# Integration of Organic Waste for Soil Stabilization through MICP
## 4 Discussion  
The improvement of soil geotechnical properties using MICP is a complex process that includes the interaction of various components: soil, microorganisms and cementation solution. For this technology to become widespread, its cost must be reduced, efficiency and productivity must be increased. Recently, methods have been actively developed to improve MICP technology using inorganic and organic additives, such as low-grade chemicals, biopolymers and others [9]. In large-scale geotechnical projects, to improve the mechanical properties of soils using MICP, standard growth media for microorganisms are not considered cost-effective. To reduce the cost of growing bacteria for soil biomineralization, various approaches are being explored. For example, in a few studies, ureolytic bacteria were cultured under nonsterile conditions [40; 41; 42]. Natural and waste materials have been used to prepare growth media, such as corn steep liquor [40; 43], lactose mother liquor from dairy industry waste [20], whey, buttermilk [44] and molasse [41]. Spent brewer's yeast is often investigated as a source of nutrients for the cultivation of microorganisms [23]. [PERSON] [45] showed that even at relatively low biomass concentrations, the urease activity of _Psychrochacillus_ sp. was twice as high when grown on brewer's yeast extract compared to standard yeast ammonia extract medium. In our work, to prepare the BY growth medium for bacterial inoculates, commercial yeast extract and peptone were replaced with spent brewer's yeast extract. For the growth of _B. cereus_ 4b and _M. luteus_ 6 in the BY medium, significantly higher values of biomass characteristics and almost the same values of urease activity were observed compared to the LB medium. _B. subtilis_ K51 and _B. subtilis_ 168 demonstrated a relatively low increase in biomass and significantly higher urease activity in the BY medium compared to the LB medium (Figures 3 and 4). Figure 8: Light microscopy and scanning electron microscopy images of MICP-treated soil samples. (**A**) light-microscopy image (10\(\times\)) of an initial soil sample before MICP treatment and shredded wastewater addition; (**B**) light microscopy image (10\(\times\)) of a shredded wastewater sample; (**C**) light-microscopy image (10\(\times\)) of a MICP-treated soil sample; (**D**) light microscopy image (10\(\times\)) of a MICP-treated soil sample with the addition of shredded waste paper. Inserts show SEM images of the soil sample after MICP treatment. Calcium carbonate crystals are marked with red arrows. Scale bars correspond to 5 μm (**C**) and 2 μm (**D**). The fragility of soil treated with MICP is a major limit for the widespread application of this innovative technology. The introduction of reinforcing synthetic or natural fibers into MICP technology enables increasing the compressive strength characteristics of soil. [PERSON] et al. reported [PERSON] et al. (2018) that the addition of 0.2% carbon fiber in sand bioccentation could significantly improve the strength and toughness of the sample. In a study conducted by [PERSON] et al. [PERSON] et al. (2018), the strength of MICP-treated sand with the addition of 0.2-0.3% homopolymer polypropylene fiber was increased more than twice compared to the sample without the fiber addition. [PERSON] and coauthors showed that the addition of natural jute fiber increased the durability of MICP-treated samples by more than 50% [PERSON] et al. (2018). [PERSON] et al. reported that the addition of 1% wastewater fiber increased the unconfined compressive strength of a sand sample, but the addition of more than 1% fiber led to a decrease in this parameter [PERSON] et al. (2018). In our work, the addition of shredded wastewater to the soil treated with MICP increased compressive strength by 2.1 times compared to the sample without additives. On the contrary, the addition of flax shives and sawdust reduced the strength characteristics. Several studies reviewed in [PERSON] et al.