# From Waste to Strength: Applying Wastepaper, Fungi and Bacteria for Soil Stabilization
## 1 Introduction  
Humanity's destructive activities have led to numerous irreversible changes on Earth, such as environmental pollution and climate change [1]. Additionally, rapid urbanization has fueled the demand for products and services, resulting in the intensive use of fossil resources and the generation of organic waste [2]. To counter these negative trends associated with technological advancement, it is essential to increasingly adopt \"green\" technologies. One promising technology that takes an interdisciplinary approach is microbially induced calcium carbonate precipitation (MICP). This process harnesses the ability of microorganisms to induce the precipitation of calcium carbonate as a result of their metabolic activity [3]. Among the various pathways leading to the biomineralization of CaCO\({}_{3}\), the microbial urea decomposition mechanism is the most widely studied and applied, owing to its high rate of reaction and ease of control [4, 5, 6]. One of the most frequently used microorganisms in biomineralization is the aerobic rod-shaped bacterium _Sporosarcina pasteuri_, which has the maximum ureolytic activity and provides the highest yield of minerals [7, 8, 9]. Bacteria of the genus _Bacillus_ also demonstrate significant urease activity and high carbonate precipitation rates [10, 11, 12]. Biogenic calcium carbonate is highly compatible with a wide range of materials, making MICP a promising solution for various engineering and environmental challenges. These include water conservation, prevention of underground fluid leakage, soil erosion control, concrete structure restoration, earthquake mitigation and addressing issues like fugitive dust and contaminated soils [3,13]. Several companies worldwide, such as <<Biomass>> in Denmark and <<Soletanche Bachy>> in France, have already implemented MICP technology for commercial engineering applications. In the Middle East, the Kingdom of Saudi Arabia is the exclusive distributor of biconcrete products [14]. Additionally, in 1993, the French company <<Calcite Biocenter>> applied a surface coating (biocalcin) produced by microorganisms to a church tower in Paris, covering an area of 50 m\({}^{2}\)[15]. In recent decades, there has been a noticeable increase in the construction industry's adoption of environmentally friendly materials and technologies. In the early stages of building infrastructure, soil strengthening is often required to enhance its mechanical properties. MICP technology offers an eco-friendly alternative to traditional chemical cementation methods, which typically involve the addition of bentonite, silicates or acrylamide to the soil. Bioccmentation allows for strengthening and stabilizing the soil by increasing the content of the solid phase, reducing the pore size and improving the rigidity of contact between particles [16]. The calcite crystals that form in the process fill voids in the soil, binding loose particles together and improving the overall strength characteristics of the material. While much of the scientific focus has been on bacterial biomineralization processes, fungi also play a significant role in biogeochemical cycles and are increasingly recognized for their potential in soil improvement [17]. Fungi are capable of precipitating minerals through processes like biomineralization and organomineralization [18,19]. Fungal hyphae contain chitin, which can bind Ca\({}^{2+}\) ions. Both live and dead fungal biomass can capture these ions on their cell walls, leading to the nucleation and deposition of mineral phases such as calcium carbonate [20]. The potential of fungi to develop soil improvement technologies is discussed in a review by [PERSON] [21]. Their ability to precipitate calcium carbonate is actively being investigated to be exploited in concrete structure restoration [19]. Additionally, fungi are widely used in organic waste disposal, owing to their production of enzymes such as cellulases, hemicellulases and ligninases, which catalyze the breakdown of various organic polymers [22,23].