## 1 Introduction  
Unprecedented societal and environmental challenges such as those related to population growth, urbanization, poverty, climate change, and natural resource depletion have increased the need for creative and sustainable solutions for challenging civil and geotechnical infrastructure problems. Microbially induced calcium carbonate precipitation (MICP), or biocementation, is a biomedical technology that can improve the geotechnical engineering properties of soils by precipitating calcium carbonate (CaCO\({}_{3}\)) on soil particle surfaces and at particle-particle contacts. Biocomentation increases the shear strength and stiffness of soils with limited reductions in soil porosity and permeability [1; 2; 3; 4]. MICP has been proposed for many different geotechnical and geoinvironmental applications, including soil improvement, the mitigation of soil liquefaction during earthquakes, erosion and scour prevention, rock fracture sealing, and contaminant immobilization, among other use cases [4; 5; 6; 7; 8; 9]. MICP is facilitated by microorganisms that contain urease enzymes, which catalyze a hydrolysis reaction in the presence of urea, resulting in the generation of ammonia (NH\({}_{3}\)) and carbonic acid (H\({}_{2}\)CO\({}_{3}\)) (Equation (1)). Generated ammonia participates in an equilibrium reaction with water and can produce ammonium (NH\({}_{4}\)\({}^{+}\)) and hydroxide (OH\({}^{-}\)) in accordance with the surrounding solution pH (Equation (2)). The resulting hydroxide production encourages generated carbonic acid to deprotonate to become bicarbonate (HCO\({}_{3}\)\({}^{-}\)) and carbonate (CO\({}_{3}\)\({}^{2-}\)) species (Equation (3)). The addition of calcium (Ca\({}^{2+}\)) ions can then supersaturate aqueous solutions with respect to calcium carbonate minerals and initiate precipitation (Equation (4)). \[(\rm NH_{2})_{2}CO+2H_{2}O\ \rightarrow\ 2\,NH_{3}+H_{2}CO_{3} \tag{1}\]  
\[\rm NH_{3}+H_{2}O\ \rightleftharpoons NH_{4}^{+}+OH^{-} \tag{2}\]  
\[\rm H_{2}CO_{3}\ \rightleftharpoons\ HCO_{3}^{-}+H^{+}\rightleftharpoons CO_{3}^{-2}+2H^{+} \tag{3}\]  
\[\rm Ca^{+2}+CO_{3}^{-2}\ \rightleftharpoons CaCO_{3(solid)} \tag{4}\]  
Establishing ureolytic activity in soils for MICP can occur either by augmentation of non-native bacteria or by the enrichment (i.e., stimulation) of native ureolytic microorganisms. Both approaches increase the soil's capacity to hydrolyze urea for the MICP process by increasing ureolytic cell densities and/or ureolytic microbial activity. To date, augmentation has been primarily used to generate ureolytic activity [4; 10; 11; 12]. However, researchers have recently shown that stimulation is effective in a diverse range of environments [13; 14; 15; 16; 17; 18] and can improve the spatial extent and uniformity of MICP by stimulating in situ ureolytic communities already present in the soil pore space, thereby eliminating issues related to cell injections and filtration in porous media [19]. Stimulation may also offer significant advantages over augmentation through the elimination of costs and environmental impacts associated with ex situ bacterial cultivation and the introduction of non-native bacterial species. For both stimulation and augmentation treatment approaches, the fate of produced NH\({}_{4}\)\({}^{+}\) byproducts remains a key environmental consideration for the deployment of MICP at field sites. If left untreated, generated NH\({}_{4}\)\({}^{+}\) concentrations may cause adverse environmental and human health impacts, thereby compromising other environmental benefits of the process. For example, when present in surface water, high NH\({}_{4}\)\({}^{+}\) concentrations can promote bacterial and algal bloom growth, thereby decreasing dissolved oxygen concentrations and producing toxins that can endanger aquatic life and other flora and fauna [20].