Microbial Stability Evaluation of Waste Containment Materials Using a Biofilm Formation Approach

A biofilm formation method was used to evaluate the stability of a phosphate-bonded ceramic (PBC) waste form (waste containment material), a cement/manganese tailings waste form, and a ceramic-coated metal strip, in the presence of Thiobacillus thiooxidans. All the waste disposal materials evaluated showed evidence of the growth of biofilm on their surfaces, and exhibited varying degrees of susceptibility to microbial degradation. Two types of PBC waste forms were evaluated, with and without fly ash. The PBC waste form without fly ash exhibited higher instability to microbial degradation than the one with fly ash. The addition of fly ash to the PBC waste form (with fly ash) was shown to improve its stability to microbial degradation. Two formulations of the cement/manganese tailings waste forms were evaluated. These are: 80% cement/20% manganese tailings and 30% cement/70% manganese tailings. The 30% cement/70% manganese tailings formulation showed higher instability to microbial degradation than the 80% cement/20% manganese tailings formulation. The growth of T. thiooxidans on the two manganese containing samples indicates that the presence of manganese did not offer antimicrobial protection. Two sets of ceramic coated metal strips (Yucca 2 and Yucca 4) were evaluated. Both sets showed evidence of instability to microbial degradation, with Yucca 2 showing slightly higher instability than Yucca 4.