concentration of the river water, the quantity of the improved material required is smaller than that of the 3-kinds-type improved material. Therefore, it is considerd that the influences of the 2-kinds-type improved material to the environment to be remarkably improved as compared to that with 3-kind-type improved material.
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