High Dissolved Oxygen Concentration Research Articles

Evaluation of granular sludge for secondary treatment of saline municipal sewage

This study examined the impact of chemical oxygen demand (COD) loading and dissolved oxygen (DO) concentration on the stability and performance of granular sludge treating high saline municipal sewage. Under high DO concentrations of 4.0–7.0 mg/L, and COD loading rates of 0.98 and 1.55 kg/m3/d, rapid settling granules were established within four weeks of start-up. Under the highest COD load, a reduction in DO lead to the rapid deterioration of the sludge volume index (SVI) and washout of granules due to prolific growth of the filament Thiothrix Type 021N. Conversely, when operated under a lower COD load, a reduction in DO concentration had no adverse impact on the stability of SVI and granules. A decrease in DO also improved nitrogen removal performance, where simultaneous removal of ammonium (98%), total nitrogen (86%) and BOD5 (98%) were achieved when median DO concentrations were between 1.0 and 1.5 mg/L. Phosphate removal was lower than expected, however the level of biological phosphate removal activity observed appeared sufficient to maintain granule stability, even under low DO concentrations. Nitrous oxide emissions were also characterised, which ranged between 2.3 and 6.8% of the total nitrogen load. Our results confirmed that granular sludge is a viable option for the treatment of saline sewage.

Predicting Total Nitrogen, Total Phosphorus, Total Organic Carbon, Dissolved Oxygen and Iron in Deep Waters of Swedish Lakes

In many lakes, the physical and chemical characteristics are monitored for surface waters but not for deep waters. Yet, deep waters may be important for understanding the dynamics of lake water chemistry variables over the year. In this study, multiple regression models have been created for five different variables, total phosphorus, total nitrogen, total organic carbon, dissolved oxygen (DO) and iron, in the deep water for 61 Swedish temperate or subarctic lakes. The investigated season was February to October, depending on the data availability. Regressions used the corresponding variables from the surface water as well as different morphometric parameters as independent variables. It was possible to construct meaningful models (r 2 > 0.65; p < 0.05) for most of the variables and months. However, it was not possible to attain this criterion for some months regarding the DO concentration. Surface water concentrations were in general most important for predicting corresponding deep water concentrations. An exception was that during summer, DO differed considerably between surface waters and deep waters and voluminous lakes had particularly high DO concentrations in deep waters. No cross-systems relationship could be found between deepwater hypoxia and total phosphorus in deep waters during summer when phosphorus diffusion from sediments is most likely. A mass-balance modelling example was applied to illustrate the use of the produced models. These findings may provide a better understanding of the dynamics of these five variables in temperate or subarctic lakes.

Effects of rainfall patterns on water quality in a stratified reservoir subject to eutrophication: Implications for management

The seasonal variation of hydrological conditions caused by shifting rainfall patterns observed in recent years has significant effects on water quality. High-volume inflows following heavy rainfall events that significantly disturb stratification lead to increased dissolved oxygen (DO) at the bottom of the reservoir, inhibiting the release of nutrients from sediments and causing a rapid reduction of algal biomass in the reservoir. However, the duration and extent of these effects depend not only on the frequency and intensity of heavy rainfall events but also on the period of thermal stratification in the reservoir. The effects of heavy rainfall events on water quality during three typical stratification periods of the reservoir were systematically investigated using extensive field data. The continuous heavy rainfall that occurred in September 2011 (stratification began to diminish) completely mixed the reservoir and produced a high concentration of DO along with a low phytoplankton concentration throughout the reservoir until stratification occurred the following year. Conversely, several days were required for anoxic conditions (in the hypolimnion) and cyanobacterial blooms to reappear after the storm runoff that occurred during the stable period of stratification (August 2012). In addition, the heavy rainfall that occurred in May 2013 accelerated the formation of an anoxic zone at the bottom of the reservoir and promoted cyanobacterial blooms due to the high nutrient input and the increased water temperature after the storm runoff ended. Water-lifting aerators (WLAs) were employed in the Shibianyu Reservoir to inhibit algal growth and to control the release of nutrients. Based on our field observations and theoretical analyses, optimized management strategies are recommended to improve water quality in the reservoir under different rainfall patterns at a reduced cost.

Blue blood on ice: modulated blood oxygen transport facilitates cold compensation and eurythermy in an Antarctic octopod.

IntroductionThe Antarctic Ocean hosts a rich and diverse fauna despite inhospitable temperatures close to freezing, which require specialist adaptations to sustain animal activity and various underlying body functions. While oxygen transport has been suggested to be key in setting thermal tolerance in warmer climates, this constraint is relaxed in Antarctic fishes and crustaceans, due to high levels of dissolved oxygen. Less is known about how other Antarctic ectotherms cope with temperatures near zero, particularly the more active invertebrates like the abundant octopods. A continued reliance on the highly specialised blood oxygen transport system of cephalopods may concur with functional constraints at cold temperatures. We therefore analysed the octopod’s central oxygen transport component, the blue blood pigment haemocyanin, to unravel strategies that sustain oxygen supply at cold temperatures.ResultsTo identify adaptive compensation of blood oxygen transport in octopods from different climatic regions, we compared haemocyanin oxygen binding properties, oxygen carrying capacities as well as haemolymph protein and ion composition between the Antarctic octopod Pareledone charcoti, the South-east Australian Octopus pallidus and the Mediterranean Eledone moschata. In the Antarctic Pareledone charcoti at 0°C, oxygen unloading by haemocyanin was poor but supported by high levels of dissolved oxygen. However, lower oxygen affinity and higher oxygen carrying capacity compared to warm water octopods, still enabled significant contribution of haemocyanin to oxygen transport at 0°C. At warmer temperatures, haemocyanin of Pareledone charcoti releases most of the bound oxygen, supporting oxygen supply at 10°C. In warm water octopods, increasing oxygen affinities reduce the ability to release oxygen from haemocyanin at colder temperatures. Though, unlike Eledone moschata, Octopus pallidus attenuated this increase below 15°C.ConclusionsAdjustments of haemocyanin physiological function and haemocyanin concentrations but also high dissolved oxygen concentrations support oxygen supply in the Antarctic octopus Pareledone charcoti at near freezing temperatures. Increased oxygen supply by haemocyanin at warmer temperatures supports extended warm tolerance and thus eurythermy of Pareledone charcoti. Limited haemocyanin function towards colder temperatures in Antarctic and warm water octopods highlights the general role of haemocyanin oxygen transport in constraining cold tolerance in octopods.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-015-0097-x) contains supplementary material, which is available to authorized users.

Effects of oxide on fatigue crack growth behaviour of type 347 stainless steel in PWR water conditions

AbstractThe fatigue crack growth behaviour of type 347 stainless steel in pressurized water reactor (PWR) conditions was investigated at two different temperatures, 25 and 316 °C. The fatigue crack growth rate was slightly increased at the elevated temperature in air. In the simulated PWR water environment, the fatigue crack growth rate was changed in a rather complicated manner with a change of the dissolved oxygen (DO) content. The DO content did not significantly change the fatigue crack growth rate at 25 °C. With the lower oxygen content of 5 ppb, which is the practical limit of deoxygenated water, the fatigue crack growth rate was similar at both 25 and 316 °C. The fatigue crack growth rate was significantly decreased at 316 °C with the higher oxygen level of 100 ppb. Under 316 °C water conditions, oxides were observed on the fatigue crack surface where the size of oxide particles was about 0.2 µm at 5 ppb and about 1 µm at 100 ppb. The thickness of the oxide layers also increased with the increase of DO. Moreover, the ΔK threshold (ΔKth) also increased as the DO increased from 5 to 100 ppb. The dissolved hydrogen levels did not affect the measured crack growth rate at the given test conditions. The decrease of the fatigue crack growth rate with higher DO content is attributed to a crack closure resulting from the formation of larger oxides near the crack tip at a rather fast loading frequency of 10 Hz that was used in this study.

Effect and behaviour of different substrates in relation to the formation of aerobic granular sludge.

When aerobic granular sludge is applied for industrial wastewater treatment, different soluble substrates can be present. For stable granular sludge formation on volatile fatty acids (e.g. acetate), production of storage polymers under anaerobic feeding conditions has been shown to be important. This prevents direct aerobic growth on readily available chemical oxygen demand (COD), which is thought to result in unstable granule formation. Here, we investigate the impact of acetate, methanol, butanol, propanol, propionaldehyde, and valeraldehyde on granular sludge formation at 35 °C. Methanogenic archaea, growing on methanol, were present in the aerobic granular sludge system. Methanol was completely converted to methane and carbon dioxide by the methanogenic archaeum Methanomethylovorans uponensis during the 1-h anaerobic feeding period, despite the relative high dissolved oxygen concentration (3.5 mg O2 L−1) during the subsequent 2-h aeration period. Propionaldehyde and valeraldehyde were fully disproportionated anaerobically into their corresponding carboxylic acids and alcohols. The organic acids produced were converted to storage polymers, while the alcohols (produced and from influent) were absorbed onto the granular sludge matrix and converted aerobically. Our observations show that easy biodegradable substrates not converted anaerobically into storage polymers could lead to unstable granular sludge formation. However, when the easy biodegradable COD is absorbed in the granules and/or when the substrate is converted by relatively slow growing bacteria in the aerobic period, stable granulation can occur.Electronic supplementary materialThe online version of this article (doi:10.1007/s00253-014-6358-3) contains supplementary material, which is available to authorized users.

Apparent redox potential discontinuity (aRPD) depth as a relative measure of sediment oxygen content and habitat quality

As hypoxic conditions spread in our oceans, indices that quickly and efficiently assess oxygen content in sediment pore water, and habitat quality are increasingly becoming desirable. Depth to the apparent redox potential discontinuity (aRPD) in sediment is one such index; however, the relationship between aRPD depth and oxygen content is still unclear. We quantified oxygen content in sediment pore water with a dissolved oxygen (DO) probe, utilizing luminescent technology, to determine how DO concentration varies with depth in the sediment, and with position relative to the aRPD (above versus below) on an intertidal mudflat in the Bay of Fundy, Canada. Based on generalized linear regression models, we found that depth in the sediment was a poor predictor of pore water DO concentration, while position in the sediment relative to the aRPD was a good predictor. Further, sediment above the aRPD had higher DO content than sediment below. We maintain that aRPD depth is a good measure of relative oxygen content in sediment pore water, as well as habitat quality. However, we recommend caution as the factors that influence aRPD depth are numerous and variable; therefore, the relationship between aRPD depth and DO content should be experimentally confirmed in any system of interest before aRPD depth is used as an indicator.

Changes in concentrations of oxygen, dissolved nitrogen, phosphate, and silicate in the southern Yellow Sea, 1980–2012: Sources and seaward gradients

To investigate the influence of nutrients on the occurrence of the world's largest trans-regional green tide bloom along the coast of the southern Yellow Sea, spatial and temporal variation in dissolved inorganic nutrients, dissolved oxygen and the dissolved inorganic nitrogen/phosphorus (N/P ratio) in the southern Yellow Sea from the 1980s to 2012 were analyzed on the basis of our field data and historical data. The transport and concentration of nutrients and oxygen may be significantly affected by the complex hydrographic conditions that were found in the southern Yellow Sea year-round. The input from diverse nutrient sources, especially from the Yangtze river plume, the rising nutrient loading from rivers and mariculture along the Subei coast, could contribute to sustaining green algal blooms. The highest chlorophyll-a concentration appeared in 2012 of the study area. The horizontal distribution of nitrate, phosphate and silicate generally decreased from the nearshore to offshore waters from the 1980s to the present. A zone of high nutrient concentrations was generally found in the southwestern southern Yellow Sea (121–123°E, 32–33°N) over the past three decades, which may be primarily induced by the input of the Yangtze river plume into this area. The lowest nutrient concentrations were found in the mid-north of the southern Yellow Sea (122–124°E, 34–36°N). A zone of high DO concentrations was identified in the northeastern region of the study area (122–123.5°E, 35–36°N). Though ammonium values fluctuated during 1984–2012, nitrate and DIN concentrations increased across the 30 years of sampling, implying the intense influence of terrestrial discharge to the southern Yellow Sea. And the high nitrogen levels may be one of the most important contributors to green algal blooms in this area. Phosphate concentrations fluctuated from the 1980s to 2005 and have since decreased. A large upward spike in the N/P ratio was apparent in 2008 and since, and the DO concentration decreased sharply in the same year. Concentrations of dissolved inorganic nutrients and oxygen were generally high in winter, lower in summer.

Mangrove shrimp farm mapping and productivity on the Brazilian Amazon coast: Environmental and economic reasons for coastal conservation

The present study evaluates the role of marine aquaculture in the conversion of mangrove forests into shrimp (Litopenaeus vannamei, Boone, 1931) farms using remote sensing and geographic information system techniques and analyzes the productivity of the installed farms in the mangroves and adjacent coastal plateau. The extension of the shrimp ponds was quantified using satellite image analysis, and the water quality of the shrimp farms was analyzed based on measurements of dissolved oxygen concentration, temperature, pH, and salinity. The productivity of the farms was measured using biometric data. The data were analyzed using ANOVA with Tukey's post-test. The results indicated that shrimp farms cover an area of ∼0.8 km2 (approximately 0.4% of Brazilian ponds), of which 29.4% are located within areas of mangroves, and 70.6% are located in the coastal plateau. Saltwater aquaculture contributed to the conversion of 0.53 km2 of the mangroves into rearing ponds, which represents only 0.007% of the total area of the Amazonian mangroves. The installations in the mangrove presented significantly higher pH, temperature, transparency, and salinity compared with the ponds installed in the coastal plateau, although coastal plateau ponds had higher dissolved oxygen concentrations. Based on these differences, the mean sizes of the shrimp raised in the mangrove and coastal plateau ponds were 5.7 g and 4.3 g, respectively. However, the estimated value of one hectare of mangrove is much higher than its potential value in the production of shrimp. The considerable value of the ecosystem services provided by the mangroves indicates that the production of shrimp in the coastal plateau is relatively less damaging in ecological and economic terms. Thus, we can consider that the production of shrimp in the coastal plateau instead of in mangrove areas is less damaging to the long-term conservation of mangrove forests, which follows the management best practices established by international organizations. The coastal zone is considered a common resource that belongs to all citizens in Iberoamerican countries, and it is defined as a zone of non-building. Therefore, we conclude that mangroves are more valuable intact than converted into aquaculture ponds. Hence, aquaculture activities in the Amazon coastal plain are not sustainable from environmental and socioeconomic perspectives.

Occurrences of growth related target dissolved oxygen and ammonia in different catfish pond production systems in southeast Arkansas

Maintaining optimum water quality is vital for catfish pond production. Water quality performance was compared among traditional earthen ponds (TP), intensively aerated ponds (IP), and split-ponds (SP), from May to October, 2012, in southeast Arkansas. Overall mean DO concentrations were above the target DO level (3.0mg/L) in all ponds without system difference. Total ammonia nitrogen (TAN) in the IP system always had higher values and the overall mean (4.2mg/L) was higher than other systems (<1.0mg/L). The current study found similar DO performance among the three production systems, with a less than significant increasing occurrences of growth related target DO level from the IP to the SP, and then to the TP systems. The IP system had a less than significant higher percentage of TAN events above the target level (70% events>1.0mg/L) and a significant higher percentage of NH3 events above the target level (47% events>0.6mg/L) than the other two systems. But the high DO concentrations may have reduced the ammonia stress on fish growth in the IP system. Catfish farmers may consider adopting the two new production systems, especially the SP system, on their farms since the overall water quality performance is comparable to and even better than the traditional TP system, plus with higher feed inputs that rendered higher production from preliminary analysis in the new systems. More comprehensive production and cost analysis need to be conducted before the large scale full adoption.

Nitrate Removal from Domestic Wastewater by Using Denitrification Limestone Filter

Nitrogen is a naturally occurring element that is essential for growth and reproduction in both plants and animals. Excessive concentrations in the water body can cause excessive growth of algae and other plants, leading to accelerate eutrophication of lakes, and occasional depletion of dissolved oxygen. To remove nitrogen conventionally from domestic wastewater requires a high cost technology due to consumption of chemicals, high operational and maintenance cost. Therefore, an alternative low cost treatment technology particularly for nutrient removal including nitrogen removal system has been developed to improve the final effluent quality that is an aerated rock filter system. However, in the previous works in the UK the system was outperformed in removing ammonia nitrogen with limited nitrate removal. Hence, the present study was carried out to investigate the removal of nitrate from domestic wastewater through denitrification process using a lab-scale limestone filter. Domestic wastewater sample used in this study was collected from Taman Bukit Perdana Wastewater Treatment Plant (WWTP), Batu Pahat, Johor owned by IWK. The treatments were run in lab-scale limestone denitrification filter for 10 weeks. Effluent from nitrification filter was passing through the limestone denitrification filter as influent for further treatment. The in fluent and effluent of the filter system have been sampled and analyzed on biweekly basis for selected parameters including pH, alkalinity, temperature, dissolved oxygen, nitrate and ammonia nitrogen to monitor the effectiveness of the filter. Results from this study show that denitrification process has took place even the percentages of nitrate removal were considerably low but it seems promising with some modification of designing the the limestone filter to enhance denitrification process. The highest removal rate was 17.66%. Low removal of nitrate was inhibited within the filter system might be due to the high DO concentration as it was found that the range of DO was 4.75-7.78 mg/L. To permit the denitrification process to take place within the filter system, it is required an anoxic condition in the presence of nitrate with minimum DO concentration. Consequently, some modifications to the filter design will be considered in the future research in order to enhance the removal of nitrate through denitrification process.

Optimization of operation conditions for preventing sludge bulking and enhancing the stability of aerobic granular sludge in sequencing batch reactors.

Sludge bulking caused by loss of stability is a major problem in aerobic granular sludge systems. This study investigated the feasibility of preventing sludge bulking and enhancing the stability of aerobic granular sludge in a sequencing batch reactor by optimizing operation conditions. Five operation parameters have been studied with the aim to understand their impact on sludge bulking. Increasing dissolved oxygen (DO) by raising aeration rates contributed to granule stability due to the competition advantage of non-filamentous bacteria and permeation of oxygen at high DO concentration. The ratio of polysaccharides to proteins was observed to increase as the hydraulic shear force increased. When provided with high/low organic loading rate (OLR) alternately, large and fluffy granules disintegrated, while denser round-shape granules formed. An increase of biomass concentration followed a decrease at the beginning, and stability of granules was improved. This indicated that aerobic granular sludge had the resistance of OLR. Synthetic wastewater combined highly and slowly biodegradable substrates, creating a high gradient, which inhibited the growth of filamentous bacteria and prevented granular sludge bulking. A lower chemical oxygen demand/N favored the hydrophobicity of granular sludge, which promoted with granule stability because of the lower diffusion rate of ammonia. The influence of temperature indicated a relatively low temperature was more suitable.

Feasibility of electrokinetic oxygen supply for soil bioremediation purposes

This paper studies the possibility of providing oxygen to a soil by an electrokinetic technique, so that the method could be used in future aerobic polluted soil bioremediation treatments. The oxygen was generated from the anodic reaction of water electrolysis and transported to the soil in a laboratory-scale electrokinetic cell. Two variables were tested: the soil texture and the voltage gradient. The technique was tested in two artificial soils (clay and sand) and later in a real silty soil, and three voltage gradients were used: 0.0 (control), 0.5, and 1.0Vcm−1. It was observed that these two variables strongly influenced the results. Oxygen transport into the soil was only available in the silty and sandy soils by oxygen diffusion, obtaining high dissolved oxygen concentrations, between 4 and 9mgL−1, useful for possible aerobic biodegradation processes, while transport was not possible in fine-grained soils such as clay. Electro-osmotic flow did not contribute to the transport of oxygen, and an increase in voltage gradients produced higher oxygen transfer rates. However, only a minimum fraction of the electrolytically generated oxygen was efficiently used, and the maximum oxygen transport rate observed, approximately 1.4mgO2L−1d−1, was rather low, so this technique could be only tested in slow in-situ biostimulation processes for organics removal from polluted soils.

Effect of dissolved oxygen concentration on the bioflocculation process in high loaded MBRs

High-loaded membrane bioreactors (HL-MBRs), i.e. MBRs which are operated at extremely short sludge and hydraulic retention times, can be applied to flocculate and concentrate sewage organic matter. The concentrated organics can be used for energy recovery, or for the production of more valuable organic chemicals. Little is known about the effect of the dissolved oxygen concentration (DO) on this bioflocculation process. To examine this effect, two HL-MBRs were operated, respectively at a low (1 mg L−1) and a higher (4 mg L−1) DO. The higher DO resulted in a better flocculation efficiency, i.e. 92% of the colloidal COD in the sewage flocculated compared to 69% at the lower DO. The difference was attributed to a higher microbial production of extracellular polymeric substances at a DO of 4 mg L−1 and to more multivalent cations (calcium, iron and aluminium) being distributed to the floc matrix. In addition, the HL-MBR that was operated at a DO of 4 mg L−1 gave a bigger mean floc size, a lower supernatant turbidity, better settleability and better membrane filterability than the HL-MBR that was operated at a DO of 1 mg L−1.

The continuum heterogeneous biofilm model with multiple limiting substrate Monod kinetics.

We describe a novel procedure to estimate the net growth rate of biofilms on multiple substrates. The approach is based on diffusion-reaction mass balances for chemical species in a continuum biofilm model with reaction kinetics corresponding to a Double-Monod expression. This analytical model considers a heterogeneous biofilm with variable distributions of biofilm density, activity, and effective diffusivity as a function of depth. We present the procedure to estimate the effectiveness factor analytically and compare the outcome with values obtained by the application of a rigorous numerical computational method using several theoretical examples and a test case. A comparison of the profiles of the effectiveness factor as a function of the Thiele modulus, φ, revealed that the activity of a homogeneous biofilm could be as much as 42% higher than that of a heterogeneous biofilm, under the given conditions. The maximum relative error between numerical and estimated effectiveness factor was 2.03% at φ near 0.7 (corresponding to a normalized Thiele modulus φ* = 1). For φ < 0.3 or φ > 1.4, the relative error was less than 0.5%. A biofilm containing aerobic ammonium oxidizers was chosen as a test case to illustrate the model's capability. We assumed a continuum heterogeneous biofilm model where the effective diffusivities of oxygen and ammonium change with biofilm position. Calculations were performed for two scenarios; Case I had low dissolved oxygen (DO) concentrations and Case II had high DO concentrations, with a concentration at the biofilm-fluid interface of 10 g O2 /m(3) . For Case II, ammonium was the limiting substrate for a biofilm surface concentration, CNs , ≤13.84 g of N/m(3) . At these concentrations ammonium was limiting inside the biofilm, and oxygen was fully penetrating. Conversely, for CNs > 13.84 g of N/m(3) , oxygen became the limiting substrate inside the biofilm and ammonium was fully penetrating. Finally, a generalized procedure to estimate the effectiveness factor for a system with multiple (n > 2) limiting substrates is given.

A study on pond purification capacity evaluation using micro bubble clarifier

This study intended to evaluate the pond purification capacity using micro bubble clarifier. Also, in order to confirm the optimal pressure condition, analysis was performed for each pressure level at 1–4 kgf/cm2. It would be the most proper to operate at 3 kgf/cm2 and carry out speculation experiments. Pilot plant experiments were conducted in a water tank of approximately 8 m3. Raw water was obtained at the ponds of S University and a Golf course in full scale with volumes of 1,800 and 1,500 m3, respectively. Pilot plant results showed that the maximum saturated DO concentration rose up to 40 mg/L at the Pilot plant; and removal efficiencies of CODCr, BOD5, T-N, T-P, SS and Chl-a were 46.6, 31.2, 34.3, 69.2, 82.8 and 69.1%, respectively. Then, a full-scale experiment was also carried out for the comparison with control site. According to the analysis of results, considerable treatment efficiencies were obtained for CODCr, BOD5, T-N, T-P, SS and Chl-a with a high DO concentration because of the micro bubble. Water purification with a micro bubble clarifier is an environment-friendly purification method that can increase the natural purification capacity of natural water systems without the use of treatment facilities and chemicals for removing pollutants.

Effect of heterotrophic activities on nitrous oxide emission during nitrification under different aeration rates

Nitrous oxide (N2O), a greenhouse gas, can be released from both nitrification and denitrification during wastewater treatment. In this study, N2O emission under three aerobic conditions (aeration rates of 100, 250, and 500 ml/min, respectively) were examined, one with only endogenous heterotrophic activities, one with heterotrophic activities using internal stored organic carbon (polyhydroxybutyrate, PHB), and the other with heterotrophic activities using external organic carbon (acetate). Under the condition with PHB as the organic carbon, the released N2O-N to the produced oxidized nitrogen (NOx-N) was 10.0% at 100 ml/min, 3.6% at 250 ml/min, and 0.6% at 500 ml/min. Under the condition with acetate as the organic carbon, the released N2O-N to the produced NOx-N was 14.5% at 100 ml/min, 4.1% at 250 ml/min, and 0.7% at 500 ml/min. Under the condition without organic carbon, the released N2O-N to the produced NOx-N was 0.18% at 100 ml/min, 0.20% at 250 ml/min, and 0.41% at 500 ml/min. These results showed that (i) heterotrophic activities affected N2O emission during nitrification significantly; (ii) there was no significant difference in N2O emission during nitrification affected by heterotrophic activities using internal or external organic carbon; and (iii) a high aeration rate with a high dissolved oxygen concentration reduced N2O emission significantly under aerobic conditions.

Water Quality of a Central Himalayan Lake, Lake Sattal, Uttarakhand

The present research was carried out in Lake Sattal, Central Himalaya, from 2011 to 2012 with the objectives to find out the changes in water quality of the lake in last 30 years and to determine the trophic status of the lake in order to decide the usefulness of the lake for human consumption and fish production. Lake Sattal is a warm monomictic water body with high DO concentration. About three decades ago, it was in oligotrophic state. Sixty times increase in the concentration of phosphorous as compared to previous study has been found. The increased concentration of phosphorous and nitrogen in water signify that the lake has become eutrophic. Occasional anoxia at mud-water interface was noticed during the investigation period which strongly suggests that the process of eutrophication has recently started. These could be attributed to changes in the land use patterns, extensive land clearance, agriculture and suburban development and other biotic activities in the catchment. At present, the lake can be exploited for fish production by artificial culture as the quality of water is suitable. The data on various parameters of water quality studied in the present investigation are also under the desirable limit for the human consumption after proper treatment.

Microbial community functional structure in response to micro-aerobic conditions in sulfate-reducing sulfur-producing bioreactor

Limited oxygen supply to anaerobic wastewater treatment systems had been demonstrated as an effective strategy to improve elemental sulfur (S0) recovery, coupling sulfate reduction and sulfide oxidation. However, little is known about the impact of dissolved oxygen (DO) on the microbial functional structures in these systems. We used a high throughput tool (GeoChip) to evaluate the microbial community structures in a biological desulfurization reactor under micro-aerobic conditions (DO: 0.02–0.33 mg/L). The results indicated that the microbial community functional compositions and structures were dramatically altered with elevated DO levels. The abundances of dsrA/B genes involved in sulfate reduction processes significantly decreased (p < 0.05, LSD test) at relatively high DO concentration (DO: 0.33 mg/L). The abundances of sox and fccA/B genes involved in sulfur/sulfide oxidation processes significantly increased (p < 0.05, LSD test) in low DO concentration conditions (DO: 0.09 mg/L) and then gradually decreased with continuously elevated DO levels. Their abundances coincided with the change of sulfate removal efficiencies and elemental sulfur (S0) conversion efficiencies in the bioreactor. In addition, the abundance of carbon degradation genes increased with the raising of DO levels, showing that the heterotrophic microorganisms (e.g., fermentative microorganisms) were thriving under micro-aerobic condition. This study provides new insights into the impacts of micro-aerobic conditions on the microbial functional structure of sulfatereducing sulfur-producing bioreactors, and revealed the potential linkage between functional microbial communities and reactor performance.

Aquatic faunal responses to an induced regime shift in the phosphorus‐impacted Everglades

Summary Wetland eutrophication increases the susceptibility of native communities to invasion by opportunistic plant species, which then commonly form monotypic stands. Wetland aquatic fauna are negatively affected by associated changes of eutrophication in the physiochemical environment, habitat structural complexity and ecological interactions. In addition to reducing external nutrient loads, it is predicted that efforts that reduce the resilience of the altered ecosystem are required to accelerate ecosystem recovery. We assessed small fish and decapod crustacean responses to a 3‐year ecosystem scale experiment that tested the effectiveness of chemical treatment and controlled burning as a management strategy to accelerate the recovery of eutrophic Everglades marsh. The management strategy resulted in the removal, on average, of 91% and 81% of the emergent macrophyte cover in two regions differing in enrichment effects. The resulting open‐water habitats were characterised by higher dissolved oxygen concentrations, greater periphyton and submersed aquatic vegetation and increased structural complexity. The average combined density and biomass of small fish and decapod crustaceans did not differ significantly between dense emergent vegetation and created openings but regional and water year differences occurred. More importantly, community composition did differ between treatments, with the crayfish Procambarus fallax dominating in dense vegetation and small fish Gambusia holbrooki, Jordanella floridae and Poecilia latipinna and grass shrimp Palaemonetes paludosus dominating in open water. We compared the whole body carbon (C), nitrogen (N) and phosphorus (P) contents (%) and C:N:P stoichiometry among small fish and decapod crustaceans. Fish had greater whole body C and P contents (low C:P) compared with the two crustaceans. While the management action did not alter the quantity (mg carbon m−2) or energy (kcal m−2) of fauna, the resultant shift in composition was coincident with an increase in the nutrient quality (mg P m−2 and low C:P) of fauna. Faunal community composition of the created open‐water habitats in the eutrophic Everglades was similar to the oligotrophic Everglades; however, density and biomass were significantly lower for the oligotrophic region. Moreover, intraspecific comparisons showed that small fish and decapod crustaceans from the oligotrophic region were smaller and had lower whole body phosphorus contents than organisms from eutrophic regions. This suggests that phosphorus limitation in the Everglades extends beyond autotrophs to include consumers. The high density of emergent macrophytes typically formed in eutrophic wetlands creates a physical barrier to predators, limiting the trophic transfer of energy. The combination of burning and chemical treatment not only maintained the abundance and biomass of aquatic fauna, but produced a compositional shift towards higher quality prey for wading birds and predatory fishes. We recognise that the contrasting nature between the created openings in the eutrophic and oligotrophic Everglades highlights major structural and functional differences in natural sloughs versus enriched created ‘sloughs’, but we suggest that active management efforts to accelerate the recovery of P‐impacted regions could provide temporary benefits to Everglades wildlife by improving access to abundant, high‐quality prey.