Purification of selenium-containing leachate in wastewater tanks at a tunnel construction site

The leachate containing heavy metals which generated from excavated soil and rock in the civil engineering works appropriate measures are required. We conducted indoor and outdoor experiments to purify heavy metal-containing leachate using a water tank, and proposed a method for treating heavy metals using the purification function of plants at civil engineering works. The plant used was Eleocharis acicularis, which belongs to the Cyperaceae family. The results of the indoor tank experiment on selenium indicated a decrease in the selenium concentration in the leachate from 0.093 to 0.008 mg/L in 14 days. The selenium content per kg of Eleocharis acicularis based on dry weight increased from 0.010 to 0.205 mg, indicating that the plant absorbed selenium. The outdoor tank experiment revealed that the selenium concentration in the leachate decreased from 0.090 to 0.007 mg/L in 21 weeks, and the daily absorption of selenium was 0.0005 mg/L. The lead concentration decreased from 0.004 to 0.001 mg/L in one week, and the arsenic concentration decreased from 0.003 to less than 0.001 mg/L in three weeks. Calculation of the leachate purification cost using Eleocharis acicularis under the current outdoor experiment conditions resulted in a 56% treatment cost reduction compared with the regular treatment cost.

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