Ecofriendly solidification of sand using microbially induced calcium phosphate precipitation.

This study introduces microbiologically induced calcium phosphate precipitation (MICPP) as a novel and environmentally sustainable method of soil stabilization. Using Limosilactobacillus sp., especially NBRC 14511 and fish bone solution (FBS) extracted from Tuna fish bones, the study was aimed at testing the feasibility of calcium phosphate compounds (CPCs) deposition and sand stabilization. Dynamic changes in pH and calcium ion (Ca2+) concentration during the precipitation experiments affected the precipitation and sequential conversion of dicalcium phosphate dihydrate (DCPD) to hydroxyapatite (HAp), which was confirmed by XRD and SEM analysis. Sand solidification experiments demonstrated improvements in unconfined compressive strength (UCS), especially at higher Urea/Ca2+ ratios. The UCS values obtained were 10.35 MPa at a ratio of 2.0, 3.34 MPa at a ratio of 1.0, and 0.43 MPa at a ratio of 0.5, highlighting the advantages of MICPP over traditional methods. Microstructural analysis further clarified the mineral composition, demonstrating the potential of MICPP in environmentally friendly soil engineering. The study highlights the promise of MICPP for sustainable soil stabilization, offering improved mechanical properties and reducing environmental impact, paving the way for novel geotechnical practices.

Eco-friendly soil stabilization method using fish bone as cement material.

The method of soil improvement by calcium phosphate precipitation is a novel, environmentally friendly, and non-toxic technique. Such technology provides advantages over ureolytic induced calcite precipitation (UICP), the most popular and widely used method in the field of geotechnical engineering. In this paper, an investigation of the consolidation of fine and coarse sand samples by enzyme induced calcium phosphate precipitation (EICPP) was carried out. Tuna bones were used as an alternative source of calcium and phosphorus ions, as one of the most popular fish species in Japan and the main source of food industry waste. Unconfined compressive strength (UCS) of the samples after 21 days of daily injection of the solution showed an increase in strength up to 6,05 MPa in fine and up to 4,3 MPa in coarse sand samples. X-ray powder diffraction (XRD), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (SEM-EDS) analysis were performed to investigate the nature and type of deposition. Analyses confirmed that deposition is composed of brushite with needle-like crystals in the case of Toyoura sand and flower-like crystals in the case of Mikawa sand. SEM-EDS showed a presence of both, calcium, and phosphorus in the precipitate, indicating the presence of calcium phosphate compounds (CPCs). This study reveals that tuna bones are a rich source of calcium and phosphorus for EICPP, which results in a strengthening of silicate soil up to 3.4-6.05 MPa and is able to reduce ammonia emissions by 85.7 % - 97.5 % compared to UICP.

State-of-the-Art Review on Engineering Uses of Calcium Phosphate Compounds: An Eco-Friendly Approach for Soil Improvement.

Greenhouse gas emissions are a critical problem nowadays. The cement manufacturing sector alone accounts for 8% of all human-generated emissions, and as the world's population grows and globalization intensifies, this sector will require significantly more resources. In order to fulfill the need of geomaterials for construction and to reduce carbon dioxide emissions into the atmosphere, conventional approaches to soil reinforcement need to be reconsidered. Calcium phosphate compounds (CPCs) are new materials that have only recently found their place in the soil reinforcement field. Its eco-friendly, non-toxic, reaction pathway is highly dependent on the pH of the medium and the concentration of components inside the solution. CPCs has advantages over the two most common environmental methods of soil reinforcement, microbial-induced carbonate precipitation (MICP) and enzyme induced carbonate precipitation (EICP); with CPCs, the ammonium problem can be neutralized and thus allowed to be applied in the field. In this review paper, the advantages and disadvantages of the engineering uses of CPCs for soil improvement have been discussed. Additionally, the process of how CPCs perform has been studied and an analysis of existing studies related to soil reinforcement by CPC implementation was conducted.