Abstract
Inorganic selenium is one of the naturally occurring heavy metals commonly contained in excavation waste rock from tunnel and road construction, and its content often exceeds the elution limit specified by the Soil Contamination Countermeasures Act of Japan. Insolubilization of the selenium contained in excavation waste rock has been an issue because selenium(Ⅵ) cannot be easily reduced to a water insoluble form.
In this study, the effect of selenium reduction by microorganisms present in excavation waste rock was investigated. In addition, lactic acid was added as a nutrient to promote the microbial metabolism, and its effect on selenium reduction was also evaluated. The results showed that the addition of lactic acid accelerated the selenium reduction and dramatically decreased the dissolved selenium concentration. The lactic acid concentration decreased in excavation waste rock where the dissolved selenium concentration decreased, demonstrating the consumption by microorganisms. It was shown that the microbial growth promoted by the added lactic acid may have contributed to efficient insolubilization of selenium contained in excavation waste rock through the combined effect of the selenium reduction in a coupled redox reaction and the selenium reduction associated with fermentative lactate degradation.
