Sustainable sand solidification via a resource-recycling microbially induced phosphate precipitation (MIPP) process utilizing commercial beer yeast and bone meal

Microbially induced phosphate precipitation (MIPP), characterized by the precipitation of calcium phosphate compounds (CPCs) between sand particles, is a promising eco-friendly alternative to conventional bio-cementation due to its ability to suppress toxic ammonia gas emissions. Despite this advantage, its practical application has not yet been realized because of unresolved challenges, including low mechanical strength, heterogeneous solidification, and high treatment costs. To address these issues and advance the process to a practical level, this study proposes a sustainable, resource-recycling MIPP framework using Pseudomonas sp., through two key perspectives: medium optimization and expansion of applicable sand conditions. Specifically, material sustainability is significantly enhanced by upcycling food-industry by-products, utilizing commercial beer yeast as a low-cost nutrient medium and bone meal as a calcium/phosphate source. Experimental results revealed that although the beer yeast-derived medium (BY4) yielded a lower cell density than the standard medium, the bacteria exhibited a higher specific urease activity, with cultivation costs drastically reduced to 101 JPY/L. Laboratory solidification tests using fine and medium sand columns further demonstrated that structural pore voids fundamentally determine crystal precipitation dynamics and process efficiency. Fine sand achieved a competitive unconfined compressive strength of approximately 1.0 MPa at the upper section due to localized crystal accumulation. Conversely, medium sand facilitated deeper resource migration, developing an average structural strength of 0.73 MPa at the bottom section primarily through efficient particle bridging with minimal mineral precipitation. These findings indicate that material consumption can be minimized by optimizing the treatment protocol according to the pore characteristics of the target soil, thereby offering that the proposed framework is an approach that combines high practical applicability with excellent cost-effectiveness.