Membrane biofilm reactors (MBfRs) deliver gaseous substrates to biofilms that develop on the outside of gas-transfer membranes. When an MBfR delivers electron donors hydrogen (H
2
) or methane (CH
4
...), a wide range of oxidized contaminants can be reduced as electron acceptors, e.g., nitrate, perchlorate, selenate, and trichloroethene. When O
2
is delivered as an electron acceptor, reduced contaminants can be oxidized, e.g., benzene, toluene, and surfactants. The MBfR’s biofilm often harbors a complex microbial community; failure to control the growth of undesirable microorganisms can result in poor performance. Fortunately, the community’s structure and function can be managed using a set of design and operation features as follows: gas pressure, membrane type, and surface loadings. Proper selection of these features ensures that the best microbial community is selected and sustained. Successful design and operation of an MBfR depends on a holistic understanding of the microbial community’s structure and function. This involves integrating performance data with omics results, such as with stoichiometric and kinetic modeling.
Microbiological conversion of CO2 into biofuels and/or organic industrial feedstock is an excellent carbon‐cycling strategy. Here, autotrophic anaerobic bacteria in the membrane biofilm reactor ...(MBfR) transferred electrons from hydrogen gas (H2) to inorganic carbon (IC) and produced organic acids and alcohols. We systematically varied the H2‐delivery, the IC concentration, and the hydraulic retention time in the MBfR. The relative availability of H2 versus IC was the determining factor for enabling microbial chain elongation (MCE). When the H2:IC mole ratio was high (>2.0 mol H2/mol C), MCE was an important process, generating medium‐chain carboxylates up to octanoate (C8, 9.1 ± 1.3 mM C and 28.1 ± 4.1 mmol C m−2 d−1). Conversely, products with two carbons were the only ones present when the H2:IC ratio was low (<2.0 mol H2/mol C), so that H2 was the limiting factor. The biofilm microbial community was enriched in phylotypes most similar to the well‐known acetogen Acetobacterium for all conditions tested, but phylotypes closely related with families capable of MCE (e.g., Bacteroidales, Rhodocyclaceae, Alcaligenaceae, Thermoanaerobacteriales, and Erysipelotrichaceae) became important when the H2:IC ratio was high. Thus, proper management of IC availability and H2 supply allowed control over community structure and function, reflected by the chain length of the carboxylates and alcohols produced in the MBfR.
Membrane delivers electron‐donor H2 to bacteria growing as a biofilm in the exterior, and they produce acetate , propionate , butyrate , caproate , octanoate , ethanol , and butanol using bicarbonate as the carbon source.
Chloroform (CF) can undergo reductive dechlorination to dichloromethane, chloromethane, and methane. However, competition for hydrogen (H2), the electron‐donor substrate, may cause poor ...dechlorination when multiple electron acceptors are present. Common acceptors in anaerobic environments are nitrate (NO3−), sulfate (SO42−), and bicarbonate (HCO3−). We evaluated CF dechlorination in the presence of HCO3− at 1.56 e− Eq/m2‐day, then NO3− at 0.04–0.15 e− Eq/m2‐day, and finally NO3− (0.04 e− Eq/m2‐day) along with SO42− at 0.33 e− Eq/m2‐day in an H2‐based membrane biofilm reactor (MBfR). When the biofilm was initiated with CF‐dechlorination conditions (no NO3− or SO42−), it yielded a CF flux of 0.14 e− Eq/m2‐day and acetate production via homoacetogenesis up to 0.26 e− eq/m2‐day. Subsequent addition of NO3− at 0.05 e− Eq/m2‐day maintained full CF dechlorination and homoacetogenesis, but NO3− input at 0.15 e− Eq/m2‐day caused CF to remain in the reactor's effluent and led to negligible acetate production. The addition of SO42− did not affect CF reduction, but SO42− reduction significantly altered the microbial community by introducing sulfate‐reducing Desulfovibrio and more sulfur‐oxidizing Arcobacter. Dechloromonas appeared to carry out CF dechlorination and denitrification, whereas Acetobacterium (homoacetogen) may have been involved with hydrolytic dechlorination. Modifications to the electron acceptors fed to the MBfR caused the microbial community to undergo changes in structure that reflected changes in the removal fluxes.
Chloroform (CF) can undergo reductive dechlorination to dichloromethane, chloromethane, and methane. However, competition for hydrogen (H2), the electron‐donor substrate, may cause poor dechlorination when multiple electron acceptors are present. Common acceptors in anaerobic environments are nitrate (NO3−), sulfate (SO42−), and bicarbonate (HCO3−).
Selenate (SeO42−) reduction in hydrogen (H2)‐fed membrane biofilm reactors (H2‐MBfRs) was studied in combinations with other common electron acceptors. We employed H2‐MBfRs with two distinctly ...different conditions: R1, with ample electron‐donor availability and acceptors SeO42− and sulfate (SO42−), and R2, with electron‐donor limitation and the presence of electron acceptors SeO42−, nitrate (NO3−), and SO42−. Even though H2 was available to reduce all input SeO42− and SO42− in R1, SeO42− reduction was preferred over SO42− reduction. In R2, co‐reduction of NO3− and SeO42− occurred, and SO42− reduction was mostly suppressed. Biofilms in all MBfRs had high microbial diversity that was influenced by the “rare biosphere” (RB), phylotypes with relative abundance less than 1%. While all MBfR biofilms had abundant members, such as Dechloromonas and Methyloversatilis, the bacterial communities were significantly different between R1 and R2. For R1, abundant genera were Methyloversatilis, Melioribacter, and Propionivibrio; for R2, abundant genera were Dechloromonas, Hydrogenophaga, Cystobacter, Methyloversatilis, and Thauera. Although changes in electron‐acceptor or ‐donor loading altered the phylogenetic structure of the microbial communities, the biofilm communities were resilient in terms of SeO42− and NO3− reductions, because interacting members of the RB had the capacity of respiring these electron acceptors.
has been traditionally used by indigenous and socioeconomically disadvantaged people to treat infectious and parasitic diseases, including amoebiasis. The goal of this study was to assess the effect ...of a crude methanolic extract, an alkaloid extract, and aporphine alkaloids from leaves of
on the viability of
trophozoite cultures and to identify the mechanism of action. Different concentrations of the extracts and alkaloids purpureine (1: ), 3-hydroxyglaucine (2: ), norpurpureine (3: ) glaziovine (4: ), and oxopurpureine (5: ) were added to the cultures, and dead parasites were counted after 24 h using a tetrazolium dye reduction assay and analyzed by flow cytometry. The crude extract did not affect the viability of amoebae, but the alkaloid extract and the derived alkaloid glaziovine (4: ) had important anti-amoebic activity with an IC
of 33.5 µM compared to that shown by metronidazole (6.8 µM). The treatments induced significant morphological changes in the trophozoites, and most parasites killed by the alkaloid extract were positive for Annexin V, suggesting that apoptosis was the main mechanism of action. In contrast, glaziovine (4: ) induced less apoptosis with more amoebic lysis. This study supports the idea that aporphine alkaloids from
, mainly (+)-(
)-glaziovine (4: ), could contribute to the development of new formulations for the treatment of amoebiasis. In addition, X-ray diffraction structural analysis and complete
H and
C NMR assignments of (+)-(
)-glaziovine (4: ) were performed and reported for the first time.
Oxyanions, such as nitrate, perchlorate, selenate, and chromate are commonly occurring contaminants in groundwater, as well as municipal, industrial, and mining wastewaters. Microorganism-mediated ...reduction is an effective means to remove oxyanions from water by transforming oxyanions into harmless and/or immobilized forms. To carry out microbial reduction, bacteria require a source of electrons, called the electron-donor substrate. Compared to organic electron donors, H
is not toxic, generates minimal secondary contamination, and can be readily obtained in a variety of ways at reasonable cost. However, the application of H
through conventional delivery methods, such as bubbling, is untenable due to H
's low water solubility and combustibility. In this review, we describe the membrane biofilm reactor (MBfR), which is a technological breakthrough that makes H
delivery to microorganisms efficient, reliable, and safe. The MBfR features non-porous gas-transfer membranes through which bubbleless H
is delivered on-demand to a microbial biofilm that develops naturally on the outer surface of the membranes. The membranes serve as an active substratum for a microbial biofilm able to biologically reduce oxyanions in the water. We review the development of the MBfR technology from bench, to pilot, and to commercial scales, and we elucidate the mechanisms that control MBfR performance, particularly including methods for managing the biofilm's structure and function. We also give examples of MBfR performance for cases of treating single and co-occurring oxyanions in different types of contaminated water. In summary, the MBfR is an effective and reliable technology for removing oxyanion contaminants by accurately providing a biofilm with bubbleless H
on demand. Controlling the H
supply in accordance to oxyanion surface loading and managing the accumulation and activity of biofilm are the keys for process success.
Although benzene can be biodegraded when dissolved oxygen is sufficient, delivering oxygen is energy intensive and can lead to air stripping the benzene. Anaerobes can biodegrade benzene by using ...electron acceptors other than O
, and this may reduce costs and exposure risks; the drawback is a remarkably slower growth rate. We evaluated a two-step strategy that involved O
-dependent benzene activation and cleavage followed by intermediate oxidation coupled to NO
respiration. We employed a membrane biofilm reactor (MBfR) featuring nonporous hollow fibers as the means to deliver O
directly to a biofilm at an accurately controlled rate. Benzene was mineralized aerobically when the O
-supply rate was more than sufficient for mineralization. As the O
-supply capacity was systematically lowered, O
respiration was gradually replaced by NO
respiration. When the maximum O
-supply capacity was only 20% of the demand for benzene mineralization, O
was used almost exclusively for benzene activation and cleavage, while respiration was almost only by denitrification. Analyses of microbial community structure and predicted metagenomic function reveal that Burkholderiales was dominant and probably utilized monooxygenase activation, with subsequent mineralization coupled to denitrification; strict anaerobes capable of carboxylative activation were not detected. These results open the door for a promising treatment strategy that simultaneously ameliorates technical and economic challenges of aeration and slow kinetics of anaerobic activation of aromatics.
Although benzene can be biodegraded when dissolved oxygen is sufficient, delivering oxygen is energy intensive and can lead to air stripping the benzene. Anaerobes can biodegrade benzene by using ...electron acceptors other than O2, and this may reduce costs and exposure risks; the drawback is a remarkably slower growth rate. We evaluated a two‐step strategy that involved O2‐dependent benzene activation and cleavage followed by intermediate oxidation coupled to NO3− respiration. We employed a membrane biofilm reactor (MBfR) featuring nonporous hollow fibers as the means to deliver O2 directly to a biofilm at an accurately controlled rate. Benzene was mineralized aerobically when the O2‐supply rate was more than sufficient for mineralization. As the O2‐supply capacity was systematically lowered, O2 respiration was gradually replaced by NO3− respiration. When the maximum O2‐supply capacity was only 20% of the demand for benzene mineralization, O2 was used almost exclusively for benzene activation and cleavage, while respiration was almost only by denitrification. Analyses of microbial community structure and predicted metagenomic function reveal that Burkholderiales was dominant and probably utilized monooxygenase activation, with subsequent mineralization coupled to denitrification; strict anaerobes capable of carboxylative activation were not detected. These results open the door for a promising treatment strategy that simultaneously ameliorates technical and economic challenges of aeration and slow kinetics of anaerobic activation of aromatics.
Nonporous hollow fibers enabled accurate O2 delivery on demands. When the maximum O2‐supply capacity was only 20% of the demand for benzene mineralization, O2 was used almost exclusively for benzene activation and cleavage, while respiration was almost only by denitrification. It opens the door for a promising treatment strategy that simultaneously ameliorates technical and economic challenges of aeration and slow kinetics of anaerobic activation of aromatics.
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