Implication of Microbial Biofilm in the Biodeterioration of Cementitious Materials in the specific context of Anaerobic Digestion Conditions

Abstract

Anaerobic digestion is a renewable energy production process based on the fermentation of biodegradable biomass. The industrial digesters are usually made of cementitious materials. However, the microbial production of several aggressive compounds (CO2, NH4 + and volatile fatty acids) during the digestion leads to the deterioration of the concrete structure. The growth of microbial biofilm on the surface of concrete is suspected to generate an even more severe biodeterioration. The goal of this study is to provide a better understanding of the biofilm involvement in the biodeterioration of cementitious materials during an anaerobic digestion process. More precisely, this study is focused on the biofilm heterogeneity and its development on cementitious materials in anaerobic digestion. Lab scale anaerobic bioreactors mimicking industrial anaerobic digestion medium were carried out to immerge CEM I cement pastes in this medium during 2, 3, 4 and 5 weeks. The deterioration of cement pastes was evaluated by using a scanning electron microscope to determine the deteriorated thickness and to quantify the volatile fatty acids in the medium. Biofilm attached on the surface of cement pastes was analyzed through molecular biology techniques, such as 16s rRNA gene sequencing analysis and qPCR.To assess the biofilm heterogeneity, successive stalls of the layers of the biofilm were realized using physical biofilm removal techniques. Three microbial fractions are defined: the planktonic microorganisms, the lousy attached and the strongly attached ones. Results showed that the methanogenic Archaea are found mainly in the medium while around half of the microbial population strongly attached is made of acidogenic bacteria. These results suggest that the biofilm could increase the biodétérioration of concrete since the fatty acids are massively produced at the proximity of the surface of the cementitious samples.

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