Microbially Induced Calcite Precipitation (MICP) is a technology to improve soil cohesion by calcite precipitation through bacterial urea hydrolysis. When the technology is to be used for the stabilization of heavy metals-contaminated soil, the effect of soil heavy metals on the bacterial urease activity needs to be clarified. In this study, the inhibitory effect of soil Cu on MICP was assessed with focus on the role of calcium ion which is an essential element for calcite precipitation. MICP-inducing solution consisting of OD 1.0 of Sporosarcina pasteurii culture, 450 mM urea, 4 g/L TSB, and 450 mM CaCl2 was introduced to two types soils (i.e., sand with 0% soil organic carbon and sandy loam with 2.6% soil organic carbon) spiked with various concentrations of Cu (i.e., 25, 50, 75, 100, 175, 250, 500 and 1000 mg/kg of Cu). Calcium carbonate precipitation by MICP decreased as Cu spiking concentration increased in both soils. The amount of calcium carbonate precipitated was determined by the amount of urea hydrolyzed, so the inhibition of MICP was critically affected by the inhibition of urea hydrolysis by Cu. The effect of calcium on the Cu concentration in soil solution was assessed. Cu concentration in soil solution increased by 18% (i.e., 10.1 to 12.0 mg/L) and 177% (i.e., 7.6 to 21.0 mg/L) in sand and sandy loam, respectively as the calcium concentration in MICP-inducing solution increased from 0 to 450 mM. Accordingly, the amount of ammonia produced decreased from 230.6±11.4 to 139.0±5.8 mM in sand and from 435.1±118.1 to 23.9±0.3 mM in sandy loam. However, Cu extracted by calcium was determined by exchangeable form Cu, and it was composed of 100 and 77.7% from exchangeable form Cu in sand and sandy loam, respectively. In additional test for the sand without exchangeable form of Cu, Cu concentration in soil solution was not increased nevertheless the calcium concentration increased. Conclusively, MICP was inhibited by soil solution Cu accelerated by calcium, but the effect was determined by exchangeable Cu.

Inhibition of microbially induced calcite precipitation by soil solution Cu determined by calcium

2019 Fall National Meeting

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