Biodeterioration of cementitious materials in biogas digester

WOS:000372185700004International audienceIn biogas production plants, concrete structures suffer chemical and biological attacks during the anaerobic digestion process. The attack on concrete may be linked to the effects of (i) organic acids; (ii) ammonium and CO2 co-produced by the microorganisms' metabolisms; and (iii) the bacteria's ability to form biofilms on the concrete surface. In a context of biogas industry expansion, the mechanisms of concrete deterioration need to be better understood in order to propose innovative, efficient solutions. This study aims, firstly, to characterise the evolution of the biochemical composition of the biodegradable wastes during digestion so as to identify the compounds that are aggressive for concrete. Secondly, it aims to evaluate the mechanisms of concrete deterioration in anaerobic digesters. CEM I paste specimens were immersed in synthetic inoculated biowaste in anaerobic digestion conditions. The liquid fractions were analysed chemically. The alteration mechanisms of the cementitious matrices were investigated using XRD and SEM analyses. The maximal total concentration of organic acids was 65 mmol/L in the liquid fraction during the digestion process. The pH evolution showed two phases: acidification in the first few days and then a slow increase to pH 7-8. In only 4 weeks, an abundant biofilm developed on the cement paste surface. Biodeterioration leads to calcium leaching and carbonation of the cement paste.In biogas production plants, concrete structures suffer chemical and biological attacks during the anaerobic digestion process. The attack on concrete may be linked to the effects of (i) organic acids; (ii) ammonium and CO2 co-produced by the microorganisms' metabolisms; and (iii) the bacteria's ability to form biofilms on the concrete surface. In a context of biogas industry expansion, the mechanisms of concrete deterioration need to be better understood in order to propose innovative, efficient solutions. This study aims, firstly, to characterise the evolution of the biochemical composition of the biodegradable wastes during digestion so as to identify the compounds that are aggressive for concrete. Secondly, it aims to evaluate the mechanisms of concrete deterioration in anaerobic digesters. CEM I paste specimens were immersed in synthetic inoculated biowaste in anaerobic digestion conditions. The liquid fractions were analysed chemically. The alteration mechanisms of the cementitious matrices were investigated using XRD and SEM analyses. The maximal total concentration of organic acids was 65 mmol/L in the liquid fraction during the digestion process. The pH evolution showed two phases: acidification in the first few days and then a slow increase to pH 7-8. In only 4 weeks, an abundant biofilm developed on the cement paste surface. Biodeterioration leads to calcium leaching and carbonation of the cement paste. Résumé-Biodétérioration des matériaux cimentaires dans les structures de méthanisation. Dans les digesteurs de méthanisation, le béton des structures subit des attaques d'origine chimique et biologique. L'attaque sur le béton serait liéeà la combinaison des effets des acides organiques, de l'ammonium et du CO2 produits par le métabolisme microbien etégalementà la capacité des bactériesà former des biofilmsà la surface du béton. Le secteur de la méthanisationétant en pleine expansion, l'enjeu de ce travail est de progresser dans la compréhension des mécanismes de détérioration des bétons dans ces environnements afin proposer des solutions durables. Cetteétude vise, dans un premier temps,à déterminer les caractéristiques chimiques des déchets organiques (pH, concentrations en composés chimiques agressifs) au cours de leur fermentation. Dans un second temps, les mécanismes de détérioration des bétons dans les conditions de méthanisation sontévalués. Des pâtes de CEM I ontété immergées dans un mélange de déchets organiques en conditions de digestion anaérobie. Le milieu aété analysé chimiquement tout au long du processus de digestion. Les pâtes de ciment ontété analysées par DRX et MEB+EDS. La concentration totale maximale en acides organiquesétait de 65 mmol/L dans les bioréacteurs. L'évolution du pH présentait deux phases : une acidification dans les premiers jours et une lente augmentation jusqu'à pH 7-8. En 4 semaines, un biofilm abondant s'est développéà la surface du matériau. La biodétérioration s'est traduite par la lixiviation du calcium et la carbonatation du matériau