###### Abstract  
Biocementation is an emerging nature-inspired method of producing eco-friendly cement for soil stabilization. This paper used the bovine-derived carbonic anhydrase (CA) enzyme to catalyse the bioprecipitation of CaCO\({}_{3}\) in a fine-grained soil and thus to biocement the soil. To increase the efficiency of the CA, an innovative copper-carbonic anhydrase (CA) hybrid was fabricated. This study is a proof-of-concept of the potential application of these enzyme carriers for soil biocementation. The hybrid carriers are aimed to enhance the stability, recovery and reusability of the enzyme used in the biocementation process. The results showed that the fabricated copper phosphate-based inorganic hybrid was stable throughout the duration of the tests (2 months) and under a wide range of pH and temperatures. Its enzymatic activity was enhanced compared to the free CA enzyme and it was proved suitable for soil biocementation. This was further confirmed by the SEM analysis. Additionally, the treated soil with the formulated hybrid carrier showed improved unconfined compressive strength, especially when the carriers were implemented into the soil by mixing. The material analysis by Raman spectroscopy confirmed calcium carbonate as the primary precipitate, consistent with soil bioementation. Overall, this innovative method of delivery of enzymes with enhanced stability and activity shows promise that, upon further development, it can be successfully used to increase the efficiency and sustainability of the biocementation process. carbonic anhydrase; enzyme carriers; ground improvement; biocementation; CO\({}_{2}\) capture capture +
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proposed to overcome these problems associated with MICP. In EICP, free enzymes derived from microbes or plant sources have been suggested and used as a catalyst to produce biocement [2; 17; 18]. The use of free enzymes facilitates the injection of biocementation treatments in fine-grained soils with narrow pore-throat sizes and bypasses the complexity of controlling living organisms in situ. However, EICP also comes with limitations, as the use of free enzymes in soils entails different challenges. These are linked predominantly to: (a) the stability of the enzyme once released into the ground; (b) the limited enzyme supply (as there is no generation of more enzymes from the soil bacteria, unlike when microbial biocementation is used) and (c) the poor reusability of the enzyme, which increases treatment costs. Previous studies for different applications have addressed these challenges by immobilizing the enzymes using suitable enzyme carriers. For example, enzyme carriers have been used in bioconcrete [19] or for CO\({}_{2}\) capture in bioreactors [20]. In CO\({}_{2}\) capture applications, hybrid enzyme-metal nanoflower carriers have been extensively used to achieve higher enzyme activity and stability [21]. The term \"nanoflower\" is used because the structure formed resembles a small flower. The formation of enzyme-inorganic hybrid nanoflowers comprises a four-step mechanism, namely (a) the coordination, (b) coprecipitation, (c) self-assembly and (d) size growth of the hybrid nanoflower carriers [22]. The process was demonstrated in previous studies, where metal ions were shown to react with phosphate ions to form the first crystals. Once the crystal is created, the metal ion complexes with the enzyme, producing a \"nanoflower\". Previous studies have shown that the formation process of nanoflower enzyme carriers by encapsulation, adsorption and covalent attachment to flower-like structures is efficient and that the carriers are stable [23; 24; 25; 26]. Because of these advantages, the present study combined an inorganic metal ion and carbonic anhydrase (CA) enzyme to fabricate a stable enzyme carrier based on the hybrid enzyme-metal nanoflower method. The study is a proof-of-concept of the hybrid nanoflower technique for soil biocementation using the CA pathway, for concurrent CO\({}_{2}\) absorption and soil stabilisation.