Granulation in thermophilic upflow anaerobic sludge blanket (UASB) reactors

Characteristics of physiology of and genomic mutations in aggregation-enhanced mutants of Methanothermobacter sp. CaT2

The thermophilic hydrogenotrophic methanogen Methanothermobacter sp. CaT2 aggregates by itself. CaT2 is known to have a surface sugar layer and extracellular proteins that may be related to its aggregation. Aggregation-enhanced mutants, CHA001 and CHA002, were isolated after repeated cultivation for more than two years. When treated with proteinase K, CHA001 and CaT2 similarly exhibited a very low degree of aggregation and CHA002 exhibited less aggregation but still retained aggregation, suggesting protein-based aggregation via extracellular proteins in both CHA001 and CHA002, presumably via a putative membrane-bound and extracellularly protruding protein, MTCT_1020, identified previously. Genomic analysis revealed that CHA001 and CHA002 shared a missense mutation of MTCT_1348 and had distinct mutations. These results suggested that the MTCT_1348 mutation provides subsidiary support to the adhesive function of extracellular proteins and that there is an additional mutation(s) in CHA002 for the non-proteinous aggregation capability.

An Aggregation-defective Mutant of Methanothermobacter sp. CaT2 Reveals Unique Protein-dependent Aggregation

The thermophilic hydrogenotrophic methanogen, Methanothermobacter sp. CaT2, which possesses an extracellular sugar layer, commonly aggregates by itself or with other microorganisms. To elucidate the molecular mechanisms responsible for this aggregation, the aggregation-defective mutant, CLA160, was isolated. Optical and electron microscopy observations revealed that the mutant exhibited a significant reduction in aggregation. Genomic sequencing showed that CLA160 has a single point mutation, causing a nonsense mutation in MTCT_1020, which encodes a hypothetical protein. Motif and domain analyses indicated that the hypothetical protein bears two membrane-spanning segments at the N- and C-terminal regions and a large middle repeat-containing region. The results of a bioinformatic analysis suggested that the first middle region (RII) of the protein or the whole structure is responsible for the function of the product of MTCT_1020 in the aggregation of CaT2. A treatment with proteinase K suppressed sedimentation in CaT2, indicating a reduction in aggregation, with almost no effect on sedimentation in CLA160. The addition of Ca²⁺ or Mg²⁺ ions enhanced sedimentation in CaT2, whereas a DNase treatment had no effect on sedimentation in either strain. These results suggest that the hypothetical protein encoded by MTCT_1020 plays a key role as a membrane-bound adhesion protein in the aggregation of CaT2, which is enhanced by the addition of Ca²⁺ or Mg²⁺ ions.

The role of conductive materials in the start-up period of thermophilic anaerobic system

The major obstacle for thermophilic anaerobic digestion (TAD) is the inhibited microorganism activity and process instability during the start-up period. This study proposed a strategy to accelerate and stabilize the thermophilic reactors start-up via adding conductive materials. The results show that methane production rate in conductive materials supplemented (CMS) reactors was almost two times higher than the control reactors. Caloramator sp., a candidate of electroactive bacteria, was significantly enriched in the carbon nano-tube (CNT) supplemented groups (12.89%) as compared to control groups (1.26% only). Together with the doubled abundance of Methanosaeta and Methanosarcina methanogens in CMS groups, it is highly possible Caloramator sp. and Methanosaeta/Methanosarcina have established syntrophic direct interspecies electron transfer (DIET), via adopting conductive materials as electron conduit. Microbial community analysis indicates DIET was likely to be an unstable condition triggered syntrophic process. This study demonstrated that conductive materials could promote microbial activity and shorten start-up period for thermophilic anaerobic system.

Anaerobic granular sludge and biofilm reactors

The long retention time of the active biomass in the high-rate anaerobic digesters is the key factor for the successful application of the high rate anaerobic wastewater treatment. The long solids retention time is achieved due to the specific reactor configuration and it is enhanced by the immobilization of the biomass, which forms static biofilms, particle-supported biofilms, or granules depending on the reactor's operational conditions. The advantages of the high-rate anaerobic digestion over the conventional aerobic wastewater treatment methods has created a clear trend for the change of the role of the anaerobic digestion in the wastewater treatment plants from a pre-treatment method to the main biological treatment method. The application of staged high-rate anaerobic digesters has shown the larger potential among the recent developments in this direction. The most common high-rate anaerobic treatment systems based on anaerobic granular sludge and biofilm are described in this chapter. Emphasis is given to a) the Up-flow Anaerobic Sludge Blanket (UASB) systems, b) the main characteristics of the anaerobic granular sludge, and c) the factors that control the granulation process. Finally, the most innovative staged anaerobic digesters are also presented.

Differentiation of methanosaeta concilii and methanosarcina barkeri in anaerobic mesophilic granular sludge by fluorescent In situ hybridization and confocal scanning laser microscopy

Oligonucleotide probes, designed from genes coding for 16S rRNA, were developed to differentiate Methanosaeta concilii, Methanosarcina barkeri, and mesophilic methanogens. All M. concilii oligonucleotide probes (designated MS1, MS2, and MS5) hybridized specifically with the target DNA, but MS5 was the most specific M. concilii oligonucleotide probe. Methanosarcina barkeri oligonucleotide probes (designated MB1, MB3, and MB4) hybridized with different Methanosarcina species. The MB4 probe specifically detected Methanosarcina barkeri, and the MB3 probe detected the presence of all mesophilic Methanosarcina species. These new oligonucleotide probes facilitated the identification, localization, and quantification of the specific relative abundance of M. concilii and Methanosarcina barkeri, which play important roles in methanogenesis. The combined use of fluorescent in situ hybridization with confocal scanning laser microscopy demonstrated that anaerobic granule topography depends on granule origin and feeding. Protein-fed granules showed no layered structure with a random distribution of M. concilii. In contrast, a layered structure developed in methanol-enriched granules, where M. barkeri growth was induced in an outer layer. This outer layer was followed by a layer composed of M. concilii, with an inner core of M. concilii and other bacteria.

Phylogenetic diversity of mesophilic and thermophilic granular sludges determined by 16S rRNA gene analysis

The microbial diversity of two types of methanogenic granular sludge, mesophilic (35 degrees C) and thermophilic (55 degrees C), which had been treating sucrose/propionate/acetate-based artificial wastewater were compared. 16S rDNA clone libraries were constructed by PCR with a prokaryote-specific primer set, and partial sequencing of the clonal 16S rDNAs was conducted for phylogenetic analysis. Of 115 mesophilic granule and 110 thermophilic granule clones sequenced, 19 and 22%, respectively, were phylogenetically affiliated with the domain Archaea, and the remainder in each case were assigned to the domain Bacteria. Within the domain Archaea, the 16S rDNA clones in both libraries showed relatively close relationships with those of methanogens. Within the Bacteria, a major group represented in the mesophilic clone library was the delta subclass of the Proteobacteria (27%), in which high degrees of relatedness were observed between the clonal 16S rDNA sequences and those of previously identified syntrophic bacteria and sulfate-reducing bacteria. In contrast, in the thermophilic clone library, the Thermodesulfovibrio group (19%), the green non-sulfur bacteria (18%) and the low G + C subclass of the Gram-positive bacteria (18%) were predominant. A significant difference between the two libraries was that no clone affiliated with the Proteobacteria was detected in the thermophilic clone library, whereas the Proteobacteria was detected in the thermophilic clone library, whereas the Proteobacteria was the most predominant group in the mesophilic clones. Thirty-six and 24 different sequences were found in the mesophilic and thermophilic clones, respectively, suggesting that the microbial diversity of the thermophilic granule was lower than that of the mesophilic granule.

Granulation in thermophilic upflow anaerobic sludge blanket (UASB) reactors

The state of the art for thermophilic UASB reactors is discussed focusing on the start-up of UASB reactors, the influence of the waste water composition and temperature on the development and maintenance of thermophilic granules, and the microbial composition and structure of thermophilic granules.