Claudia Etchebehere

Effect of phenol on the nitrogen removal performance and microbial community structure and composition of an anammox reactor.

The effects of phenol on the nitrogen removal performance of a sequencing batch reactor (SBR) with anammox activity and on the microbial community within the reactor were evaluated. A phenol concentration of 300 mg L(-1) reduced the ammonium-nitrogen removal efficiency of the SBR from 96.5% to 47%. The addition of phenol changed the microbial community structure and composition considerably, as shown by denaturing gradient gel electrophoresis and 454 pyrosequencing of 16S rRNA genes. Some phyla, such as Proteobacteria, Verrucomicrobia, and Firmicutes, increased in abundance, whereas others, such as Acidobacteria, Chloroflexi, Planctomycetes, GN04, WS3, and NKB19, decreased. The diversity of the anammox bacteria was also affected by phenol: sequences related to Candidatus Brocadia fulgida were no longer detected, whereas sequences related to Ca. Brocadia sp. 40 and Ca. Jettenia asiatica persisted. These results indicate that phenol adversely affects anammox metabolism and changes the bacterial community within the anammox reactor.

A time-course analysis of four full-scale anaerobic digesters in relation to the dynamics of change of their microbial communities

This study describes the microbial community richness, -dynamics, and -organization of four full-scale anaerobic digesters during a time-course study of 45 days. The microbial community was analyzed using a Bacteria- and Archaea-targeting 16S rRNA gene-based Terminal-Restriction Fragment Length Polymorphism approach. Clustering analysis separated meso- and thermophilic reactors for both archaeal and bacterial communities. Regardless of the operating temperature, each installation possessed a distinct community profile. For both microbial domains, about 8 dominant terminal-restriction fragments could be observed, with a minimum of 4 and a maximum of 14. The bacterial community organization (a coefficient which describes the specific degree of evenness) showed a factor 2 more variation in the mesophilic reactors, compared with the thermophilic ones. The archaeal community structure of the mesophilic UASB reactor was found to be more stable. The community composition was highly dynamic for Bacteria and Archaea, with a rate of change between 20-50% per 15 days. This study illustrated that microbial communities in full-scale anaerobic digesters are unique to the installation and that community properties are dynamic. Converging complex microbial processes such as anaerobic digestion which rely on a multitude of microbial teams apparently can be highly dynamic.

Impact of inocula and operating conditions on the microbial community structure of two anammox reactors

The microbial community structure of the biomass selected in two distinctly inoculated anaerobic oxidation of ammonium (anammox) reactors was investigated and compared with the help of data obtained from 454-pyrosequencing analyses. The anammox reactors were operated for 550 days and seeded with different sludges: sediment from a constructed wetland (reactor I) and biomass from an aerated lagoon part of the oil-refinery wastewater treatment plant (reactor II). The anammox diversity in the inocula was evaluated by 16S rRNA gene-cloning analysis. The diversity of anammox bacteria was greater in the sludge from the oil-refinery (three of the five known genera of anammox were detected) than in the wetland sludge, in which only Candidatus Brocadia was observed. Pyrosequencing analysis demonstrated that the community enriched in both reactors had differing compositions despite the nearly similar operational conditions applied. The dominant phyla detected in both reactors were Proteobacteria, Chloroflexi, Planctomycetes, and Acidobacteria. The phylum Bacteroidetes, which is frequently observed in anammox reactors, was not detected. However, Acidobacteria and GN04 phyla were observed for the first time, suggesting their importance for this process. Our results suggest that, under similar operational conditions, anammox populations (Ca. Brocadia sinica and Ca. Brocadia sp. 40) were selected in both reactors despite the differences between the two initial inocula. Taken together, these results indicated that the type of inoculum and the culture conditions are key determinants of the general microbial composition of the biomass produced in the reactors. Operational conditions alone might play an important role in anammox selection.

Microbial communities from 20 different hydrogen-producing reactors studied by 454 pyrosequencing

To provide new insight into the dark fermentation process, a multi-lateral study was performed to study the microbiology of 20 different lab-scale bioreactors operated in four different countries (Brazil, Chile, Mexico, and Uruguay). Samples (29) were collected from bioreactors with different configurations, operation conditions, and performances. The microbial communities were analyzed using 16S rRNA genes 454 pyrosequencing. The results showed notably uneven communities with a high predominance of a particular genus. The phylum Firmicutes predominated in most of the samples, but the phyla Thermotogae or Proteobacteria dominated in a few samples. Genera from three physiological groups were detected: high-yield hydrogen producers (Clostridium, Kosmotoga, Enterobacter), fermenters with low-hydrogen yield (mostly from Veillonelaceae), and competitors (Lactobacillus). Inocula, reactor configurations, and substrates influence the microbial communities. This is the first joint effort that evaluates hydrogen-producing reactors and operational conditions from different countries and contributes to understand the dark fermentation process.

High organic loading rate on thermophilic hydrogen production and metagenomic study at an anaerobic packed-bed reactor treating a residual liquid stream of a Brazilian biorefinery.

This study evaluated the influence of a high organic loading rate (OLR) on thermophilic hydrogen production at an up-flow anaerobic packed-bed reactor (APBR) treating a residual liquid stream of a Brazilian biorefinery. The APBR, filled with low-density polyethylene, was operated at an OLR of 84.2 kg-COD m(-3) d(-1). This value was determined in a previous study. The maximum values of hydrogen production and yield were 5,252.6 mL-H2 d(-1) and 3.7 mol-H2 mol(-1)(total carbohydrates), respectively. However, whereas the OLR remained constant, the specific organic load rate (sOLR) decreased throughout operation from 1.38 to 0.72 g-Total carbohydratesg-VS(-1) h(-1), this decrease negatively affected hydrogen production. A sOLR of 0.98 g-Total carbohydratesg-VS(-1) h(-1) was optimal for hydrogen production. The microbial community was studied using 454-pyrosequencing analysis. Organisms belonging to the genera Caloramator, Clostridium, Megasphaera, Oxobacter, Thermoanaerobacterium, and Thermohydrogenium were detected in samples taken from the reactor at operation days 30 and 60, suggesting that these organisms contribute to hydrogen production.

Microbial community composition and reactor performance during hydrogen production in a UASB reactor fed with raw cheese whey inoculated with compost.

This study investigated the microbial community developed in a UASB reactor for hydrogen production and correlated it to reactor performance. The reactor was inoculated with kitchen waste compost and fed with raw cheese whey at two organic loading rates, 20 gCOD/Ld and 30 gCOD/Ld. Hydrogen production was very variable, using an OLR of 30 gCOD/Ld averaged 1.0 LH(2)/Ld with no methane produced under these conditions. The hydrogen yield was also very variable and far from the theoretical. This low yield could be explained by selection of a mixed fermentative population with presence of hydrogen producing organisms (Clostridium, Ruminococcus and Enterobacter) and other non-hydrogen producing fermenters (Lactobacillus, Dialister and Prevotella). The molecular analysis of the raw cheese whey used for feeding revealed the presence of three predominant organisms that are affiliated with the genera Buttiauxella (a low-yield hydrogen producer) and Streptococcus (a lactic acid-producing fermenter). Although these organisms did not persist in the reactor, the continuous addition of these fermenters could decrease the reactors hydrogen yield.

How to use molecular biology tools for the study of the anaerobic digestion process

Anaerobic digestion is used with success for the treatment of solid waste, urban and industrial effluents with a concomitant energy production. The process is robust and stable, but the complexity of the microbial community involved in the process is not yet fully comprehensive. Nowadays, the study of this complex ecosystem is facilitated by the availability of different molecular tools, but it is very important to choose the adequate tool to answer specific questions. The aim of this review is to describe different molecular techniques, indicate the questions that can be addressed by each technique, enumerate their limitations and give practical advices for their use. Examples of how the molecular tools have been used to address various questions in anaerobic digestion are presented. The key point now is to apply all this information to improve anaerobic digestion. The integration of concepts of microbial-ecology, environmental-engineering, modeling and bioinformatics is currently necessary.

Microbial communities in anammox reactors: a review

ABSTRACT The anammox (anaerobic ammonium oxidation) process has been used to remove nitrogen from wastewaters and is considered a promising approach due to its advantages over conventional processes (nitrification and denitrification). The development of molecular biology tools has allowed for great advances in describing the microbial communities in anammox reactors, which is important to understand the complex reactions and interactions that occur inside these systems. This study presents a review of the microbial diversity studies in anammox reactors. Several researchers have investigated the microbial community composition in anammox reactors, in order to elucidate the roles that the different microbial groups (besides the anammox bacteria) play in these systems. The microbial communities of anammox reactors appear to be affected by several factors, such as the configuration of the reactors, the biomass growth mode inside of the reactors, operational conditions and type of inoculum used for start-up. However, independent of reactors characteristics, some microbial groups such as Proteobacteria and Chloroflexi have always been found with Planctomycetes in anammox reactors. Moreover, other microbial groups such as Chlorobi, Acidobacteria and Bacteroidetes are often detected in these systems. Identifying the roles and interactions of such microorganisms inside anammox reactors is a great challenge for future studies.

Sludge deterioration in a full scale UASB reactor after a pH drop working under low loading conditions

A full scale UASB reactor treating the effluent of a malting plant was operated during nearly two years. During 37 weeks of operation the reactor worked with a COD removal efficiency of 80% and a biogas production of nearly 300 m(3)/d with a methane content of 77%. After the start up and during these months of operation the volumetric organic load was 4 kgCOD/m(3).d and the specific organic load was between 0.2-0.4 kgCOD/kgVSS.d. The sludge SMA in this period was around 0.25 kgCOD/kg VSS.d. On week 37 as a result of a problem at the industrial process the pH in the reactor dropped to a value of 4.8. After pH recovering, the reactor worked with fluctuating COD values in the exit and showed a downward trend in the COD removal efficiency. On week 81 the presence of filaments in the granules was detected. High proportion of Chloroflexi filaments were detected by FISH in the sludge. Changes in the microbial population caused by the low pH probably destabilize the reactor performance. The presence of filamentous granules in the sludge and its further growing could be encouraged by the pH drop and the low specific organic load applied to the reactor. The low specific organic load was a consequence of the high VSS content in the UASB reactor, due to the lack of purges. The length of the filaments attached to the granules grew throughout time. In order to eliminate the sludge with poor settlement properties a recycle was applied to the reactor. As a consequence, low amount of granular sludge stayed in the reactor. At the end, COD concentration in the influent reached higher values than in normal operation; at the same time a complete sludge wash out occurred. On the other hand, using the same sludge (after the recycle implementation) in a bench scale reactor the good properties of the sludge were completely recovered.

Microbial Community Pathways for the Production of Volatile Fatty Acids From CO2 and Electricity

This study aims at elucidating the metabolic pathways involved in the production of volatile fatty acids from CO2 and electricity. Two bioelectrochemical systems (BES) were fed with pure CO2 (cells A and B). The cathode potential was first poised at -574 mV vs. standard hydrogen electrode (SHE) and then at -756 mV vs. SHE in order to ensure the required reducing power. Despite of applying similar operation conditions to both BES, they responded differently. A mixture of organic compounds (1.87 mM acetic acid, 2.30 mM formic acid, 0.43 mM propionic acid, 0.15 mM butyric acid, 0.55 mM valeric acid and 0.62 mM ethanol) was produced in cell A while mainly 1.82 mM acetic acid and 0.23 mM propionic acid were produced in cell B. The microbial community analysis performed by 16S rRNA gene pyrosequencing showed a predominance of Clostridium sp. and Serratia sp. in cell A whereas Burkholderia sp. and Xanthobacter sp. predominated in cell B. The coexistence of three metabolic pathways involved in carbon fixation was predicted. Calvin cycle was predicted in both cells during the whole experiment while Wood-Ljungdahl and Arnon-Buchanan pathways predominated in the period with higher coulombic efficiency (CE). Metabolic pathways which transform organic acids into anabolic intermediaries were also predicted, indicating the occurrence of complex trophic interactions. These results further complicate the understanding of these mixed culture microbial processes but also expand the expectation of compounds that could potentially be produced with this technology.