Methanogenic biofilm: structure and microbial population activity in an anaerobic fluidized bed reactor treating synthetic wastewater (original) (raw)
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Characteristics of a methanogenic biofilm on sand particles in a fluidized bed reactor
Latin American Applied Research, 2005
The typical microbiological groups reported in literature under the experienced environmental conditions are present in the biofilm structure investigated on sand particles. This is concluded based on microorganism morphology analyzed by scanning electron microscopy. Methanosarcina sp. (acetate consumers) and filamentous microorganisms with morphology similar to Methanospirillum sp. (H 2-utilizing archaea) are distinguished among methanogens. Based on acetate levels and microorganism's threshold concentration, a predominance of Methanosarcina mazei rather than Methanosarcina barkeri is concluded. Among acetogens, bacillus morphologically similar to the syntrophic acetogenic Syntrophobacter wolinii are observed together with Desulfovibrio sp. (hydrogen-utilizing, sulfatereducing). With respect to acidogens, short and long rod-shaped bacteria, diplococcus in chains (probably Streptococcus-like bacteria) and filamentous bacilli are morphologically distinguished but cannot be characterized from this study. A methanogenic biofilm fluidized bed reactor inoculated with the biofilm population investigated showed process efficiencies up to 98% of chemical oxygen demand reduction for treating an acetate-based substrate.
Early stages in biofilm development in methanogenic fluidized-bed reactors
Applied Microbiology and Biotechnology, 1990
Biofilm development in methanogenic fluidized-bed reactors with sand as the carrier was studied on a laboratory scale. The microorganisms present in consecutive layers of the biofilm of mature sludge granules were preliminarily characterized on the basis of their morphology, element composition and adhesion capacity and were compared to bacteria which take part in the initial colonization of sand. The early phase of biofilm development was monitored with reactors receiving waste-waters containing different mixtures of volatile fatty acids and inoculated with fluidized-bed reactor effluent for different lengths of time. The results obtained indicate that facultative anaerobic bacteria abundantly present in the outermost biofilm layers of mature sludge granules are probably the main primary colonizers of the sand. M e t h a n o t h r i x spp. or other methanogens were rarely observed among the primary colonizers. The course of biofilm formation was comparable under the various start-up conditions employed including variations in waste-water composition, inoculation and anaerobicity. However, omission of waste-water and thus of substrate resulted in rapid wash-out of the attached biomass. tem has several advantages compared to other retained biomass systems, for instance a higher amount of biomass retention, less accumulation of inert sediment and better mass transfer to the biofilm ).
Biofilm development in laboratory methanogenic fluidized bed reactors
Biotechnology and Bioengineering, 1989
Biofilm development on sand with different heterogeneous inocula was studied in laboratory-scale methanogenic fluidized bed reactors. Both the course of biofilm formation during reactor start-up and the bacterial composition of newly developed biofilms at steady-state were found to be similar irrespective of the type of inoculum applied. Biofilm formation proceeded according to a fixed pattern that could be subdivided in three consecutive phases, designated as the lag phase, biofilm production phase, and steady-state phase. Methanogenic activity and biomass content of the fluidized bed granules were found to be accurate parameters of the course of biofilm formation. More indirect parameters monitored did not give unambiguous results in all instances. The composition of the newly developed biomass as assessed on the basis of potential methanogenic activities on different substrates and of the concentration of specific methanogenic cofactors was consistent with electron microscopic observations.
Microbiology and performance of a methanogenic biofilm reactor during the start-up period
Journal of Applied Microbiology, 2009
Aims: To understand the interactions between anaerobic biofilm development and process performances during the start-up period of methanogenic biofilm reactor. Methods and Results: Two methanogenic inverse turbulent bed reactors have been started and monitored for 81 days. Biofilm development (adhesion, growth, population dynamic) and characteristics (biodiversity, structure) were investigated using molecular tools (PCR-SSCP, FISH-CSLM). Identification of the dominant populations, in relation to process performances and to the present knowledge of their metabolic activities, was used to propose a global scheme of the degradation routes involved. The inoculum, which determines the microbial species present in the biofilm influences bioreactor performances during the start-up period. FISH observations revealed a homogeneous distribution of the Archaea and bacterial populations inside the biofilm. Conclusion: This study points out the link between biodiversity, functional stability and methanogenic process performances during start-up of anaerobic biofilm reactor. It shows that inoculum and substrate composition greatly influence biodiversity, physiology and structure of the biofilm. Significance and Impact of the Study: The combination of molecular techniques associated to a biochemical engineering approach is useful to get relevant information on the microbiology of a methanogenic growing biofilm, in relation with the start-up of the process.
Microbiological study of the development of biofilm in an anaerobic fixed-bed reactor
2002
The treatment capacity in anaerobic systems is basically determined for the active population concentration of microorganisms retained in the reactor. Anaerobic filter is a treatment system developed to favor the immobilization and biomass adherence, reaching good performance in the removal of organic matter. However, several factors interfere in the biomass adherence on supports in fixed bed reactors, such as: form, size, porosity, specific surface and the nature of the solid supports, besides their electrostatics charges. Such factors may influence the performance of the anaerobic fixed bed reactor (Characklis & Trulear, 1982; Vijayalakshimi et al., 1990). According to Ince (1999), anaerobic filter with supports of high porosity and specific surface, presents better efficiencies in both start up and steady state of the system than the reactors with conventional support. This study was carried out to verify the influence of the support materials on the growth and retention of the biomass, using resources of optical, fluorescence and scanning electron microscopy (SEM) to examine the structure and biological composition of cell aggregates in biofilms and the possible influence of those support materials on the colonization pattern.
Holos Environment, 2010
Biofilm dynamics in anaerobic fluidized bed reactor was studied since start-up during a 600-day operation time. Specific methanogenic activity tests revealed gas production by the anaerobic biomass since 30th operation day. Scanning Electron Microscopy (SEM) micrographs permitted to verify three bacterial development stages depending on the organic loading imposed to the system. Increasing of organic loading caused methanogenic specific activity depletion due to diffusion resistance through anaerobic biofilm. With maximum organic loading of 28.5 kg COD.m-3.day-1, almost 10% of the volatile solids fixed in inert particle surface were detected as polymeric extracellular material.
Microbial Ecology, 2008
The formation, structure, and biodiversity of a multispecies anaerobic biofilm inside an Upflow Anaerobic Sludge Bed (UASB) reactor fed with brewery wastewater was examined using complementary microbial ecology methods such us fluorescence in situ hybridization (FISH), denaturing gradient gel electrophoresis (DGGE), and cloning. The biofilm development can be roughly divided into three stages: an initial attachment phase (0-36 h) characterized by random adhesion of the cells to the surface; a consolidation phase (from 36 h to 2 weeks) defined by the appearance of microcolonies; and maturation phase (from 2 weeks to 2 months). During the consolidation period, proteobacteria with broad metabolic capabilities, mainly represented by members of alpha-Proteobacteria class (Oleomonas, Azospirillum), predominated. Beta-, gamma-, delta-(both syntrophobacteria and sulfate-reducing bacteria) and epsilon-(Arcobacter sp.) Proteobacteria were also noticeable. Archaea first appeared during the consolidation period. A Methanospirillum-like methanogen was detected after 36 h, and this was followed by the detection of Methanosarcina, after 4 days of biofilm development. The mature biofilm displayed a hill and valley topography with cells embedded in a matrix of exopolymers where the spatial distribution of the microorganisms became well-established. Compared to the earlier phases, the biodiversity had greatly increased. Although alpha-Proteobacteria remained as predominant, members of the phyla Firmicutes, Bacteroidete, and Thermotogae were also detected. Within the domain Archaea, the acetoclastic methanogen Methanosaeta concilii become dominant. This study provides insights on the trophic web and the shifts in population during biofilm development in an UASB reactor.
Biofilm development in down flow anaerobic fluidised bed reactors under transient conditions
Water science and technology : a journal of the International Association on Water Pollution Research, 2002
Biofilm development onto polypropylene particles (<4 mm) was studied in a laboratory-scale down flow anaerobic fluidised bed reactor. The reactor was fed with a synthetic solution containing sucrose and nutrients, and operated at 35 degrees C during 65 days at 44% bed expansion rate and 36 h HRT. Scanning electron microscopy (SEM) monitored the biofilm development. Initial adhesion occurred within the first 6 hours and after day 44 biofilm structure was complete. The presence of attached cells morphologically similar to Methanotrix bacilli and Methanosarcina sp. was observed by Scanning Electron Microscopy (SEM). The biofilm and the carrier surface roughness were measured by atomic force microscopy (AFM) and yielded 9.1 and 75 nm respectively. Results also showed good correlation between the SEM characterisation and the conventional anaerobic reactor parameters.
Water research, 2008
The influence of the hydraulic retention time (HRT) on the start-up phase of a methanogenic inverse turbulent bed bioreactor was investigated. Two identical reactors were monitored, the only differing parameter being the HRT: one of the reactors was fed with a diluted wastewater at a constant HRT of 1 day, the organic loading rate (OLR) being increased by decreasing the substrate dilution; the second reactor was fed at a constant influent concentration of 20 g COD L(-1), the OLR being increased by decreasing the HRT from 40 days to 1 day. After 45 days of start-up, both reactors were operated at an OLR of 20 g COD L(-1)d(-1) and a HRT of 1 day. However, strong differences were observed on biofilm growth. In the reactor operated at a constant short HRT, biofilm concentration was 4.5 as high as in the reactor operated at an increasing HRT. This difference was attributed to the competition between planktonic and biofilm microorganisms in the latter reactor, whereas suspended biomass wa...
AFRICAN JOURNAL OF BIOTECHNOLOGY, 2012
Anaerobic biofilm behavior on polyethylene and Extendosphere™ supports was evaluated during startup of an inverse fluidized bed reactor using methane yield and microscopic observation as parameter monitoring techniques. Two anaerobic inverse fluidized bed reactors were used, one filled with triturated polyethylene as solid carrier material (diameter = 380 m, density = 926 kg/m 3) and the other with Extendosphere™ (diameter = 147 m, density = 700 kg/m 3). Each support material was used at up to 25% of its working volume (polyethylene = 1.2 l, Extendosphere™ = 1.9 l). Both reactors were started up in sequencing batch mode, applying organic loading rates of 0.5 to 14 g COD/l.d. Both supports exhibited rapid biofilm growth during start-up. Maximum surface colonization was 46% with the polyethylene and 100% with Extendosphere™. Both supports had a methane yield of 0.298 l CH 4 /g COD at 10 and 14 g COD/l.d, respectively. Digital microscopic observation results coincided with methane yield results, confirming each to be viable for parameter monitoring of biofilm growth. Data generated by these two techniques is different and complementary, and in conjunction they constitute a highly effective monitoring method of biofilm growth.