A sequential operation of lime treatment, carbonation and coagulation of wastewater from tunnel construction works including water glass and portland cement for grouting was designed. Through jar tests of model suspensions containing water glass, portland cement and kaolin, the operational characteristics were examined. Treated effluent was evaluated by S.SiO₂, turbidity, Ca²⁺ and electric conductivity, and accute toxicity to rainbow trouts (Salmo gairdneri).
The results are summarized as follows : (1) The contact time requiered was about 60 min to remove S.SiO₂ from some hundreds mg·l^-1 to under 30 mg·l^-1 with approximately equimoller dosing of lime slurry to water glass solution. With the increase of lime dosage, the required contact time become shorter. (2) Regardless of the S.SiO₂ concentration of the wastewater, S.SiO₂ and turbidity were removed to less than 30 mg·l^-1 and less than several turbidity unit, respectively, only adjusting pH more than 11.9 (ca. 25°C). (3) Sufficient precipitation of CaCO₃ was observed from the wastewater at pH9.5 10.5. The optimum pH of the precipitated CaCO₃ by alum was about pH = 8.5. (4) It was difficult to decrease electric conductivity less than 0.3μS·cm^-1 (25°C) by this treatment method. (5) Accute toxicity to rainbow trouts were not observed in the effluent treated by the lime treatment.

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The nutritional requirements of Skeletonema costatum, a red tide phytoplankter, and effects of the preparation of inoculum on algal growth potential (AGP) assay using this alga as a test organism were studied. In addition, the AGP of Osaka Bay waters was measured and the growth limiting nutrients were determined.
The nutrient concentrations necessary for the maximum growth of S. costatum were 1.6 mg·l^-1 of nitrogen, 0.5 mg·l^-1 of phosphorus, 5 10 mg·l^-1 of silicon, and 5 10 ng·l^-1 of vitamin B₁₂. The AGP was found to be dependent on the preparation of the algal inoculum. The accurate AGP was obtained only when sufficient nutrient-starved algal cells were inoculated into the samples, but insufficient starvation of cells gave an overestimation. The satisfactory inoculum was obtained from twice starvation with vitamin B₁₂-free medium but contained 1/100 of the other nutrients as much as the concentration necessary for maximum growth. Based from the results of the assay methods, the AGPs of Osaka Bay waters were about 10⁵ cells·ml^-1, and the growth limiting nutrients were determined to be nitrogen and phosphorus.

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Effect of biomass on the soil hydraulic conductivity was clarified for andosol soil. The approximate value of the maximum allowable density of biomass was determined as 30mg·cm^-3, which corresponds to the minimum hydraulic conductivity of the clogged andosol soil : 2 ×10^-5 cm·s^-1.
Two-dimensional infiltration experiments were carried out. Infiltration rate decreased as the synthetic sewage percolated into the soil, but finally it achieved the steady state. TOC removal and ATP distribution were measured, and on the basis of these results and the mass balance of the substrate, the mechanisms of the biological clogging was discussed.
In addition, a numerical model was constructed, and the biomass growth and the change of permeability were simulated. Calculated results were compared with the results of two dimensional infiltration flow experiments. By using the model, the conditions to avoid the infiltration failure were determined. The allowable wastewater feed rate of 0.04m³·m-trench^-1·d^-1 for the BOD concentration of 100mg·l^-1 was obtained, which is smaller than the expected value in the empirical criteria.

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[in Japanese]

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