Microbiologically Induced Calcite Precipitation Research Articles

An Experimental Investigation on Mechanical Properties of Bacterial Concrete Using Bacillus Subtilis

Abstract: This Concrete is susceptible to micro crack formation and has pores which are highly undesirable because they provide an open pathway for the ingress of water and other deleterious substances. The use of concrete surface treatments with water proofing materials to prevent the access of aggressive substances is a common way of contributing to concrete durability. However, the most common surface treatments use organic polymers (epoxy, acrylics and polyurethanes) all of which have some degree of toxicity. Bio inspired materials can lead to a more sustainable construction industry, especially when providing new low toxic solutions. Hence, there is an urgent need to pay more attention for improving the properties of concrete with respect to strength and durability, especially in aggressive environments. One effective remedy for closure of cracks is the Bacterial Concrete (BC) which will continuously deposit calcite in concrete. This, phenomenon is called as Microbiologically Induced Calcite Precipitation (MICP). The urease enzyme enables the deposition of calcium carbonate (CaCO3) with the help of bacteria. The bacterial remediation technique surpasses other techniques as it is bio-based, eco-friendly and durable. Bacteria need to offer resistance to withstand high pH of concrete and mechanical stresses during mixing. In these present investigations bacterial sample name Bacillus Subtilis (BS) is considered in concentrations of 104 , 105 and 106 cells/ml of mixing of water. investigations are carried out on strength-related properties such as compressive strength, splitting tensile strength and flexural strength to assess the quality of concrete. The optimum dosage of cell concentration of bacteria is found to be 105 cells/ml for BS based on compressive strength results. M25 grade concrete is designed and used for embedding Bacillus subtilis bacteria.

Microbiologically induced calcite precipitation (MICP) in situ remediated heavy metal contamination in sludge nutrient soil

Microbiologically induced calcite precipitation (MICP), as a newly developing bioremediation technology, could redeem heavy metal contamination in diverse scenarios. In this study, MICP bacterium Sporosarcina ureilytica ML-2 was employed to suppress the pollution of Pb, Cd and Zn in municipal sludge nutrient soil. After MICP remediation, the exchangeable Cd and Zn in sludge nutrient soil were correspondingly reduced by 31.02 % and 6.09 %, while the carbonate-bound Pb, Cd and Zn as well as the residual fractions were increased by 16.12 %, 6.63 %, 13.09 % and 6.10 %, 45.70 %, 3.86 %, respectively. In addition, the extractable Pb, Cd and Zn either by diethylenetriaminepentaacetic acid (DTPA) or toxicity characteristic leaching procedure (TCLP) in sludge nutrient soil were significantly reduced. These results demonstrated that the bio-calcite generated via MICP helped to immobilize heavy metals. Furthermore, MICP treatment improved the abundance of functional microorganisms related to urea cycle, while reduced the overall abundance of metal resistance genes (MRGs) and antibiotic resistance genes (ARGs). This work confirmed the feasibility of MICP in remediation of heavy metal in sludge nutrient soil, which expanded the application field of MICP and provided a promising way for heavy metal pollution management.

The comparison of the experimental investigations of strength characteristics of conventional and bacterial concrete

Conventional concrete (CC) is the greatest used construction material in the world, especially in aggressive environments. This is due to the element's size and shape. The world's consumption of concrete is on the order of 5.5 billion metric tons a year. The advancement of concrete technology, as well as the development of materials and mechanisms, has resulted in increased strength needs. Maintenance, repair, and rehabilitation of present concrete structures challenge a lot of difficulties, resulting in significant expenditure. Concrete is vulnerable to microcracks creation and has extremely undesirable pores. Hence, there is an urgent need to pay more attention to improving the properties of concrete in terms of strength. The effective remedy for the closure of cracks is Bacterial concrete (BC) which will constantly be in concrete and this phenomenon is called Microbiologically Induced Calcite Precipitation (MICP). The urease enzyme enables the deposition of calcium carbonate (CaCO3) with the advantage of bacteria. The bacterial remediation technique exceeds added techniques. The examinations were carried out with variety an of quantitative evaluations of the optimal concentration of bacterial cells to be collected in concrete. Based on the state-of-the-art evidence obtainable in the literature, in these existing soundings two different bacterial illustrations specifically Bacillus Megaterium (BM) and Bacillus Subtilis (BS) are measured in concentrations of 104, 105, and 106 cells/ml of mixing of water. The optimum amount of cell concentration of bacteria is created to be 104 cells/ml for BM and 105 cells/ml for BS based on the results of compressive strength. This investigation is carried out on strength-related properties such as compressive strength, splitting tensile strength, and flexural strength. It is determined that BM and BS bacteria can be firmly used for refining the performance and strength characteristics of concrete.

Experimental Investigation on Self-Healing Efficiency of Mortar with Bacillus subtilis and Bacillus cereus

With the development of cracks on their surfaces, mortar’s service life dramatically shortens. Self-healing concrete by Microbiologically Induced Calcite Precipitation (MICP) is one of the high-tech concretes being used to address these issues. This type of mortar can start biological processes to repair itself and deal with its cracks. The self-healing effectiveness of two different bacteria, in this paper, Bacillus subtilis and Bacillus cereus, added to the mortar is examined experimentally. In order to conduct this investigation, artificial cracks were made in the mortar. A 3D optical microscope was used to take repeated pictures of the cracked mortar. The mechanical and durability tests conducted on the bacterial mortar were used to gauge the efficacy of self-healing. Mortar samples were left for 7, 14, and 28 days to cure. Compressive strength, flexural strength, water absorption, and sorptivity were measured during various times of the curing process. The test results showed that the mortar with bacteria had an increase in strength and durability compared to the control mix. In the sample of mortar containing bacteria, Bacillus subtilis and Bacillus cereus a maximum increase of 17.29% and 11.31% in flexural strength, 17.77% and 12.84% in compressive strength were observed and a 34.48% and 26.43% decrease in water absorption in the mortar sample containing bacteria, Bacillus subtilis and Bacillus cereus at 28 days, respectively. The results of the mortar absorption test showed that the addition of bacteria to the mortar matrix significantly reduced the primary and secondary absorption rates of bacterial mortars B-M-1 and B-M-2. Using a 3D light microscope, the cracks in the bacterial mortar showed that larger amounts of white crystal precipitates were generated that nearly filled the surface of the crack. Overall, Bacillus subtilis appeared to be superior to Bacillus cereus based on the results of mechanical and mortar durability tests because calcium carbonate precipitates more rapidly.

Improvement of tensile strength and durability of mortar through bio cementation

Throughout the field of construction, intrinsic brittleness of the mortar that lead to cracking, especially after plastering, has been frequently observed, which makes it a common hurdle in most of the constructed structures, due to the significant loss of water tightness and durability. Cementous structures are subject to damage continuously by harassment conditions. Therefore, special biological systems can be exploited to overcome such problems. Many bacterial species have been employed to precipitate calcium carbonate through the oxidation of organic carbon, changing the properties of the construction material. The oxidation process would fill the pores between cement matrices, which shows significant decrease in the porosity, permeability and capillary water penetration. Deposition of calcium carbonate by bacteria is a phenomenon known as microbiologically induced calcite precipitation (MICP), biomineralization, or bio cementation, which considered as natural and eco-friendly process. Such deposition is a promising practice for integrating and protecting various building materials. The strength refinement is due to growth of filler material inside the pores of the cement matrix. In addition, a modification in pores’ size, distribution, and total volume are also noted, that could enhance durability properties. Due to the relative dryness and shortage of nutrients required for bacterial growth in concrete, those common bacteria unable to thrive. Some extremophiles spore forming species are able to survive in such hostile environment and boost the durability, compressive strength, and self-healing and repairing of micro-cracks in the cement concrete. Bacillus spizizenii 6633 was added to cement mortar, and found that the tensile strength was increased up to 12.6%, and the deterioration was decreased through the reduction of the microcracks by self-healing process.

Mechanism of microbiologically induced calcite precipitation for cadmium mineralization

Microbiologically induced calcite precipitation (MICP) technology shows potential for remediating heavy metal pollution; however, the underlying mechanism of heavy metal mineralization is not well-understood, limiting the application of this technology. In this study, we targeted Cd contamination (using 15:1, 25:1, and 50:1 Ca2+/Cd2+ molar ratios) and showed that the ureolytic bacteria Sporosarcina ureilytica ML-2 removed >99.7 % Cd2+ with a maximum fixation capacity of 75.61 mg-Cd/g-CaCO3 and maximum precipitation production capacity of 135.99 mg-CaCO3/mg-cells. Quantitative PCR analysis showed that Cd2+ inhibited the expression of urease genes (ureC, ureE, ureF, and ureG) by 70 % in the ML-2 strain. Additionally, the pseudo-first-order kinetics model (R2 = 0.9886), intraparticle diffusion model (R2 = 0.9972), and Temkin isotherm model (R2 = 0.9828) described the immobilization process of Cd2+ by bio calcite in MICP-Cd system. The three Cd2+ mineralization products generated by MICP were attributed to surface precipitation (Cd2+ → Cd(OH)2), direct binding with the CO32−/substitution calcium site of calcite (Cd2+ → CdCO3, otavite), and calcite lattice vacancy anchors (Cd2+ → (CaxCd1-x)CO3). Our findings improve the understanding of the mechanisms by which MICP can achieve in situ stabilization of heavy metals.

Microbiologically induced calcite precipitation for in situ stabilization of heavy metals contributes to land application of sewage sludge

Microbiologically induced calcite precipitation (MICP) has shed new light on solving the problem of in situ stabilization of heavy metals (HMs) in sewage sludge before land disposal. In this study, we examined whether MICP treatment can be integrated into a sewage sludge anaerobic digestion-land application process. Our results showed that MICP treatment not only prevented the transfer of ionic-state Cd from the sludge to the supernatant (98.46 % immobilization efficiency) but also reduced the soluble exchangeable Pb and Cd fractions by up to 100 % and 48.54 % and increased the residual fractions by 22.54 % and 81.77 %, respectively. In addition, the analysis of the stability of HMs in MICP-treated sludge revealed maximum reductions of 100 % and 89.56 % for TCLP-extractable Pb and Cd, respectively. Three-dimensional fluorescence, scanning electron microscopy-energy-dispersive X-ray spectroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy analyses confirmed the excellent performance of the ureolytic bacteria Sporosarcina ureilytica ML-2 in the sludge system. High-throughput sequencing showed that the relative abundance of Sporosarcina sp. reached 53.18 % in MICP-treated sludge, and the urease metabolism functional genes unit increased by a maximum of 239.3 %. The MICP technology may be a feasible method for permanently stabilizing HMs in sewage sludge before land disposal.

Best-performing Bacillus strains for microbiologically induced CaCO3 precipitation: Screening of relative influence of operational and environmental factors

The microbiologically induced calcite precipitation (MICP) can be an emerging approach that could tap onto soil bacterial diversity and use as a bioremediation technique. Based on the concept that bacteria with biomineralization capacity could be effective CaCO3 inductance agents, this study aimed to evaluate the simultaneous influence of 11 operational and environmental factors on the MICP process, for the first time. Therefore, Bacillus muralis, B. lentus, B. simplex, B. firmus, and B. licheniformis, isolated from alkaline soils, were used in the selection of the best performing bacterium compared with a well-known MICP bioagent Sporosarcina pasteurii DSM 33. Plackett-Burman's experimental design was labouring to screen all independent variables for their significances on five outputs (pH value, number of viable cells and spores, amount of urea and CaCO3 precipitate). According to experimentally obtained data, an artificial neural network model based on the Broyden-Fletcher-Goldfarb-Shanno algorithm showed good prediction capabilities, while differences in the relative influences were observed at the bacterial strain level. B. licheniformis turn out to be the most potent bioagent, with a maximum amount of CaCO3 precipitate of 3.14 g/100 mL in the optimal conditions.

Geotechnical properties of yellow silty sand soil modified by bio-stimulation with presence of NiCl2

Microbiologically induced calcite precipitation (MICP) is now widely tried to improve the quality of mostly sandy soil due to its application prospect to sustainability, environment-friendly and cost-efficiency. The present study is aiming to evaluate the feasibility of bio-stimulation, one of MICP techniques, for strengthening the engineering quality of Shanghai silty sand soil, a special type of soil located in low hillside of west Shanghai, as well as the influence of two factors: CaCl2 as a cementing material and NiCl2 as a co-factor, which was rarely researched before and can be viewed as the influence of urease activity on bio-stimulation result. The direct shear test, unconfined compressive test, supersonic wave test and calcite mass test have been carried out to evaluate engineering performance of yellow silty sand soil enhanced by bio-stimulation method as well as their relationship with concentration of CaCl2 and NiCl2 solutions. The result shows that bio-stimulation method can significantly promote the characteristics of Shanghai yellow silty sand soil and there seems to be extreme point for concentration of CaCl2 and NiCl2 solution in improving the quality of Shanghai yellow silty sand. Microstructure and composition of treated soil by bio-stimulation method have also been analyzed by Scanning Electron Microscope (SEM) and Energy dispersive Spectrometer (EDS), with giving the corresponding micro-mechanism of bio-cementation among soil particles.

An Experimental Study of Strengthing of Concrete by Bacterial Mineral Precipitation

Abstract: A new technique in remediating cracks and fissures in concrete by utilizing microbiologically induced Calcite (CaCo3) precipitation is discussed. Microbiologically induced calcite precipitation (MICP) is a technique that comes under a broader category of science called Bio Mineralization. It is a process by which living organisms form inorganic solids. Bacillus subtilis, a common soil bacterium can induce the precipitation of calcite. The objective of the present investigation is to study the potential application of bacterial species i.e. Bacillus subtilis to improve the strength of cement concrete. Here we have made an attempt to incorporate dormant but viable bacteria in the concrete matrix which will contribute to the strength of the concrete. In this project, bacterial concrete is prepared under grade of concrete M30.The design mix proportioning also carried under IS code provision. Testing of specimens are carried at 7 days, 14 days and 28 days of curing by Compression Testing Machine and Universal Testing Machine for corresponding specimens.

Contribution of bacterial cells as nucleation centers in microbiologically induced CaCO3 precipitation-A mathematical modeling approach.

The microbiologically induced calcite precipitation (MICP) has been extensively studied for geotechnical engineering through simultaneous action of natural phenomena and engineering processes. The focus of bacterial contribution to the MICP has been directed to calcium carbonate productivity, while the additional bacterial role as a crystal nucleation center was not explained especially from a mathematical prediction modeling point of view. Therefore, this study provides explanations and a mathematical modeling approach of bacterial influence on the MICP induced by newly-isolated ureolytic Bacillus strains and Sporosarcina pasteurii DSM 33. Using the obtained results of low-cost, rapid, and simple assays, artificial neural network modeling was applied for cell surface predispositions, pH changes as well as calcium-involved function in biofilm formation during the MICP, for the first time. Based on the obtained contribution of the alkalophilic/alkaloresistant bacteria, calcite precipitation can be significantly directed by the presence, of ureolytic bacterial cells as nucleation centers during CaCO3 precipitation as well as their morphology, surface characteristics, potential to form a biofilm, and/or generate pH changes.

Microbiologically induced calcite precipitation technology for mineralizing lead and cadmium in landfill leachate

As a new bioremediation technology for toxic metals, microbiologically induced calcite precipitation (MICP) is gradually becoming a research focus. This study investigated the application of MICP to mineralize toxic metals (lead and cadmium) in landfill leachate for the first time. In the experiment of remediating synthetic landfill leachate (SLL) contaminated by Pb2+, 100% of the 20 mg/L Pb2+ was removed when the maximum urease activity was only 20.96 U/ml. Scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS) and laser particle size characterizations of the precipitates indicate the formation of agglomerated square particles, 76.9% of which had sizes that ranged from 33.93 to 57.06 μm. Fourier transform infrared spectroscopic and X-ray diffraction analyses confirmed that the precipitates consisted predominantly of calcite crystals, and the unit cell lattice constants of the precipitates (a = b = 4.984 Å, c = 17.171 Å) matched those of calcite, while lead was fixed as hydrocerussite. In addition, the Pb-MICP precipitates were stable under continuous acid degradation (pH = 5.5), and only 1.76% of the lead was released after 15 days. In the verification test of toxic metals remediation in a real landfill leachate (RLL), all of the Pb2+ and Cd2+ (initial concentrations: Pb2+ = 25 mg/L; Cd2+ = 5.6205 mg/L) was mineralized simultaneously, which further confirmed the feasibility of MICP for toxic metal remediation in landfill leachate. However, optimizing the urea dosage and combining the ammonium recovery are necessary strategies required for improving the economic and environmental benefits of the MICP process.

Geotechnical properties of unprocessed soil from abandoned Mamut mine in Sabah, Borneo

The issue related to the geotechnical stability of land mining area in Malaysia had become more critical after a strong earthquake struck Sabah, Borneo in 2015 centred in Ranau District where Mamut copper mine is located. As part of safety assessment and future planning, knowledge of soil characteristics in this risky area is necessary. This paper presents some findings on geotechnical properties of unprocessed soil obtained from the abandoned mine. Results found that Mamut soil can be classified as SW and has higher coarse-grained percentage (97.4%) compared to other copper mines elsewhere. The soil also has higher permeability (3.61 x 10−3 m/s), lower organic content (0.15%), lower pH (4.53), higher specific gravity (2.75) and higher maximum dry density (1780 kg/m3). Mamut soil is found to be cohesionless, while the angle of friction shows a variation with the relative compaction. Chemical analysis shows that SiO2 and C12H10MgO6S2 are the two predominant compounds of the soil. Morphologically, Mamut soil appears to be composed of powdered and hardened particles with dark brown colour. They contain higher amount of irregular-shaped particles but well-rounded and spherical shapes are also observed. Smooth surfaces with no agglomeration between particles indicates that the strength value of the soil is low due to the weak bonding between the loose grain structure. These findings suggest that Mamut soil is suitable for chemical stabilisation or remediation method such as microbiologically induced calcite precipitation (MICP).

A Study On Strength Characters of Bacterial Concrete

Concrete is unique in all construction material because it is specificallydesigned for civil engineering purpose. It plays a critical role in the construction of the nation’s infrastructure. The cracks in concrete whether major or minor are one of the weakness of concrete. These cracks will be developed over a period of time which adversely affect its strength and durability. Hence an attempt is made here using bacteria belongs to bacillus family used to heal minor cracks in concrete. These types of bacteria were introduced externallyto improve the process of Microbiologically Induced Calcite Precipitation (MICP) in concrete. It (MICP) is a technique that comes under thestudy of science called bio mineralization. Bacillus subtilis, one of the soil bacterium can induce the Precipitation of calcite. The present work is to study the potential application of bacterial species bacillus subtilis in healing the minor cracks there by improving the strength of cement concrete. Here M20 grade of concrete was used for the study. The concrete mix was prepared as per IS specifications. Testing on specimens for compression was carried out after 28 days of curing using both CTM and NDT equipment’s and results are tabulated. Minor cracks less than one millimeter are induced artificially in concrete and the broth solution having bacterial culture in it are injected along the crack pattern. After healing, compressive strength was tested using NDT equipment and was found a marginal improvement in the strength criteria.

Effect of Bacillus cohnii on Some Physicomechanical and Microstructural Properties of Ordinary Portland Cement

Cement-made materials face durability and sustainability challenges. This is majorly caused by the presence of cracks. Cracking affects the mechanical strength of cement-based materials. Microbiologically induced calcite precipitation (MICP) has been found to enhance compressive strength, thus enhancing on the mechanical and durability properties of these materials. This paper presents the findings of a study conducted to investigate the effect of Bacillus cohnii on compressive strength development of OPC mortar prisms and the effect of Bacillus cohnii on cement setting time and soundness. Microbial concentration of 1.0 × 107 cells·ml−1 was used. Compressive strength tests analyses were carried out for each category of mortar prisms. Compressive strength tests were carried out on the 2nd, 7th, 14th, 28th, 56th, and 90th day of curing in distilled water and microbial solutions. All microbial mortars exhibited a greater compressive strength compared to the control with the highest observed at 90 days. Highest percentage gain in compressive strength was observed at 90 days which is 28.3%. Microstructural analysis was carried out using a scanning electron microscope (SEM) after 28 days of curing. The results indicated the presence of calcium carbonate and more calcium silicate hydrate (CSH) deposits on the bacterial mortars. The bacteria did not have an effect on cement soundness. Setting time was significantly accelerated.

Preliminary approach to bio-based surface healing of structural repair cement mortars

Mitigating the maintenance and repair costs of structures and infrastructures is a major problem in all countries. The aim of this research work is to analyse the performance of surface healing technique for crack control of cement-based mortars for structural repair in maritime environments. Microbiologically induced calcite precipitation (MICP) with ureolytic bacteria Sporosarcina pasteuri DSM 33 was introduced for crack-healing. Only main cracks were filled with the bioagent (bacterial cells and nutrients) for cost-saving purpose. It is intended to analyse the effectiveness of this technique for structural application in areas exposed to cyclic moisture changes. Hygric properties and their relation to durability increase were analysed through moisture buffering tests, capillary, porosity, compressive strength, SEM and microscopy analysis before and after bio-agent application to evaluate the evolution of the precipitation. For the first time, moisture buffering value (MBV) was used to evaluate the performance of the self-healed mortar and time needed for bacterial precipitation. The treated material can be classified as good in terms of MBV, and there was a general increasing trend of moisture buffering behaviour in self-healed samples. SEM analysis showed distinctive differences between the treated and non-treated cracks. The results show that bio-agent had remarkable effect on compressive strength recovery (over 87% of original value) after 21 days of healing and positively affected the initial stage of capillary absorption.

Impact of Bacillus subtilis bacterium on the properties of concrete

The activity life span of concrete sharply decreases with the formation of cracks on its surface which leads to corrosion of concrete. To deal with such problems newer technologies are being adopted for concrete production and one such high-tech concrete is self-healing concrete by Microbiologically Induced Calcite Precipitation (MICP). This kind of concrete can initiate biological activity to deal with its cracks and to recover itself. This research paper throws light on the experimental investigation carried out to evaluate the impacts of Bacillus subtilis bacteria on concrete properties. The experiment has been carried out using six different bacterial concentrations in the concrete mixes, such as 10, 102, 103, 104, 105 and 106 cells/ml of water. Concrete specimens were left for 7 days, 14 days and 28 days of curing. Tests were conducted for measuring properties like compressive strength, split tensile strength, flexural strength were measured in different interval of curing period. The research showed that concrete having bacterial infusion in all cell concentration have increment in strength in comparison to control mix. Maximum of 32% increase in compressive strength, 14% increase in split tensile strength and 29% increase in flexural strength were observed in the specimen having bacterial concentration of 105 cells/ml of water. Microbial calcite precipitation was visualized by Scanning Electron Microscopy (SEM), which showed the growth of filler materials i.e. calcite deposition inside the concrete pores, which results in denser concrete causing a rise in its strength.

Use of Genetically Modified Bacteria to Repair Cracks in Concrete.

In this paper, we studied the crack-repair by spraying bacteria-based liquid around the cracks in concrete. To enhance the repair efficiency and speed up the repair process, the transposon mutagenesis method was employed to modify the genes of Bacillus halodurans and create a mutant bacterial strain with higher efficiency of calcium carbonate productivity by catalyzing the combination of carbonate and calcium ion. The efficiency of crack-repairing in concrete by spraying two kinds of bacterial liquid was evaluated via image analysis, X-ray computed tomography (X-CT) scanning technology and the sorptivity test. The results show that the crack-repair efficiency was enhanced very evidently by spraying genetically modified bacterial-liquid as no microbiologically induced calcite precipitation (MICP) was found within the cracks for concrete samples sprayed using wild type bacterial-liquid. In addition, the crack-repair process was also shortened significantly in the case of genetically modified bacteria.

Performance enhancement of brick aggregate concrete using microbiologically induced calcite precipitation

The use of brick aggregates is very common in Bangladesh and nearby regions as artificial aggregate replacing natural stone. To ensure sustainable construction, finding a way to enhance its durability is extremely necessary. Microbiologically Induced Calcite Precipitation (MICP) using indigenous urease positive bacteria collected from soil showed promising results in initial research, hence further investigation has been carried out for comprehensive understanding on the effectiveness of this method. Two incubation periods of 24 hours and 48 hours were considered for bacterial culture. Absorptiometric method was used to examine population growth of bacteria due to varying incubation period. Both Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were used to identify the presence of CaCO3 due to bio-treatment. In addition to Rapid Migration Test (RMT), Rapid Chloride Penetration Test (RCPT) was conducted to evaluate reduction of concrete permeability due to application of treated brick aggregate. It has been found that 48 hours incubation was more effective than 24 hours incubation. The longer incubation resulted in almost twofold reduction in aggregate absorption test. Compressive Strength, RCPT and RMT of brick aggregate concrete resulting from 48 hours incubation showed 14%, 27% and 43% improvement over untreated brick concrete, respectively.

In-vitro bio-mineralization of arsenic and lead from aqueous solution and soil by wood rot fungus, Trichoderma sp.

In the present study, we investigated the role of calcite, i.e., microbiologically-induced precipitate by ureolytic Trichoderma sp. MG, in remediation of soils contaminated with arsenic (As) and lead (Pb). The fungus tolerates high concentrations of As (500 mg/L) and Pb (650 mg/L). The effects of three factors, i.e., urea concentration, CaCl2 concentration and pH, on urease production and bio-mineralization of As and Pb were investigated using Box-Behnken design. The maximum urease production (920 U/mL) and metal removal efficiency (68% and 59% for Pb and AS, respectively) were observed in the medium containing urea of 300 mM and CaCl2 of 75 mM at pH 9.0. Fourier transform infrared spectroscopy result revealed the formation of metal carbonates by the isolate MG. Sequential extraction of metals revealed that the carbonate fractions of As and Pb were increased to 46.4% and 42.4% in bioremediated soil, whereas in control they were 35.5% and 32.5%, respectively. The X-ray powder diffraction result further confirmed the role of calcite precipitate in bioremediation of As- and Pb-contaminated soils. The results points out that the microbiologically-induced calcite precipitation is a feasible, eco-friendly technology for the bioremediation of As- and Pb-contaminated sites.