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1
de Beer, Dirk, Andreas Schramm, Cecilia M. Santegoeds, and Helle K. Nielsen. "Anaerobic processes in activated sludge." Water Science and Technology 37, no. 4-5 (February 1, 1998): 605–8. http://dx.doi.org/10.2166/wst.1998.0726.
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We found anoxic zones in aerated activated sludge flocs, and demonstrated denitrification under normal operating conditions. Sulfate reduction was not found. Micro-environments and microbial conversions in flocs from bulking and non-bulking activated sludge were determined with microsensors for H2S, O2, NO2− and NO3−. Denitrification and sulfate reduction rates were mmeasured with 15N- and 35S-tracer techniques. We showed that under normal reactor conditions (ca. 20% air saturation) anoxic zones develop within flocs allowing denitrification. The denitrification rates amounted to 40% of the rates under anoxic conditions. At 100% air saturation no anoxic zones were found and no denitrification occurred. However, in flocs from bulking sludge (at 20% air saturation) anoxic zones were absent and denitrification did not occur. In bulking sludge only at total anoxia was denitrification found. Confocal microscopy showed that flocs from bulking sludge were much looser than those from non-bulking sludge. The absence of anoxic zones and of denitrification was attributed to the open floc structure, allowing advective oxygen transport. Sulfate reduction was not detected in any of the sludges tested by microsensors or by tracer techniques even under anoxic conditions. this indicates that the sulfur cycle (sulfate reduction and sulfide oxidation) does not play a role in mineralization processes and bulking in activated sludge. Preliminary molecular work (in situ hybridization with the 16S-rRNA probe SRB385) indicated the presence of small amounts of sulfate reducing bacteria in all sludges. Either the probe is not specific or the sulfate reducers present are not active under reactor conditions.
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Deutsch, Curtis, William Berelson, Robert Thunell, Thomas Weber, Caitlin Tems, James McManus, John Crusius, et al. "Centennial changes in North Pacific anoxia linked to tropical trade winds." Science 345, no. 6197 (August 7, 2014): 665–68. http://dx.doi.org/10.1126/science.1252332.
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Climate warming is expected to reduce oxygen (O2) supply to the ocean and expand its oxygen minimum zones (OMZs). We reconstructed variations in the extent of North Pacific anoxia since 1850 using a geochemical proxy for denitrification (δ15N) from multiple sediment cores. Increasing δ15N since ~1990 records an expansion of anoxia, consistent with observed O2 trends. However, this was preceded by a longer declining δ15N trend that implies that the anoxic zone was shrinking for most of the 20th century. Both periods can be explained by changes in winds over the tropical Pacific that drive upwelling, biological productivity, and O2 demand within the OMZ. If equatorial Pacific winds resume their predicted weakening trend, the ocean’s largest anoxic zone will contract despite a global O2 decline.
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Albertson, O. E., and H. D. Stensel. "Aerated Anoxic Biological NdeN Process." Water Science and Technology 29, no. 7 (April 1, 1994): 167–76. http://dx.doi.org/10.2166/wst.1994.0334.
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The conventional practice for an anoxic denitrification basin has been to minimize oxygen input on the basis that it is detrimental to the process. For existing secondary treatment systems, allotting 25-35% of the aeration volume for an unaerated anoxic zone will significantly reduce plant capacity. Further, one group has held that bulking control is best achieved by eliminating all forms of oxygen from the initial contact or biological selector zones. The Phoenix 91st Avenue WWTP was designed with nitrate recycle to aerated selector zones and the anoxic zones were provided with a dense array of fine bubble diffusers. The prototype NdeN process was able to maintain the 1.31 m3/s secondary capacity with aerated anoxic zone receiving 20-25% of the total airflow. Net sludge yields were 30-50% higher than anticipated due to primary clarifier solids losses at higher flows which reduced SRTT to ≤ 5 days. At 5.0-5.5 day SRTT, effluent averaged 8.3 mg/L TN, 1.75 mg/L NH4N and 5.7 mg/L NO3N. Nitrobacter N oxidation rates were unexplainably lower than the Nitrosomonas N oxidation rates causing effluent NO2N.
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Stevens, Gerald M., James L. Barnard, and Barry Rabinowitz. "Optimizing Biological Nutrient Removal in anoxic zones." Water Science and Technology 39, no. 6 (March 1, 1999): 113–18. http://dx.doi.org/10.2166/wst.1999.0275.
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During the initial years of the development of Biological Nutrient Removal (BNR) technology, it was assumed that the bacterial species responsible of the removal of phosphorus (BioP organisms) could not use nitrates as a final electron acceptor and could thus not denitrify. The carbon taken up in the form of Volatile Fatty Acids (VFA) in the anaerobic zone was thus deemed to be unavailable for denitrification in the anoxic zone. This was reinforced through experiments in which BioP organisms cultured in the high-rate Phoredox system in which no nitrification took place, did not denitrify when nitrates were added. Many researchers (e.g. Dold and Barker) have since shown that in BNR systems such as the 3-Stage Bardempho system, where nitrates are recycled to the anoxic zone which follows the anaerobic zone, a high degree of phosphorus uptake through denitrification does occur. In addition, the partial diversion of primary effluent directly to the anoxic zone has significantly improved phosphorus uptake under anoxic conditions. Full-scale operations at the Westbank, British Columbia, plant showed a substantial uptake of phosphorus in the anoxic zone in the absence of oxygen. The Westbank configuration includes side stream primary sludge fermentation, VFA rich fermenter supernatant addition directly to the anaerobic zone and diversion of a portion of primary effluent to the anoxic zone. This configuration stimulates P-uptake under anoxic conditions, demonstrates the efficient use of carbon and is instrumental in achieving an annual average effluent Total-P concentration of less than 0.17 mg/l. The phenomenon of denitrification by BioP organisms was included in the Biowin Model developed by Dold (Biowin Manual). This paper describes experiments and full-scale plant observations to establish the role of BioP organisms in the removal of nitrates in the anoxic zone of a plant which also receives a portion of the primary effluent and verification of the Biowin model.
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Jacobs, Judith. "Anoxic “dead zones” in oceans." Eos, Transactions American Geophysical Union 85, no. 14 (2004): 134. http://dx.doi.org/10.1029/2004eo140006.
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Schramm, Andreas, Cecilia M. Santegoeds, Helle K. Nielsen, Helle Ploug, Michael Wagner, Milan Pribyl, Jiri Wanner, Rudolf Amann, and Dirk de Beer. "On the Occurrence of Anoxic Microniches, Denitrification, and Sulfate Reduction in Aerated Activated Sludge." Applied and Environmental Microbiology 65, no. 9 (September 1, 1999): 4189–96. http://dx.doi.org/10.1128/aem.65.9.4189-4196.1999.
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ABSTRACT A combination of different methods was applied to investigate the occurrence of anaerobic processes in aerated activated sludge. Microsensor measurements (O2, NO2 −, NO3 −, and H2S) were performed on single sludge flocs to detect anoxic niches, nitrate reduction, or sulfate reduction on a microscale. Incubations of activated sludge with15NO3 − and35SO4 2− were used to determine denitrification and sulfate reduction rates on a batch scale. In four of six investigated sludges, no anoxic zones developed during aeration, and consequently denitrification rates were very low. However, in two sludges anoxia in flocs coincided with significant denitrification rates. Sulfate reduction could not be detected in any sludge in either the microsensor or the batch investigation, not even under short-term anoxic conditions. In contrast, the presence of sulfate-reducing bacteria was shown by fluorescence in situ hybridization with 16S rRNA-targeted oligonucleotide probes and by PCR-based detection of genes coding for the dissimilatory sulfite reductase. A possible explanation for the absence of anoxia even in most of the larger flocs might be that oxygen transport is not only diffusional but enhanced by advection, i.e., facilitated by flow through pores and channels. This possibility is suggested by the irregularity of some oxygen profiles and by confocal laser scanning microscopy of the three-dimensional floc structures, which showed that flocs from the two sludges in which anoxic zones were found were apparently denser than flocs from the other sludges.
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Garcia-Robledo, Emilio, Cory C. Padilla, Montserrat Aldunate, Frank J. Stewart, Osvaldo Ulloa, Aurélien Paulmier, Gerald Gregori, and Niels Peter Revsbech. "Cryptic oxygen cycling in anoxic marine zones." Proceedings of the National Academy of Sciences 114, no. 31 (July 17, 2017): 8319–24. http://dx.doi.org/10.1073/pnas.1619844114.
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Oxygen availability drives changes in microbial diversity and biogeochemical cycling between the aerobic surface layer and the anaerobic core in nitrite-rich anoxic marine zones (AMZs), which constitute huge oxygen-depleted regions in the tropical oceans. The current paradigm is that primary production and nitrification within the oxic surface layer fuel anaerobic processes in the anoxic core of AMZs, where 30–50% of global marine nitrogen loss takes place. Here we demonstrate that oxygenic photosynthesis in the secondary chlorophyll maximum (SCM) releases significant amounts of O2to the otherwise anoxic environment. The SCM, commonly found within AMZs, was dominated by the picocyanobacteriaProchlorococcusspp. Free O2levels in this layer were, however, undetectable by conventional techniques, reflecting a tight coupling between O2production and consumption by aerobic processes under apparent anoxic conditions. Transcriptomic analysis of the microbial community in the seemingly anoxic SCM revealed the enhanced expression of genes for aerobic processes, such as nitrite oxidation. The rates of gross O2production and carbon fixation in the SCM were found to be similar to those reported for nitrite oxidation, as well as for anaerobic dissimilatory nitrate reduction and sulfate reduction, suggesting a significant effect of local oxygenic photosynthesis on Pacific AMZ biogeochemical cycling.
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Bartlett, Rick, Maya Elrick, James R. Wheeley, Victor Polyak, André Desrochers, and Yemane Asmerom. "Abrupt global-ocean anoxia during the Late Ordovician–early Silurian detected using uranium isotopes of marine carbonates." Proceedings of the National Academy of Sciences 115, no. 23 (May 21, 2018): 5896–901. http://dx.doi.org/10.1073/pnas.1802438115.
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Widespread marine anoxia is hypothesized as the trigger for the second pulse of the Late Ordovician (Hirnantian) mass extinction based on lithologic and geochemical proxies that record local bottom waters or porewaters. We test the anoxia hypothesis using δ238U values of marine limestones as a global seawater redox proxy. The δ238U trends at Anticosti Island, Canada, document an abrupt late Hirnantian ∼0.3‰ negative shift continuing through the early Silurian indicating more reducing seawater conditions. The lack of observed anoxic facies and no covariance among δ238U values and other local redox proxies suggests that the δ238U trends represent a global-ocean redox record. The Hirnantian ocean anoxic event (HOAE) onset is coincident with the extinction pulse indicating its importance in triggering it. Anoxia initiated during high sea levels before peak Hirnantian glaciation, and continued into the subsequent lowstand and early Silurian deglacial eustatic rise, implying that major climatic and eustatic changes had little effect on global-ocean redox conditions. The HOAE occurred during a global δ13C positive excursion, but lasted longer indicating that controls on the C budget were partially decoupled from global-ocean redox trends. U cycle modeling suggests that there was a ∼15% increase in anoxic seafloor area and ∼80% of seawater U was sequestered into anoxic sediments during the HOAE. Unlike other ocean anoxic events (OAE), the HOAE occurred during peak and waning icehouse conditions rather than during greenhouse climates. We interpret that anoxia was driven by global cooling, which reorganized thermohaline circulation, decreased deep-ocean ventilation, enhanced nutrient fluxes, stimulated productivity, which lead to expanded oxygen minimum zones.
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Raven, M. R., R. G. Keil, and S. M. Webb. "Microbial sulfate reduction and organic sulfur formation in sinking marine particles." Science 371, no. 6525 (December 17, 2020): 178–81. http://dx.doi.org/10.1126/science.abc6035.
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Climate change is driving an expansion of marine oxygen-deficient zones, which may alter the global cycles of carbon, sulfur, nitrogen, and trace metals. Currently, however, we lack a full mechanistic understanding of how oxygen deficiency affects organic carbon cycling and burial. Here, we show that cryptic microbial sulfate reduction occurs in sinking particles from the eastern tropical North Pacific oxygen-deficient zone and that some microbially produced sulfide reacts rapidly to form organic sulfur that is resistant to acid hydrolysis. Particle-hosted sulfurization could enhance carbon preservation in sediments underlying oxygen-deficient water columns and serve as a stabilizing feedback between expanding anoxic zones and atmospheric carbon dioxide. A similar mechanism may help explain more-extreme instances of organic carbon preservation associated with marine anoxia in Earth history.
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Ruano, M. V., J. Ribes, A. Seco, and J. Ferrer. "Low cost-sensors as a real alternative to on-line nitrogen analysers in continuous systems." Water Science and Technology 60, no. 12 (December 1, 2009): 3261–68. http://dx.doi.org/10.2166/wst.2009.607.
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This paper is focused on the evaluation of the applicability of low-cost sensors (pH and ORP) versus nutrient analysers for controlling biological nitrogen removal in WWTPs. A nutrient removal pilot plant located in Carraixet WWTP (Valencia, Spain) that is equipped with a significant number of nutrient analysers and low-cost sensors was used. The relations between reliable, cheap on-line sensors such as pH and ORP (located in anaerobic, anoxic and aerobic zones) and the nitrification/denitrification processes are provided. The nitrification process can be evaluated by measuring the pH difference between the first and last aerobic zones. The denitrification process can be evaluated by measuring the pH difference between the first and last anoxic zones and the ORP in the last anoxic zone. Furthermore, when WWTPs include an anaerobic reactor, the ORP in the anaerobic zone can also be used. With all these factors in mind, these sensors give valuable information for applying advanced control systems such as fuzzy logic-based controllers. Also, low-cost sensors involve lower investment, maintenance and operational costs and lower energy consumption derived from aeration and pumping than nutrient analysers. Thus, low-cost sensors can be successfully used as an attractive alternative to nutrient analysers to control biological nitrogen removal in WWTPs.
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Wolke, Philipp, Yoni Teitelbaum, Chao Deng, Jörg Lewandowski, and Shai Arnon. "Impact of Bed Form Celerity on Oxygen Dynamics in the Hyporheic Zone." Water 12, no. 1 (December 22, 2019): 62. http://dx.doi.org/10.3390/w12010062.
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Oxygen distribution and uptake in the hyporheic zone regulate various redox-sensitive reactions and influence habitat conditions. Despite the fact that fine-grain sediments in streams and rivers are commonly in motion, most studies on biogeochemistry have focused on stagnant sediments. In order to evaluate the effect of bed form celerity on oxygen dynamics and uptake in sandy beds, we conducted experiments in a recirculating indoor flume. Oxygen distribution in the bed was measured under various celerities using 2D planar optodes. Bed morphodynamics were measured by a surface elevation sensor and time-lapse photography. Oxygenated zones in stationary beds had a conchoidal shape due to influx through the stoss side of the bed form, and upwelling anoxic water at the lee side. Increasing bed celerity resulted in the gradual disappearance of the upwelling anoxic zone and flattening of the interface between the oxic (moving fraction of the bed) and the anoxic zone (stationary fraction of the bed), as well as in a reduction of the volumetric oxygen uptake rates due shortened residence times in the hyporheic zone. These results suggest that including processes related to bed form migration are important for understanding the biogeochemistry of hyporheic zones.
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Sarioglu, M., and N. Horan. "An equation for the empirical design of anoxic zones used to eliminate rising sludges at nitrifying activated sludge plants." Water Science and Technology 33, no. 3 (February 1, 1996): 185–94. http://dx.doi.org/10.2166/wst.1996.0070.
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Anoxic zones are designed for the removal of nitrogen in nitrifying activated sludge plants. This can be carried out either to achieve a nitrogen discharge consent or to eliminate the problem of rising sludges. The rising sludge problem is mostly encountered in medium and small size plants in warm conditions and there is limited information as to the appropriate design of anoxic zones to protect against rising sludges in the secondary sedimentation tanks. Therefore a series of batch experiments were undertaken in order to establish the critical concentration of nitrate-nitrogen which causes rising sludge in the secondary settling tank and the effect of environmental factors such as temperature (15°C to 30°C) and residual carbon source (100 to 600 mg/1 COD) were examined. Based on the results of these experiments an empirical equation was presented which can be used to size an anoxic zone to eliminate rising sludges. The application of this equation at full-scale plants is discussed.
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Lüdemann, Heiner, Inko Arth, and Werner Liesack. "Spatial Changes in the Bacterial Community Structure along a Vertical Oxygen Gradient in Flooded Paddy Soil Cores." Applied and Environmental Microbiology 66, no. 2 (February 1, 2000): 754–62. http://dx.doi.org/10.1128/aem.66.2.754-762.2000.
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ABSTRACT Molecular ecology techniques were applied to assess changes in the bacterial community structure along a vertical oxygen gradient in flooded paddy soil cores. Microsensor measurements showed that oxygen was depleted from 140 μM at the floodwater/soil interface to nondetectable amounts at a depth of approximately 2.0 mm and below. Bacterial 16S rRNA gene (rDNA)-based community fingerprint patterns were obtained from 200-μm-thick soil slices of both the oxic and anoxic zones by using the T-RFLP (terminal restriction fragment length polymorphism) technique. The fingerprints revealed a tremendous shift in the community patterns in correlation to the oxygen depletion measured with depth. 16S rDNA clone sequences recovered from the oxic or anoxic zone directly corresponded to those terminal restriction fragments which were highly characteristic of the respective zone. Comparative sequence analysis of these clones identified members of the α and β subclasses of Proteobacteria as the abundant populations in the oxic zone. In contrast, members of clostridial cluster I were determined to be the predominant bacterial group in the oxygen-depleted soil. The extraction of total RNA followed by reverse transcription-PCR of the bacterial 16S rRNA and T-RFLP analysis resulted for both oxic and anoxic zones of flooded soil cores in community fingerprint patterns similar to those obtained by the rDNA-based analysis. This finding suggests that the microbial groups detected on the rDNA level are the metabolically active populations within the oxic and anoxic soil slices examined.
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Rensink, J. H., J. van der Ven, G. van Pamelen, F. Fedder, and E. Majoor. "The modified renphosystem: a high biological nutrient removal system." Water Science and Technology 35, no. 10 (May 1, 1997): 137–46. http://dx.doi.org/10.2166/wst.1997.0376.
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Pilot plant studies on high biological nutrient removal and using settled domestic wastewaters have been carried out with the so-called Modified Renphosystem. The system consists of a bioreactor which has been divided into four zones: anaerobic, aerobic, anoxic and aerobic, respectively. In the by-pass of the bioreactor a part of the return sludge was stripped in a stripper tank. The process of P-release was accelerated by dosage of acetate. The Modified Renphosystem is characterized by distribution of the stripped sludge to the first aerobic zone and the anoxic zone. In the aerobic nitrification and P-accumulation take place. In the anoxic zone denitrification and P-accumulation run simultaneously. The experiments carried out at low F/M-ratios resulted in very low concentrations of P and N in the effluent. For achieving a high degree of nitrate removal the first part of the mainstream of the Modified Renphosystem was retrofitted to a AAO-system followed by an anoxic and aerobic zone respectively. This process configuration resulted in Pt and Nt of the unfiltered effluent of 0.4 and 2 mg/l respectively.
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Ulloa, O., D. E. Canfield, E. F. DeLong, R. M. Letelier, and F. J. Stewart. "Microbial oceanography of anoxic oxygen minimum zones." Proceedings of the National Academy of Sciences 109, no. 40 (September 11, 2012): 15996–6003. http://dx.doi.org/10.1073/pnas.1205009109.
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Karakitsios, V., H. Tsikos, K. Agiadi - Katsiaouni, S. Dermitzoglou, and E. Chatziharalambous. "THE USE OF CARBON AND OXYGEN STABLE ISOTOPES IN THE STUDY OF GLOBAL PALAEOCEANOGRAPHIC CHANGES: EXAMPLES FROM THE CRETACEOUS SEDIMENT ROCKS OF WESTERN GREECE." Bulletin of the Geological Society of Greece 39, no. 1 (September 10, 2006): 64. http://dx.doi.org/10.12681/bgsg.18445.
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In the present paper we examine the use of carbon and oxygen stable isotopes in the study of global palaeoceanographic changes, with special reference to the oceanic anoxic events (OAEs). The analysis of stable isotopes was applied to the examination of Cretaceous sediments from the Ionian and Pindos zones of Western Greece. In the Ionian zone the carbon and oxygen stable isotopes, combined with biostratigraphic data, record the palaeoenvironmental change corresponding to the anoxic events Bonarelli (Cenomanian/Turonian, OAE2) and Paquier (Lower Albian, OAE1b). In the Pindos zone, within the Cretaceous sediments, we observed two organic-carbon-rich levels. According to the biostratigraphic and isotopie analysis, the first level corresponds to an OAE of Santonian age. This local oceanic anoxic event is described for the first time. The second level, Aptian - Albian age, possibly correlates to either the Paquier event (OAE 1b) or the Selli event (OAE 1a), which in Greece were until now known only in the Ionian zone.
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Phung, Anh Duc, M. Othman, and J. Yulian. "Effect of sucrose on denitrification through simulation, lab-scaled batch tests and pilot plants." Science and Technology Development Journal 17, no. 4 (December 31, 2014): 22–32. http://dx.doi.org/10.32508/stdj.v17i4.1535.
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The aim of this study was to assess the impact of sucrose as external carbon source on denitrification. The specific denitrification rate (SDNR) determined using batch tests showed that acclimation to sucrose can increase SDNR in post and pre-anoxic denitrification zones by 47% and 116%, respectively. The use of sucrose in pre-anoxic zone led to an SDNR of 2.72±0.15 mg NO3- N/g MLVSS/h. This is 2.1 times higher than in the absence of external carbon and 1.7 times higher than the SDNR when sucrose was added into post-anoxic zone. The experiment has also tested the effect of sucrose on a pre-anoxic denitrification system with low carbon-to-nitrogen ratio (C/N) influent of 7.2 by adding roughly 150mgCOD/L of sucrose into the pre-anoxic zone. This was done through two simulation modellings before the results were verified with a pilot plant trial run. The two simulation models (a basic conceptual model and Biowin) showed a drop of effluent TN from 31.8±8 mg/L to 17.7±2.2 mg/L and 23.7±10.3 mg/L respectively. While the pilot plant test showed a clear drop from 32.7±4.7 mg/L down to 17.7±5.5 mg/L after adding sucrose. The result showed that the conceptual model was providing a more accurate simulation run than the Biowin model in this case.
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Wanner, Jiri, and Petr Grau. "Filamentous Bulking in Nutrient Removal Activated Sludge Systems." Water Science and Technology 20, no. 4-5 (April 1, 1988): 1–8. http://dx.doi.org/10.2166/wst.1988.0149.
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Behaviour of filamentous microorganisms under anaerobic, anoxic, and oxic conditions has been reviewed from the point of view of filamentous bulking in nutrient removal activated sludge systems. It was concluded that the growth of most filamentous microorganisms is considerably suppressed under anaerobic and anoxic conditions and that the filamentous bulking in nutrient removal systems is chiefly caused by the growth of filamentous microorganisms in oxic zones. The role of particulate substrate hydrolysis was also discussed and the necessity of compartmentalization of oxic zones was shown.
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Çinar, Ö., T. Deniz, and C. P. L. Grady. "Effect of oxygen on the stability and inducibility of the biodegradative capability of benzoate." Water Science and Technology 48, no. 8 (November 1, 2003): 247–54. http://dx.doi.org/10.2166/wst.2003.0475.
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Anoxic zones in biological nitrogen removal systems are typically open to the atmosphere and receive oxygen from the atmosphere and the recirculation flow from the aerobic zone. This raises the question of how such oxygen input might influence the stability and inducibility of the enzyme systems involved in biodegradation of aromatic compounds. To investigate this, various amounts of oxygen were added to mixed culture denitrifying chemostats receiving benzoate at 667 mg/h as chemical oxygen demand (COD), and the stability and inducibility of the culture’s benzoate biodegradative capability (BBC) were tested in aerobic and anoxic fed-batch reactors (FBRs). Cultures from chemostats receiving oxygen at 0, 33, 133, 266, and 466 mg O2/h lost almost all of their anoxic BBC within one hour after being transferred to an aerobic FBR and the first three cultures did not recover it upon being returned to anoxic conditions. The last two cultures recovered their anoxic BBC between 9 and 16 h during the 16 h aerobic exposure period that preceded their return to anoxic conditions and continued to increase their anoxic BBC as they were retained under anoxic conditions. In contrast, the culture from a chemostat receiving oxygen at 67 mg O2/h retained its anoxic BBC longer, recovered it within 3 h after its return to anoxic conditions, and increased it linearly thereafter. None of the cultures developed any aerobic BBC during the 16 h aerobic exposure period in FBRs. The results suggest that higher oxygen inputs into anoxic reactors helped the mixed microbial cultures recover and/or induced anoxic BBC more easily when they were exposed to alternating aerobic/anoxic environments. The exceptional behavior of the culture from the chemostat receiving oxygen at a rate of 67 mg O2/h may have been caused by the presence of a protective mechanism against the toxic forms of oxygen.
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Naqvi, S. W. A., H. W. Bange, L. Farías, P. M. S. Monteiro, M. I. Scranton, and J. Zhang. "Coastal hypoxia/anoxia as a source of CH<sub>4</sub> and N<sub>2</sub>O." Biogeosciences Discussions 6, no. 5 (October 2, 2009): 9455–523. http://dx.doi.org/10.5194/bgd-6-9455-2009.
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Abstract. We review here available information on distributions of methane (CH4) and nitrous oxide (N2O) from major, mostly coastal, oxygen (O2)-deficient zones produced due to both natural processes and human activities (mainly eutrophication). Concentrations of both gases in subsurface waters are affected by ambient O2 levels. In the case of CH4, bottom-water O2 content probably affects emission from sediments, believed to be the main source of water-column CH4, as well as its oxidative loss in water itself. Highest CH4 accumulation (several μM) occurs in silled basins having anoxic deep waters such as the Black Sea and the Cariaco Basin. One to two orders of magnitude smaller, but still significant, accumulation also occurs in bottom waters of open margins experiencing anoxia and in silled basins containing suboxic/severely hypoxic waters. In highly eutrophic waters over open continental shelves (such as the upwelling zone off Namibia and the "dead zone" in the Gulf of Mexico) high CH4 concentrations (several hundred nM) may occur in non-sulphidic waters as well, but in these regions it is difficult to differentiate the hypoxia-induced enhancement from in situ production of CH4 in the water column and, sometimes, large inputs of CH4 associated with freshwater runoff or seepage from sediments. Despite the observed CH4 build-up in low-O2 bottom waters, methanotrophic activity severely restricts its emission from the ocean. As a result, an intensification or expansion of coastal hypoxic zones will probably not drastically change the present status where emission from the ocean as a whole forms an insignificant term in the atmospheric CH4 budget. The situation is different for N2O, the production of which is greatly enhanced in severely hypoxic waters, and although it is lost through denitrification in most suboxic and anoxic environments, the peripheries of such environments offer most suitable conditions for its production, with the exception of semi-enclosed/land-locked anoxic basins such as the Black Sea. Most O2-deficient systems serve as strong net sources of N2O to the atmosphere. This is especially true for regions of coastal upwelling with shallow oxygen minimum zones where a dramatic increase in N2O production often occurs in rapidly denitrifying waters. Nitrous oxide emissions from these zones are globally significant, and so their ongoing intensification and expansion is likely to lead to a significant increase in N2O emission from the ocean. However, a meaningful quantitative prediction of this increase is not possible at present because of continuing uncertainties concerning the formative pathways to N2O as well as insufficient data from some key coastal regions.
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MARYNOWSKI, LESZEK, PAWEŁ FILIPIAK, and MICHAŁ ZATOŃ. "Geochemical and palynological study of the Upper Famennian Dasberg event horizon from the Holy Cross Mountains (central Poland)." Geological Magazine 147, no. 4 (January 15, 2010): 527–50. http://dx.doi.org/10.1017/s0016756809990835.
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AbstractIntegrated palynological, organic and inorganic geochemical and petrographical methods have been used for deciphering the depositional redox conditions and character of organic matter of the Famennian Dasberg event horizon from the deep-shelf Kowala succession of the Holy Cross Mountains. The ages of the investigated samples have been established, using miospore data, as VF (Diducites versabilis–Grandispora famenensis) and LV (Retispora lepidophyta–Apiculiretusispora verrucosa) miospore Zones of the Middle/Upper Famennian. In the standard conodont zonation, this corresponds to the uppermost postera to lowermost praesulcata Zones. The presence of green sulphur bacteria biomarkers and dominance of small-sized framboids together with the presence of large framboids and low values of the U/Th ratio may indicate that during sedimentation of the lower Dasberg shale, intermittent anoxia occurred in the water column, or the anoxic conditions prevailed in the upper part of the water column, while the bottom waters were oxygenated, at least briefly. Deposition of the upper Dasberg shale was characterized by both bottom water and water column anoxia. The lack of acritarcha taxa from these intervals could have been due to anoxia in the photic zone. Moreover, organic content is high in those samples. There is no geochemical evidence for anoxia during sedimentation of the deposits sandwiched between the lower and upper Dasberg shales, or in the deposits which underlie and overlie both Dasberg shale horizons. The two discrete anoxic events are interpreted to be the result of major transgressions and the blooming of primary producers. Above the Dasberg shales, small fragments of charcoal and raised concentrations of polycyclic aromatic hydrocarbons are detected. This supports the presence of wildfires during deposition of shales just above the boundary of VF/LV palynological zones. Temperatures calculated from the fusinite reflectance values suggest that the charcoal was formed in low-temperature ground and/or surface fires. The typical marine character of sedimentation combined with the high proportion of charcoals suggests that wildfires were large-scale, and that there was intensive transport of terrestrial material. The main causes of intensive wildfires were a significant rise of O2 in the atmosphere and important progress in the land plant diversity during Late Devonian times. Palynofacies studies suggest that the transgression corresponds to the part IIf of the Late Devonian sea-level curve.
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Funamizu, Naoyuki, Shoichiro Yamamoto, Yoshio Kitagawa, and Tetsuo Takakuwa. "Simulation of the operational conditions of the full-scale municipal wastewater treatment plant to improve the performance of nutrient removal." Water Science and Technology 36, no. 12 (December 1, 1997): 9–18. http://dx.doi.org/10.2166/wst.1997.0425.
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Simulation analysis based on a mathematical model is one of the powerful tools for determining the operational conditions for a full scale biological nutrient removal plant. The model that included the Activated Sludge Model No.2 was developed for simulating the performance of the plant in Sapporo City. The investigated plant has the biological reaction basin which consists of the four zones, anaerobic-aerobic-anoxic-aerobic phases with the step feed of the primary effluent to the anaerobic and anoxic zones. We performed three experiments to calibrate and verify our model: (i) Characterization of organic matters in the influent of the reaction basin with the OUR measurement method; (ii) Measurement of COD and nutrient concentration at the plant; (iii) Lab-scale batch experiments with the anaerobic-aerobic-anoxic-aerobic phases. The calibrating process of the model showed that no modification of parameter values was required to evaluate the performance of the plant and population of the activated sludge. Simulated results showed that the choice of the sewage step feed ratio did not affect the nitrogen removal and that the denitrification rate in the anoxic zone was controlled by the hydrolysis rate of the slowly biodegradable organic matters. The results of the lab-scale experiment and simulation results showed that the addition of the readily biodegradable organic matters like fermentation products of the primary settler sludge was effective to improve the performance of nitrogen removal.
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Huang, Yu, Yongzhen Peng, Donghui Huang, Jiarui Fan, and Rui Du. "Enhanced Nitrogen Removal from Domestic Wastewater by Partial-Denitrification/Anammox in an Anoxic/Oxic Biofilm Reactor." Processes 10, no. 1 (January 6, 2022): 109. http://dx.doi.org/10.3390/pr10010109.
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A partial-denitrification coupling with anaerobic ammonium oxidation (anammox) process (PD/A) in a continuous-flow anoxic/oxic (A/O) biofilm reactor was developed to treat carbon-limited domestic wastewater (ammonia (NH4+-N) of 55 mg/L and chemical oxygen demand (COD) of 148 mg/L in average) for about 200 days operation. Satisfactory NH4+-N oxidation efficiency above 95% was achieved with rapid biofilm formation in the aerobic zone. Notably, nitrite (NO2−-N) accumulation was observed in the anoxic zone, mainly due to the insufficient electron donor for complete nitrate (NO3−-N) reduction. The nitrate-to-nitrite transformation ratio (NTR) achieved was as high as 64.4%. After the inoculation of anammox-enriched sludge to anoxic zones, total nitrogen (TN) removal was significantly improved from 37.3% to 78.0%. Anammox bacteria were effectively retained in anoxic biofilm utilizing NO2−-N produced via the PD approach and NH4+-N in domestic wastewater, with the relative abundance of 5.83% for stable operation. Anammox pathway contributed to TN removal by a high level of 38%. Overall, this study provided a promising method for mainstream nitrogen removal with low energy consumption and organic carbon demand.
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Fontanos, P. M., K. Yamamoto, and F. Nakajima. "Effect of upflow velocity on the performance of an inclined plate membrane bioreactor treating municipal wastewater." Water Science and Technology 64, no. 5 (September 1, 2011): 1102–7. http://dx.doi.org/10.2166/wst.2011.142.
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An inclined plate membrane bioreactor (iPMBR) was introduced to meet the challenge of handling high mixed liquor suspended solids when operating at long sludge retention times. During the first 407 days of operation, the iPMBR was able to rezone more sludge (1.5–10.5 times greater) in its upstream, anoxic tank compared to its downstream, aerobic tank. This could extend membrane filtration by diverting most of the sludge from the aerobic zone. During this period, the upflow velocities through the inclined plates of the anoxic tank ranged from 2.3 × 10−4 to 7.7 × 10−4 m/s. After Day 407, the operating conditions were changed to determine whether the iPMBR would fail to create a sludge concentration difference between its two tanks. When the upflow velocity was increased to 1.8 × 10−3 m/s, the sludge concentration difference between the two zones was removed. This indicated that the upflow velocity had increased sufficiently to overcome the settling velocities of most flocs, resulting in more solids being carried from the anoxic to the aerobic tank. For the configuration of this iPMBR, operating at flow rates where the upflow velocity through the inclined plates was less than 1.0 × 10−3 m/s would be necessary to keep a significant sludge concentration difference between its two zones.
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Wielinga, Bruce, Juliette K. Lucy, Johnnie N. Moore, October F. Seastone, and James E. Gannon. "Microbiological and Geochemical Characterization of Fluvially Deposited Sulfidic Mine Tailings." Applied and Environmental Microbiology 65, no. 4 (April 1, 1999): 1548–55. http://dx.doi.org/10.1128/aem.65.4.1548-1555.1999.
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ABSTRACT The fluvial deposition of mine tailings generated from historic mining operations near Butte, Montana, has resulted in substantial surface and shallow groundwater contamination along Silver Bow Creek. Biogeochemical processes in the sediment and underlying hyporheic zone were studied in an attempt to characterize interactions consequential to heavy-metal contamination of shallow groundwater. Sediment cores were extracted and fractionated based on sediment stratification. Subsamples of each fraction were assayed for culturable heterotrophic microbiota, specific microbial guilds involved in metal redox transformations, and both aqueous- and solid-phase geochemistry. Populations of cultivable Fe(III)-reducing bacteria were most prominent in the anoxic, circumneutral pH regions associated with a ferricrete layer or in an oxic zone high in organic carbon and soluble iron. Sulfur- and iron-oxidizing bacteria were distributed in discrete zones throughout the tailings and were often recovered from sections at and below the anoxic groundwater interface. Sulfate-reducing bacteria were also widely distributed in the cores and often occurred in zones overlapping iron and sulfur oxidizers. Sulfate-reducing bacteria were consistently recovered from oxic zones that contained high concentrations of metals in the oxidizable fraction. Altogether, these results suggest a highly varied and complex microbial ecology within a very heterogeneous geochemical environment. Such physical and biological heterogeneity has often been overlooked when remediation strategies for metal contaminated environments are formulated.
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Elshaw, Andrew, Nur M. S. Hassan, and M. Masud K. Khan. "Computational Fluid Dynamic Modelling and Optimisation of Wastewater Treatment Plant Bioreactor Mixer." Energies 11, no. 12 (December 18, 2018): 3530. http://dx.doi.org/10.3390/en11123530.
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This study aims to determine the optimal configuration (position and operation duration) for wall mounted mechanical mixers based on the comparison of three-dimensional computational fluid dynamics (CFD) modelling results and physical data collected from the treatment plant. A three dimensional model of anoxic zone in 1, 2 and 3 of Northern Wastewater Treatment Plant (NWWTP) located at Cairns Regional Council, Cairns, Queensland, Australia was developed and validated. The model was used to simulate the flow pattern of the WWTP and the simulation results are in good agreement with the physical data varying between 0% to 15% in key locations. The anoxic zones were subject to velocities less than the desired 0.3 m per second however results for mixed liquor suspended solids (MLSS) concentration indicate that good mixing is being achieved. Results for suspended solids concentrations suggest that the anoxic zones are towards the upper limits recommended by literature for specific power dissipation. The duration for operation of mechanical mixers was investigated and identified that the duration could be reduced from 900 s down to 150 s. Alternative mixer positioning was also investigated and identified positioning which would increase the average flow velocity with decreased duration (150 s). The study identified that Council may achieve savings of $28,500 per year through optimisation of the mechanical mixers and would be expected to extend the operational life of the mixers.
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Brenner, Asher. "Modification of Small Activated Sludge Plants to Recycled Systems for Nitrogen Removal and Control of Settling Properties." Water Science and Technology 22, no. 3-4 (March 1, 1990): 117–22. http://dx.doi.org/10.2166/wst.1990.0191.
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Modification of small activated sludge plants to recycled systems is proposed as a means to improve nitrogen removal and control of settling properties. The modification process involves separation of the aeration basin to anoxic and aerobic zones and addition of internal recycle of mixed liquor from the aerobic to the anoxic zone. This mode of operation may prevent problems of floating sludge in the final clarifier caused by uncontrolled denitrification. In the recycled system, part of the organic carbon is removed under anoxic conditions. Therefore, it may assist in the selection of microbial population with better settling characteristics, since most filamentous microbes have been reported to lack denitrifying ability. The modification considerations and guidelines are discussed based on experimental results obtained from operation of bench-scale recycled units. Influent COD/ammonia ratio, aerobic volume fraction, and recycle rate are shown to be critical parameters in the modification and operation of such systems.
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van der Wielen, P. W. J. J., M. Blokker, and G. J. Medema. "Modelling the length of microbiological protection zones around phreatic sandy aquifers in The Netherlands." Water Science and Technology 54, no. 3 (August 1, 2006): 63–69. http://dx.doi.org/10.2166/wst.2006.449.
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The aim of the current study was to calculate the size of protection zones around (sub)oxic and anoxic sandy aquifers without confining layers using a virus infection and transport model. The maximum allowable virus infection risk was 10−4/person/year at the 95% confidence level. Model results demonstrated that phreatic (sub)oxic sandy aquifers in The Netherlands required protection areas with a residence time of 43–117 d to ensure that the maximum virus infection risk would not be exceeded. This was 0.7–2× the current guideline of 60 d. In contrast, phreatic anoxic sandy aquifers without confining layers needed protection zones of 555–898 d to stay below the maximum virus infection risk, 9.5–15× the current guideline. A sensitivity analysis of the model demonstrated that the calculated protection zone was most sensitive for virus inactivation rate and collision efficiency. Values of both parameters were predicted from values obtained from previously published field and laboratory studies. At present, as it is unknown if these values can also be used at other locations, model results should be interpreted with care.
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Zakem, Emily J., Amala Mahadevan, Jonathan M. Lauderdale, and Michael J. Follows. "Stable aerobic and anaerobic coexistence in anoxic marine zones." ISME Journal 14, no. 1 (October 17, 2019): 288–301. http://dx.doi.org/10.1038/s41396-019-0523-8.
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Abstract Mechanistic description of the transition from aerobic to anaerobic metabolism is necessary for diagnostic and predictive modeling of fixed nitrogen loss in anoxic marine zones (AMZs). In a metabolic model where diverse oxygen- and nitrogen-cycling microbial metabolisms are described by underlying redox chemical reactions, we predict a transition from strictly aerobic to predominantly anaerobic regimes as the outcome of ecological interactions along an oxygen gradient, obviating the need for prescribed critical oxygen concentrations. Competing aerobic and anaerobic metabolisms can coexist in anoxic conditions whether these metabolisms represent obligate or facultative populations. In the coexistence regime, relative rates of aerobic and anaerobic activity are determined by the ratio of oxygen to electron donor supply. The model simulates key characteristics of AMZs, such as the accumulation of nitrite and the sustainability of anammox at higher oxygen concentrations than denitrification, and articulates how microbial biomass concentrations relate to associated water column transformation rates as a function of redox stoichiometry and energetics. Incorporating the metabolic model into an idealized two-dimensional ocean circulation results in a simulated AMZ, in which a secondary chlorophyll maximum emerges from oxygen-limited grazing, and where vertical mixing and dispersal in the oxycline also contribute to metabolic co-occurrence. The modeling approach is mechanistic yet computationally economical and suitable for global change applications.
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Goggin, Danica E., and Timothy D. Colmer. "Intermittent anoxia induces oxidative stress in wheat seminal roots: assessment of the antioxidant defence system, lipid peroxidation and tissue solutes." Functional Plant Biology 32, no. 6 (2005): 495. http://dx.doi.org/10.1071/fp04194.
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The effects of continuous and intermittent anoxia on components of the antioxidant defence system were evaluated in the expanded zones of wheat seedling roots. Intermittent anoxia caused oxidative stress (measured by the proportion of reduced glutathione) after three cycles of anoxia–aeration. The concentration of glutathione and activities of glutathione reductase (GR) and catalase (CAT) were decreased by 50% under both continuous and intermittent anoxia. Ascorbate peroxidase (APX) activity was unaffected by anoxia but stimulated almost 2-fold during the aerated periods of intermittent anoxia. Superoxide dismutase activity was decreased by 20% under continuous anoxia but ultimately returned to aerated activities under intermittent anoxia. Membrane damage appeared to be negligible or reversible, as K+ concentrations recovered to original levels under intermittent anoxia and there was no increase in terminal lipid peroxidation products. Addition of 5 mm exogenous ascorbate to intermittently anoxic roots prevented oxidative stress and avoided the decreases in glutathione, GR and CAT. Therefore, it is likely that the oxidative stress resulted from inadequate levels of, or damage to, these two enzymes.
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Morard, Alain, Jean Guex, Annachiara Bartolini, Elena Morettini, and Patrick de Wever. "A new scenario for the Domerian - Toarcian transition." Bulletin de la Société Géologique de France 174, no. 4 (July 1, 2003): 351–56. http://dx.doi.org/10.2113/174.4.351.
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Abstract In contrast to the majority of recently published hypotheses, we believe that the main trigger for early Toarcian anoxia is neither increased primary productivity during the Tenuicostatum and Falciferum Zones nor sudden methane hydrate degassing close to the transition between these two zones. In our opinion, this peculiar paleoceanographic episode is linked to a major, though short-lived, regression at the end of Upper Domerian. Sea-level fall resulted from sudden cooling due to increased volcanic activity. This generated global thermal insulation and subsequent glaciation. The regression is responsible for a major hiatus over NW-European epicontinental seas and is later followed by the well-known Lower Toarcian transgression. The interval corresponding to this hiatus allowed vegetation to colonise vast newly emerged surfaces. The leaching and drowning of the accumulated organohumic matter then triggered the anoxic cycle at the transgressive maximum, concomitant with a global warming.
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Naqvi, S. W. A., H. W. Bange, L. Farías, P. M. S. Monteiro, M. I. Scranton, and J. Zhang. "Marine hypoxia/anoxia as a source of CH<sub>4</sub> and N<sub>2</sub>O." Biogeosciences 7, no. 7 (July 12, 2010): 2159–90. http://dx.doi.org/10.5194/bg-7-2159-2010.
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Abstract. We review here the available information on methane (CH4) and nitrous oxide (N2O) from major marine, mostly coastal, oxygen (O2)-deficient zones formed both naturally and as a result of human activities (mainly eutrophication). Concentrations of both gases in subsurface waters are affected by ambient O2 levels to varying degrees. Organic matter supply to seafloor appears to be the primary factor controlling CH4 production in sediments and its supply to (and concentration in) overlying waters, with bottom-water O2-deficiency exerting only a modulating effect. High (micromolar level) CH4 accumulation occurs in anoxic (sulphidic) waters of silled basins, such as the Black Sea and Cariaco Basin, and over the highly productive Namibian shelf. In other regions experiencing various degrees of O2-deficiency (hypoxia to anoxia), CH4 concentrations vary from a few to hundreds of nanomolar levels. Since coastal O2-deficient zones are generally very productive and are sometimes located close to river mouths and submarine hydrocarbon seeps, it is difficult to differentiate any O2-deficiency-induced enhancement from in situ production of CH4 in the water column and its inputs through freshwater runoff or seepage from sediments. While the role of bottom-water O2-deficiency in CH4 formation appears to be secondary, even when CH4 accumulates in O2-deficient subsurface waters, methanotrophic activity severely restricts its diffusive efflux to the atmosphere. As a result, an intensification or expansion of coastal O2-deficient zones will probably not drastically change the present status where emission from the ocean as a whole forms an insignificant term in the atmospheric CH4 budget. The situation is different for N2O, the production of which is greatly enhanced in low-O2 waters, and although it is lost through denitrification in most suboxic and anoxic environments, the peripheries of such environments offer most suitable conditions for its production, with the exception of enclosed anoxic basins. Most O2-deficient systems serve as strong net sources of N2O to the atmosphere. This is especially true for coastal upwelling regions with shallow O2-deficient zones where a dramatic increase in N2O production often occurs in rapidly denitrifying waters. Nitrous oxide emissions from these zones are globally significant, and so their ongoing intensification and expansion is likely to lead to a significant increase in N2O emission from the ocean. However, a meaningful quantitative prediction of this increase is not possible at present because of continuing uncertainties concerning the formative pathways to N2O as well as insufficient data from key coastal regions.
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Saunders, Jaclyn K., Clara A. Fuchsman, Cedar McKay, and Gabrielle Rocap. "Complete arsenic-based respiratory cycle in the marine microbial communities of pelagic oxygen-deficient zones." Proceedings of the National Academy of Sciences 116, no. 20 (April 29, 2019): 9925–30. http://dx.doi.org/10.1073/pnas.1818349116.
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Microbial capacity to metabolize arsenic is ancient, arising in response to its pervasive presence in the environment, which was largely in the form of As(III) in the early anoxic ocean. Many biological arsenic transformations are aimed at mitigating toxicity; however, some microorganisms can respire compounds of this redox-sensitive element to reap energetic gains. In several modern anoxic marine systems concentrations of As(V) are higher relative to As(III) than what would be expected from the thermodynamic equilibrium, but the mechanism for this discrepancy has remained unknown. Here we present evidence of a complete respiratory arsenic cycle, consisting of dissimilatory As(V) reduction and chemoautotrophic As(III) oxidation, in the pelagic ocean. We identified the presence of genes encoding both subunits of the respiratory arsenite oxidase AioA and the dissimilatory arsenate reductase ArrA in the Eastern Tropical North Pacific (ETNP) oxygen-deficient zone (ODZ). The presence of the dissimilatory arsenate reductase gene arrA was enriched on large particles (>30 um), similar to the forward bacterial dsrA gene of sulfate-reducing bacteria, which is involved in the cryptic cycling of sulfur in ODZs. Arsenic respiratory genes were expressed in metatranscriptomic libraries from the ETNP and the Eastern Tropical South Pacific (ETSP) ODZ, indicating arsenotrophy is a metabolic pathway actively utilized in anoxic marine water columns. Together these results suggest arsenic-based metabolisms support organic matter production and impact nitrogen biogeochemical cycling in modern oceans. In early anoxic oceans, especially during periods of high marine arsenic concentrations, they may have played a much larger role.
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Kafousia, N., V. Karakitsios, E. Mattioli, and H. C. Jenkyns. "Chemostratigraphy of the Toarcian oceanic anoxic event from the Ionian Zone, Greece." Bulletin of the Geological Society of Greece 47, no. 2 (January 24, 2017): 825. http://dx.doi.org/10.12681/bgsg.11119.
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A global perturbation in the carbon cycle has been recorded in the Early Toarcian (~ 183 Ma) and is marked by enhanced organic-carbon burial and mass extinction. It is also associated with high palaeotemperatures, both positive and negative excursions in carbon-isotope ratios, and the development of anoxic to euxinic conditions in marine environments: together these phenomena have been designated as constituting an Oceanic Anoxic Event. Here we provide a high-resolution, multiproxy biostratigraphic and chemostratigraphic study from a section that belongs to the central Ionian Zone in Greece. Calcareous nannofossil distribution, as well as the TOC, δ13Ccarb and δ13Corg, have all been determined. The nannofossil zones NJT 5b, NJT 6 and NJT 7 have been recognized in the section. In the NJT 5b zone a small positive excursion in TOC and negative excursion in δ13Ccarb is recorded, tentatively assigned to the Pliensbachian/Toarcian boundary. In the NJT 6 zone, the main negative carbon-isotope excursion characteristic of this interval is developed, associated with a relative increase in TOC. The difference in this section, compared with sections from the Pindos Zone but in common with sections elsewhere, is the record of a positive excursion in the NJT 7 zone in both organic and carbonate carbon isotopes. This study offers new biostratigraphic and geochemical data for the Ionian Zone, and further illustrates the impact of Toarcian Oceanic Anoxic Event in the Tethyan region.
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Rensink, J. H., E. Eggers, and H. J. G. W. Donker. "High Biological Nutrient Removal from Domestic Wastewater in Combination with Phosphorus Recycling." Water Science and Technology 23, no. 4-6 (February 1, 1991): 651–57. http://dx.doi.org/10.2166/wst.1991.0515.
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Pilot plant studies on biological nutrient removal and using settled domestic waste water have been carried out in combination with phosphorus recycling on the basis of crystallisation of calcium phosphate on sand pellets in a fluidized bed-reactor. The bioreactor had been divided into four zones, respectively anaerobic, aerobic, anoxic and aerobic. To eliminate nitrate sludge recirculation for denitrification, a part of the influent was led to the anoxic zone. In the by-pass of the bioreactor a phostripper tank was incorporated followed by a fluidized bed-reactor. The experiments carried out at low F/M ratios and at a constant and variable influent flow resulted in nearly 100% P-removal. P-total effluent was lower than 0.1 mg P/l. The total nitrogen content in the effluent amounted to an average value of approximately 16 mg N/l.
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Jakobs, G., G. Rehder, G. Jost, K. Kießlich, M. Labrenz, and O. Schmale. "Comparative studies of pelagic microbial methane oxidation within two anoxic basins of the central Baltic Sea (Gotland Deep and Landsort Deep)." Biogeosciences Discussions 10, no. 7 (July 20, 2013): 12251–84. http://dx.doi.org/10.5194/bgd-10-12251-2013.
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Abstract. Pelagic methane oxidation was investigated in dependence on differing environmental conditions within the redox zone of the Gotland Deep (GD) and Landsort Deep (LD), central Baltic Sea. The redox zone of both deeps, which indicates the transition between oxic and anoxic conditions, was characterized by a pronounced methane concentration gradient between the deep water (GD: 1233 nM, LD: 2935 nM) and the surface water (GD and LD < 10 nM), together with a 13C CH4 enrichment (δ13C CH4 deep water: GD −84‰, LD −71‰ ; redox zone: GD −60‰, LD −20‰ ; δ13C CH4 vs. Vienna Pee Dee Belemnite standard), clearly indicating microbial methane consumption in that specific depth interval. Expression analysis of the methane monooxygenase identified one active type I methanotrophic bacterium in both redox zones. In contrast, the turnover of methane within the redox zones showed strong differences between the two basins (GD: max. 0.12 nM d–1 and LD: max. 0.61 nM d–1), with a four times higher turnover rate constant (k) in the LD (GD: 0.0022 d–1, LD: 0.0079 d–1). Vertical mixing rates for both deeps were calculated on the base of the methane concentration profile and the consumption of methane in the redox zone (GD: 2.5 × 10–6 m2 s–1 LD: 1.6 × 10–5 m2 s–1). Our study identified vertical transport of methane from the deep water body towards the redox zone as well as differing hydrographic conditions within the oxic/anoxic transition zone of these deeps as major factors that determine the pelagic methane oxidation.
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Asadi, A., A. A. Zinatizadeh, M. Van Loosdrecht, and H. Younesi. "Nitrogen removal by ANAMMOX and simultaneous nitrification–denitrification (SND) processes in a novel single airlift bioreactor." RSC Advances 6, no. 78 (2016): 74367–71. http://dx.doi.org/10.1039/c6ra11174b.
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The aim of this research was to assess anaerobic ammonium oxidation and simultaneous nitrification–denitrification processes in a novel continuous feed and intermittent discharge airlift bioreactor which provides anaerobic, anoxic and aerobic zones by physical separation.
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Bishop, Janice L., Brandy L. Anglen, Lisa M. Pratt, Howell G. M. Edwards, David J. Des Marais, and Peter T. Doran. "A spectroscopy and isotope study of sediments from the Antarctic Dry Valleys as analogues for potential paleolakes on Mars." International Journal of Astrobiology 2, no. 4 (October 2003): 273–87. http://dx.doi.org/10.1017/s1473550403001654.
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A spectroscopy and isotope study has been performed on igneous sediments from Lake Hoare, a nearly isolated ecosystem in the Dry Valleys region of Antarctica. The mineralogy and chemistry of these sediments were studied in order to gain insights into the biogeochemical processes occurring in a permanently ice-covered lake and to assist in characterizing potential habitats for life in paleolakes on Mars. Obtaining visible/near-infrared, mid-infrared and Raman spectra of such sediments provides the ground truth needed for using reflectance, emittance and Raman spectroscopy for exploration of geology, and perhaps biology, on Mars. Samples measured in this study include a sediment from the ice surface, lake bottom sediment cores from oxic and anoxic zones of the lake and the magnetic fractions of two samples.These sediments are dominated by quartz, pyroxene, plagioclase and K-feldspar, but also contain calcite, organics, clays, sulphides and iron oxides/hydroxides that resulted from chemical and biological alteration processes. Chlorophyll-like bands are observed in the spectra of the sediment-mat layers on the surface of the lake bottom, especially in the deep anoxic region. Layers of high calcite concentration in the oxic sediments and layers of high pyrite concentration in the anoxic sediments are indicators of periods of active biogeochemical processing in the lake. Micro-Raman spectra revealed the presence of ~5 μm-sized pyrite deposits on the surface of quartz grains in the anoxic sediments. C, N and S isotope trends are compared with the chemistry and spectral properties. The δ13C and δ15N trends highlight the differences in the balance of microbial processes in the anoxic sediments versus the oxic sediments. The biogenic pyrite found in the sediments from the anoxic zone is associated with depleted δ34S values, high organic C levels and chlorophyll spectral bands and could be used as a potential biomarker mineral for paleolakes on Mars.
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Bellandi, Giacomo, Jose Porro, Elisa Senesi, Cecilia Caretti, Simone Caffaz, Stefan Weijers, Ingmar Nopens, and Riccardo Gori. "Multi-point monitoring of nitrous oxide emissions in three full-scale conventional activated sludge tanks in Europe." Water Science and Technology 77, no. 4 (November 30, 2017): 880–90. http://dx.doi.org/10.2166/wst.2017.560.
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Abstract The large global warming potential of nitrous oxide (N2O) is currently of general concern for the water industry, especially in view of a new regulatory framework concerning the carbon footprint of water resource recovery facilities (WRRFs). N2O can be generated through different biological pathways and from different treatment steps of a WRRF. The use of generic emission factors (EF) for quantifying the emissions of WRRFs is discouraged. This is due to the number of different factors that can affect how much, when and where N2O is emitted from WRRFs. The spatial and temporal variability of three WRRFs in Europe using comparable technologies is presented. An economically feasible and user-friendly method for accounting for the contribution of anoxic zones via direct gas emission measurements was proven. The investigation provided new insights into the contribution from the anoxic zones versus the aerobic zones of biological WRRF tanks and proved the unsuitability of the use of a single EF for the three WRRFs. Dedicated campaigns for N2O emissions assessment are to be advised. However, similarities in the EF magnitude can be found considering treatment strategy and influent water composition.
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Lee, T. T., F. Y. Wang, and R. B. Newell. "On the modelling and simulation of a BNR activated sludge process based on distributed parameter approach." Water Science and Technology 39, no. 6 (March 1, 1999): 79–88. http://dx.doi.org/10.2166/wst.1999.0266.
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A computational algorithm, based on an orthogonal collocation approach is developed to simulate a BNR activated sludge process consisting of anaerobic, anoxic and aerobic zones in a back-to-back scheme. The hydraulic model employed in this study considers backmixing or intermixing, which can represent the actual process more accurately than the idealised flow schemes commonly employed for modelling and/or design of the activated sludge bioreactor. The kinetic model of the International Association on Water Quality (IAWQ) - Activated Sludge Model No. 2 (ASM No. 2) was reduced to submodels representing the anaerobic, anoxic and aerobic zones. Validation of simulated results against pilot-scale experimental data suggested that the new computational algorithm is able to predict the behaviour of components of interest reasonably well despite uncertainties with processes and parameters related to phosphorus accumulating organisms. Predicted transient properties may be gainfully employed for improvement to the operation and control of the process.
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Sriwiriyarat, Tongchai, and Clifford W. Randall. "THE PERFORMANCE OF IFAS MEDIA IN ANOXIC ZONES OF BNR SYSTEMS." Proceedings of the Water Environment Federation 2007, no. 2 (January 1, 2007): 1075–97. http://dx.doi.org/10.2175/193864707787976830.
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Penn, Justin L., Thomas Weber, Bonnie X. Chang, and Curtis Deutsch. "Microbial ecosystem dynamics drive fluctuating nitrogen loss in marine anoxic zones." Proceedings of the National Academy of Sciences 116, no. 15 (March 25, 2019): 7220–25. http://dx.doi.org/10.1073/pnas.1818014116.
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The dynamics of nitrogen (N) loss in the ocean’s oxygen-deficient zones (ODZs) are thought to be driven by climate impacts on ocean circulation and biological productivity. Here we analyze a data-constrained model of the microbial ecosystem in an ODZ and find that species interactions drive fluctuations in local- and regional-scale rates of N loss, even in the absence of climate variability. By consuming O2to nanomolar levels, aerobic nitrifying microbes cede their competitive advantage for scarce forms of N to anaerobic denitrifying bacteria. Because anaerobes cannot sustain their own low-O2niche, the physical O2supply restores competitive advantage to aerobic populations, resetting the cycle. The resulting ecosystem oscillations induce a unique geochemical signature within the ODZ—short-lived spikes of ammonium that are found in measured profiles. The microbial ecosystem dynamics also give rise to variable ratios of anammox to heterotrophic denitrification, providing a mechanism for the unexplained variability of these pathways observed in the ocean.
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Haberstroh, P. R., and F. J. Sansone. "Reef framework diagenesis across wave-flushed oxic-suboxic-anoxic transition zones." Coral Reefs 18, no. 3 (September 23, 1999): 229–40. http://dx.doi.org/10.1007/s003380050187.
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Canfield, Don E., Beate Kraft, Carolin R. Löscher, Richard A. Boyle, Bo Thamdrup, and Frank J. Stewart. "The regulation of oxygen to low concentrations in marine oxygen-minimum zones." Journal of Marine Research 77, no. 3 (May 1, 2019): 297–324. http://dx.doi.org/10.1357/002224019828410548.
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The Bay of Bengal hosts persistent, measurable, but sub-micromolar, concentrations of oxygen in its oxygen-minimum zone (OMZ). Such low-oxygen conditions are not necessarily rare in the global ocean and seem also to characterize the OMZ of the Pescadero Basin in the Gulf of California, as well as the outer edges of otherwise anoxic OMZs, such as can be found, for example, in the Eastern Tropical North Pacific. We show here that biological controls on oxygen consumption are required to allow the semistable persistence of low-oxygen conditions in OMZ settings; otherwise, only small changes in physical mixing or rates of primary production would drive the OMZ between anoxic and oxic states with potentially large swings in oxygen concentration. We propose that two controls are active: an oxygen-dependent control on oxygen respiration and an oxygen inhibition of denitrification. These controls, working alone and together, can generate low-oxygen concentrations over a wide variability in ocean mixing parameters. More broadly, we discuss the oxygen regulation of organic matter cycling and N2 production in OMZ settings. Modern biogeochemical models of nitrogen and oxygen cycling in OMZ settings do contain some of the parameterizations that we explore here. However, these models have not been applied to understanding the persistence of low, but measurable, concentrations of oxygen in settings like the Bay of Bengal, nor have they been applied to understanding what biological/physical processes control the transition from a weakly oxygenated state to a “functionally” anoxic state with implications for nitrogen cycling. Therefore, we believe that the approach here illuminates the relationship between oxygen and the biogeochemical cycling of carbon and nitrogen in settings like the Bay of Bengal. Furthermore, we believe that our results could further inform large-scale ocean models seeking to explore how global warming might influence the spread of low-oxygen waters, influencing the cycles of oxygen, carbon, and nitrogen in OMZ settings.
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van Grinsven, Sigrid, Kirsten Oswald, Bernhard Wehrli, Corinne Jegge, Jakob Zopfi, Moritz F. Lehmann, and Carsten J. Schubert. "Methane oxidation in the waters of a humic-rich boreal lake stimulated by photosynthesis, nitrite, Fe(III) and humics." Biogeosciences 18, no. 10 (May 20, 2021): 3087–101. http://dx.doi.org/10.5194/bg-18-3087-2021.
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Abstract. Small boreal lakes are known to contribute significantly to global CH4 emissions. Lake Lovojärvi is a eutrophic lake in southern Finland with bottom water CH4 concentrations up to 2 mM. However, the surface water concentration, and thus the diffusive emission potential, was low (< 0.5 µM). We studied the biogeochemical processes involved in CH4 removal by chemical profiling and through incubation experiments. δ13C-CH4 profiling of the water column revealed a methane-oxidation hotspot just below the oxycline and zones of CH4 oxidation within the anoxic water column. In incubation experiments involving the addition of light and/or oxygen, CH4 oxidation rates in the anoxic hypolimnion were enhanced 3-fold, suggesting a major role for photosynthetically fueled aerobic CH4 oxidation. We observed a distinct peak in CH4 concentration at the chlorophyll-a maximum, caused by either in situ CH4 production or other CH4 inputs such as lateral transport from the littoral zone. In the dark anoxic water column at 7 m depth, nitrite seemed to be the key electron acceptor involved in CH4 oxidation, yet additions of Fe(III), anthraquinone-2,6-disulfonate and humic substances also stimulated anoxic CH4 oxidation. Surprisingly, nitrite seemed to inhibit CH4 oxidation at all other depths. Overall, this study shows that photosynthetically fueled CH4 oxidation can be a key process in CH4 removal in the water column of humic, turbid lakes, thereby limiting diffusive CH4 emissions from boreal lakes. Yet, it also highlights the potential importance of a whole suite of alternative electron acceptors, including humics, in these freshwater environments in the absence of light and oxygen.
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Chao, Yeong-Nan, Jui-Hsien Lin, Kok-Kwang Ng, Chung-Hsin Wu, Pui-Kwan Andy Hong, and Cheng-Fang Lin. "Improving total nitrogen removal in aeration basin retrofitted with entrapped biomass." Water Science and Technology 69, no. 7 (February 4, 2014): 1558–64. http://dx.doi.org/10.2166/wst.2014.053.
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This study presented a method to upgrade existing aeration tanks to remove total nitrogen (TN). Bioplates carrying entrapped biomass were installed in an aeration basin to create anoxic/anaerobic zones where denitrification can proceed. In a reactor that coupled bioplates containing entrapped biomass (equivalent to as high as 7,500 mg/L of biomass) and an activated sludge suspension (at mixed liquor suspended solids of 1,300–2,400 mg/L), nitrification efficiency exceeded 95% for an influent wastewater containing 21–54 mg/L of NH3-N. In all cases amended with alkalinity and with or without added methanol as an electron source, TN removal was between 60 and 70%. The results demonstrated anoxic/oxic or anaerobic/anoxic/oxic processes could be incorporated in a conventional aeration basin, requiring no substantial modifications of the vessel and operation, and thus providing improved treatment in terms of nitrogen removal in the conventional suspended-growth process.
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Shuo, Liu, Wang Baozhen, Han Hongjun, and Liu Yanping. "New process for alleviation of membrane fouling of modified hybrid MBR system for advanced domestic wastewater treatment." Water Science and Technology 58, no. 10 (November 1, 2008): 2059–66. http://dx.doi.org/10.2166/wst.2008.755.
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A pilot-scale hybrid membrane bioreactor using a submerged flat panel membrane was designed and applied for advanced treatment of domestic wastewater. The new process adapted to the hybrid membrane bioreactor exhibits substantial decrease in membrane fouling and much easier cleaning. In this study, the new process configurations including the addition of anoxic/anaerobic zones, the package of synthetic fibrous fabric carrier for biofilm attached growth, activated sludge recycling and modified dosage of polished diatomite with high activity and multi-functions were investigated to select the optimal operational parameters for the hybrid membrane bioreactor system. The carrier package in the aerobic zone contributed 3.65 g/L (maximum) of fixed biomass to the system, thus reducing the suspended biomass, and has decreased the membrane cleaning cycle remarkably. The operation performance at the sludge recycle rate 0, 100%, 200% and 300% showed that, the trans-membrane pressure of flat panel membrane declined sharply with the increase of sludge recycling rate within a certain range, and 200% was decided to be optimal for in the membrane bioreactor system. EPS concentration in each sludge recycling rate was 135 mg/L, 92 mg/L, 68 mg/L and 55 mg/L respectively. The addition of anoxic and anaerobic zones degraded some large molecular organic compounds, which facilitated the biodegradation and removal of organic substances in aerobic zone. The modified dosage of polished diatomite has played a major important role for both preventing of membrane from fouling and its much easier cleaning when it formed.
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Berndmeyer, C., V. Thiel, O. Schmale, N. Wasmund, and M. Blumenberg. "Biomarkers in the stratified water column of the Landsort Deep (Baltic Sea)." Biogeosciences 11, no. 23 (December 11, 2014): 7009–23. http://dx.doi.org/10.5194/bg-11-7009-2014.
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Abstract. The water column of the Landsort Deep, central Baltic Sea, is stratified into an oxic, suboxic, and anoxic zone. This stratification controls the distributions of individual microbial communities and biogeochemical processes. In summer 2011, particulate organic matter was filtered from these zones using an in situ pump. Lipid biomarkers were extracted from the filters to establish water-column profiles of individual hydrocarbons, alcohols, phospholipid fatty acids, and bacteriohopanepolyols (BHPs). As a reference, a cyanobacterial bloom sampled in summer 2012 in the central Baltic Sea Gotland Deep was analyzed for BHPs. The biomarker data from the surface layer of the oxic zone showed major inputs from cyanobacteria, dinoflagellates, and ciliates, while the underlying cold winter water layer was characterized by a low diversity and abundance of organisms, with copepods as a major group. The suboxic zone supported bacterivorous ciliates, type I aerobic methanotrophic bacteria, sulfate-reducing bacteria, and, most likely, methanogenic archaea. In the anoxic zone, sulfate reducers and archaea were the dominating microorganisms as indicated by the presence of distinctive branched fatty acids: archaeol and pentamethylicosane (PMI) derivatives, respectively. Our study of in situ biomarkers in the Landsort Deep thus provided an integrated insight into the distribution of relevant compounds and describes useful tracers to reconstruct stratified water columns in the geological record.
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Atkinson, B. W., D. D. Mudaly, and F. Bux. "Contribution of Pseudomonas spp. to phosphorus uptake in the anoxic zone of an anaerobic-anoxic-aerobic continuous activated sludge system." Water Science and Technology 43, no. 1 (January 1, 2001): 139–46. http://dx.doi.org/10.2166/wst.2001.0034.
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A continuously operated laboratory-scale (32 L) nitrification denitrification biological excess phosphorus removal (NDBEPR) activated sludge system (modeled on the 3-stage Phoredox configuration) was maintained for 140 d. The transition from a non-biological excess phosphorus removal (BEPR) sludge to one exhibiting a strong BEPR mechanism was monitored. Mixed liquor seed inoculum was obtained from a full-scale single aerobic activated sludge installation and subjected to conditions conducive to BEPR, i.e. increasing influent acetate (HAc) concentrations. At a sludge age of 10 d with 100% HAc feed, the system was capable of removing a maximum of ca. 40 mgPO4–P/L from the bulk liquid; P/VSS of ca. 0.27 (mgP/mgVSS); and VSS/TSS of 0.53 (mgVSS/mgTSS) in the aerobic zone was attained. Although typical BEPR phosphorus transformation patterns were routinely observed, i.e. anaerobic phosphate release and aerobic phosphate uptake, phosphate uptake in the anoxic zone was also recorded indicating the presence of denitrifying phosphorus accumulating organisms (DPAOs) in the sludge community. The microbial community was screened (using both isolation and direct methods of analysis) for the presence of Pseudomonas spp. as this genus is known to perform both polyphosphate accumulation and denitrification processes. Isolation of anoxic mixed liquor bacteria on solid media and identification using the API 20NE system resulted in the total dominance of the Pseudomonads (>50%). However, direct fluorescent in situ hybridizations (FISH) revealed that Pseudomonas spp. only constituted ca. 3% of the total bacterial community indicating that other bacterial genera are contributing to simultaneous polyphosphate accumulation and denitrification processes in the anoxic zones of NDBEPR systems.
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Kurochkin, I. O., A. V. Ivanina, S. Eilers, C. A. Downs, L. A. May, and I. M. Sokolova. "Cadmium affects metabolic responses to prolonged anoxia and reoxygenation in eastern oysters (Crassostrea virginica)." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 297, no. 5 (November 2009): R1262—R1272. http://dx.doi.org/10.1152/ajpregu.00324.2009.
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Benthic marine organisms such as mollusks are often exposed to periodic oxygen deficiency (due to the tidal exposure and/or seasonal expansion of the oxygen-deficient dead zones) and pollution by metals [e.g., cadmium, (Cd)]. These stressors can strongly affect mollusks' survival; however, physiological mechanisms of their combined effects are not fully understood. We studied the effects of Cd exposure on metabolic responses to prolonged anoxia and subsequent recovery in anoxia-tolerant intertidal mollusks Crassostrea virginica (eastern oysters). Anoxia led to an onset of anaerobiosis indicated by accumulation of l-alanine, acetate, and succinate. Prolonged anoxia (for 6 days) caused a decline in the maximum activity of electron transport chain and ADP-stimulated ( state 3) oxygen uptake by mitochondria (MO2), but no change in the resting ( state 4) MO2 of oyster mitochondria, along with a slight but significant reduction of mitochondrial respiratory control ratio. During reoxygenation, there was a significant overshoot of mitochondrial MO2 (by up to 70% above the normoxic steady-state values) in control oysters. Mild mitochondrial uncoupling during prolonged shutdown in anoxic tissues and a subsequent strong stimulation of mitochondrial flux during recovery may help to rapidly restore redox status and protect against elevated reactive oxygen species formation in oysters. Exposure to Cd inhibits anaerobic metabolism, abolishes reoxygenation-induced stimulation of mitochondrial MO2, and leads to oxidative stress (indicated by accumulation of DNA lesions) and a loss of mitochondrial capacity during postanoxic recovery. This may result in increased sensitivity to intermittent hypoxia and anoxia in Cd-exposed mollusks and will have implications for their survival in polluted estuaries and coastal zones.