Thermodynamically enhancing propionic acid degradation by using sulfate as an external electron acceptor in a thermophilic anaerobic membrane reactor

Electrical stress and acid orange 7 synergistically clear the blockage of electron flow in the methanogenesis of low-strength wastewater

“…Beware that AO7, with a higher reduction potential than the redox couples Acetate/CH 4 and HCO 3 − /CH 4 (about −0.24 V), may compete with methanogens for acetate and hydrogen, which could explain the contradictory effects of AO7 on methanogenesis in R4. Similar issues arise with other electron acceptors like sulfate and iron ions [ 7 ]. Theoretically, whether electron acceptors competitively inhibit methanogenesis depends on various factors, such as the type of electron donors, the concentration of electron acceptors, and their degradation dynamics [ 63 , 64 ].…”

“…In typical AD systems, the conversion of fermentation intermediates to acetate and hydrogen mainly relies on syntrophic hydrogen-producing acetogens (HPA) [ 43 , 44 ]. As the symbiotic partner, HPA's evolution and metabolism are regulated by methanogenesis and are difficult to develop in low-strength wastewater [ 6 , 7 ]. In this experiment, only three acetogenic genera were detected with extremely low abundances (1.0 ± 0.4% without AO7 and 3.2 ± 0.3% with AO7), including two HPA ( Candidatus Cloacamonas and Syntrophomonas ) [ [45] , [46] , [47] ] and one homoacetogen ( Acetobacterium ), which produces acetate from CO 2 and H 2 [ 48 ].…”

“…The metabolism rate of acetoclastic methanogens (AM) is generally very low, approximately a quarter of that of fermentative bacteria (FB), and further decreases when acetate is insufficient (with a half-saturation rate constant of 150 mg L −1 for AM) [ 5 ]. Additionally, in the absence of an adequate population of methanogens as hydrogen scavengers, the anaerobic oxidation of fermentation intermediates (mainly volatile fatty acids) to acetate (i.e., acetogenesis) becomes thermodynamically unfavorable [ 6 , 7 ]. This results in the trapping of electrons in fermentation products and exacerbates the starvation of methanogens.…”

“…), and they are characterized by the ability of extracellular electron transfer through cytochromes, conductive pili, or redox-active shuttles [ 19 , 23 ]. Interestingly, observations from studies on pollutant remediation indicated that EAB could be easily enriched in systems with exogenous electrophiles serving as electron acceptors, such as sulfate [ 7 ], nitrate [ 24 ], ferric iron [ 25 ], and even certain organic pollutants [ 26 , 27 ]. This presents an opportunity to enhance EAB development and metabolism by using exogenous electron acceptors as a special domestication method.…”

Enhancement of organic matter degradation and methane gas production of anaerobic granular sludge by degasification of dissolved hydrogen gas

“…Propionate can only be oxidized if a syntrophic association is conducted by propionate-oxidizing bacteria and hydrogen-consuming bacteria. As propionate degraders, syntrophic propionate-oxidizing bacteria play an important role in the anaerobic food chain (Qiao et al, 2016). However, propionate-degradation is often inhibited by propionate (substrate inhibition).…”