Abstract
The following two novel devices, pH microelectrode and glucose-enzyme microelectrode were originally fabricated in this study, to clarify pH and substrate in situ profiles within anaerobically grown microbial-aggregates. The glucose microsensor consists of double glass-tips in order to eliminate an effect of pH, and has a measurement range of 0-500 mg/L. The inner glass-tip of 10 μm diameter was coated with glucose oxidase and covered with the outer glass-tip of 30μm diameter. The pH microsensor has a 10 μm diameter of glass-tip which was filled with ion selective membrane liquid, and covers the pH range of 4-10.
Both microelectrodes were applied to anaerobic granular sludge having a diameter of approximately 2 mm harvested from an UASB (upflow anaerobic sludge blanket) reactor treating an artificial wastewater. It proved that the pH profile in the granule tended to firstly decrease toward granule depth, and then to increase after attaining a minimum point at which the glucose concentration decreased to around zero. With higher glucose concentration in the bulk liquid, pH gradient within granules became steeper and the minimum pH value dropped more significantly.
A simple mathematical model consisting of diffusion and consumption of substrate was developedto estimate substrate profiles within granule. The model could simulate well thepH and glucose profiles measured by the microelectrodes. The results of measurements and simulations suggests that acetogenic bacteria should dominate near the granule surface, on the other hand methanogenic bacteria should be dominate inside of the granule.
