Direct interspecies electrons transfer (DIET) is a syntrophic metabolism in which free electrons flow from one cell to another without being shuttled by reduced molecules such as molecular hydrogen or formate. As more and more microorganisms show a capacity for electron exchange, either to export or import them, it becomes obvious that DIET is a syntrophic metabolism that is much more present in nature than previously thought. This article reviews literature related to DIET, specifically in reference to anaerobic digestion. Anaerobic granular sludge, a biofilm, is a specialized microenvironment where syntrophic bacterial and archaeal organisms grow together in close proximity. Exoelectrogenic bacteria degrading organic substrates or intermediates need an electron sink and electrotrophic methanogens represent perfect partners to assimilate those electrons and produce methane. The granule extracellular polymeric substances by making the biofilm matrix more conductive, play a role as electrons carrier in DIET.

Direct Interspecies Electron Transfer in Anaerobic Digestion: A Review

granules suspended ina mineral mediumlacking glucose exhibited a distinct internal pHdecrease ofabout1U within thegranule, suggesting strong metabolism bytheacidogenic bacteria. Molasses-acclimatized andagedgranules suspended inmineral mediumdidnotexhibit such apHdecrease, suggesting theimportance ofthemetabolic state ofthese acidogens. ThepHgradient didnotoccurindeactivated granules andwas notobservable in strongly buffered media(mineral mediumcontaining 33mM phosphate or reactor liquid). Whenglucose (0.5 to5.0mM) was addedtothemineral medium, granules exhibited a convexpHprofile. Glucose consumption was located exclusively intheouter200to300 .moftheaggregates (meandiameter = 1.5mm).Theaddition of20mM 2-bromoethanesulfonic acidtothemineral mediumindicated that thehigher pHlevels inthecentre ofthegranule appeared toberelated totheactivity ofmethanogens. Itissuggested thatacidogenic activity occurspredominantly intheouter200to300,umoftheaggregate andmethanogenic activity occurs predominantly inthecenter oftheinvestigated granules. Themicrobial community involved inanaerobic digestion processes innatural habitats aswellasinmanufactured digestion systems isknowntobequite complex, comprising hydrolytic, fermentative, acidogenic, andmethanogenic bacteria. Complete anaerobic degradation oforganic matter to methane (CH4)andcarbon dioxide (CO2) requires theconcerted action ofthese different microbial species (4,13,63). Anaerobic wastewater treatment relies onthecontrol of these microbial interactions byapplying appropriate reactor conditions andreactor configurations (22, 40). Theupflow anaerobic sludge blanket (UASB)reactor concept (29, 30) uncouples solid andhydraulic retention times bybiomass accumulation incompact, well-settling aggregates. This granular configuration hasseveral engineering advantages suchasamaximal microorganism-to-space ratio andfacili

/pdf/heterogeneous-distribution-of-microbial-activity-in-2uadtxzfpy.pdf

Heterogeneous Distribution of Microbial Activity in Methanogenic Aggregates: pH and Glucose Microprofiles

The phenomenon of granulation was studied in anaerobic sequencing batch reactors (ASBRs) treating a synthetic sucrose wastewater. The objective was to study methods of minimizing the time typically required for start-up of anaerobic processes, such as the ASBR. Specifically, it was hypothesized that development of a granular biomass soon after initial start-up of the ASBR would significantly decrease the overall time required to achieve given organic and hydraulic loading rates. Laboratory-scale ASBRs were seeded with anaerobically digested municipal biosolids and operated until granulation was observed or for a period of 5 months without granule development, whichever occurred first. Granule development was measured by determination of the average particle diameter of a representative sample of biosolids from the ASBRs. Granulation enhancements were added to the ASBRs to initiate early granule development and to aid in start-up. Enhancements included powdered activated carbon, granular activated carbon,silica sand, garnet, polymers, and ferric chloride. The cationic polymer had the most beneficial effects on granulation enhancement, reducing the time required to form granules by approximately 75% compared to an unenhanced control ASBR. Water Environ. Res., 68, 883 (1996).

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=11522&context=rtd

Enhancement of granulation and start-up in the anaerobic sequencing batch reactor

Anaerobic digestion 1981: D. E. Hughes, D. A. Stafford, B. I. Wheatley, W. Baader, G. Lettinga, E.J. Myas, W. Verstraete and R. L. Wentworth (Eds). Elsevier Biomedical Press, Amsterdam, New York. 1982. 436 pp. Price: US$80·00 (Dfl. 172·00)

Impact of liquid-to-gas hydrogen mass transfer on substrate conversion efficiency of an upflow anaerobic sludge bed and filter reactor

The upflow anaerobic sludge bed (UASB) concept, first proposed by Hemens et al. (1962), has been developed and extensively promoted by the Lettinga school, and applied to a large variety of wastewaters (Lettinga et al. 1980, 1983). The UBF reactor used in this study hybridized the UASB reactor with a packing filter (Guiot and van den Berg 1984). These reactors are characterized by the ability to accumulate a large amount of biomass due to adhesion of bacterial cells to each other. In the UASB and UBF reactors, the upflow velocity will select for organisms which can adhere to each other to form well settling granules which can be several millimeters in diameter. The granules accumulate in the reactor and then are exposed to the continuous feeding which is injected into the bottom of the reactor.

Thermodynamical and Microbiological Evidence of Trophic Microniches for Propionate Degradation in a Methanogenic Sludge-Bed Reactor

Processand Hydrogen in the Biomethanation Processes: Inevitable Transfer Limitations of Liquid-to-Gas Mass Transfer in Anaerobic

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Thermodynamical and Microbiological Evidence of Trophic Microniches for Propionate Degradation in a Methanogenic Sludge-Bed Reactor

Processand Hydrogen in the Biomethanation Processes: Inevitable Transfer Limitations of Liquid-to-Gas Mass Transfer in Anaerobic