# From Waste to Strength: Applying Wastepaper, Fungi and Bacteria for Soil Stabilization
## 3 Results and Discussion
### Properties of MICP-Treated Soil Samples with Wastepaper Additives
In the present experiment, the strength of Control and Bact samples increased with the addition of wastepaper, while the total CaCO\({}_{3}\) content decreased (Figures 2 and 3A). In the study by [PERSON] [27], the effect of adding varying amounts (0-8%) of wastepaper fibers to sand was investigated. The results showed that the optimal fiber content was 1%, as further increases in fiber content resulted in a decrease in the strength of the samples. In summary, as the wastepaper content increased, the CaCO\({}_{3}\) content in most samples decreased. We suggest that 2% wastepaper is the optimal amount, as it does not interfere with microbial biomineralization and enhances strength through reinforcement. Surprisingly, the use of fungi in soil treatment led to unexpected results. As mentioned in Section 3.1.1, the introduction of wastepaper reduced the soil strength and was accompanied by a proportional decrease in CaCO\({}_{3}\) content (Figure 3A). A comparison of the Bact and Fng samples without additives shows that the fungi-treated sample contained 1.6 times less calcium carbonate than the bacteria-treated sample (0.96% in Fng vs. 1.53% in Bact samples). However, the strength of the Fng sample was almost four times higher (236.6 kPa in Fng vs. 60.63 kPa in Bact). This discrepancy may be due to the presence of other microorganisms in the non-sterile soil, which could contribute to mineralization through mechanisms other than ureolysis. For example, phosphate mineralization induced by phytases represents another possible pathway for mineral precipitation [41]. Alternatively, it is possible that fungal biomass itself, through the release of polysaccharides and proteins [42], affects soil aggregate stability, thus enhancing the overall strength. This mechanism remains an area for further investigation. The strength of the Mix sample without wastepaper was higher than that of the corresponding Bact sample but lower than the strength of the Fng sample. However, the Mix sample containing 2% wastepaper exhibited the highest strength (161.1 kPa) among all samples with the same wastepaper content, which correlated with an increase in calcium carbonate content. The strength of this sample was enhanced compared to untreated soil (61 kPa) and the bacteria-only (66.5 kPa) and fungi-only (140.12 kPa) treatments, by 2.6, 2.4 and 1.15 times, respectively. This suggests that the increased strength of the Mix sample with 2% wastepaper results from the combined effects of wastepaper addition and the mineralizing activity of microorganisms, possibly augmented by an additional, yet unexplained, contribution from the fungal biomass. The SEM images of the Bact sample (Figure 4A,C) show calcite formation within the soil pores, induced by microbial activity. [PERSON] [43] demonstrated that bacteria act as nucleation sites for calcium carbonate crystals. In Figure 4A, a trace left by a bacterium on the surface of calcite can be seen, which likely functioned as a crystal nucleation site (indicated by the blue arrows). The light microscope images (Figure 4B,D) show the branched hyphal network formed during the soil treatment with fungal biomass. [PERSON] [21] showed that fungal hyphae of _Pleurotus ostreatus_ can lead to the enmeshment and entanglement of sand particles, with hyphae and sclerotia transforming loose sand into a cohesive mass. It can be inferred that the fungi create an organic framework within the soil, providing a surface onto which bacteria can deposit calcium carbonate crystals. This process enhances the strength of the structure and ensures its distribution throughout the sample. However, the calcium content in the Fng samples did not increase after MICP treatment (Figure 3A). Fungal hyphae are known for their high mechanical stability, which is due to the rigid cell wall and the turgor pressure exerted by the protoplast on the inner side of the cell wall. These factors enable hyphae to actively penetrate mineral substrates [17].