Microbially Induced Desaturation and Carbonate Precipitation through Denitrification: A Review

Microbial-induced calcium precipitation: Bibliometric analysis, reaction mechanisms, mineralization types, and perspectives

Microbial-induced calcium precipitation (MICP) refers to the formation of calcium precipitates induced by mineralization during microbial metabolism. MICP has been widely used as an ecologically sustainable method in environmental, geotechnical, and construction fields. This article reviews the removal mechanisms of MICP for different contaminants in the field of water treatment. The nucleation pathway is explained at both extracellular and intracellular levels, with a focus on evaluating the contribution of extracellular polymers to MICP. The types of mineralization and the regulatory role of enzyme genes in the MICP process are innovatively summarized. Based on this, the environmental significance of MICP is illustrated, and the application prospects of calcium precipitation products are discussed. The research hotspots and development trends of MICP are analyzed by bibliometric methods, and the challenges and future directions of MICP technology are identified. This review aims to provide a theoretical basis for further understanding of the MICP phenomenon in water treatment and the effective removal of multiple pollutants, which will help researchers to find the breakthroughs and innovations in the existing technologies, with a view to making significant progress in MICP technology.

New insights into Saccharomyces cerevisiae induced calcium carbonate precipitation

Our previous study reported that Saccharomyces cerevisiae could induce calcium carbonate (CaCO3) precipitation, but the associated mechanism was unclear. In the present study, Saccharomyces cerevisiae was cultured under various conditions, including the presence of different organic acids and initial pH, and the yields of CaCO3 formation induced by the different organic acids were compared. The metabolism of organic acid by the metabolites of S. cerevisiae was also assessed in vitro. The SEM-EDS and XRD results showed that only acetate acid, pyruvic acid, and α-ketoglutaric acid could induce CaCO3 formation, and the weight order of the produced CaCO3 was pyruvic acid, acetate acid, α-ketoglutaric acid. In addition, the presence of only yeast metabolites and the initial neutral or alkaline environment also limited the CaCO3 formation. These results illustrated that organic acid oxidation intracellularly, especially the tricarboxylic acid cycle, was the major mechanism, and the CaCO3 yield was related to the amount of CO2 produced by the metabolism of organic acids. These findings will deepen the knowledge of the mineralization capacity of S. cerevisiae and provide a theoretical basis for the future application of yeast as an alternative microorganism in MICP.

Microbially induced calcium precipitation driven by denitrification: Performance, metabolites, and molecular mechanisms

Microbially induced calcium precipitation (MICP) driven by denitrification has attracted extensive attention due to its application potential in nitrate removal from calcium-rich groundwater. However, little research has been conducted on this technique at the molecular level. Here, Pseudomonas WZ39 was used to explore the molecular mechanisms of nitrate-dependent MICP and the effects of Ca²⁺ on bacterial transcriptional regulation and metabolic response. The results exhibited that appropriate Ca²⁺ concentration (4.5 mM) can promote denitrification and the production of ATP, EPSs, and SMPs. Genome-wide analysis showed that the nitrate-dependent MICP was accomplished through heterotrophic denitrification and CO₂ capture. During this process, EPS biosynthesis and Ca²⁺ signaling regulation were involved in the nucleation template supply and Ca²⁺ homeostasis balance. Untargeted transcriptome- and metabolome-association analyses revealed that the addition of Ca²⁺ triggered the significant up-regulation in several key pathways, such as transmembrane transporter and channel activities, amino acid metabolism, fatty acid biosynthesis, and carbon metabolism, which played a momentous role in the mineral nucleation and energy provision. The detailed information provided novel insights for understanding the active control of bacteria on MICP, and has great significance for deepening the cognition of groundwater remediation using nitrate-dependent MICP technique.

Synergistic interactions of microbial fuel cell and microbially induced carbonate precipitation technology with molasses as the substrate

The application of microbially induced carbonate precipitation (MICP) technology is critical, but many challenges remain. In this paper, a microbial fuel cell (MFC) is used to treat molasses wastewater, and the effluent is used as the substrate to promote the growth of urease-producing bacteria. The results showed that the maximum voltage of MFC was 500 mV, and the maximum power density was 169.86 mW/m². The mineralization rate reached 100% on the 15^th day, and the mineralized product was calcite CaCO₃. According to the microbial community analysis, the unclassified_Comamondaceae, Arcobacter, and Aeromonas, which could improve the OH^-, signal molecular transmission and small molecular nutrients to promote the urease activity of urease-producing bacteria. The above conclusions provide a new way to reuse molasses wastewater efficiently and to apply MICP technology in dust suppression.

Microbially induced calcium precipitation coupled with medical stone-coated sponges: A targeted strategy for enhanced nitrate and fluoride removal from groundwater

The coexistence of nitrate and fluoride in groundwater is of high concern due to its potential environmental impacts and health risks. Medical stone-coated sponges, as a microbial activity promoter and slow-release calcium source, were introduced into an immobilized bioreactor for enhanced removal of nitrate and fluoride. Under the hydraulic retention time of 3 h, nitrate, fluoride, and calcium contents of 16.5, 3.0, and 100 mg L^-1, the average removal efficiencies of nitrate, fluoride, and calcium reached 99.49%, 74.26%, and 70.43%, respectively. Co-precipitation and chemisorption were the mechanisms for fluoride and calcium removal. Medical stone load improved the competitiveness of dominant bacteria and electron transport activity, accelerated the denitrification process, and stimulated biofilm formation. High fluoride level (5.0 mg L^-1) inhibited the nitrate removal and aromatic protein production. The fluoride content changes altered the carbon source preference of the microbial community, which preferred to use amino acids and carbohydrates under a higher fluoride content. The introduction of medical stones significantly accelerated the fluoride and nitrate removal, providing a new insight for the application of microbially induced calcium precipitation technique in the remediation of low-calcium groundwater.

Experimental Study on Silt Soil Improved by Microbial Solidification with the Use of Lignin

At present, in the field of geotechnical engineering and agricultural production, with increasingly serious pollution an environmentally friendly and efficient means is urgently needed to improve the soil mass. This paper mainly studied the microbial induced calcium carbonate precipitation (MICP) technology and the combined effect of MICP technology and lignin on the improvement of silt in the Beijing area. Through unconfined compressive strength and dynamic triaxial test methods, samples improved by microorganisms were studied to obtain the optimal values of cement concentration and lignin under these two test schemes. The results show that after the incubation time of Sporosarcina pasteurii reached 24 h, the OD600 value was 1.7-2.0 and the activity value (U) was 930-1000 mM ms/min. In the unconfined static pressure strength test, after MICP treatment the optimal concentration of cementitious solution for constant temperature and humidity samples and constant-temperature immersion samples was 1.25 mol/L. The compressive strength of the constant temperature and humidity sample was 1.73 MPa, and the compressive strength of the constant-temperature immersion sample was 3.62 Mpa. At the concentration of 1.25 mol/L of cement solution, MICP technology combined with lignin could improve the constant temperature and humidity silt sample. The optimal addition ratio of lignin was 4%, and its compressive strength was 1.9 MPa. The optimal lignin addition ratio of the sample soaked at a constant temperature was 3%, and the compressive strength was 4.84 MPa. In the dynamic triaxial multi-stage cyclic load test, the optimal concentration of cementation solution for the constant temperature and humidity sample after MICP treatment was 1.0 mol/L, and the failure was mainly inclined cracks. However, in the condition of joint improvement of MICP and lignin, the sample mainly had a drum-shaped deformation, the optimal lignin addition ratio was 4%, and the maximum axial load that the sample could bear was 306.08 N. When the axial dynamic load reached 300 N, the strain accumulation of the 4% group was only 2.3 mm. In this paper, lignin, an ecofriendly material, was introduced on the basis of MICP technology. According to the failure shape and relevant results of the sample, the addition of lignin was beneficial for the improvement of the compressive strength of the sample.

Simultaneous removal of nitrate and heavy metals in a biofilm reactor filled with modified biochar

A biofilm reactor filled with chia seeds gum modified biochar was set up for the simultaneous removal of nitrate, cadmium and zinc from calcium-containing wastewater via denitrification and microbially-induced (calcium) carbonate precipitation. The reactor performance was studied under different conditions of pH, Cd concentration, and hydraulic retention time. The optimal removal efficiency of the reactor for NO₃^--N, Ca²⁺, Cd²⁺, and Zn²⁺ were 99.98, 79.89, 100, and 99.84 %, respectively. 3D-EEM indicated the aromatic compounds confirming the stability of the reactor. FTIR illustrated the presence of -OH, CaCO₃, C-O-C, and C-O-H indicating the precipitation and role of gum in MICP. SEM confirmed that the seed crystal induced the repeated crystallization of free metal ions. XRD showed that heavy metals were removed in the form of CaCO₃, CdCO₃, ZnCO₃, Ca₃(PO₃)₂, Cd₃(PO₃)₂, and Zn₃(PO₃)₂ co-crystallization. SEM-EDS showed the composition and distribution of elements. High-throughput sequencing showed that Curpriavidus sp. GMF1 and Ochrobactrum sp. GMC12 were the dominant bacterial species, with powerful denitrification and MICP mineralization capabilities.

Enhanced nitrate, fluoride, and phenol removal using polyurethane sponges loaded with rice husk biochar in immobilized bioreactor

Polyurethane sponges loaded with rice husk biochar were prepared to immobilize Aquabacterium sp. CZ3 for intensified removal of nitrate, fluoride (F-), and phenol, with the maximum efficiency of 100 %, 91 %, and 99 %, respectively. The biochar load and increased carbon-to-nitrogen (C:N) ratio (below 3.0) stimulated the secretion of soluble microbial product, improved the electron transport system activity, and promoted denitrification, phenol co-metabolism, and F- and calcium crystallization. The characterization results suggested that F- was removed as fluoride-containing calcium precipitates. According to the microbial community analyses, Aquabacterium was the dominant bacterium. PICRUSt analyses showed that biochar and adequate carbon sources (C:N ratio 3.0) significantly increased the functional abundances of amino acid metabolism, carbohydrate metabolism, energy metabolism, and cell motility. The introduction of biochar reduces the demand for C:N ratio in the system, and expands the application potential of biomineralization technique in the remediation of multiple pollutants contaminated water.

Single-step removal of calcium, fluoride, and phenol from contaminated water by Aquabacterium sp. CZ3 via facultative anaerobic microbially induced calcium precipitation: Kinetics, mechanism, and characterization

Confronting the complex contaminated water, Aquabacterium sp. CZ3 could perform microbially induced calcium precipitation (MICP) under facultative anaerobic condition using phenol as supplementary carbon source. Strain CZ3 exhibited a remarkable ability to remove nitrate, fluoride, calcium and phenol with removal rates of 100.00, 87.50, 66.24 and 100.00%, respectively. The Modified Gompertz model was used for kinetic analysis to determine the optimum conditions for denitrification and degradation of phenol. The mechanism of anaerobic MICP was enhanced by measuring the self-aggregation properties of the isolates. The mechanism of fluoride removal was identified as co-precipitation and adsorption by characterization analysis of the bioprecipitation. Furthermore, the changes in soluble metabolites under phenol stress explained the utilization of phenol as a co-substrate by microorganisms. This is a novel report on phenol degradation by anaerobic MICP, which provides a theoretical basis for expanding its practical application.

Long-amplicon MinION-based sequencing study in a salt-contaminated twelfth century granite-built chapel

The irregular damp dark staining on the stonework of a salt-contaminated twelfth century granite-built chapel is thought to be related to a non-homogeneous distribution of salts and microbial communities. To enhance understanding of the role of microorganisms in the presence of salt and damp stains, we determined the salt content and identified the microbial ecosystem in several paving slabs and inner wall slabs (untreated and previously bio-desalinated) and in the exterior surrounding soil. Soluble salt analysis and culture-dependent approaches combined with archaeal and bacterial 16S rRNA and fungal ITS fragment as well as with the functional genes nirK, dsr, and soxB long-amplicon MinION-based sequencing were performed. State-of-the-art technology was used for microbial identification, providing information about the microbial diversity and phylogenetic groups present and enabling us to gain some insight into the biological cycles occurring in the community key genes involved in the different geomicrobiological cycles. A well-defined relationship between microbial data and soluble salts was identified, suggesting that poorly soluble salts (CaSO4) could fill the pores in the stone and lead to condensation and dissolution of highly soluble salts (Ca(NO3)2 and Mg(NO3)2) in the thin layer of water formed on the stonework. By contrast, no direct relationship between the damp staining and the salt content or related microbiota was established. Further analysis regarding organic matter and recalcitrant elements in the stonework should be carried out. KEY POINTS : • Poorly (CaSO4) and highly (Ca(NO3)2, Mg(NO3)2) soluble salts were detected • Halophilic and mineral weathering microorganisms reveal ecological impacts of salts • Microbial communities involved in nitrate and sulfate cycles were detected.

New Insights Into Microbial Induced Calcium Carbonate Precipitation Using Saccharomyces cerevisiae

Saccharomyces cerevisiae plays an important role in the mineralization of many metal ions, but it is unclear whether this fungus is involved in the mineralization of calcium carbonate. In this study, S. cerevisiae was cultured under various conditions to explore its ability to perform microbially induced calcium carbonate precipitation (MICP). Organic acids, yeast extract, and low-carbon conditions were the factors influencing the biomineralization of calcium carbonate caused by S. cerevisiae, and biomolecules secreted by the fungus under different conditions could change the morphology, size, and crystal form of the biosynthesized mineral. In addition, transcriptome analysis showed that the oxidation of organic acids enhanced the respiration process of yeast. This implied that S. cerevisiae played a role in the formation of calcium carbonate through the mechanism of creating an alkaline environment by the respiratory metabolism of organic acids, which could provide sufficient dissolved inorganic carbon for calcium carbonate formation. These results provide new insights into the role of S. cerevisiae in biomineralization and extend the potential applications of this fungus in the future.