Factors Affecting Soybean Crude Urease Extraction and Biocementation via Enzyme-Induced Carbonate Precipitation (EICP) for Soil Improvement

Abstract

Enzyme-induced carbonate precipitation (EICP) is a new biogeotechnical ground improvement technique that uses calcium carbonate (CaCO3) formed by biochemical processes to increase soil strength and stiffness. In this paper, crude urease extracted from soybeans was employed to catalyze the precipitation of CaCO3 in sand. To optimize the urease extraction efficiency, factors affecting the soybean crude urease extraction, including the powdered soybean particle size, concentration, soaking time, and soaking temperature, were addressed. This paper also provided further insight regarding the impact of the urease activity of soybean crude extract on the chemical conversion efficiency and the biocementation performance in EICP. The findings revealed that the powdered soybean concentration and the particle size were the two most important factors affecting the urease activity of the soybean crude extract. The enzyme activity utilized in the EICP process might further lead to different reactant efficiencies of urea-CaCl2 solution, and consequently, the improvement in the physical and mechanical properties of biocemented sand. Considering the chemical conversion efficiency and the biocementation performance, 60 g/L of powdered soybean was concluded as the preferred quantity for extracting the crude urease, with an enzyme activity of 6.62 mM urea min−1. Under this condition, a chemical conversion efficiency of approximately 95% for 0.5 M urea-0.5 M CaCl2 could be obtained in merely 12 h, and the unconfined compressive strength (UCS) of the EICP-treated sand exceeded 4 MPa with a CaCO3 content of ~8%. As a high-efficient cost-effective alternative to the purified enzyme for carbonate precipitation, the soybean crude urease showed great potential for ground improvement.

Quality assessment and quality control of deep soil mixing columns based on a cement-content controlled method

“…Modified EDTA titration method. The EDTA titration method measures cement content by detecting free calcium ions Ca 2+ in stabilized soil 29 . Calcium hydroxide [Ca(OH) 2 ] and gels containing calcium were generated during the cement hydration reaction.…”

Pengaruh Variasi Ukuran Butiran Tepung Kedelai pada Metode Calcite Precipitation untuk Peningkatan Kekuatan Tanah Pasir

“…Massa yang tidak terlarut tersebut dapat mempengaruhi reaksi pembentukan kalsit menjadi kurang efektif dan menyumbat pori-pori tanah sehingga kalsit tidak dapat terdistribusi secara merata di dalam tanah [2]. Ukuran butiran serbuk kedelai yang berbeda dapat menghasilkan viskositas larutan dan laju hidrolisis urea yang berbeda [5]. Penelitian ini mengevaluasi pengaruh ukuran butiran bubuk kedelai yang berbeda pada metode presipitasi kalsit dengan menggunakan larutan ekstrak kedelai yang diperoleh dengan perlakuan saring dan pengaruhnya terhadap nilai UCS pada tanah.…”

“…Semakin kecil ukuran diameter tepung kedelai yang digunakan, menghasilkan presipitasi kalsit yang semakin optimum. Berdasarkan kalsit yang dihasilkan dari urease activity, tepung kedelai dengan ukuran 0-0.250 mm merupakan ukuran terbaik yang digunakan pada metode calcite precipitation karena menghasilkan presipitasi kalsit yang optimum [7]. Nilai rasio presipitasi kalsit pada uji pengendapan kalsit dapat dilihat pada Gambar 2.…”

Extraction of urease from soybean for preparing biocement: Laboratory study

“…10b). The urease extracted from Chinese soybean can also be used to hydrolyze urea and bind sandy soil (Shu et al, 2022). Their cementation effect is similar to Canadian soybean when the CaCO 3 content is similar in sands (Shu et al, 2022).…”

“…The urease extracted from Chinese soybean can also be used to hydrolyze urea and bind sandy soil (Shu et al, 2022). Their cementation effect is similar to Canadian soybean when the CaCO 3 content is similar in sands (Shu et al, 2022). When the cementation levels are higher than that of one, it is di cult for SPF to be poured into sand blocks manually.…”