e Microbially induced carbonate precipitation (MICP) applied in the construction industry poses several disadvantages such as ammonia release to the air and nitric acid production. An alternative MICP from calcium formate by Methylocystis parvus OBBP is presented here to overcome these disadvantages. To induce calcium carbonate precipitation, M. parvus was incubated at different calcium formate concentrations and starting culture densities. Up to 91.4% ؎ 1.6% of the initial calcium was precipitated in the methane-amended cultures compared to 35.1% ؎ 11.9% when methane was not added. Because the bacteria could only utilize methane for growth, higher culture densities and subsequently calcium removals were exhibited in the cultures when methane was added. A higher calcium carbonate precipitate yield was obtained when higher culture densities were used but not necessarily when more calcium formate was added. This was mainly due to salt inhibition of the bacterial activity at a high calcium formate concentration. A maximum 0.67 ؎ 0.03 g of CaCO 3 g of Ca(CHOOH) 2 ؊1 calcium carbonate precipitate yield was obtained when a culture of 10 9 cells ml ؊1 and 5 g of calcium formate liter ؊1 were used. Compared to the current strategy employing biogenic urea degradation as the basis for MICP, our approach presents significant improvements in the environmental sustainability of the application in the construction industry. Microbially induced carbonate precipitation (MICP) is a wellknown process and has been extensively described in the past (1-3). In short, MICP produces carbonate minerals, e.g., calcium carbonate, as a result of alterations in environmental conditions. In nature, examples of MICP include calcite formation in soils (4), limestone caves (5), seas (6), and soda lakes (7). Four different key parameters that govern microbially induced calcium carbonate precipitation are the: (i) concentration of nonprecipitated calcium, (ii) concentration of the total inorganic carbon, (iii) pH, and (iv) availability of nucleation sites for calcium carbonate crystal formation (3). Among the four parameters, bacterial activities mainly influence the pH of the environment (1).MICP is the basis for several biotechnological applications in the construction sector (for a review, see reference 1 and references therein). These include the use of calcium carbonate precipitate to protect concrete surface against the ingress of deleterious substances (e.g., chloride ions) (8) or to heal cracks in aging concrete (9, 10). Among the bacterial activities that can induce calcium carbonate precipitation, urea degradation by heterotrophic bacteria is typically used for applications on building materials. In biogenic urea degradation, urea is transformed to ammonia and carbonate ions to initiate precipitation (11). Bacillus spp. (e.g., B. sphaericus) is the most commonly applied urea degrader for MICP in the construction sector due to several advantages such as the high initial urea degradation rate by the strain and a highly negative potential ...

Biological treatment using methane-oxidizing bacteria (MOB) immobilized on six porous carrier materials have been used to mitigate methane emission. Experiments were performed with different MOB inoculated in building materials at high (~20 % (v/v)) and low (~100 ppmv) methane mixing ratios. Methylocystis parvus in autoclaved aerated concrete (AAC) exhibited the highest methane removal rate at high (28.5 ± 3.8 μg CH₄ g⁻¹ building material h⁻¹) and low (1.7 ± 0.4 μg CH₄ g⁻¹ building material h⁻¹) methane mixing ratio. Due to the higher volume of pores with diameter >5 μm compared to other materials tested, AAC was able to adsorb more bacteria which might explain for the higher methane removal observed. The total methane and carbon dioxide-carbon in the headspace was decreased for 65.2 ± 10.9 % when M. parvus in Ytong was incubated for 100 h. This study showed that immobilized MOB on building materials could be used to remove methane from the air and also act as carbon sink.

The effectiveness of Microbiologically Induced Carbonate Precipitation (MICP) from the formate oxidation by Methylocystis parvus OBBP as an alternative process for concrete protection was investigated. MICP was induced on Autoclaved Aerated Concrete (AAC), the model material, by immersing the material in 109 M. parvus cells mL−1 containing 5 g L−1 of calcium formate. A 2 days immersion of the material gave the maximum weight increase of the specimens (38 ± 19 mg) and this was likely due to the deposition of calcium carbonate, biomass, and unconverted calcium formate. The solid deposition mainly occurred in the micropores of the specimen, close to the outer surface. A significantly lower water absorption was observed in the bacterially treated specimens compared to the non-treated ones (up to 2.92 ± 0.91 kg m−2) and this could be attributed to the solid deposition. However, the sonication test demonstrated that the bacterial treatment did not give a consolidating effect to the material. Overall, compared to the currently employed urea hydrolysis process, the formate-based MICP by M. parvus offers a more environmentally friendly approach for the biotechnological application to protect concrete.

The methane removal capacity of mixed methane-oxidizing bacteria (MOB) culture in a biofilter setup using autoclaved aerated concrete (AAC) as a highly porous carrier material was tested. Batch experiment was performed to optimize MOB immobilization on AAC specimens where optimum methane removal was obtained when calcium chloride was not added during bacterial inoculation step and 10-mm-thick AAC specimens were used. The immobilized MOB could remove methane at low concentration (~1000 ppmv) in a biofilter setup for 127 days at average removal efficiency (RE) of 28.7 %. Unlike a plug flow reactor, increasing the total volume of the filter by adding a biofilter in series did not result in higher total RE. MOB also exhibited a higher abundance at the bottom of the filter, in proximity with the methane gas inlet where a high methane concentration was found. Overall, an efficient methane biofilter performance could be obtained using AAC as the carrier material.

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