Potential Sulfate Reduction Research Articles

34S/ 32S fractionation by sulfate-reducing microbial communities in estuarine sediments

Sulfur isotope fractionation during microbial sulfate reduction in brackish estuarine sediments was studied using an experimental flow-through reactor approach designed to preserve the in situ physical, geochemical and microbial structure of the sediment. Concurrent measurements of potential sulfate reduction rates and 34S/ 32S fractionations were carried out using intact sediment slices (2 cm thick, 4.2 cm diameter) from unvegetated, intertidal sites adjoining a salt marsh along the Scheldt estuary, The Netherlands. A total of 30 reactor experiments were performed with sediments collected in February, May and October 2006. The effects of incubation temperature (10, 20, 30 and 50 °C) and sediment depth (0–2, 4–6 and 8–10 cm) were investigated. Sulfate was supplied in non-limiting concentrations via the reactor inflow solutions; no external electron donor was supplied. Isotope fractionations ( ε values) were calculated from the measured differences in sulfate δ 34S between in- and outflow solutions of the reactors, under quasi-steady state conditions. Potential sulfate reduction rates (SRR) varied over one order of magnitude (5–49 nmol cm −3 h −1) and were highest in the 30 °C incubations. They decreased systematically with depth, and were highest in the sediments collected closest to the vegetated marsh. Isotope fractionations ranged from 9‰ to 34‰ and correlated inversely with SRR, as predicted by the standard fractionation model for enzymatic sulfate reduction of Rees (1973). The ε versus SRR relationship, however, varied between sampling times, with higher ε values measured in February, at comparable SRRs, than in May and October. The observed ε versus SRR relationships also deviated from the previously reported inverse trend for sediments collected in a marine lagoon in Denmark ( Canfield, 2001b). Thus, isotope fractionation during sulfate reduction is not uniquely determined by SRR, but is site- and time-dependent. Factors that may affect the ε versus SRR relationship include the structure and size of the sulfate-reducing community, and the nature and accessibility of organic substrates. Whole-sediment data such as those presented here provide a link between isotopic fractionations measured with pure cultures of sulfate-reducing prokaryotes and sulfur isotopic signatures recorded in sedimentary deposits.

A cryptic sulfur cycle driven by iron in the methane zone of marine sediment (Aarhus Bay, Denmark)

Sulfate reduction and sulfur–iron geochemistry were studied in 5–6 m deep gravity cores of Holocene mud from Aarhus Bay (Denmark). A goal was to understand whether sulfate is generated by re-oxidation of sulfide throughout the sulfate and methane zones, which might explain the abundance of active sulfate reducers deep below the main sulfate zone. Sulfate penetrated down to 130 cm where methane started to build up and where the concentration of free sulfide peaked at 5.5 mM. Below this sulfate–methane transition, sulfide diffused downwards to a sulfidization front at 520 cm depth, below which dissolved iron, Fe 2+, accumulated in the pore water. Sulfate reduction rates measured by 35S-tracer incubations in the sulfate zone were high due to high concentrations of reactive organic matter. Within the sulfate–methane transition, sulfate reduction was distinctly stimulated by the anaerobic oxidation of methane. In the methane zone below, sulfate remained at positive “background” concentrations of <0.5 mM down to the sulfidization front. Sulfate reduction decreased steeply to rates which at 300–500 cm depth were 0.2–1 pmol SO 4 2− cm −3 d −1, i.e., 4–5 orders of magnitude lower than rates measured near the sediment surface. The turn-over time of sulfate increased from 3 years at 12 cm depth to 100–1000 years down in the methane zone. Sulfate reduction in the methane zone accounted for only 0.1% of sulfate reduction in the entire sediment column and was apparently limited by the low pore water concentration of sulfate and the low availability of organic substrates. Amendment of the sediment with both sulfate and organic substrates immediately caused a 10- to 40-fold higher, “potential sulfate reduction” which showed that a physiologically intact community of sulfate reducing bacteria was present. The “background” sulfate concentration appears to be generated from the reaction of downwards diffusing sulfide with deeply buried Fe(III) species, such as poorly-reactive iron oxides or iron bound in reactive silicates. The oxidation of sulfide to sulfate in the sulfidic sediment may involve the formation of elemental sulfur and thiosulfate and their further disproportionation to sulfide and sulfate. The net reaction of sulfide and Fe(III) to form pyrite requires an additional oxidant, irrespective of the formation of sulfate. This could be CO 2 which is reduced with H 2 to methane. The methane subsequently diffuses upwards to become re-oxidized at the sulfate–methane transition and thereby removes excess reducing power and enables the formation of excess sulfate. We show here how the combination of these well-established sulfur–iron–carbon reactions may lead to the deep formation of sulfate and drive a cryptic sulfur cycle. The iron-rich post-glacial sediments underlying Holocene marine mud stimulate the strong sub-surface sulfide reoxidation observed in Aarhus Bay and are a result of the glacial to interglacial history of the Baltic Sea area. Yet, processes similar to the ones described here probably occur widespread in marine sediments, in particular along the ocean margins.

Sulfate reduction below the sulfate–methane transition in Black Sea sediments

A sudden increase in salinity about 7000 years ago caused a shift in the deposited sediments of the Black Sea from limnic to brackish-marine. Due to the development of an anoxic deep water basin and a relatively high sulfate concentration, organic matter is mineralized primarily through sulfate reduction in modern Black Sea sediments. Earlier studies showed that sulfate-reducing bacteria are abundant within the limnic sub-surface sediment in spite of extremely low concentrations of sulfate and organic carbon. A main objective of the present study was therefore to understand the depth distribution of sulfate reduction across the different sediment units, even deep below the sulfate–methane transition. Our study combined experimental measurements of sulfate reduction using 35S radiotracer with analyses of sulfur and iron geochemistry in pore water and sediment. Potential sulfate reduction rates were measured with 35S in sediment samples that were amended with sulfate and organic substrates and incubated in time-series up to 48 h. Sulfate reduction could thereby be detected and quantified at depths where concentrations of sulfate were otherwise too low to enable calculation of the rates. The results demonstrate that sulfate-reducing bacteria are active several meters below the sulfate–methane transition in Black Sea sediments. The cryptic sulfate reduction below the sulfate–methane transition may be driven by sulfate produced from re-oxidation of reduced sulfur species with oxidized iron minerals buried in the deep limnic sediment.

Correlation of bacterial communities supported by different organic materials with sulfate reduction in metal-rich landfill leachate

Several different organic materials, typical of those used in passive treatment systems for mine influenced water, were tested for their ability to support sulfate-reducing bacteria and sulfate reduction in an anaerobic biological reactor (ABR). The quantity of sulfate-reducing bacteria (SRB) in each organic material, as determined using quantitative polymerase chain reaction (q-PCR) of the dissimilatory sulfite reductase (dsr) gene, correlated with the initial C/N ratio of each material. Potential sulfate reduction rates measured in the laboratory ranked silage > compost = molasses/hay > cattails > pulp mill biosolids and correlated with the q-PCR estimates of SRB in the submerged materials. A comparison of bacterial communities using 16S rRNA gene clone library sequencing revealed similar distribution of clones among the phyla Bacteroidetes, Firmicutes and Proteobacteria for silage, compost and molasses/hay after 174 days of exposure in the seepage water. Silage, the most successful material tested, contained more δ-Proteobacteria-related sequences than the other materials and Spirochaetes-related clones were more abundant in silage than in compost or molasses/hay. According to sequenced dsr clones, the SRB community in silage differed from that for compost and molasses/hay, with fewer Desulfovibrio- and more Desulfomicrobium-related sequences in the silage. Pulp mill biosolids used in the ABR since 2004 contained an overall bacterial community that was more diverse than those for the freshly submerged organics, but only Desulfovibrio desulfuricans-related sequences were found in the dsr library.

Ultrastructure, tactic behaviour and potential for sulfate reduction of a novel multicellular magnetotactic prokaryote from North Sea sediments

Multicellular magnetotactic prokaryotes (MMPs) represent highly organized, spherical and motile aggregates of 10-40 bacterial cells containing magnetosomes. Although consisting of different cells, each with its own magnetosomes and flagellation, MMPs orient themselves within a magnetic field and exhibit magnetotaxis. So far, MMPs have only been found in several North and South American coastal lagoons and salt marshes. In the present study, a novel type of MMP was discovered in coastal tidal sand flats of the North Sea. High-resolution scanning electron microscopy revealed the presence of bullet-shaped magnetosomes which were aligned in several parallel chains. Within each aggregate, the magnetosome chains of individual cells were oriented in the same direction. Energy dispersive X-ray (EDX) analysis showed that the magnetosomes are composed of iron sulfide. This particular morphology and arrangement of magnetosomes has previously not been reported for other MMPs. 16S rRNA gene sequence analysis revealed a single phylotype which represented a novel phylogenetic lineage with >or= 4% sequence divergence to all previously described MMP sequences and was related to the dissimilatory sulfate-reducing Desulfosarcina variabilis within the family Desulfobacteraceae of the subphylum Deltaproteobacteria. Fluorescence in situ hybridization with a specific oligonucleotide probe revealed that all MMPs in the tidal flat sediments studied belonged to the novel phylotype. Within each MMP, all bacterial cells showed a hybridization signal, indicating that the aggregates are composed of cells of the same phylotype. Genes for dissimilatory sulfite reductase (dsrAB) and dissimilatory adenosine-5'-phosphate reductase (aprA) could be detected in purified MMP samples, suggesting that MMPs are capable of sulfate reduction. Chemotaxis assays with 41 different test compounds yielded strong responses towards acetate and propionate, whereas other organic acids, alcohols, sugars, sugar alcohols or sulfide did not elicit any response. By means of its coordinated magnetotaxis and chemotaxis, the novel type of MMP is well adapted to the steep chemical gradients which are characteristic for intertidal marine sediments.

Temperature dependence of Fe(III) and sulfate reduction rates and its effect on growth and composition of bacterial enrichments from an acidic pit lake neutralization experiment

ABSTRACTMicrobial Fe(III) and sulfate reduction are important electron transport processes in acidic pit lakes and stimulation by the addition of organic substrates is a strategy to remove acidity, iron and sulfate. This principle was applied in a pilot‐scale enclosure in pit lake 111 (Brandenburg, Germany). Because seasonal and spatial variation of temperature may affect the performance of in situ experiments considerably, the influence of temperature on Fe(III) and sulfate reduction was investigated in surface sediments from the enclosure in the range of 4–28 °C. Potential Fe(III) reduction and sulfate reduction rates increased exponentially with temperature, and the effect was quantified in terms of the apparent activation energy Ea measuring 42–46 kJ mol−1 and 52 kJ mol−1, respectively. Relatively high respiration rates at 4 °C and relatively low Q10 values (∼2) indicated that microbial communities were well adapted to low temperatures. In order to evaluate the effect of temperature on growth and enrichment of iron and sulfate‐reducing bacterial populations, MPN (Most Probable Number) dilution series were performed in media selecting for the different bacterial groups. While the temperature response of specific growth rates of acidophilic iron reducers showed mesophilic characteristics, the relatively high specific growth rates of sulfate reducers at the lowest incubation temperature indicated the presence of moderate psychrophilic bacteria. In contrast, the low cell numbers and low specific growth rates of neutrophilic iron reducers obtained in dilution cultures suggest that these populations play a less significant role in Fe and S cycling in these sediments. SSCP (Single‐Strand Conformation Polymorphism) or DGGE (Denaturing Gradient Gel Electrophoresis) fingerprinting based on 16S rRNA genes of Bacteria indicated different bacterial populations in the MPN dilution series exhibiting different temperature ranges for growth.

Accelerated Sulfur Cycle in Coastal Marine Sediment beneath Areas of Intensive Shellfish Aquaculture

Prokaryotes in marine sediments taken from two neighboring semi-enclosed bays (the Yamada and Kamaishi bays) at the Sanriku coast in Japan were investigated by the culture-independent molecular phylogenetic approach coupled with chemical and activity analyses. These two bays were chosen in terms of their similar hydrogeological and chemical characteristics but different usage modes; the Yamada bay has been used for intensive shellfish aquaculture, while the Kamaishi bay has a commercial port and is not used for aquaculture. Substantial differences were found in the phylogenetic composition of 16S rRNA gene clone libraries constructed for the Yamada and Kamaishi sediments. In the Yamada library, phylotypes affiliated with delta-Proteobacteria were the most abundant, and those affiliated with gamma-Proteobacteria were the second-most abundant. In contrast, the Kamaishi library was occupied by phylotypes affiliated with Planctomycetes, gamma-Proteobacteria, delta-Proteobacteria, and Crenarchaeota. In the gamma-Proteobacteria, many Yamada phylotypes were related to free-living and symbiotic sulfur oxidizers, whereas the Kamaishi phylotype was related to the genus Pseudomonas. These results allowed us to hypothesize that sulfate-reducing and sulfur-oxidizing bacteria have become abundant in the Yamada sediment. This hypothesis was supported by quantitative competitive PCR (qcPCR) with group-specific primers. The qcPCR also suggested that organisms closely related to Desulfotalea in the Desulfobulbaceae were the major sulfate-reducing bacteria in these sediments. In addition, potential sulfate reduction and sulfur oxidation rates in the sediment samples were determined, indicating that the sulfur cycle has become active in the Yamada sediment beneath the areas of intensive shellfish aquaculture.

Sulfate Reduction Potential in Sediments in the Norilsk Mining Area, Northern Siberia

The purpose of this study was to characterize the distribution and activity of sulfate-reducing bacteria in tailings and sediments impacted by effluents from mining and smelting operations in the Norilsk area in northern Siberia. The Norilsk mining complex involves three smelter operations, a hydrometallurgical plant, and extensive tailings areas located in the permafrost zone. Sulfate reduction rates measured with a 35SO4 2− tracer technique under various in-situ conditions ranged from 0.05 to 30 nmol S cm−3 day−1. Acetate and glucose addition greatly stimulated sulfate reduction, whereas lactate had less effect. The most pronounced stimulation of sulfate reduction (6.5-fold) was observed with phosphate amendment. Most-probable-number (MPN) counts of sulfate-reducing bacteria in media with glucose, ethanol, lactate, and acetate as electron donors were generally highest at around 107 cells ml−1. The actual MPN counts varied with the sample, electron donor, and incubation conditions (pH 7.2 vs. pH 3.5; 28°C vs. 4°C). Enrichment cultures of sulfate-reducing bacteria were established from a sample that showed the highest rate of sulfate reduction. After multiple serial transfers, the dominant sulfate-reducers were identified by fluorescence in situ hybridization using genus and group-specific 16S rRNA-targeted oligonucleotide probes. Desulfobulbus spp. prevailed in ethanol and lactate enrichments and the Desulfosarcina-Desulfococcus group dominated in acetate and benzoate enrichments. Psychrophilic Desulfotalea-Desulfofustis and moderately psychrophilic Desulforhopalus spp. were identified in enrichments incubated at 4°C, but they were also found in mesophilic enrichments.

Kinetics of bacterial sulfate reduction in an activated sludge plant

The kinetics of sulfate reduction and cell densities of sulfate-reducing bacteria (SRB) were determined in activated sludge at Aalborg East wastewater treatment plant, a modern 100 000 person equivalent plant, where SRB are subjected to alternating cycles of oxic and anoxic conditions. The number of SRB was relatively constant over the year, ranging from 2.1×10 5 to 1.1×10 6 cells ml −1 as determined by 35S-radiotracer most probable number (MPN) in a growth medium prepared from anaerobic, sterilized sludge. Under anoxic conditions, the sulfide production in the activated sludge followed a biphasic pattern, being linear for approximately 5 h, followed by an exponential phase with doubling times of sulfide production of 4.2–12.6 h. Sulfate reduction started immediately after the onset of the anoxic cycle. Addition of antibiotics (chloramphenicol and streptomycin) to the activated sludge prevented the exponential phase of sulfate reduction for up to 100 h and this treatment was found to yield precise estimates of potential sulfate reduction rates. The addition of sulfate, sodium dithionite or single carbon compounds (lactate, acetate and glucose) did not decrease the length of the linear phase of sulfate reduction, nor did it affect the sulfate reduction rate. Our results indicate a tight and efficient metabolic coupling between populations of SRB and fermenting bacteria in activated sludge and a high capacity for sulfate reduction in sludge stored in settling tanks. Bacterial sulfate reduction may therefore be an important process in the destabilization of the floc structure when activated sludge is stored anaerobically for several days prior to dewatering.

Sulfate reduction in Louisiana marsh soils of varying salinities

Potential sulfate reduction and in situ hydrogen sulfide emission rates for three Louisiana marsh soils of varying salinities (salt, brackish, and freshwater) were used to evaluate the influence of soil physicochemical parameters on sulfur transformations in different seasons (summer, winter, and spring). Solid adsorbent preconcentration and emission flux chambers were used in field experiments to measure hydrogen sulfide emissions. Soil redox potential (Eh) was measured at depths between 5 and 50 cm. Duplicate soil cores were obtained and sectioned for laboratory analysis. The fresh and brackish marsh soils were composed predominantly of organic matter, while the salt marsh soils were composed of predominantly minerals. Fresh marsh soils were generally the most oxidized and salt marsh soils the most reduced. In situ hydrogen sulfide emissions, but not potential sulfate reduction rates, were highest for the brackish marsh. Potential sulfate reduction assays may have overestimated in-situ rates, particularly for the more oxidized fresh marsh. Sulfate turnover times were longer in the salt marsh (approximately 40 days) than in either the fresh or the brackish marshes (3–8 days). Tidal action replenishes sulfate less frequently in the fresh and brackish marshes, thus sulfate depletions are more likely. The lowest potential sulfate reduction rates for all marshes occurred in winter. This was attributed to lower temperature and decreased soil sulfate content.

Spotting zones of dissimilatory sulfate reduction in a forested catchment: the 34S- 35S approach

The localization of sulfate reducing sites in forested catchments is of major importance, because dissimilatory sulfate reduction can be a considerable sink for deposited sulfate. To localize dissimilatory sulfate reduction sites in a forested catchment (northeastern Bavaria, Germany), three sites within the catchment (upland site, intermittent seep, fen) were investigated for δ 34S depth profiles of soil sulfur and potential sulfate reduction rates were measured with 35S radiolabeling. Stable sulfur isotopes indicate that aerobic metabolism is the dominant process on the upland site and the intermittent seep (δ 34S of soil sulfur between +1.6 and +9.0‰) and dissimilatory reduction is not a significant sink for sulfate. However, results of the 35S radiolabeling indicated for the upland site that the soil has potentially high sulfate reduction rates under laboratory conditions. Soil sulfur of the fen was markedly depleted in 34S (δ 34S between −6 and +2.6‰). Both, 34S and 35S data indicated that dissimilatory sulfate reduction is an ongoing process on this site. The 34S and 35S approaches are complementary. While measurements using 35S can show momentary potential for dissimilatory bacterial sulfate reduction, δ 34S data reflect long-term predominance of either assimilatory or dissimilatory S metabolism at a particular site.

Sulfate-reducing Bacteria in Rice Field Soil and on Rice Roots

Rice plants that were grown in flooded rice soil microcosms were examined for their ability to exhibit sulfate reducing activity. Washed excised rice roots showed sulfate reduction potential when incubated in anaerobic medium indicating the presence of sulfate-reducing bacteria. Rice plants, that were incubated in a double-chamber (phylloshpere and rhizosphere separated), showed potential sulfate reduction rates in the anoxic rhizosphere compartment. These rates decreased when oxygen was allowed to penetrate through the aerenchyma system of the plants into the anoxic root compartment, indicating that sulfate reducers on the roots were partially inhibited by oxygen or that sulfate was regenerated by oxidation of reduced S-compounds. The potential activity of sulfate reducers on rice roots was consistent with MPN enumerations showing that H2-utilizing sulfate-reducing bacteria were present in high numbers on the rhizoplane (4.1 x 10(7) g-1 root fresh weight) and in the adjacent rhizosperic soil (2.5 x 10(7) g-1 soil dry weight). Acetate-oxidizing sulfate reducers, on the other hand, showed highest numbers in the unplanted bulk soil (1.9 x 10(6) g-1 soil dry weight). Two sulfate reducing bacteria were isolated from the highest dilutions of the MPN series and were characterized physiologically and phylogenetically. Strain F1-7b which was isolated from the rhizoplane with H2 as electron donor was related to subgroup II of the family Desulfovibrionaceae. Strain EZ-2C2, isolated from the rhizoplane on acetate, grouped together with Desulforhabdus sp. and Syntrophobacter wolinii. Other strains of sulfate-reducing bacteria originated from bulk soil of rice soil microcosms and were isolated using different electron donors. From these isolates, strains R-AcA1, R-IbutA1, R-PimA1 and R-AcetonA170 were Gram-positive bacteria which were affiliated with the genus Desulfotomaculum. The other isolates were members of subgroup II of the Desulfovibrionaceae (R-SucA1 and R-LacA1), were related to Desulforhabdus sp. (strain BKA11), Desulfobulbus (R-PropA1), or culstered between Desulfobotulus sapovorans and Desulfosarcina variabilis (R-ButA1 and R-CaprA1).

Contribution of hydrogen to methane production and control of hydrogen concentrations in methanogenic soils and sediments

Hydrogen is, with acetate, one of the most important intermediates in the methanogenic degradation of organic matter and serves as substrate for methanogenic archaea. Hydrogen should theoretically account for 33% of total methanogenesis when carbohydrates or similar forms of organic matter are degraded. Many methanogenic environments show both much lower and much higher contributions of H2 to CH4 production than is considered normal. While the lower contributions are relatively easily explained (e.g. by the contribution of homoacetogenesis), the mechanisms behind higher contributions are mostly unclear. In methanogenic environments H2 is rapidly turned over, its concentration being the result of simultaneous production by fermenting plus syntrophic bacteria and consumption by methanogenic archaea. The steady-state concentration observed in most methanogenic environments is close to the thermodynamic equilibrium of H2-dependent methanogenesis. The threshold is usually equivalent to a Gibbs free energy of −23 kJ mol−1 CH4 that is necessary to couple CH4 production to the generation of 1/3 ATP. Methanogenesis from H2 is inhibited if the H2 concentration decreases below this threshold. Concentrations of H2 can only be decreased below this threshold if a H2-consuming reaction with a lower H2 threshold (e.g. sulfate reduction) takes over at a rate that is equal to or higher than that of methanogenesis. The instantaneous and complete inhibition of H2-dependent CH4 production that is often observed upon addition of sulfate can only be explained if a comparably high sulfate reduction potential is cryptically present in the methanogenic environment.

微小電極を用いた微好気性生物膜内の硫酸塩還元反応の検討

The vertical zonation of 02 respiration, NO3- respiration, H2S oxidation and SO42- reduction in microaerobic biofilms grown on rotating biological contactors (RBCs) of treating domestic wastewater was studied by measuring concentration profiles in the biofilms with microelectodes for 02, NO3-, H2S and pH. From those profiles, in situ specific reaction rates and substrate fluxes were calculated by using a simple one-dimensional deffusion reaction model and were related to population densities of sulfate-reducing bacteria (SRB) and potential sulfate reduction rates determined by standard batch experiments. The maximum population densities and the highest potential sulfate reduction rates were found in the outermost biofilm. On the contrary, the in situ sulfate reduction rates were restricted in a narrow zone located in the middle biofilm incubated DO=100 μmol·l-1. An increase in the O2 and/or NO3- penetration depth in the biofilm induced a shift of sulfate reduction zone to the deeper biofilm and a decrease in the specific sulfate reduction rate. This is probably because that the potential sulfate reduction rate decreased toward the depth and addition of nitrate enhanced oxidation of the produced sulfide or increased competition for electron donor with denitrifiers, or both. The microelectrode measurements with the high spatial resolution enable us to quantitatively measure in situ SO42- reduction rate in microaerobic biofilms, which could not be detected measureing sulfide or sulfate flux across the water-biofilm interface.

Influence of oxygen on biofilm growth and potential sulfate reduction in gravity sewer biofilm

Under conditions of high organic surface load and high hydraulic shear the influence of bulk water dissolved oxygen (DO) concentration on biofilm oxygen consumption, biofilm growth and sulfate reduction in biofilms was investigated using both domestic wastewater and synthetic glucose - yeast extract medium. The biofilm thickness apparently did not approach a steady-state value; instead biofilm thickness increased linearly until the entire biofilm eventually sloughed. Potential activity of sulfate-reducing bacteria was highest when the biofilms were grown at low DO levels in bulk water. Potential sulfide production measured per biofilm volume remained fairly constant during the growth of the biofilms. Only at oxygen levels close to 0 ppm was sulfide production into bulk water under aerobic conditions evident; at higher oxygen levels, complete reoxidation of sulfide occurred within the biofilm. For biofilms growing at bulk oxygen conditions below 1 ppm, the sulfate reduction (and thus sulfide production) was of significance for the processes in the biofilm system in terms of oxygen consumption and COD removal.

Sulfate reducing and methane producing bacteria in aerobic wastewater treatment systems

A selection of aerobic biofilm reactors and activated sludge plants were investigated for the presence of methane producing bacteria (MPB) and sulfate reducing bacteria (SRB). Detection tests showed that acetotrophic and hydrogenotrophic MPB as well as lactate, acetate and propionate oxidizing SRB were present in all reactor types investigated, except in an activated sludge reactor aerated with pure oxygen. Methane production rates from acetate by biomass samples of aerobic reactors were less than 1% of the rates measured in anaerobic UASB sludge. The presence of SRB was independent of the reactor configuration, the organic loading and the influent sulfate concentration. Aerobic biofilms growing in a trickling filter packed with plastic carrier and in a rotating biological contactor contained between 5.7 × 10 7 to 1.1 × 10 8 CFU/g VS of lactate oxidizing SRB and showed a potential sulfate reduction rate using lactate as electron donor of about 10 mg SO 2− 4/g VS·h. The latter is comparable to the values found in sludges from typical anaerobic wastewater treatment reactors. In activated sludges, SRB densities were some 10 3 time lower and the maximum sulfate reduction rate was ca 3 times lower compared to the aerobic biofilm reactors. In biofilms, high sulfate reduction rates, in combination with the high sulfide removal rates (11.6 to 131.7 mg HS −/g VS·h) suggest that in situ reoxidation of sulfide might sustain the SRB population. The SRB enumeration, together with activity and oxygen microprofile measurements showed that the biomass of aerobic wastewater treatment systems can serve as inoculum or as site for a wide spectrum of redox related biotransformation processes.

Influence of oxygen on biofilm growth and potential sulfate reduction in gravity sewer biofilm

Under conditions of high organic surface load and high hydraulic shear the influence of bulk water dissolved oxygen (DO) concentration on biofilm oxygen consumption, biofdm growth and sulfate reduction in biofilms was investigated using both domestic wastewater and synthetic glucose - yeast extract medium. The biofilm thickness apparently did not approach a steady-state value; instead biofilm thickness increased linearly until the entire biofilm eventually sloughed.Potential activity of sulfate-reducing bacteria was highest when the biofilms were grown at low DO levels in bulk water. Potential sulfide production measured per biofilm volume remained fairly constant during the growth of the biofilms. Only at oxygen levels close to 0 ppm was sulfide production into bulk water under aerobic conditions evident; at higher oxygen levels, complete reoxidation of sulfide occurred within the biofilm. For biofihns growing at bulk oxygen conditions below 1 ppm, the sulfate reduction (and thus sulfide production) was of significance for the processes m the biofilm system in terms of oxygen consumption and COD removal.

Organic Matter Mineralization in the Littoral and open Lake Sediments of the Shallow Neusiedlersee, Österreich

AbstractNeusiedlersee is a very shallow lake located in the eastern part of Austria. It is characterized by a reed belt that covers nearly 70% of its perimeter. Extended mixing and sediment resuspension due to wind action is observed in the open lake. Autochthonous seston and organic matter accumulates at the fringe and inside the reed belt. Space‐time fluctuations of bacterial populations in the open lake and littoral sediments and mineralization of organic matter in the littoral sediments were studied. Total number of bacteria was determined by epifluorescence. Ammonifying bacteria were determined by an MPN method. Experiments to evaluate organic matter mineralization were performed. Potential proteolysis and sulfate reduction were evaluated. Evidence of organic matter aggregation affecting the patchiness of bacterial populations in the sediments was found. Bacterial populations in the littoral sediments were more numerous and more active than those in the open‐lake sediments. Results suggest that the microbial community in Neusiedlersee littoral sediments play a key role in the carbon and energy flow for the whole lake.