Organic Carbon Consumption Research Articles

Processes of organic carbon in mangrove ecosystems

In addition to carbon accumulation in plants, processes of organic carbon in mangrove ecosystems include origins of sediment organic carbon, carbon fluxes between mangroves and their adjacent systems (coastal waters and atmosphere), and cycling processes. Sediment organic carbon originates from suspending solids in coastal waters, mangrove plants and benthic algae. In mangroves with low organic carbon content in sediments, tidal seawater is the main origin of sediment organic carbon, while in mangroves with high sediment organic carbon contents, sediment organic carbon mainly originates from mangrove plants. Due to tidal flush, there is large material exchange between mangrove ecosystems and their adjacent coastal waters. In China, exports of organic carbon in litter falls and dissolved organic carbon from mangroves to their adjacent coastal waters have not been documented. Processes of mangrove litter falls, including production, decomposition, export and animal consumption, determine linkages among organic carbon among mangrove plants, secondary production and coastal ocean. Consumers especially benthic animals may influence organic carbon in mangrove ecosystems, because (1) their consumption rates are high, and their selective feeding on some food sources will change the relative quantities of export, bury and mineralization of organic carbon from different origins; (2) their consumption is much more than assimilation, resulting in the changes in sizes, forms and qualities of non-assimilated organic matters, and then the changes in availability of export, consumption or mineralization of organic carbon. Respiration and sulfate reduction are important mineralization processes of organic carbon in mangrove sediments. Mineralization rates of organic carbon in mangrove sediments are influenced by quantities, activities and particle sizes of organic matters, and other factors such as forest ages, root activities and animal burrowing activities. Researches on processes of mangrove organic carbon should be based on open systems, and ecological processes of organic carbon should be coupled with vegetation restoration.

Kinetics of Organic Carbon Consumption by Yeast Strain UY7

Kinetics of Organic Carbon Consumption by Yeast Strain UY7

Significant roles of bacteriochlorophylla supplemental to chlorophylla in the ocean

Bacteriochlorophylla (BChla)-based phototrophy cannot be ignored in understanding of carbon cycle in the ocean. However, the role of BChla relative to chlorophylla (Chla) along environmental gradients remains unclear. On the basis of the investigations in the Pacific, Indian Oceans and the China Seas, we show that the average contribution of BChla relative to Chla is higher in open-ocean compared with shelf environments, the estimated BChla-based phototrophy could reduce respiratory organic carbon consumption of 2.4% and 5.4% of the primary productions in the shelf and oceanic waters, respectively. This suggests that BChla-based phototrophy has an important role supplemental to Chla-based photosynthesis in the ocean's carbon cycle and would be critical for a marine region to be a sink or a source of atmospheric CO(2).

Microelectrode Study of Oxygen Uptake and Organic Matter Decomposition in The Sediments of Xiamen Western Bay

Sediment cores were sampled from Xiamen Western Bay at five sites during the summer and winter of 2006 and Hg–Au microelectrodes were used to make on board measurements of the concentration gradients of dissolved oxygen, Mn2+, and Fe2+ within the sediments. The O2 concentrations decreased sharply from about 200 μmol L−1 in the bottom seawater to zero within a depth of a few millimeters into the sediment. Dissolved Mn2+ was detected below the oxic zones with peak concentrations up to 600 μmol L−1, whereas dissolved Fe2+ had peak concentrations up to 1,000 μmol L−1 in deeper layers. The elemental contents of organic carbon and nitrogen within the sediments were analyzed and their C/N ratios were in the range of 9.0 to 10.1, indicative of heavy terrestrial origin. Sediments from two sites near municipal wastewater discharge outlets had higher organic contents than those from the other sites. These high organic contents corresponded to shallow O2 penetration depths, high dissolved Mn2+ and Fe2+ concentrations, and negative redox potentials within the sediments. This indicated that the high organic matter content had promoted microbial respiration within the sediments. Overall, the organic content did not show any appreciable decrease with increasing sediment depths, so a quadratic polynomial function was used to fit the curve of O2 profiles within the sediments. Based on the O2 profiles, O2 fluxes across the seawater and sediment interface were estimated to be in the range 6.07 to 14.9 mmol m−2 day−1, and organic carbon consumption rates within the surface sediments were estimated to be in the range 3.3 to 20.8 mgC cm−3 a−1. The case demonstrated that biogeochemistry within the sediments of the bay was very sensitive to human activities such as sewage discharge.

Distribution, fluxes and bacterial consumption of total organic carbon in a populated Mediterranean Gulf

Saronikos Gulf (Greece) practically constitutes the sea border of the metropolitan city of Athens and the alongshore outskirts, and it receives the treated wastes of ∼4 million people from a point source that discharges on the sea bottom at ∼65 m water depth. Total organic carbon (TOC) was measured in 477 seawater samples collected in the Saronikos Gulf, during 10 cruises, from August 2001 to May 2004 and analyzed with the High Temperature Catalytic Oxidation method (HTCO). TOC concentrations ranged from 49 to 198 μmol C L −1 in agreement with other Mediterranean coastal waters. The highest TOC concentrations were found in the upper waters (0–75 m), whereas in the deeper parts of the Gulf (between 100 and 400 m) TOC concentrations were kept constantly low (49–70 μmol C L −1). A general pattern towards higher TOC concentrations during summer was also observed. Calculations of non-refractory (labile+semi-labile) organic material based on a one-dimensional (1D) conceptual model showed that it corresponds to 33% of the bulk TOC during summer and to 27% during winter. Bacterial production (BP) was measured at selected stations of ∼70–80 m depth using the [ 3H] leucine method. Depth integrated BP values varied from 2.8 to 10.9 mmol m −2 d −1, whereas extraordinary high integrated BP values (126 and 140 mmol m −2 d −1) were observed at the station over the treated sewage outflow. From the turnover time, τ, of the non-refractory TOC by bacteria it was implied that organic matter in the effluents is extremely labile (2–58 days). Moreover, τ values at the other sites showed that during summer non-refractory organic material resisted bacterial degradation (1–8 months), whereas during early spring it was easily degradable (20–50 days). The balance of TOC fluxes for the Inner Gulf for June and September 2003 showed that the Inner Gulf acts as a net producer of TOC during summer. Our results suggest that the presence of the Athens treated sewage outfall does not contribute to the observed summer accumulation of TOC in the Inner Gulf and other causes such as increased bacteria predation and/or nutrient limitation must be responsible.

Study of Relationship between Consumption of Potassium Permanganate and Total Organic Carbon on Plastic Kitchen Utensils, Food Packages and Toys

Consumption of potassium permanganate and total organic carbon (TOC) were investigated as indices of total organic matter migrated into water from plastic kitchen utensils, food packages and toys for children. The samples were soaked in water at 60 or 95 degrees C for 30 min for kitchen utensils and food packages, and at 40 degrees C for 30 min for toys and the eluates were examined, using the two indices. The quantitation limits were both 0.5 microg/mL. Among 97 kitchen utensils and food packages tested, consumption of potassium permanganate and TOC were 0.5-10.9 microg/mL and ND-18.9 microg/mL for polyvinyl chloride (PVC) tea-pot spouts and nylon kitchen utensils, respectively. Among 32 toys tested, the levels were 0.8-45.5 microg/mL and 0.5-8.9 microg/mL from PVC toys and block toys made by ethylene vinyl acetate resin. The levels for other samples were very low. There were large discrepancies between consumption of potassium permanganate and TOC for some PVC products and nylon kitchen utensils. The cause may be a marked difference of the oxidation decomposition rate by potassium permanganate, depending on the kind of organic matter that migrated from the plastics.

Evaluation of oxygen injection as a means of controlling sulfide production in a sewer system

Oxygen injection is often used to control biogenic production of hydrogen sulfide in sewers. Experiments were carried out on a laboratory system mimicking a rising main to investigate the impact of oxygen injection on anaerobic sewer biofilm activities. Oxygen injection (15–25 mg O 2/L per pump event) to the inlet of the system decreased the overall sulfide discharge levels by 65%. Oxygen was an effective chemical and biological oxidant of sulfide but did not cause a cessation in sulfide production, which continued in the deeper layers of the biofilm irrespective of the oxygen concentration in the bulk. Sulfide accumulation resumed instantaneously on depletion of the oxygen. Oxygen did not exhibit any toxic effect on sulfate reducing bacteria (SRB) in the biofilm. It further stimulated SRB growth and increased SRB activity in downstream biofilms due to increased availability of sulfate at these locations as the result of oxic conditions upstream. The oxygen uptake rate of the system increased with repeated exposure to oxygen, with concomitant consumption of organic carbon in the wastewater. These results suggest that optimization of oxygen injection is necessary for maximum effectiveness in controlling sulfide concentrations in sewers.

Interaction of Colloidal Fe/Mn Oxides Concentration and Shear Stress on Biofilm Formation

Six test runs were carried out to explore the interaction of shear stress and Fe/Mn oxides concentration on the growth of heterotrophic micro-organisms in biofilms. Experimental results revealed that the existence of Fe/Mn colloids was beneficial to biofilm formation. Significant interactions existed (p < 0.001) between shear stress and influent Fe/Mn concentration on biofilm bacteria growth and dissolved organic carbon consumption. Biofilm bacteria numbers were positively related to the dissolved organic carbon consumption rate. This implies that the influent Fe/Mn concentration did not interfere with the uptake of the carbon source by biofilm bacteria. At a higher Fe/Mn concentration (HCS), the biofilm HPC number significantly increased with an increase in shear stress. However, the opposite relation was found at a lower Fe/Mn concentration (LCS). A significant interaction existed between influent colloidal Fe/Mn concentration and shear stress on the kinetic and yield parameters specific growth rate (μb), specific substrate utilization rate (q), and observed growth yield (γobs). The size distribution of particles based on particle concentration (No · ml−1) was also examined in the study.

Response of microbial growth to orthophosphate and organic carbon influx in copper and plastic based plumbing water systems

Consequences of orthophosphate addition for corrosion control in water distribution pipes with respect to microbial growth were investigated using batch and dynamic tests. Batch tests showed that the release of copper in either low or high organic carbon content water was decreased by 69% and 56% with addition 206 μg PO 4–P, respectively. Dosing of orthophosphate against corrosion did not increase microbial growth potential in the water and in the biofilm in both corroded and uncorroded systems receiving tap water with a low content of organic carbon and of biodegradable organic fraction. However, in tap water having a high concentration of organic carbon from acetate addition, orthophosphate addition promoted the growth of bacteria, allowed more bacteria to assemble on corroded and uncorroded surfaces, and increased the consumption of organic carbon. Orthophosphate consumption did not exceed 1% of the amount of easily biodegradable organic carbon required for microbial growth, and the orthophosphate demand for corrosion control greatly exceeded the nutritional requirement of microbial growth. The results of the dynamic tests demonstrated that there was a significant effect of interaction between biodegradable organic carbon and orthophosphate on biofilm growth, whereby the effect of orthophosphate flux on microbial growth was dependent on the levels of biodegradable organic carbon. Controlling an easily biodegradable organic carbon would be therefore necessary to minimize the microbial growth potential induced by orthophosphate-based anticorrosion treatment.

Effect of loading rate on TOC consumption efficiency in a sulfate reducing process: sulfide effect in batch culture

AbstractBACKGROUND: The sulfate reducing process (SRP) was analyzed in order to identify factors that diminish the effectiveness of the SRP during wastewater treatment. The effect of different sulfate loading rates (SLR, 290 to 981 mg SO4‐S L−1d−1) and lactate at a stoichiometric C/S ratio of 0.75 on SRP was studied in an upflow anaerobic sludge blanket (UASB) reactor. The effect of sulfide concentration (0 to 200 mg sulfide‐S L−1) on SRP in batch culture was evaluated.RESULTS: When the SLR was increased, the total organic carbon (TOC) and sulfate consumption efficiencies decreased from 93% ± 3 to 66% ± 2 and 60% ± 5 to 45% ± 4, respectively. Acetate and propionate were accumulated. Microbial analysis showed the presence of microorganisms related with the SRP, fermentation and methanogenesis. In batch culture, when lactate and sulfate were present, SRP and fermentation were observed. When sulfide was added only SRP was observed. At concentrations higher than 150 mg sulfide‐S L−1 the efficiencies, yields and specific consumption rates (q) decreased.CONCLUSION: Based on the sulfide‐S/volatile suspended solid ratio, it was found that the decrease in efficiency and accumulation of acetate and propionate in the UASB reactor was not related to sulfide inhibition but to the q of acetate and propionate, which were up to 11 times lower than lactate. Copyright © 2008 Society of Chemical Industry

Microbial fuel cells for simultaneous carbon and nitrogen removal

The recent demonstration of cathodic nitrate reduction in a microbial fuel cell (MFC) creates opportunities for a new technology for nitrogen removal from wastewater. A novel process configuration that achieves both carbon and nitrogen removal using MFC is designed and demonstrated. The process involves feeding the ammonium-containing effluent from the carbon-utilising anode to an external biofilm-based aerobic reactor for nitrification, and then feeding the nitrified liquor to the MFC cathode for nitrate reduction. Removal rates up to 2 kg COD m −3 NCC d −1 (chemical oxygen demand: COD, net cathodic compartment: NCC) and 0.41 kg NO 3 −-N m −3 NCC d −1 were continuously achieved in the anodic and cathodic compartment, respectively, while the MFC was producing a maximum power output of 34.6±1.1 W m −3 NCC and a maximum current of 133.3±1.0 A m −3 NCC. In comparison to conventional activated sludge systems, this MFC-based process achieves nitrogen removal with a decreased carbon requirement. A COD/N ratio of approximately 4.5 g COD g −1 N was achieved, compared to the conventionally required ratio of above 7. We have demonstrated that also nitrite can be used as cathodic electron acceptor. Hence, upon creating a loop concept based on nitrite, a further reduction of the COD/N ratio would be possible. The process is also more energy effective not only due to the energy production coupled with denitrification, but also because of the reduced aeration costs due to minimised aerobic consumption of organic carbon.

Topographic influences on wildfire consumption of soil organic carbon in interior Alaska: Implications for black carbon accumulation

We measured characteristics of soil organic carbon (SOC) and black carbon (BC) along opposed north‐ and south‐facing toposequences in recent (2004) and old (∼1860–1950) burn sites throughout interior Alaska. Surface fuel consumption did not vary between different topographic positions, with 3.3 (±0.5) kg C m−2 being consumed on toe slope sites, 4.0 (±0.2) kg C m−2 on north‐slope sites, and 3.6 (±0.3) kg C m−2 on south‐slope sites. On a relative scale, 43% of the organic matter depth was removed through biomass burning on toe slopes, 62% on north‐slopes, and 77% on south‐slope sites. Mineral soil BC stocks (measured using a chemical/thermal oxidation method isolating more graphitic BC) ranged from 112 ± 24 g C m−2 to 173 ± 43 g C m−2 on north‐ and south‐facing aspects, respectively. These data supported the expectation that deeper and wetter ground fuels occurring in north‐facing and toe‐slope forests burned less completely, which decreased the amount of BC incorporated into mineral soil where it could be protected from subsequent fires. Thus, warmer and drier forests harbored less total SOC, but following wildfire aggraded larger BC stocks. BC was therefore an important component of stable soil C in warmer and drier forests which had higher C turnover rates in other soil pools (determined by density fractionation, δ13C, and Δ14C). These data provide a basis for understanding how variable patterns of organic layer depths and soil moisture mediate the consumption of SOC in wildfire, as well as the long‐term accumulation of BC.

Simultaneous nitrification and p-cresol oxidation in a nitrifying sequencing batch reactor

The tolerance, kinetic behavior and oxidizing ability of a nitrifying sludge exposed to different initial concentrations of p-cresol (25–150 mg/l) were evaluated in a sequencing batch reactor (SBR) fed with 200 mg NH 4 +-N/l d. The nitrifying SBR operated up to 300 mg/l d of p-cresol, achieving simultaneously the complete ammonium oxidation to nitrate and the total consumption of p-cresol and its transitory intermediates from the culture. p-Cresol induced a significant decrease in the values for specific rates of ammonium consumption, showing that the ammonium oxidation pathway was mainly inhibited. After 7 months of operation in SBR, the specific rates of NH 4 +-N oxidation, NO 3 −-N formation, and total organic carbon consumption were 0.6 g NH 4 +-N/g microbial protein-N h, 0.3 g NO 3 −-N/g microbial protein-N h, and 0.24 g total organic carbon/g microbial protein h, respectively. The microbial growth rate was always low (maximum value of 12.2±0.4 mg protein-N/l d) and settleability of the sludge was good with sludge volume index values lower than 21 ml/g. The oxidation of p-cresol and its intermediates was carried out faster throughout the cycles and nitrification inhibition decreased with the number of cycles.

Importance of planktonic community respiration on the carbon balance of the East China Sea in summer

The East China Sea (ECS) is one of the largest continental shelves in the world; however, the role that biota plays in the carbon fluxes of this shelf ecosystem is still obscure. To evaluate the organic carbon balance and the roles played by planktonic communities in organic carbon consumption, two cruises with stations covering almost the entire shelf were conducted during the high productivity and high river flow season of the ECS in June (the early summer) and August (the middle summer) 2003. Results showed that biological activity was significantly higher in the early summer. To flourish in the early summer, plankton need a significant fluvial input of dissolved inorganic nutrients and organic matter from the Chinese coast, especially from the Changjiang (aka Yangtze River), might be one of the main driving forces. Further analysis showed that most planktonic community respiration (PCR) could be attributed to phytoplankton and bacterioplankton, which accounted for over 96% of the total planktonic biomass (in carbon units) in summer. This might partially explain why mean PCR was higher in June (∼114 mg C m−3 d−1), with higher phytoplankton biomass, than in August (∼40 mg m−3 d−1). The ratio of integrated primary production to PCR (i.e., the P/R ratio) was, however, less than 1, with a mean ± SD value of 0.35 ± 0.41 for all the pooled data. This indicates a significant amount of organic carbon has been regenerated through planktonic activity in the water column. The sea‐air difference in fCO2, however, changed from a mean value of −64.5 ± 61.3 ppm in June to 10.0 ± 37.5 ppm in August. To explain the contradictory results between PCR and fCO2, we suggest that the dissolved inorganic carbon regenerated through planktonic respiration could be stored in the subsurface layer and may affect the fCO2 in the surface water, which is what controls the shelf sea either as an atmospheric CO2 sink or as a source, depending on the prevailing physical forces. These results also suggest that the controversy between atmospheric CO2 sink or source in the ECS shelf needs further exploration.

Quantifying archaeal community autotrophy in the mesopelagic ocean using natural radiocarbon

An ammonia-oxidizing, carbon-fixing archaeon, Candidatus "Nitrosopumilus maritimus," recently was isolated from a salt-water aquarium, definitively confirming that chemoautotrophy exists among the marine archaea. However, in other incubation studies, pelagic archaea also were capable of using organic carbon. It has remained unknown what fraction of the total marine archaeal community is autotrophic in situ. If archaea live primarily as autotrophs in the natural environment, a large ammonia-oxidizing population would play a significant role in marine nitrification. Here we use the natural distribution of radiocarbon in archaeal membrane lipids to quantify the bulk carbon metabolism of archaea at two depths in the subtropical North Pacific gyre. Our compound-specific radiocarbon data show that the archaea in surface waters incorporate modern carbon into their membrane lipids, and archaea at 670 m incorporate carbon that is slightly more isotopically enriched than inorganic carbon at the same depth. An isotopic mass balance model shows that the dominant metabolism at depth indeed is autotrophy (83%), whereas heterotrophic consumption of modern organic carbon accounts for the remainder of archaeal biomass. These results reflect the in situ production of the total community that produces tetraether lipids and are not subject to biases associated with incubation and/or culture experiments. The data suggest either that the marine archaeal community includes both autotrophs and heterotrophs or is a single population with a uniformly mixotrophic metabolism. The metabolic and phylogenetic diversity of the marine archaea warrants further exploration; these organisms may play a major role in the marine cycles of nitrogen and carbon.

Pathways of Carbon Assimilation and Ammonia Oxidation Suggested by Environmental Genomic Analyses of Marine Crenarchaeota

Marine Crenarchaeota represent an abundant component of oceanic microbiota with potential to significantly influence biogeochemical cycling in marine ecosystems. Prior studies using specific archaeal lipid biomarkers and isotopic analyses indicated that planktonic Crenarchaeota have the capacity for autotrophic growth, and more recent cultivation studies support an ammonia-based chemolithoautotrophic energy metabolism. We report here analysis of fosmid sequences derived from the uncultivated marine crenarchaeote, Cenarchaeum symbiosum, focused on the reconstruction of carbon and energy metabolism. Genes predicted to encode multiple components of a modified 3-hydroxypropionate cycle of autotrophic carbon assimilation were identified, consistent with utilization of carbon dioxide as a carbon source. Additionally, genes predicted to encode a near complete oxidative tricarboxylic acid cycle were also identified, consistent with the consumption of organic carbon and in the production of intermediates for amino acid and cofactor biosynthesis. Therefore, C. symbiosum has the potential to function either as a strict autotroph, or as a mixotroph utilizing both carbon dioxide and organic material as carbon sources. From the standpoint of energy metabolism, genes predicted to encode ammonia monooxygenase subunits, ammonia permease, urease, and urea transporters were identified, consistent with the use of reduced nitrogen compounds as energy sources fueling autotrophic metabolism. Homologues of these genes, recovered from ocean waters worldwide, demonstrate the conservation and ubiquity of crenarchaeal pathways for carbon assimilation and ammonia oxidation. These findings further substantiate the likely global metabolic importance of Crenarchaeota with respect to key steps in the biogeochemical transformation of carbon and nitrogen in marine ecosystems.

Biogeochemical controls on the oxygen, nitrogen and sulfur distributions in the water column of Golfo Dulce: an anoxic basin on the Pacific coast of Costa Rica revisited

Chemical distributions, respiration rates, and bacterial distributions were measured in 1994 in the water column and sediments of a small, tropical, anoxic basin (Golfo Dulce, Pacific coast of Costa Rica) to examine the biogeochemical controls on anoxia, sulfide, dissolved inorganic nitrogen, and organic carbon consumption. As reported previously, the deepest 100 m of the water column were anoxic, and sulfide concentrations in the bottom waters were less than 7 μM and then only transiently. Both free-swimming sulfide-oxidizing bacteria and Beggiatoa sp. (containing large vacuoles) were observed in the anoxic bottom waters or at the sediment-water interface. Aerobic respiration dominated the decomposition of organic matter in the surface waters and pycnocline, whereas sulfate reduction was principally restricted to the sediments. Bacteria were distributed in discrete zones and exhibited the highest densities where oxygen decreased below 1 μM around 100 m depth, and near the sediment-water interface. The sub-oxic, sub-pycnocline water column was characterized by a dissolved inorganic nitrogen (DIN) deficit of 2.9 mole m-2. With a water residence time of 35 – 57 d, estimated from a salt balance, this deficit corresponded to a DIN loss of 51 – 85 mmol m-2 d-1, comparable to the sub-pycnocline oxygen consumption. Sulfide in the water column was maintained at low concentrations by frequent inputs of oxygenated water from the Pacific Ocean. Sulfide production in the sediments due to bacterial sulfate reduction was scavenged by frequent deposition of iron-rich turbidites. Based on 210Pb distributions, the most recent emplacement of a turbidite in the basin sediments was determined to have occurred between 1989 and 1992. Rev. Biol. Trop. 54 (Suppl. 1): 171-191. Epub 2006 Sept. 30.

Effect of operating parameters on molinate biodegradation

The effect of operating conditions during molinate degradation by the defined mixed bacterial culture DC, previously described as able to mineralize molinate, was evaluated in a batch reactor. Parameters such as the rate of molinate degradation, the dissolved organic carbon (DOC) consumption and the accumulation of molinate degradation products were monitored along the culture growth. The effect of conditions such as temperature, pH, aeration rate, salinity, and presence of additional carbon and/or nitrogen sources, was tested independently. Degradation of molinate in river water was also evaluated. Culture DC was able to grow and to mineralize molinate at all the conditions assayed. Temperature was the factor with the strongest influence on bacterial growth and molinate mineralization. The lowest and the highest rate values of growth (0.010 and 0.110 h −1) and of molinate degradation (0.027 and 0.180 g molinate g −1 cell dry wt h −1) were obtained at 15 and 35 °C, respectively. In cultures with approximately 187 mg l −1 of molinate, 2-oxo-molinate was the major molinate degradation product accumulated in the medium, in concentrations below 0.133 mg l −1. Degradation of molinate was also evaluated in a continuous stirred tank reactor (CSTR). Operating the CSTR at a hydraulic retention time (HRT) of 83 h, fed with medium containing molinate concentrations ranging from 1 to 3 mM, culture DC degraded the herbicide with specific degradation rates similar to those obtained in the batch systems.

Change of Microbial Populations in a Suspended-sludge Reactor Performing Completely Autotrophic N-removal

In recent years, several novel processes for N-removal almost without consumption of organic carbon under oxygen-limited conditions have been discovered, which may be a promising option for low-cost N-removal from ammonia-rich wastewater. In this study, a laboratory scale suspended-sludge reactor was continuously operated under low dissolved oxygen concentration. High N-removal efficiency and subsequently degradation of the reactor were observed. Molecular analysis based on a partial-16S rRNA gene library showed that, at the stage of high efficiency, the biomass was composed of Planctomycete-like bacteria (up to 40%) and heterotrophic organisms (approximately 60%) as well as a few ammonia-oxidizing bacteria and at the stage of degradation, the autotrophic ammonia-oxidizing bacteria were dominant (up to 70%) and Planctomycete-like bacteria were no longer found in the sludge. Three specific Planctomycete-16S rRNA-targeted probes were used for fluorescence in situ hybridization (FISH). The results showed that at the high-efficiency stage, Planctomycete-like bacteria, present at approximately 20% of the total bacteria, lay frequently in the middle of flocs, while the heterotrophic bacteria occurred within the outer layers. This work revealed that the change of the microbial populations is the key reason for reactor deterioration, and the heterotrophic bacteria probably play an important role in sustaining the biomass structure of the sludge.

Differences in temperature, organic carbon and oxygen consumption among lowland streams

Summary1. Temperature, organic carbon and oxygen consumption were measured over a year at 13 sites in four lowlands streams within the same region in North Zealand, Denmark with the objectives of determining: (i) spatial and seasonal differences between open streams, forest streams and streams with or without lakes, (ii) factors influencing the temperature dependence of oxygen consumption rate, (iii) consequences of higher temperature and organic content in lake outlets on oxygen consumption rate, and (iv) possible consequences of forecasted global warming on degradation of organic matter.2. High concentrations of easily degradable dissolved (DOC) and particulate organic carbon (POC) were found in open streams downstream of plankton‐rich lakes, while high concentrations of recalcitrant DOC were found in a forest brook draining a forest swamp. Concentrations of predominantly recalcitrant POC and DOC were low in a groundwater‐fed forest spring. Overall, DOC concentration was two to 18 times higher than POC concentrations.3. Oxygen consumption rate at 20 °C was higher during summer than winter, higher in open than shaded streams and higher in lake outlets than inlets. Rate was closely related to concentrations of chlorophyll and POC but not to DOC. The ratio of oxygen consumption rate to total organic concentrations (DOC + POC), serving as a measure of organic degradability, was highest downstream of lakes, intermediate in open streams and lowest in forest streams.4. Temperature coefficients describing the exponential increase of oxygen consumption rate between 4 and 20 °C averaged 0.121 °C−1(Q10of 3.35) in 70 measurements and showed no significant variations between seasons and stream sites or correlations with ambient temperature and organic content.5. Oxygen consumption rate was enhanced downstream of lakes during summer because of higher temperature and, more significantly, greater concentrations of degradable organic carbon. Oxygen consumption rates were up to seven times higher in the stream with three impoundments than in a neighbouring unshaded stream and 21 times higher than in the groundwater‐fed forest spring.6. A regional climate model has calculated a dramatic 4–5 °C rise in air temperature over Denmark by 2070–2100. If this is realised, unshaded streams are estimated to become 2–3 °C warmer in summer and winter and 5–7 °C warmer in spring and, thereby, increase oxygen consumption rates at ambient temperature by 30–40% and 80–130%, respectively. Faster consumption of organic matter and dissolved oxygen downstream of point sources should increase the likelihood of oxygen stress of the stream biota and lead to the export of less organic matter but more mineralised nutrients to the coastal waters.