懸濁液型水ガラス系注入剤を含むトンネル工事排水の石灰と硫酸アルミニウムの同時添加法による処理

概要

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A lime-alum treatment method for wastewater discharged from tunnel costruction works which contains water glass (soluble silicate) and portland cement for chemical grouting was designed. The wastewater was treated with calcium hydroxide and aluminum sulfate simultaneously. The operational characteristics of model suspensions containing water glass, portland cement and kaolin were examined by the jar test. The results are summarized as follows :(1) Turbidity was not removed to less than several turbidity units by lime treatment alone when the S. SiO2 concentration of wastewater was under 145 mg·l-1.(2) In the case of the lime-alum treatment, regardless of the S. SiO2 concentration of wastewater, turbidity was removed completely by adjusting the pH to more than 10.7 with lime and alum dosages depending on the effluent turbidity.(3) The lime and alum requirements for treatment of the model suspensions (S. SiO2 43.5-290mg·l-1, kaolin 1,000mg·l-1 and portland cement 100-5000mg·l-1) were 60-100mg·l-1 and 0-40mg·l-1, respectively.(4) The sediment volume of 60min. sedimentation (SV60), which increased with S. SiO2, concentration of wastewater, was 0.5-5.0% throughout all of the experiments.(5) The contact time required was 5-10min.(6) S. SiO2 was only slightly removed.From these results, the lime-alum treatment method was considered to be useful for the wastewater discharged from a tunnel construction site using chemical grouting.