The effect of pH profiles in methanogenic aggregates on the kinetics of acetate conversion

Abstract

Allatragt--Due to the conversion of acetic acid into the weaker carbonic acid and methane, the pH inside methanogani¢ aggregates is higher than in the bulk liquid. The pH profiles in aggregates were measured with pH microelectrodes. These profiles strongly determine the macro-kinetics of the aggregate, by their influence on the values of the growth parameters/(1 and ~. Acetate transport resistances were not limiting for the conversion rate in methanogenic aggregates. Nevertheless, the effectiveness factor v/did not approach unity, but amounted to 0.57-0.62 in the acetate concentration range relevant for most methanoge.nic reactors. The value of ¢ is determined almost entirely by the pH profiles inside the aggregates. It was concluded that for the physical/mathematical description of the conversion in methanogenic aggregates, information on the pH gradients and the pH dependency of the growth pa~rs is indispensable. Batch experiments showed that acetate uptake by aggregates was not coupled directly to methanogenesis. Consumed acetate was not converted instantaneously to methane, suggesting the conversion to proceed via a pool of acetate or reserve material.

Effects of Organic Loading Rate on the Performance of a Pressurized Anaerobic Filter in Two-Phase Anaerobic Digestion

“…This might be attributed to the thick biofilm formed in the reactor with the help of the sintered glass as a carrier material. Several papers reported that there were pH gradients in the biofilm system and the pH value inside methanogenic aggregates was higher than that in the process liquid [17,18]. Thus, the adverse impact might have been smoothed.…”

Layered Structure of Bacterial and Archaeal Communities and Their In Situ Activities in Anaerobic Granules

“…The spatial distributions of in situ metabolic functions in anaerobic granules are poorly understood, mainly due to a lack of specific analytical tools with sufficient spatial resolution. Only a few studies have analyzed the distributions of glucose-degrading, fermentative, and sulfate-reducing activities in UASB granules by using microsensors for glucose, pH, and hydrogen sulfide (H 2 S) (13,21,42). In those studies, CH 4 production rates were not, however, directly measured with microsensors.…”

Explaining the enhanced performance of pulsed bioreactors by mechanistic modeling

“…Some authors affirm that external and internal mass transfer resistance influences the substrate consumption rate, 6-10 while others did not observe mass transport limitations in this type of biomass. 11,12 In fact, pH gradient within the granule would have more influence on the conversion rate than mass transfer resistance. 12 It has been found that external mass transport resistance (liquid-solid) was negligible in denitrifying filters 13 and, in theory, in methanogenic biofilms with a thickness lower than 1 mm 14 and in fixed bed bioreactors with aggregates higher than 2 mm.…”

“…11,12 In fact, pH gradient within the granule would have more influence on the conversion rate than mass transfer resistance. 12 It has been found that external mass transport resistance (liquid-solid) was negligible in denitrifying filters 13 and, in theory, in methanogenic biofilms with a thickness lower than 1 mm 14 and in fixed bed bioreactors with aggregates higher than 2 mm. 15 In another work, 10 external mass transfer was practically null operating at upflow velocities higher than 1 m/h.…”