Microbial-ecological significance of sulfide precipitation within anaerobic granular sludge revealed by micro-electrodes study

Micro-electrodes were applied to anaerobic granular sludge, which was devel oped in a UASB reactor, to examine intra-granule profiles with respect to p H, glucose and sulfide. When glucose was employed as a bulk liquid substrat e, the micro-electrodes study demonstrated the pH behavior along granule de pth: pH decrement at the granule exterior portion due to acid formation (bu ildup of acidity), and subsequent pH increment at the granule inner portion due to the consumption of acid (buildup of alkalinity), Sulfide micro-elec trode proved sulfate reduction that mostly occurred at the granule exterior portion. Chemical equilibrium consideration evidently explained the occurr ence of ferric sulfide predominantly in the interior portion, which account s well for the morphology of a representative double-layered structure of g ranules grown on a low level of sulfate, Inorganic elements distribution wi thin anaerobic granule was examined by electron probe X-ray micro analysis (EPMA) and ICP methods. The presence of crystalline calcium carbonate (calc ite) was identified by X-ray diffraction analysis. (C) 2001 Elsevier Scienc e Ltd. All rights reserved.