Experimental Study on the Effective Production of Biocement for Soil Solidification and Wind Erosion Control

Abstract

Biocement can be achieved through the microbially induced carbonate precipitation (MICP) process. Such a method can potentially be utilized as an eco-friendly method for civil and environmental engineering applications such as soil ground improvement and wind erosion control of surface soil. In this method, one key step is the effective production of ureolytic bacteria. In previous laboratory and field studies, the cultivation and production of the bacteria used for the MICP were usually expensive and time-consuming. The purpose of this study was to optimize the cultivation method of the ureolytic bacteria (Sporosarcina pasteurii), and soil stabilization tests were conducted to verify the effectiveness of the cultured bacteria used to strengthen soil against the wind-induced erosion. Bacterial cultivation methods were studied by investigating the effects of different cultivation media and conditions. Testing variables included the types and concentrations of nitrogen sources (urea or NH4Cl), pH values (7.5–9.5), cultivation conditions (batch or chemostat condition), and different carbon sources. It was found that, with the same amount of nitrogen source, the test with pure urea had the highest biomass yield, urease activity, and specific urease activity than the other tests with pure NH4Cl or both NH4Cl and urea. The use of urea as the nitrogen source in the media also led to an increase in pH, which was not found in the test with pure NH4Cl. As for the factor of urea concentration, the tests with a higher urea concentration had a higher biomass yield, urease activity, and pH. The factor of pH values also played an important role. The test with an 8.5 initial pH value had a higher biomass yield, urease activity, and specific urease activity than the tests with 7.5 and 9.5 initial pH values. In the chemostat condition, the ureolytic bacteria could be effectively produced with urease activity up to 7 mmol/L/min, as compared with around 12 mmol/L/min activity in the batch condition. Thus, the optimum nitrogen source, pH value, and cultivation condition for the cultivation of Sporosarcina pasteurii was urea, 8.5, and batch condition, respectively. In addition, when soybean milk powder or milk powder was used as the carbon source, the urease activity was around 2.5 mmol/L/min, which is also high enough to be used for biocement.

Increased Microbially Induced Calcium Carbonate Precipitation (MICP) Efficiency in Multiple Treatment Sand Biocementation Processes by Augmentation of Cementation Medium with Ammonium Chloride

“…However, when error bars are taken into consideration, there appears to be minimal difference between the two sets of results shown. Similarly, Hang et al [43], reported that the use of urea as the nitrogen source for MICP, when conducting aqueous studies over 24 h, led to an increase in pH and that this increase wasn't not observed when supplying ammonium chloride (NH4Cl) only as the only nitrogen source. The results for the mass of precipitate (assumed at this stage to be calcium carbonate) deposited within the centrifuge tubes after 24 h, are presented in Figure 4.…”

“…Results indicate that it may be possible to include less ammonium chloride in the medium than used in this study. While the nitrogen source provided for ureolytic MICP studies is typically urea, ammonium chloride can also be a source of nitrogen [43]. Hang et al [43] reported that the optimum nitrogen source for MICP, when compared to ammonium chloride, was urea.…”

“…Hang et al [43] reported that the optimum nitrogen source for MICP, when compared to ammonium chloride, was urea. Furthermore, Hang et al [43] found that the use of urea as the nitrogen source in the medium also led to an increase in pH, which was not observed when supplying NH4Cl as the only nitrogen source. The higher pH of effluent from columns treated with ammonium While the nitrogen source provided for ureolytic MICP studies is typically urea, ammonium chloride can also be a source of nitrogen [43].…”

“…Furthermore, Hang et al [43] found that the use of urea as the nitrogen source in the medium also led to an increase in pH, which was not observed when supplying NH4Cl as the only nitrogen source. The higher pH of effluent from columns treated with ammonium While the nitrogen source provided for ureolytic MICP studies is typically urea, ammonium chloride can also be a source of nitrogen [43]. Hang et al [43] reported that the optimum nitrogen source for MICP, when compared to ammonium chloride, was urea.…”

“…The higher pH of effluent from columns treated with ammonium While the nitrogen source provided for ureolytic MICP studies is typically urea, ammonium chloride can also be a source of nitrogen [43]. Hang et al [43] reported that the optimum nitrogen source for MICP, when compared to ammonium chloride, was urea. Furthermore, Hang et al [43] found that the use of urea as the nitrogen source in the medium also led to an increase in pH, which was not observed when supplying NH 4 Cl as the only nitrogen source.…”