The efficiency of ureolytic bacteria isolated from historical adobe structures in the production of bio-bricks

Building and construction sector contributes to climate change due to the massive amounts of global energy use and greenhouse gas emissions; therefore, developing sustainable alternatives for manufacturing construction materials is of high priority. The cementation of sand into the sandstone through microbially induced carbonate precipitation is an environmentally friendly technology with multiple prospective applications, mainly in con-struction and geotechnical engineering. This study introduces ureolytic bacterial strains with high urease activity found in Iran's historical adobe structures and deserts, which were evaluated for the production of biologically cemented bricks as an alternative to conventional brick manufacturing methods. In the present study, 25 soil samples were collected from historical adobe structures and deserts in the central provinces of Iran. Samples were screened for urease-producing bacteria to find native bacteria and assess the possibilities of producing biologically cemented bricks. The urease activity and calcium carbonate precipitation mass of the ureolytic bacteria were determined. Among all the collected isolates, the most efficient carbonate-producing bacteria was compared with Sporocarsina pasteurii and Sporocarsina ureae control strains in point of the growth rate, urease activity, and calcite precipitation amounts. The isolate with highest urease activity was identified as Bacillus sp. and nominated as strain AF1 by 16S rRNA gene sequencing. The selected bacteria was further used to construct bio-bricks from silica sand through the immersion method. The produced bio-bricks showed an average compressive strength and water absorption percentage of 3000 kPa and 8.5%, respec-tively. The bio-treated bricks also showed satisfying durability when subjected to wet-dry cycles and their flexural stress-strain curve reached the peak of 1300 kPa. X-ray diffraction and Scanning electron microscopy confirmed the presence of calcite crystals, bonding the soil particles. In conclusion, the current study results show that future sustainable buildings can benefit from bacterial species with high urease activity similar to historical sustainable buildings in central provinces of Iran.