Abstract
Inhibitory action of mercury on anaerobic digestion, which is composed of many steps degrading organic matters to methane with various bacteria, is studied by batch experiments using glucose as a substrate.
Inhibition by mercury was often observed as a retardation of beginning of acidogenesis and methanogenesis, a decrease of production rate of volatile fatty acids (VFA) and/or methane, and a color change in mixed liquor from coal-black to whitish black. The recovery of color to black was observed when acidogenesis was recovered from inhibition, while methanogenesis remained being inhibited. From detail researches, it is concluded that inhibitory action of mercury is intensely affected by sulfide coexisting in the environment because mercury must capture a sulfide ion from many sulfides in precipitation such as FeS and then precipitate as a very stable HgS to become non-toxic. It is also concluded that each process of digestion has a specific sensitivity to mercury, i.e. methanogenesis is far more sensitive than acidogenesis in total process, and n-butyric acid production is more sensitive than acetic acid production in acidogenesis.
