Evaluating Strategies to Improve Process Efficiency of Denitrification-Based MICP

Abstract

Microbially induced carbonate precipitation (MICP) through denitrification can potentially be applied as a bio-based ground improvement technique. Two strategies involving multiple batch treatments in a modified triaxial test setup were used to study the process efficiency. Both strategies aim to achieve 1 weight percentage (% by weight) of precipitated calcium carbonate (CaCO 3 ) and differ in number of flushes, hydraulic residence time, and substrate concentrations. In the experiment with few flushes and high substrate concentrations the microbial process was inhibited, only 0.28% by weight CaCO 3 was measured in the sand after 5 weeks of treatment. The regime with many flushes and low substrate concentrations stimulated microbial growth resulting in 0.65% by weight CaCO 3 within the same time period. Biomass growth and nitrogen gas production were stable throughout the experiment at low concentration, reducing the hydraulic conductivity of the sand, which eventually led to clogging. Precipitation rates up to 0.26% by weight/day CaCO 3 were observed. Applying a suitable substrate regime and residence time is important to limit inhibition and maintain the cell activity, allow for an efficient conversion, and generate a good precipitation rate.

Microbial-Induced Desaturation in Stratified Soil Conditions

“…Bench-scale tests have been performed to demonstrate the effect of MID on the cyclic shear resistance and its potential to mitigate liquefaction [18][19][20][21]. However, these were all column tests on poorly graded sands and the flow was vertical either downward [12] or upward [2,7,22]. Several of these studies found that when applying multiple flushes aiming for sufficient calcium carbonate precipitation, the hydraulic conductivity significantly reduced, eventually leading to clogging and interrupted fluid flow [1,7,22,23].…”

Applications of Microbial Processes in Geotechnical Engineering

“…Although by-products of the denitrification reaction are not toxic, they do affect the hydro-mechanical behavior of soils and may affect the crystallization process. For example, during the experiments reported by Pham et al (2018), hydraulic conductivity reduced significantly, which was mainly attributed to the combined formation and entrapment of nitrogen gas and biomass.…”

“…O'Donnell et al 2017reported that CaCO 3 precipitation of 1 to 2% (by mass) was sufficient to increase cyclic shear strength in cyclic direct simple shear tests by 40% on both natural and laboratory standard sands. Pham et al (2018) found that treatment resulting in a CaCO 3 content of 0.65% more-than-doubled the small strain stiffness under static compressive loading conditions. Through shear wave velocity measurements O'Donnell (2016) observed that sands treated by denitrification showed a greater improvement in the shear stiffness of the soil when compared to ureolysis-treated specimens at the same carbonate content.…”

The diversity of molecular mechanisms of carbonate biomineralization by bacteria

“…Nitrate reduction and ammonification of amino-acids are prone to induce the precipitation of CaCO 3 [121,122]. Some of these processes are dissimilatory, i.e.…”

“…Nitrate reduction has been studied as a driver of bacterially-induced carbonate precipitation in several geotechnical applications [121] but also in environmental microbial mats where calcification occurs [129]. Although it seems to have a lower efficiency than ureolysis for carbonatogenesis [122], nitrate reduction has been proposed as an alternative pathway for applications where the production of ammonium would be unwanted and/or where wastewater with elevated nitrates concentrations are available [130]. Nitrate reduction may even supplement ureolysis in some cases, and improve CaCO 3 precipitation efficiency [130].…”