# Integration of Organic Waste for Soil Stabilization through MICP
## 1 Introduction  
In recent decades, the trend towards using environmentally friendly materials and technologies in geotechnical engineering has noticeably increased. Microbial-induced calcite precipitation (MICP) is an innovative technology among engineering developments. Its appeal is based mainly on simplicity and environmental friendliness [1, 2]. Technologies are actively being developed to prevent the liquefaction of sandy soil and the processes of slope destruction, repair cracks in cement-concrete structures and reduce erosion [3, 4]. Soil with specified geotechnical properties is a prerequisite at the initial stage of any infrastructure construction; therefore, a lot of research is devoted to improving its mechanical properties. Of particular interest is the stabilization of soils using biological methods. MICP technology uses certain strains of bacteria, widely present in nature, capable of causing calcium carbonate precipitation due to their metabolic activity. The mechanisms of microbial induction of mineralization are based on numerous enzymatic reactions, leading to the formation of biocement from carbonate. A number of publications describe in detail several ways of mineral precipitation [5, 6, 7]. The most common and widely studied process is the induction of calcium carbonate precipitation using bacteria capable of hydrolyzing urea. The process is based on several sequential chemical reactions [8]. First, urea hydrolyzes to ammonia and carbon dioxide, increasing the pH value of the environment. Carbon dioxide reacts with water to form bicarbonate and then carbonateions, which, together with calcium ions, form precipitated calcium carbonate. The general process can be described using Equation (1):  
\[\text{CO}(\text{NH}_{2})_{2}+2\text{H}_{2}\text{O}+\text{Ca}^{2+}\to 2\text{NH}_{4}^{+}+ \text{CaCO}_{3}. \tag{1}\]  
The resulting biocement demonstrates high strength and stability and is able to fill the gaps between particles, connecting them to each other [9]. Biological cementation makes it possible to strengthen and stabilize the soil by increasing the solid content, reducing the pore size and increasing the rigidity of the contact between particles [10]. Microbial soil strengthening is an environmentally friendly and cost-effective alternative to chemical cementation, which causes ecological problems due to mixing bentonite, silicates, or acrylic with the soil. To implement biocementation in practice and meet the requirements of civil engineering, a number of problems must be solved. Soils treated with MICP are known to exhibit uneven calcium carbonate deposition and fragility [11]. For a long time, mechanical methods such as synthetic reinforcement have been used as a traditional approach to soil stabilization. However, due to the high energy costs of producing and introducing these materials into the soil, as well as the hazardous environmental impact, this approach does not seem attractive [12]. Soil reinforcement with natural fibers has potential due to its environmental friendliness, abundance of resources and cost-effectiveness compared to other materials [13]. With increasing levels of prosperity in industrialized countries, the volume of organic waste is also increasing significantly. The nutrient-rich composition of some industrial wastes provides a source of value-added products (biofuels, biopesticides, biohydrogen and bioplasticity) produced through microbial fermentation [14; 15]. Some types of waste can be used for soil restoration [16; 17]. As part of the development of environmentally friendly valorization strategies, it seems advisable to use by-products or production waste to strengthen soils using MICP technology [18; 19]. To stabilize large volumes of soil through biocementation, it is necessary to produce a significant amount of microbial biomass, retaining its biomineralizing properties. The costs of the growth medium used for microorganism cultivation constitute a significant part of the cost of MICP technology [20].