Effects of Microorganisms Growth on the Long-Term Stability of Cement and Bitumen

Cement is used as a coating matrix for nuclear waste or as an engineered barrier of waste repositories situated in geological formations. The effect of mineral acids excreted by bacteria (Thiobacillus) or organic acids produced by fungi, on the biodegradation of cement is discussed. Organic acids are quantitatively and qualitatively determined during growth of fungi over a two-year period. Even with high pH conditions, pH of the cement ≈11, growth of microorganisms occurs. Biodeterioration of cement is expressed in terms of bioleaching velocity of calcium and is observed by electron microscopy. Bitumen is commonly used as a matrix for the long-term storage of radioactive wastes. Long-term biodegrability of bitumen is discussed as a function of its chemical composition and various studied microorganisms.