A 6-L, completely mixed anaerobic bioreactor with an external ultrafiltration membrane module was operated for 300 days to evaluate the startup and performance of an anaerobic membrane bioreactor ...(AnMBR) treating swine manure. The reactor had a successful startup at the initial loading rate of 1
g volatile solids (VS)/L/day. After a two-fold increase in loading rate followed by a sudden, two-fold increase in flow velocity through the membrane module on day 75, the performance of the AnMBR deteriorated as measured by volatile fatty acid (VFA) accumulation, decrease in pH, and decrease in biogas production. The methanogenic population dynamics in the reactor were monitored with terminal restriction fragment length polymorphism (T-RFLP). Changes in the relative levels of
Methanosarcinaceae and
Methanosaetaceae were consistent with changes in VFA concentrations, i.e., high and low levels of acetate corresponded to a high abundance of
Methanosarcinaceae and
Methanosaetaceae, respectively. The levels of hydrogenotrophic methanogens of the order of
Methanomicrobiales increased during decreased reactor performance suggesting that syntrophic interactions involving hydrogenotrophic methanogens remained intact regardless of the degree of shear in the AnMBR.
Changes in methanogenic population levels were followed during startup of a full-scale, farm-based anaerobic sequencing batch reactor (ASBR) and these changes were linked to operational and ...performance data. The ASBR was inoculated with anaerobic digester sludge from a municipal wastewater treatment facility. During an acclimation period of approximately 3 months, the ASBR content was diluted to maintain a total ammonia-N level of approximately 2000
mg
l
−1. After this acclimation period, the volatile solids loading rate was increased to its design value of 1.7
g
l
−1
day
−1 with a 15-day hydraulic retention time, which increased the total ammonia-N level in the ASBR to approximately 3600
mg
l
−1. The 16
S ribosomal RNA (rRNA) levels of the acetate-utilizing methanogens of the genus
Methanosarcina decreased from 3.8% to 1.2% (expressed as a percentage of the total 16
S rRNA levels) during this period, while the 16
S rRNA levels of
Methanosaeta concilii remained low (below 2.2%). Methane production and reactor performance were not affected as the 16
S rRNA levels of the hydrogen-utilizing methanogens of the order
Methanomicrobiales increased from 2.3% to 7.0%. Hence, it is likely that during operation with high ammonia levels, the major route of methane production is through a syntrophic relationship between acetate-oxidizing bacteria and hydrogen-utilizing methanogens. Anaerobic digestion at total ammonia-N levels exceeding 3500
mg
l
−1 was sustainable apparently due to the acclimation of hydrogen-utilizing methanogens to high ammonia levels.
A laboratory-scale anaerobic sequencing batch reactor was used to treat a model substrate mixture representing pharmaceutical wastewater at an organic loading rate of 2.9 g COD/(L d). After reaching ...stable operation the reactor was first exposed to low (1 mg/L) and, subsequently, to high (200 mg/L) concentrations of the antibiotic erythromycin. The addition of low levels of erythromycin resulted in a significant but limited reduction of biogas production by 5% and the higher level of erythromycin did not impact biogas production further, suggesting that a substantial fraction of the microbial populations in the ASBR were resistant to the antibiotic. Effluent soluble COD could not be accounted for in measured volatile fatty acids, perhaps suggesting the production of soluble microbial products. In batch tests evaluating the specific methanogenic activity, conversion of the model substrate mixture was only slightly affected by the presence of erythromycin. However, the conversion of butyric acid was inhibited when erythromycin was present. After 47 days of exposure to erythromycin, the conversion of butyric acid was inhibited to a lesser extent, suggesting the development of antibiotic resistance in the biomass. Exposure to antibiotics can affect specific substrate degradation pathways, leading to the accumulation of volatile fatty acids, soluble microbial products, and potentially to overall system instabilities.
The tobacco (Nicotiana tabacum) cultivar Xanthi-nc (genotype NN) produces high levels of salicylic acid (SA) after inoculation with the tobacco mosaic virus (TMV). Gaseous methyl salicylate (MeSA), a ...major volatile produced in TMV-inoculated tobacco plants, was recently shown to be an airborne defense signal. Using an assay developed to measure the MeSA present in tissue, we have shown that in TMV-inoculated tobacco plants the level of MeSA increases dramatically, paralleling increases in SA. MeSA accumulation was also observed in upper, noninoculated leaves. In TMV-inoculated tobacco shifted from 32 to 24 degrees C, the MeSA concentration increased from nondetectable levels to 2318 ng/g fresh weight 12 h after the temperature shift, but subsequently decreased with the onset of the hypersensitive response. Similar results were observed in plants inoculated with Pseudomonas syringae pathovar phaseolicola, in which MeSA levels were highest just before the hypersensitive response-induced tissue desiccation. Transgenic NahG plants unable to accumulate SA also did not accumulate MeSA after TMV inoculation, and did not show increased resistance to TMV following MeSA treatment. Based on the spatial and temporal kinetics of its accumulation, we conclude that tissue MeSA may play a role similar to that of volatile MeSA in the pathogen-induced defense response
Anaerobic reactor systems are essential for the treatment of solid and liquid wastes and constitute a core facility in many waste treatment plants. Although much is known about the basic metabolism ...in different types of anaerobic reactors, little is known about the microbes responsible for these processes. Only a few percent of Bacteria and Archaea have so far been isolated, and almost nothing is known about the dynamics and interactions between these and other microorganisms. This lack of knowledge is most clearly exemplified by the sometimes unpredictable and unexplainable failures and malfunctions of anaerobic digesters occasionally experienced, leading to sub-optimal methane production and wastewater treatment. Using a variety of molecular techniques, we are able to determine which microorganisms are active, where they are active, and when they are active, but we still need to determine why and what they are doing. As genetic manipulations of anaerobes have been shown in only a few species permitting in-situ gene expression studies, the only way to elucidate the function of different microbes is to correlate the metabolic capabilities of isolated microbes in pure culture to the abundance of each microbe in anaerobic reactor systems by rRNA probing. This chapter focuses on various molecular techniques employed and problems encountered when elucidating the microbial ecology of anaerobic reactor systems. Methods such as quantitative dot blot/fluorescence in-situ probing using various specific nucleic acid probes are discussed and exemplified by studies of anaerobic granular sludge, biofilm and digester systems.
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