Influence of humic acid on microbial induced carbonate precipitation for organic soil improvement

Abstract

Microbial Induced Carbonate Precipitation (MICP) is one of the most commonly researched topics on biocementation, which achieves cementation of soil particles by carbonate from urea hydrolysis catalyzed by microbial urease. Although most MICP studies are limited to stabilizing sandy soils, more researchers are now turning their interest to other weak soils, particularly organic soils. To stabilize organic soils, the influence of humic substances should be investigated since it has been reported to inhibit urease activity and disrupt the formation of calcium carbonate. This study investigates the effect of humic acid (HA), one fraction of humic substances, on MICP. For this purpose, the effects of HA content on CaCO3 precipitation using three strains and on CaCO3 morphology were examined. The results showed that native species in organic soils were less adversely affected by HA addition than the exogenous one. Another interesting finding is that bacteria seem to have strategies to cope with harsh conditions with HA. Observation of CaCO3 morphology revealed that the crystallization process was hindered by HA to some extent, producing lots of fine amorphous precipitates and large aggregated CaCO3. Overall, this study could provide an insightful understanding of possible obstacles when using MICP to stabilize organic soils.

Macroscale preparation of nanosized calcium carbonate by exploiting biogas slurry synchronous metathesis encapsulation method

“…Most HA with negative electricity tends to chelate Ca 2+ ions to decrease the crystal surface energy of CaCO 3 to form stable and small nuclei. 48 Therefore, HA in biogas slurry has a significant influence on the crystal growth of CaCO 3 in this study.…”

Preliminary Study on the Preparation of Conductive Nanosized Calcium Carbonate Utilizing Biogas Slurry by a Synchronous Double Decomposition Coating Method

“…Meanwhile, the NCC was coated by the carbon layer that originated from soluble organic matter, such as HA from biogas slurry ( Figure 2 d,e). This might be related to the high surface activation energy of CaCO 3 and the formation of a carbon skeleton by high-temperature carbonization of soluble organic matter such as HA [ 34 , 35 ]. The results indicate that the CNCC should be further crushed and classified or put into a dispersant to control its particle size within 100 nm [ 36 ].…”

“…The soluble organic matter of HA, with carboxyl, hydroxyl, and other groups, was uniformly dispersed in the biogas slurry [ 45 ]. The Ca atoms in the surface molecules of NCC readily chelated with the O atoms in the -OH and -COOH chains of HA [ 35 ]. This result was similar to the findings of previous studies on the mechanism of HA regulating the morphology and specific surface area of CaCO 3 in the carbonization process [ 34 , 35 ].…”

Feasibility of bacterial-enzyme induced carbonate precipitation technology for stabilizing fine-grained slope soils

“…It should be noted, however, the applicability of the B-EICP method for the case of clay soils might be still a challenge due to their extremely low permeability characteristics, which may require mechanical mixing or pressurized supply of the treatment solutions, as reported in previous works (Islam et al, 2020;Gowthaman et al, 2021a). Moreover, fine-grained soils are often reported to consist of certain percentage of organic matter (Chen et al, 2022); therefore, the impact of humus on enzyme-induced cementation needs to be addressed in future works to make the technology fully feasible.…”