Towards a monitoring tool to quantify urease during biocementation treatment at microscale

¹ Instituto Superior Técnico – University of Lisbon, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
² Civil Engineering Research and Innovation for Sustainability, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
³ INESC Microsistemas e Nanotecnologias, Rua Alves Redol, 9, 000-029 Lisboa, Portugal
⁴ INL, International Nanotechnology Laboratory, 4715-330 Braga, Portugal

^* Corresponding author: ines.borges@ist.utl.pt

Abstract

Biocementation consists in using urease enzyme and a solution rich in urea and in calcium to precipitate calcium carbonate (biocement). When applying this treatment in soils, the biocement minerals bond the grains improving overall soil’s hydro-mechanical properties. For the practical use of this technique, it is necessary to be able to predict the properties of the treated soil after following specific protocols, by preference avoiding non-destructive testing such as those performed on samples extracted after the treatment. The amount of biocement precipitated depends on the amount of urease enzyme, urea and calcium. This idea has inspired the development of one magnetoresistive biosensor to detect urease, to be used as a non-destructive monitoring tool during the treatment. A magnetoresistive platform was used to quantify the signal, which is related to the urease concentration through a calibration curve. The sensor was tested to measure the enzyme present in the inflow and outflow fluids used to treat cylindrical soil samples (2.5 cm diameter and 2.0 cm height), prepared with a uniform grading size sand (D₅₀=0.3 mm). Purified urease from Canavalia ensiformis, was used. The improvement of the biocemented sand samples was quantified through measuring the calcium carbonate content of the soil after the treatment and the values were related with the amount of enzyme retained by the soil, determined using the sensor readings. This work found, for the first time, the relationship between the measured concentration of urease retained by soil and the calcium carbonate content precipitated. This relationship is an important tool for monitoring the treatment, without the need to use destructive tests or even stop the treatment.