Changes in microbial ecology in an anaerobic reactor

This study examined the behaviour of the microbial population in an anaerobic reactor, in terms of changes in numbers of total bacterial community, autofluorescent methanogens, non-methanogens and morphology of the autofluorescent methanogens, using epifluorescence microscopy and microbiological enumeration techniques. A laboratory-scale, continuous flow-completely mixed anaerobic reactor, coupled with a conventional gravity settling tank and a continuous recycling system, was operated at an HRT range between 24 and 12 h, using dairy wastewater as the substrate. The numbers of the total bacterial community and autofluorescent methanogens both decreased during start-up. Also, the proportion of the number of autofluorescent methanogens in the total bacterial community varied from 5% to 16% during operation. In particular, the activity of the methane-forming bacteria decreased significantly at HRTs of 16 and 12 h. A membrane module, instead of a conventional settling tank, would obviously have been a more effective method if recycling were required in the anaerobic treatment system.     

Competition and coexistence of sulfate-reducing bacteria,acetogens and methanogens in a lab-scale anaerobic bioreactor as affected by changing substrate to sulfate ratio

The microbial population structure and function of natural anaerobic communities maintained in lab-scale continuously stirred tank reactors at different lactate to sulfate ratios and in the absence of sulfate were analyzed using an integrated approach of molecular techniques and chemical analysis. The population structure, determined by denaturing gradient gel electrophoresis and by the use of oligonucleotide probes, was linked to the functional changes in the reactors. At the influent lactate to sulfate molar ratio of 0.35 mol mol⁻¹, i.e., electron donor limitation, lactate oxidation was mainly carried out by incompletely oxidizing sulfate-reducing bacteria, which formed 80–85% of the total bacterial population. Desulfomicrobium- and Desulfovibrio-like species were the most abundant sulfate-reducing bacteria. Acetogens and methanogenic Archaea were mostly outcompeted, although less than 2% of an acetogenic population could still be observed at this limiting concentration of lactate. In the near absence of sulfate (i.e., at very high lactate/sulfate ratio), acetogens and methanogenic Archaea were the dominant microbial communities. Acetogenic bacteria represented by Dendrosporobacter quercicolus-like species formed more than 70% of the population, while methanogenic bacteria related to uncultured Archaea comprising about 10–15% of the microbial community. At an influent lactate to sulfate molar ratio of 2 mol mol⁻¹, i.e., under sulfate-limiting conditions, a different metabolic route was followed by the mixed anaerobic community. Apparently, lactate was fermented to acetate and propionate, while the majority of sulfidogenesis and methanogenesis were dependent on these fermentation products. This was consistent with the presence of significant levels (40–45% of total bacteria) of D. quercicolus-like heteroacetogens and a corresponding increase of propionate-oxidizing Desulfobulbus-like sulfate-reducing bacteria (20% of the total bacteria). Methanogenic Archaea accounted for 10% of the total microbial community.     

Diurnal variations in bacterial numbers and fluid parameters in ruminal contents of animals fed low- or high-forage diets.

Differential carbohydrate media and anaerobic replica plating techniques were used to assess the degrees of diurnal variations in the direct and viable cell counts as well as the carbohydrate-specific subgroups within the mixed rumen bacterial populations in cattle fed maintenance (metabolizable energy) levels of either a high-forage or a high-concentrate diet once daily. The rumen was sampled at 1 h before feeding and 2, 4, 8, 12, and 16 h after feeding, and selected microbiological parameters of the isolated bacterial populations were assessed. Corresponding samples of ruminal fluid were assayed for fermentation acids, carbohydrate, ammonia, and pH changes. The data showed that regardless of diet, total bacterial numbers remained fairly constant throughout the day. The number of viable bacteria declined 40 to 60% after feeding and then increased to a maximum at 16 h postfeeding. Changes occurred in the carbohydrate-specific subgroups within the bacterial populations, and some of the changes were consistent with a predicted scheme of ruminal feedstuff carbohydrate fermentation. Regardless of diet, however, soluble-carbohydrate-utilizing bacteria predominated at all times. Xylan-xylose and pectin subgroups respectively comprised about one-half and one-third of the population when the high-forage diet was given. These subgroups, along with the cellulolytics, constituted lesser proportions of the population when the high-concentrate diet was given. The cellulolytic subgroup was the least numerous of all subgroups regardless of diet but followed a diurnal pattern similar to that predicted for cellulose fermentation. There were few diurnal variations or differences in bacterial cell compositions and ruminal fluid parameters between diets. The observed similarities and dissimilarities of the rumen bacterial populations obtained when the two diets were given are discussed. The data are consistent with the versatility and constancy of the rumen as a stable, mature microbial system under the specific low-level feeding regimens used.     

Application of DNA amplification fingerprinting (DAF) to mixed culture bioreactors

Summary The use of DNA amplification fingerprinting (DAF) as a tool for monitoring mixed microbial populations in bioreactors was evaluated. Short (8-mer or 10-mer) oligonucleotides were used to prime DNA extracts from various biological reactors during polymerase chain reaction (PCR) amplification. The reactors examined in this study included two sets of anaerobic stirred tank continuous flow bioreactors. One set of anaerobic reactors was operated under methanogenic conditions and one set was operated under sulfate-reducing conditions. The anaerobic reactor communities in the methanol-fed reactors showed extensive DAF homology. DAF was also applied to a fixed-film azo dye degrading reactor to examine the degree of uniformity of colonization of the substratum in representative regions of the reactor. This method is a quick and relatively inexpensive means of monitoring microbial community structure during biological processes. Since no cultivation of the sample is involved, the genetic profile of the community is not biased by outgrowth conditions. DAF profiles may be useful for comparisons of population changes over time or of bench-scale vs pilot-scale reactors but not adequate for assessing community diversity.     

Microbiology and performance of a methanogenic biofilm reactor during the start-up period

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.     

Influence of co-substrates on structure of microbial aggregates in long-chain fatty acid-fed anaerobic digesters

AIMS: The purpose of this study was to investigate the influence of co-substrates, such as glucose and cysteine, on the structure of microbial aggregates in anaerobic digesters treating oleate, a long-chain fatty acid (LCFA). METHODS AND RESULTS: Transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM) were used to examine the structure of microbial aggregates. Fluorescence in situ hybridization (FISH) techniques were also used to characterize and localize the different trophic groups present in the aggregates. Oleate was found to inhibit the methanogenic activity and formation of granular biomass in digesters. The addition of co-substrates, such as glucose and cysteine either singly or in combination, increased the methanogenic activity and formation of granular biomass. Glucose was more effective than cysteine in reducing the inhibition by oleate on the methanogenic bacteria and in enhancing the formation of granules. CONCLUSIONS: The addition of nutrient substrate, such as glucose and cysteine could decrease the toxicity of LCFA on anaerobic granulation. SIGNIFICANCE AND IMPACT OF THE STUDY: The results suggest that the addition of other substrates might decrease the toxicity of LCFA on the granulation of biomass in anaerobic digesters and enhance methanogenic activity. A combination of TEM, CLSM and FISH techniques provides a better tool for visualizing microbial aggregates and for differentiating and localizing different microbial groups within these aggregates.     

Degradation of 2-nitrodiphenylamine, a component of Otto Fuel II, by Clostridium spp

Otto Fuel II, a propellant in torpedoes, is composed of 76% 1,2 propanediol dinitrate (PGDN), 22.5% di-n-butyl sebacate, and 1.5% 2-nitrodiphenylamine (NDPA), and is largely recalcitrant to aerobic microbial degradation. Anaerobic microbial degradation of Otto Fuel II was tested by inoculating anaerobic enrichment media, containing either 2% (vol:vol) complete Otto Fuel II or 2% of a 0.02% solution of Otto Fuel II in methanol, with soil and water from sites contaminated with munitions or with landfill leachate. Anaerobic bacterial growth was completely inhibited by 2% Otto Fuel II. Two mixed bacterial enrichments developed in anaerobic media containing 2% (v/v) of a 0.02% solution of Otto Fuel II in methanol. After incubation, PGDN could not be detected in either enrichment, but was also not detectable in sterile controls, suggesting abiotic degradation of low concentrations of PGDN in reduced anaerobic medium. NDPA did not degrade in either enrichment. Similarly, complete Otto Fuel was recalcitrant to degradation by highly reducing methanogenic biomass collected from an upflow anaerobic sludge blanket bioreactor (UASB). A comparison of the degradative ability of autoclaved and viable biomass showed that low concentrations of PGDN autodegraded, however unlike the autoclaved anaerobic biomass, the viable anaerobic biomass degraded the NDPA component of Otto Fuel II. Two strains of anaerobic clostridia, strains SP3 and SPF, that caused the disappearance of NDPA at its limit of solubility in culture media, were isolated from the UASB bioreactor biomass. SP3 and SPF were shown, by comparison of 16S rDNA sequences, to be most closely related to Clostridium butyricum and Clostridium cochlearium respectively. Although NDPA was lost from cultures of both strains, metabolic end products were not identified. Neither strain could degrade NDPA unless supplied with an alternative energy source. In the culture system used, NDPA stimulated the growth of SP3 but it had no appreciable effect on the growth of SPF. Both SP3 and SPF degraded low concentrations of trinitrotoluene (TNT), without the production of detectable concentrations of aromatic amines. A possible method for the remediation of small spills of Otto Fuel II is suggested.     

Comparison of techniques to determine the abundance of predatory bacteria attacking chromatiaceae

Abstract This work quantifies the number of bacterial predators attacking the population of Chromatiaceae in the hypolimnion of Lake Estanya to assess the potential role of these microorganisms in controlling phototrophic bacterial populations. The abundance of predators was estimated from total counts of infected prey cells and by counting plaque-forming units. In spite of the large difference between both determinations, their variations with depth and time followed very similar patterns. During the summer, in the hypolimnion, and during the winter in the entire lake, up to 60% of the prey cells had potential predators attached. In comparison, plaque counts showed that viable predators represented less than 1% of the population of the prey. Our results demonstrated that predatory bacteria were far more abundant than indicated by the low viable counts obtained, suggesting that they play a more important role in controlling phototrophic bacterial populations than is currently assumed.     

Microbial growth and resuscitation alter community structure after perturbation

Abstract: An increase in the number of culturable organisms and a decrease in the diversity of recoverable microbiota have been reported in deep subsurface materials after storage perturbation. The magnitude of the microbial community shift in stored samples was more pronounced at 4°C compared to −20°C. Phospholipid fatty acid analyses and acridine orange direct counts indicated that biomass did not increase significantly throughout storage. Changes in the types of fatty acid methyl esters determined over the time course indicated that some of the microbial community shift was due to bacterial proliferation. However, the recovery of new bacterial types only after the storage process suggested that some of the increase in culturable cell count was due to the resuscitation of dormant microorganisms, possibly activated by some aspect of sampling, sample handling, and/or storage. Comparison of acridine orange direct counts with phospholipid and diglyceride fatty acid content suggested that much of the biomass may have been non-living at early time points; however, after 30 days of storage most of the bacterial biomass was viable.     

Microbial populations associated with treatment of an industrial dye effluent in an anaerobic baffled reactor.

Fluorescent in situ hybridization (FISH) using 16S and 23S rRNA-targeted probes together with construction of an archaeal 16S ribosomal DNA (rDNA) clone library was used to characterize the microbial populations of an anaerobic baffled reactor successfully treating industrial dye waste. Wastewater produced during the manufacture of food dyes containing several different azo and other dye compounds was decolorized and degraded under sulfidogenic and methanogenic conditions. Use of molecular methods to describe microbial populations showed that a diverse group of Bacteria and Archaea was involved in this treatment process. FISH enumeration showed that members of the gamma subclass of the class Proteobacteria and bacteria in the Cytophaga-Flexibacter-Bacteroides phylum, together with sulfate-reducing bacteria, were prominent members of a mixed bacterial population. A combination of FISH probing and analysis of 98 archaeal 16S rDNA clone inserts revealed that together with the bacterial population, a methanogenic population dominated by Methanosaeta species and containing species of Methanobacterium and Methanospirillum and a relatively unstudied methanogen, Methanomethylovorans hollandica, contributed to successful anaerobic treatment of the industrial waste. We suggest that sulfate reducers, or more accurately sulfidogenic bacteria, together with M. hollandica contribute considerably to the treatment process through metabolism of dye-associated sulfonate groups and subsequent conversion of sulfur compounds to carbon dioxide and methane.     

Structural analysis of anaerobic granules in a phase separated reactor by electron microscopy

This paper discusses the microbial community structure of anaerobic granules and the effect of phase separation in anaerobic reactor on the characteristics of granules. Electron micrographs revealed that the core of anaerobic granular sludge consists predominantly of Methanosaeta-like cells, a key microorganism in granulation process. Granules in the methanogenic dominant zone of the reactor were stable and densely packed with smooth regular surface. On the other hand, granules subjected to acidogenic activities were less stable structures with broken parts and an irregular fissured surface. Anaerobic granules consisted of a vast diversity of species from the outer surface to the core of the granule and possessed a multi-layered structure. Viruses in the granules suggests the presence of bacteriophage in the granular biomass. These could be responsible for destroying cells and weakening the internal structure of granules, and thus possibly causing the breaking of granules. The observation of protozoa-like microorganism on the exterior zone of granular structure is believed to play an important role as bacterial predator and control the growth of bacterial cells. The images observed in this study shows that anaerobic granule harbour diverse number of microbial species, and act differently in acidogenic and methanogenic microbial zones.     

Small-Scale Vertical Distribution of Bacterial Biomass and Diversity in Biological Soil Crusts from Arid Lands in the Colorado Plateau

We characterized, at millimeter resolution, bacterial biomass, diversity, and vertical stratification of biological soil crusts in arid lands from the Colorado Plateau. Microscopic counts, extractable DNA, and plate counts of viable aerobic copiotrophs (VAC) revealed that the top centimeter of crusted soils contained atypically large bacterial populations, tenfold larger than those in uncrusted, deeper soils. The plate counts were not always consistent with more direct estimates of microbial biomass. Bacterial populations peaked at the immediate subsurface (1–2 mm) in light-appearing, young crusts, and at the surface (0–1 mm) in well-developed, dark crusts, which corresponds to the location of cyanobacterial populations. Bacterial abundance decreased with depth below these horizons. Spatially resolved DGGE fingerprints of Bacterial 16S rRNA genes demonstrated the presence of highly diverse natural communities, but we could detect neither trends with depth in bacterial richness or diversity, nor a difference in diversity indices between crust types. Fingerprints, however, revealed the presence of marked stratification in the structure of the microbial communities, probably a result of vertical gradients in physicochemical parameters. Sequencing and phylogenetic analyses indicated that most of the naturally occurring bacteria are novel types, with low sequence similarity (83–93%) to those available in public databases. DGGE analyses of the VAC populations indicated communities of lower diversity, with most types having sequences more than 94% similar to those in public databases. Our study indicates that soil crusts represent small-scale mantles of fertility in arid ecosystems, harboring vertically structured, little-known bacterial populations that are not well represented by standard cultivation methods.     

Elevated abundance of bacteriophage infecting bacteria in soil

Here we report the first direct counts of soil bacteriophage and show that substantial populations of these viruses exist in soil (grand mean = 1.5 x 10(7) g(-1)), at least 350-fold more than the highest numbers estimated from traditional viable plaque counts. Adding pure cultures of a Serratia phage to soil showed that the direct counting methods with electron microscopy developed here underestimated the added phage populations by at least eightfold. So, assuming natural phages were similarly underestimated, virus numbers in soil averaged 1.5 x 10(8) g(-1), which is equivalent to 4% of the total population of bacteria. This high abundance was to some extent confirmed by hybridizing colonies grown on Serratia and Pseudomonas selective media with cocktails of phage infecting these bacteria. This showed that 8.9 and 3.9%, respectively, hybridized with colonies from the two media and confirmed the presence of phage DNA sequences in the cultivable fraction of the natural population. Thus, soil phage, like their aquatic counterparts, are likely to be important in controlling bacterial populations and mediating gene transfer in soil.     

Microbial colonization of different support materials used to enhance the methanogenic process

Macrobial colonization of the different support materials used to enhance methane production in anaerobic digestors is rapid and occurs in the first 24 h of sludge incubation. Scanning electron microscopy studies reveal a predominant presence of filamentous methanogenic forms, closely resemblingMethanosaeta (Methanothrix), which are located on the outer layer and in the bacterial framework of the biofilm. These findings are consistent with the results obtained from microbial counts using both the most probable number and epifluorescence microscopic techniques, which show an increase in the numbers of aceticlastic methanogens compared to other microbial groups involved, such as sulphate-reducing bacteria, the numbers of which are similar to those obtained under the initial conditions. Moreover, a sharp increase in the bacterial counts is observed by using the epifluorescence microscopic technique applied to homogenized samples, probably due to the count of bacteria released from the support materials.     

Population Dynamics of a Single-Stage Sulfidogenic Bioreactor Treating Synthetic Zinc-Containing Waste Streams

Waste streams from industrial processes such as metal smelting or mining contain high concentrations of sulfate and metals with low pH. Dissimilatory sulfate reduction carried out by sulfate-reducing bacteria (SRB) at low pH can combine sulfate reduction with metal-sulfide precipitation and thus open possibilities for selective metal recovery. This study investigates the microbial diversity and population changes of a single-stage sulfidogenic gas-lift bioreactor treating synthetic zinc-rich waste water at pH 5.5 by denaturing gradient gel electrophoresis of 16S rRNA gene fragments and quantitative polymerase chain reaction. The results indicate the presence of a diverse range of phylogenetic groups with the predominant microbial populations belonging to the Desulfovibrionaceae from δ-Proteobacteria. Desulfovibrio desulfuricans-like populations were the most abundant among the SRB during the three stable phases of varying sulfide and zinc concentrations and increased from 13% to 54% of the total bacterial populations over time. The second largest group was Desulfovibrio marrakechensis-like SRB that increased from 1% to about 10% with decreasing sulfide concentrations. Desulfovibrio aminophilus-like populations were the only SRB to decrease in numbers with decreasing sulfide concentrations. However, their population was <1% of the total bacterial population in the reactor at all analyzed time points. The number of dissimilatory sulfate reductase (DsrA) gene copies per number of SRB cells decreased from 3.5 to 2 DsrA copies when the sulfide concentration was reduced, suggesting that the cells' sulfate-reducing capacity was also lowered. This study has identified the species present in a single-stage sulfidogenic bioreactor treating zinc-rich wastewater at low pH and provides insights into the microbial ecology of this biotechnological process.     

Microwave radiation and reactor design influence microbial communities during methane fermentation

The effect of reactor design and method of heating on the efficiency of methane fermentation and composition of microbial communities, especially methanogenic Archaea, were determined. The research was carried out using submerge- and trickling-bed reactors fed with wastewater and the heat supply into the reactors included a convection heating method and microwave radiation. The polymerase chain reaction-denaturing gradient gel electrophoresis and relative real-time PCR were used in order to assess the biofilm communities. The best fermentation results and the highest abundance of methanogenic Archaea in biomass were observed in microwave heated trickling-bed reactors. The research proved that in reactors of identical design, the application of microwaves enabled a higher fermentation efficiency to be obtained and simultaneously increased the diversity of methanogenic Archaea communities that favors process stability. All the identified sequences of Archaea belonged to Methanosarcina sp., suggesting that species from this genera are susceptible to non-thermal effects of microwaves. There were no effects from microwaves on the bacterial communities in both types of reactors, however, the bacterial species composition varied in the reactors of different design.     

Functional patterns and temperature response of cellulose-fermenting microbial cultures containing different methanogenic communities

The effect of microbial composition on the methanogenic degradation of cellulose was studied using two lines of anaerobic cellulose-fermenting methanogenic microbial cultures at two different temperatures: that at 15 degrees C being dominated by Methanosaeta and that at 30 degrees C by Methanosarcina. In both cultures, CH4 production and acetate consumption were completely inhibited by either 2-bromoethanesulfonate or chloroform, whereas H2 consumption was only inhibited by chloroform, suggesting that homoacetogens utilized H2 concomitantly with methanogens. Hydrogen was the intermediate that was consumed first, while acetate continued to accumulate. At 15 degrees C, acetoclastic methanogenesis smoothly followed H2-dependent CH4 production. Fluorescence in situ hybridization showed that populations of Methanosaeta steadily increased with time from 5 to 25% of total cell counts. At 30 degrees C, two phases of CH4 production were obtained, with acetate consumed after the abrupt increase of Methanosarcina from 0 to 45% of total cell counts. Whereas populations of Methanosaeta were able to adapt after transfer from 15 to 30 degrees C, those of Methanosarcina were not, irrespective of during which phase the cultures were transferred from 30 degrees C to 15 degrees C. Our results thus show that the community structure of methanogens indeed affects the function of a cellulose-fermenting community with respect to temperature response.     

Seasonal microbial community dynamics in a flowerpot-using personal composting system for disposal of household biowaste

Microbial community dynamics in a flowerpot-using solid biowaste composting (FUSBIC) process were monitored seasonally by quinone profiling and conventional microbiological methods. The FUSBIC system, which consisted of three flowerpots (14 L or 20 L capacity) with 5-6 kg each of a soil-compost mixture (SCM) as the primary reactors, was loaded daily with household biowaste from November 1998 to October 1999. The monthly average waste reduction rate was 88.2% for the 14-L system and 92.5% for the 20-L system on a wet weight basis. The direct total microbial count detected in the 14-L primary reactors ranged from 4.5 to 9.6x10(11) cells.g(-1) of dry wt of SCM, and the viable count of aerobic heterotrophic bacteria recovered on agar plates at 28 degrees C varied from 1.9 to 5.7x10(11) CFU.g(-1) of dry wt. The quinone content of SCM samples from the 14-L and 20-L systems ranged from 160 to 353 nmol.g(-1) of dry SCM. Ubiquinones, unsaturated menaquinones, and partially saturated menaquinones constituted 15.0-36.4, 14.8-22.0, and 41.8-61.6 mol% of the total content, respectively. The major quinone types detected were usually MK-8(H(2)), MK-9(H(2)), and Q-10. Variations in quinone profiles were evaluated numerically by using two parameters, the dissimilarity index (D) and microbial divergence index (MD(q)). The upper limit of seasonal changes in the microbial community structure was about 30% as expressed by D values. The MD(q) values calculated ranged from 18 to 22. A significant positive correlation was found between seasonal temperature and bacterial populations containing partially saturated menaquinones. These results indicated that the FUSBIC system contained highly diverse microbial populations that fluctuated to some extent depending on seasonal temperature. Members of the Actinobacteria were suggested to be the major constituents of the total population present.     

Granulation and Sludge Bed Stability in Upflow Anaerobic Sludge Bed Reactors in Relation to Surface Thermodynamics

Adhesion of bacteria involved in anaerobic consortia was investigated in upflow anaerobic sludge bed reactors and was related to surface thermodynamics. The adhesion of hydrophilic cells appeared to be enhanced at a low liquid surface tension ((gamma)(infLV)), while the adhesion of hydrophobic cells was favored at a high (gamma)(infLV). Growth in protein-rich growth media resulted in low granular biomass yields; addition of polycations, such as poly-l-lysine and chitosan, increased the (gamma)(infLV) and the granular biomass yield. On the basis of the results of activity tests and microbial counts with wash-out cells, we identified two types of structured granules that were related to the influence of (gamma)(infLV). In one type of granules, hydrophilic acidogens surrounded a more hydrophobic methanogenic association. These granules were selected at a low (gamma)(infLV) provided that carbohydrates were available as substrates. The other type of granules was selected at a high (gamma)(infLV); hydrophobic cells (i.e., methanogens) were predominant throughout these granules. The granules which had acidogens as solid-phase emulsifiers around a methanogenic association appeared to allow more stable reactor performance. Decreasing the (gamma)(infLV) in the reactor by adding trace amounts of a surfactant also increased reactor stability.     

Studies on reaction techniques concerning reactor design for the anaerobic degradation of complex substrates with the example of the methanation of effluents in the fermentation industry

Two fixed-bed loop reactors were used to evaluate singleand separated-phase anaerobic treatments of a high strength waste-water from ethanol fermentation. The one-phase system consisted of an anaerobic fixed-bed loop reactor containing both acidogenic as well as methanogenic populations allowing a complete conversion of the carbon source into gaseous end products and biomass.The two-phase system consisted of a second fixed-bed loop reactor operated as a methanogenic unit, which was proceeded by a CSTR for acidification, both connected in series allowing sequential acidogenesis and methanogenesis of the organic components. The reactors were operated under steady state and variable process conditions. By gradually increasing the feed supply in both systems, maximum turnover of COD was determined.The separated-phase system consistently gave a better quality effluent with lower suspended solids and total COD. Maximum loading rates and COD elimination of the methanogenic phase of the two-phase system was over two times higher than that of the one-phase system. Process stability was also higher.On overloading the methane reactor of the two phase system accumulation of different fatty acids within the reactor was observed. Hydrogen concentration in the biogas can be used as a reliable indicator for system overloadings. At least, continuous online monitoring of hydrogen in the methanogenic reactor gas should provide a convenient alternative to other analyses for process control.