Microbially induced CaCO3 precipitation (MICP) has been utilized for sand consolidation and fracture sealing and has the potential to expand to applications including groundwater remediation and stabilization of waste products. MICP is driven by the bacterially catalyzed hydrolysis of urea, which produces inorganic carbon and ammonium and increases pH to supersaturate and promote precipitation of CaCO3. In this work, MICP is investigated in laboratory-scale reactors for remediation applications. The studies provide better understanding and ability to predict the rates of and optimal conditions for MICP. The kinetics of ureolysis, oxygen consumption and CaCO3 precipitation were studied during MICP in saturated porous media column reactors, mimicking a groundwater environment. Laboratory-scale MICP experiments were performed in two-foot-long sand-packed columns, with sampling ports installed along the column length to characterize pore fluids over time and along the flow path. A pulsed injection strategy was used in all column experiments. Urea hydrolysis by the bacterium Sporosarcina pasteurii promoted MICP. Different sources of MICP substrates and schedules of substrate additions were evaluated in column experiments. The dynamics of oxygen consumption, ureolysis and calcium precipitation kinetics indicated a direct correlation between the biofilm driven and abiotic reactions. MICP is also being used in this research to drive co-precipitation of heavy metals in laboratory systems including porous media flow cells and gravel-filled laboratory columns. Both a ureolytic bacterium isolated from heavy metal contaminated sediments and the lab strain S. pasteurii have been used to promote MICP in mine influenced water and artificial groundwater. MICP is able to reduce concentrations of several dissolved metals, including strontium, zinc, copper and manganese. This research demonstrates that MICP can be promoted in contaminated water containing a mixture of potentially toxic heavy metals, though by-products of MICP, such as NH3, should be considered. Finally, MICP is being investigated in this work for stabilization of mining wastes such as mine tailings and waste ore. Strategies developed from the porous media column studies were used to promote MICP in the tailings, with the goal to prevent leaching of heavy metals into the aqueous phase. MICP is promoted on the tailings surface for permeability reduction, minimizing particle and heavy metal mobilization.

Microbially driven calcium carbonate precipitation: Kinetics and remediation applications

256th National Meeting (2018)

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