Investigating ammonia-free urea hydrolysis biocementation processes

Biocementation (i.e., the production of biomimetic cement through the metabolic activity of microorganisms) has attracted the vivid interest of researchers worldwide in the last decade. To date most research works and commercial products proposed biocementation using the urea hydrolysis metabolic route, as it is a fast and easy to control process. However, its major limitation is ammonia production, with adverse environmental impacts. Consequently, research effort has focused on how to alleviate or mitigate ammonia by-products, while using this metabolic route. The paper presents results of soft organic soil biocementation using an ex-situ urea hydrolysis process, developed so that the produced ammonia does not reach the soil. Indigenous ureolytic bacteria extracted from the soil of a site in East Anglia, UK were used to produce the urease enzyme, which catalyses the urea hydrolysis reaction. Following the proposed ex situ process, measured ammonia contents were found to be within acceptable limits. Soil strength increased and calcite precipitated in the soil although biocementation by bioaugmentation with the same indigenous bacteria gave higher soil strengths and CaCO3 precipitation than the ammonia-free process. After the presentation of results, further advantages and disadvantages of the respective biocementation methods (ex situ vs. in situ) are then discussed.