Bio-geochemical reactive transport modeling of microbial induced calcite precipitation to predict the treatment of sand in one-dimensional flow B.C. Martinez b , J.T. DeJong a,⇑ , T.R. Ginn a a Department of Civil and Environmental Engineering, University of California, Davis, United States b Geosyntec Consultants Incorporated, Oakland, CA, United States article info Article history: Received 9 July 2013 Received in revised form 16 November 2013 Accepted 26 January 2014 Available online 28 February 2014 Keywords: Bio-mediated soil improvement Microbially induced calcite precipitation Soil improvement abstract Microbial induced calcite precipitation (MICP) has been well studied to date in the laboratory as a viable alternative soil improvement technique that harnesses a natural bacterial process to induce cementation. Specifically, MICP utilizes the microbial process of hydrolysis of urea to induce pH increase leading to cal- cite precipitation. The study presented herein demonstrates the utility of a simple bio-geochemical reac- tive transport model to predict MICP in one-dimensional column experiments. The mathematical model was originally developed in the framework of the TOUGHREACT code to include kinetically controlled reaction rates for urea hydrolysis and calcite precipitation. Inverse modeling, via UCODE-2005, is utilized to calibrate and verify the model to experimental data including aqueous and mineral chemistry. Results indicate good agreement between data and simulated results for capturing the trends and magnitudes of a variety of MICP treatment schemes in half meter, one-dimensional flow columns. A design procedure is presented for predicting MICP in one-dimensional flow by sequentially coupling UCODE-2005 with TOUGHREACT. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Until recently, research on microbial induced calcite precipita- tion (MICP) for geotechnical application has focused on character- izing strength, monitoring cementation, and optimizing treatment at small and large scales in laboratory and field experiments. MICP is a cementation process that harnesses natural subsurface bacteria using urea hydrolysis (ureolysis) to induce calcite precipitation at particle–particle contacts in soil environments [6,36,23]. MICP has been extensively evaluated for geotechnical ground improve- ment including increasing undrained shear strength [6,8], non- destructive geophysical monitoring [40,1], and solidification at laboratory and field scales [7,19,37,41,42]. MICP has also been identified as an engineering solution for a wide-range of disciplines including mineral plugging [11], environmental remediation of heavy metals [13], structural concrete repair [33,32,39], and carbon sequestration [35]. However, research to understand how MICP can be conceptually and quantitatively modeled is in its earliest stages. Available mathematical modeling studies have addressed par- ticular aspects of MICP including mechanical, hydro-geological, biological, and chemical processes. Many of the earliest studies fo- cus particular attention to capturing the appropriate kinetic rates of ureolysis induced by single species and native microbes [12,18,24,25,26,15,13,14] as well as cell-free enzymes [16], and calcite precipitation [28]. Later studies evaluated the development of multi-component reactive transport by coupling similar ureoly- sis rate expressions to calcite precipitation kinetics and fluid trans- port in one- and two-dimensions [10,38,4,20,2]. A few studies have also examined the effects of reactive transport to mechanical changes in soil studies through finite element analysis [46]. Most of the models have been able to capture reaction rates for a variety of biological and chemical conditions within small-scale batch experiments via kinetic expressions accounting for chemical variants. There are needs to improve the quantitative modeling of MICP toward the coupling of constitutive theory from every involved discipline, and to improve the individual components for macro-scale reactive transport in porous media. The study presented herein, builds from Barkouki et al. [2], implementing MICP into a bio-geo-chemical reactive transport code (TOUGHREACT; [43]) and calibrating unknown parameters (UCODE-2005; [31]) to verify the model and develop a procedure http://dx.doi.org/10.1016/j.compgeo.2014.01.013 0266-352X/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +1 530 754 8995. E-mail address: jdejong@ucdavis.edu (J.T. DeJong). Computers and Geotechnics 58 (2014) 1–13 Contents lists available at ScienceDirect Computers and Geotechnics journal homepage: www.elsevier.com/locate/compgeo