High Nitrogen Loading Research Articles

Niche differentiation in nitrogen metabolism among methanotrophs within an operational taxonomic unit.

BackgroundThe currently accepted thesis on nitrogenous fertilizer additions on methane oxidation activity assumes niche partitioning among methanotrophic species, with activity responses to changes in nitrogen content being dependent on the in situ methanotrophic community structure Unfortunately, widely applied tools for microbial community assessment only have a limited phylogenetic resolution mostly restricted to genus level diversity, and not to species level as often mistakenly assumed. As a consequence, intragenus or intraspecies metabolic versatility in nitrogen metabolism was never evaluated nor considered among methanotrophic bacteria as a source of differential responses of methane oxidation to nitrogen amendments.ResultsWe demonstrated that fourteen genotypically different Methylomonas strains, thus distinct below the level at which most techniques assign operational taxonomic units (OTU), show a versatile physiology in their nitrogen metabolism. Differential responses, even among strains with identical 16S rRNA or pmoA gene sequences, were observed for production of nitrite and nitrous oxide from nitrate or ammonium, nitrogen fixation and tolerance to high levels of ammonium, nitrate, and hydroxylamine. Overall, reduction of nitrate to nitrite, nitrogen fixation, higher tolerance to ammonium than nitrate and tolerance and assimilation of nitrite were general features.ConclusionsDifferential responses among closely related methanotrophic strains to overcome inhibition and toxicity from high nitrogen loads and assimilation of various nitrogen sources yield competitive fitness advantages to individual methane-oxidizing bacteria. Our observations proved that community structure at the deepest phylogenetic resolution potentially influences in situ functioning.

Achievement of high rate nitritation with aerobic granular sludge reactors enhanced by sludge recirculation events

A ratio control strategy has been used to demonstrate the feasibility of this automatic control procedure for the achievement of stable full and partial nitritation. The control strategy assured constant ratio between the dissolved oxygen (DO) and the total ammonia nitrogen (TAN) concentrations in the bulk liquid of aerobic granular sludge reactors operating in continuous mode. Three different set-ups with different reactor capacities were used (3, 110, and 150 L). High strength synthetic wastewaters and reject water were tested with similar performance. Achieved nitrogen loading rates ranged between 0.4 and 6.1 kgN·m−3·d−1, at temperatures between 20°C and 30°C. Granular sludge and nitritation were stable in the long term continuous operation of the reactors. Suitable stable effluent for Anammox has been obtained using the desired TAN setpoint (i.e. 50% of influent ammonium oxidation). An existing biofilm model developed incorporating the implemented control loops and validated in a previous publication was used to investigate the effects of the ammonium concentration of the influent and the biofilm density on the achievement of full nitritation. The model demonstrated how sludge recirculation events led to a stable and significant increase of the biomass concentration in the reactor, which in turn resulted in the achievement of high nitrogen loading rates, due to the action of the control strategy. The model predicted an enhancement of stable full nitritation at higher ammonium concentrations in the influent. Poor influence of the biofilm density in the achievement of full nitritation was predicted with the model.

Comparative performance of air-lift partial nitritation processes with attached growth and suspended growth without biomass retention

Partial nitritation is an essential first step in anaerobic ammonium oxidation. This study compared the performance of air-lift partial nitritation reactors with attached growth (AG) and suspended growth (SG) without biomass retention using ammonium-rich recirculated liquor produced from the dewatering of anaerobically digested sludge. The steady-state results showed that the AG can effectively retain ammonium-oxidizing bacteria (AOB) with high activity and allow minimizing biomass discharge (∼10 mg volatile suspended solids/L) in the effluent. The nitrogen loading (based on the total reactor volume) satisfying the effluent characteristics could be suggested to be 0.42 g N/L/d for the SG, and 0.76 g N/L/d for the AG, respectively. Compared with the SG, the AG achieved a higher ammonium loading rate (∼1.8 times), maximal ammonium oxidation activity (48 mg N/L-h based on liquid-phase volume) under a short hydraulic retention time (HRT) and a long solids retention time (SRT>80 d). The overall performance confirmed that AG is a promising configuration for partial nitritation in terms of the process stability, maximization of the AOB activity and minimization of the effluent biomass under a short HRT and high nitrogen loading rate.

Synthesis of nitrogen-doped hollow carbon nanospheres for CO2capture

Here, we report the synthesis of nitrogen-doped hollow carbon nanospheres (N-HCSs) via a two-step Stöber method. The resultant N-HCSs possess a uniform size of ∼220 nm, a high nitrogen loading content of 14.8 wt% and a high surface area of 767 m(2) g(-1), as well as exhibit a considerable performance for CO2 capture with a capacity of 2.67 mmol g(-1) and a high selectivity in a mixture gas (N2 or O2).

Robust biological nitrogen removal by creating multiple tides in a single bed tidal flow constructed wetland

Achieving effective total nitrogen (TN) removal is one of the major challenges faced by constructed wetlands (CWs). To address this issue, multiple “tides” were proposed in a single stage tidal flow constructed wetland (TFCW). With this adoption, exceptional TN removal (85% on average) was achieved under a high nitrogen loading rate (NLR) of around 28gNm−2day−1, which makes the proposed system an adequate option to provide advanced wastewater treatment for peri-urban communities and rural area. It was revealed that the multiple “tides” not only promoted TN removal performance, but also brought more flexibility to TFCWs. Adsorption of NH4+–N onto the wetland medium (during contact period) and regeneration of the adsorption capacity via nitrification (during bed resting) were validated as the key processes for NH4+–N conversion in TFCWs. Moreover, simultaneous nitrification denitrification (SND) was found to be significant during the bed resting period. These findings will provide a new foundation for the design and modeling of nitrogen conversion and oxygen transfer in TFCWs.

Achieving high-rate autotrophic nitrogen removal via Canon process in a modified single bed tidal flow constructed wetland

This study attempts to explore the Complete Autotrophic Nitrogen removal Over Nitrite (Canon) process to enhance the nitrogen removal in constructed wetlands (CWs). To achieve a stable and high-rate nitrogen removal via Canon, a single stage tidal flow constructed wetland (TFCW) system was modified by adopting internal upflow recirculation, shorter unsaturated time, and creating a pre-saturated zone. It was found that reduction of recirculation reduced oxygen supply, which favored partial nitrification and anammox process but decreased the overall nitrogen conversion rate. On the contrary, increasing the recirculation cycles enhanced the overall ammonium oxidization, but partial nitrification and anammox process could no longer be maintained. The setup of a pre-saturated zone in CW was beneficial to maintaining the stability of the Canon route. The effect of inorganic carbon (IC) on Canon was tested and the results revealed that high inorganic carbon (IC) could promote both partial nitrification and anammox activities but had no substantial effect on nitrite oxidization, which provided a strong selective method to maintain the Canon pathway. By integrating the control of oxygen supply (internal recirculation and pre-saturated zone) and high influent IC concentration, this study finally achieved total inorganic nitrogen (TIN) removal of >80% under high nitrogen loading rate of 15gN/m2/d from long-term stored livestock wastewater, which was characterized as having extremely low BOD5/TN ratio of <0.2.

Estimation of nitrogen flow change in Beijing, China, for the years 1995, 2000, and 2004

Rapid economic growth in China has led to environmental pollution. Recycling nutrients is essential for sustainable agriculture, and it is necessary to estimate the amount of available organic resources in order to achieve this. Using nitrogen as a tracer, we estimated the organic resource flows in 1995, 2000, and 2004 in Beijing. The agricultural nitrogen flow was calculated from the fertilizer, agricultural product, and byproduct flows. The livestock nitrogen flow was calculated from the feed, excretion, and stock flows. The human nitrogen flow was calculated from the food intake, excretion, and food waste flows. The amounts of recyclable organic resources were estimated from these nitrogen flows. The Daxing, Fangshan, Miyun, Shunyi, and Tongzho areas had high nitrogen loads in 2004, as did the outer suburbs, but Beijing proper had an extremely low nitrogen flow and the inner suburbs had low nitrogen flows. The estimated amount of compost that could be produced from domestic organic waste across Beijing was equivalent to 88,100 t of nitrogen. The Beijing area contains 394,100 ha of farmland, so, if the compost was applied at an equivalent of 100 kg of nitrogen per hectare, the equivalent of 48,000 t of nitrogen would be surplus.

Biological nutrient removal by internal circulation upflow sludge blanket reactor after landfill leachate pretreatment

The removal of biological nutrient from mature landfill leachate with a high nitrogen load by an internal circulation upflow sludge blanket (ICUSB) reactor was studied. The reactor is a set of anaerobic-anoxic-aerobic (A2/O) bioreactors, developed on the basis of an expended granular sludge blanket (EGSB), granular sequencing batch reactor (GSBR) and intermittent cycle extended aeration system (ICEAS). Leachate was subjected to stripping by agitation process and poly ferric sulfate coagulation as a pretreatment process, in order to reduce both ammonia toxicity to microorganisms and the organic contents. The reactor was operated under three different operating systems, consisting of recycling sludge with air (A2/O), recycling sludge without air (low oxygen) and a combination of both (A2/O and low oxygen). The lowest effluent nutrient levels were realised by the combined system of A2/O and low oxygen, which resulted in effluent of chemical oxygen demand (COD), NH3-N and biological oxygen demand (BOD5) concentrations of 98.20, 13.50 and 22.50 mg/L. The optimal operating conditions for the efficient removal of biological nutrient using the ICUSB reactor were examined to evaluate the influence of the parameters on its performance. The results showed that average removal efficiencies of COD and NH3-N of 96.49% and 99.39%, respectively were achieved under the condition of a hydraulic retention time of 12 hr, including 4 hr of pumping air into the reactor, with dissolved oxygen at an rate of 4 mg/L and an upflow velocity 2 m/hr. These combined processes were successfully employed and effectively decreased pollutant loading.

Sequential batch reactor for dairy wastewater treatment: Parametric optimization; kinetics and waste sludge disposal

Dairy industry wastewater is characterized by high nitrogen load and chemical oxygen demand (COD). Present study deals with treatment of simulated dairy wastewater (SDW) in terms of COD and total Kjeldahl nitrogen (TKN) removal by aerobic sequential batch reactor (SBR). SBR was optimized for various operating parameters and four phase study was carried out by varying hydraulic retention time (HRT), filling time of SDW to the reactor, anoxic phase introduction after filling phase and react phase. Kinetic study has also been performed at various HRT. Optimum HRT (HRTopt) of 1d with volume exchange ratio of 0.5 was found to sufficient to treat SDW. In view of fixing the problem of disposal of wasted activated sludge (AS) during the SBR cycle, elemental and thermo-degradation analysis of sludge was performed to understand its thermal degradation characteristics and possibility to utilize wasted AS as fuel.

Purifying synthetic high-strength wastewater by microalgae chlorella vulgaris under various light emitting diode wavelengths and intensities

The high-strength wastewater is now well known as a threat to the natural water since it is highly possible to arouse water eutrophication or algal blooms. The effects of various light emitting diode wavelengths and intensities on the microalgae biological wastewater treatment system was studied in this research. The various nutrient removals and economic efficiencies represented similar variation trends, and these variations under both high C and N loading treatments were similar too. The order for microalgae C. vulgaris reproduction in terms of dry weight and nutrient removal efficiency both were red > white > yellow > blue, under high carbon and nitrogen loading treatments, indicating that the red light was the optimum light wavelength. Furthermore, considering the optimal light intensity in terms of nutrient removal efficiency was 2500 and 2000 μmol/m2•s, while in terms of economic efficiency was 1000, 1500 and 2000 μmol/m2•s. Therefore, the optimum light intensity was found to be 2000 μmol/m2•s. In addition, the optimal experimental illumination time was determined as 120 h. The Chlorella vulgaris microalgae biological wastewater treatment system utilized in this research was able to purify the high-strength carbon and nitrogen wastewater effectively under optimum light wavelength and intensity.

Relevance and Diversity of Nitrospira Populations in Biofilters of Brackish RAS

Lithoautotrophic nitrite-oxidizing bacterial populations from moving-bed biofilters of brackish recirculation aquaculture systems (RAS; shrimp and barramundi) were tested for their metabolic activity and phylogenetic diversity. Samples from the biofilters were labeled with 13C-bicarbonate and supplemented with nitrite at concentrations of 0.3, 3 and 10 mM, and incubated at 17 and 28°C, respectively. The biofilm material was analyzed by fatty acid methyl ester - stable isotope probing (FAME-SIP). High portions of up to 45% of Nitrospira-related labeled lipid markers were found confirming that Nitrospira is the major autotrophic nitrite oxidizer in these brackish systems with high nitrogen loads. Other nitrite-oxidizing bacteria such as Nitrobacter or Nitrotoga were functionally not relevant in the investigated biofilters. Nitrospira-related 16S rRNA gene sequences were obtained from the samples with 10 mM nitrite and analyzed by a cloning approach. Sequence studies revealed four different phylogenetic clusters within the marine sublineage IV of Nitrospira, though most sequences clustered with the type strain of Nitrospira marina and with a strain isolated from a marine RAS. Three lipids dominated the whole fatty acid profiles of nitrite-oxidizing marine and brackish enrichments of Nitrospira sublineage IV organisms. The membranes included two marker lipids (16∶1 cis7 and 16∶1 cis11) combined with the non-specific acid 16∶0 as major compounds and confirmed these marker lipids as characteristic for sublineage IV species. The predominant labeling of these characteristic fatty acids and the phylogenetic sequence analyses of the marine Nitrospira sublineage IV identified organisms of this sublineage as main autotrophic nitrite-oxidizers in the investigated brackish biofilter systems.

Nitrogen turnover during the spring outflows of the nitrate-rich Curonian and Szczecin lagoons using dual nitrate isotopes

Coastal zones that receive high nitrogen loads from rivers often suffer from intense eutrophication. This is the case in the Baltic Sea, where nutrient concentrations decrease rapidly offshore, but uptake and turnover processes in the highly eutrophic near-shore areas are not well understood. The Oder and Nemunas Rivers, the second and third largest nitrogen contributors (70 and 45ktNy−1), drain into the Szczecin and Curonian lagoons, respectively, and thus into the coastal waters of the Baltic. In this study, nitrate turnover processes in the coastal zones of the Baltic Sea were determined in March 2009 by measuring nutrient concentrations, nitrate uptake rates, and dual isotopes in nitrate (δ15N-NO3− and δ18O-NO3−) in the lagoon outflows. While mixing processes dominated in the outflow of the Curonian lagoon, a phytoplankton spring bloom largely accounted for the nitrogen processes in the outflow of the Szczecin lagoon. Here, nitrate assimilation in the surface waters was evidenced by a parallel enrichment of 15N and 18O. In the near-bottom waters of the Szczecin lagoon, a deviation from the 1:1 relationship between δ18O-NO3− and δ15N-NO3−, typical of denitrification, suggested the coupling of nitrification and denitrification, triggered by the presence of organic material from the spring bloom. The particulate material may be rapidly sequestered in the sandy sediments off the outflow and generate the isotope signal of nitrate. The highly enriched δ15N-NO3− and δ18O-NO3− values (up to 28‰) in the near-bottom layer implied that the impact of isotopic enrichment from sediment processes in the water column is higher in sandy than in muddy sediments.

Comparison of high pressure and ambient pressure aerobic granulation sequential batch reactor processes

Due to granule size, substrate and oxygen become limited in the core of granules leading to cell lysis at the core. Loss of granule stability is still a major barrier for practical application of AG. Compared to ambient pressure condition (AP), operation of AG under high pressure (HP) is a favorable condition for formation and stability of granules. Experimental results show that granulation was facilitated under HP condition. MLSS and size of granules under AP system are higher than those under HP system. However, SS of effluent in AP is higher than those in HP and is consisted mainly of flocculent sludge. Longer SRT and lower biomass yield are obtained in HP system, indicating that less sludge will be produced in HP system. HP system can operate at high nitrogen loading. Complete nitrification was observed earlier in HP, indicating that the growth of NOB was facilitated under high dissolved oxygen.

Quantifying cyanobacterial phycocyanin concentration in turbid productive waters: A quasi-analytical approach

In this research, we present a novel technique to monitor cyanobacterial bloom using remote sensing measurements. We have used a multi-band quasi analytical algorithm that determines phytoplankton absorption coefficients, aϕ(λ), from above surface remote sensing reflectance, Rrs(λ). In situ data including remote sensing reflectance, phytoplankton pigment concentration, and absorption coefficients of optically active constituents in the water were collected from highly turbid and productive aquaculture ponds. These shallow (<1.5m) ponds in northwestern Mississippi, USA, were used for channel catfish Ictalurus punctatus aquaculture and had high nitrogen and phosphorus loading rates from manufactured feeds added to ponds to promote rapid fish growth. These practices resulted in high phytoplankton biomass (chlorophyll-a concentrations=59.4–1376.6mgm−3) with communities dominated by filamentous, gas-vacuolate cyanobacteria. A novel technique was developed to further decompose the aϕ to obtain phycocyanin absorption coefficient, aPC, at 620nm, a primary peak of phycocyanin absorption spectrum. Validation of the model produced mean and median absolute relative errors of 36.2% and 22.0%. Overall, the model performance was higher in the higher range of PC concentration (>150μgl−1). Results demonstrate that the new approach will be suitable for quantifying phycocyanin concentration in cyanobacteria dominated turbid productive waters.

Physicochemical assessment of Unio crassus habitat quality in a small upland stream and implications for conservation

The abundance of Unio crassus (Philipsson 1788) has declined over the last decades. Despite the high conservation status of this species, knowledge on its ecological requirements is scarce. The objective of this study was to identify key habitat characteristics in areas with recent recruitment of U. crassus in a small upland stream. Furthermore, we investigated stretches where the species is presently absent. Sediment deposition, redox potential, flow velocity, water depth, nitrogen and phosphorus load were investigated. Fine sediment deposition was high with 19.4 kg m−2 month−1 at colonized and 13.3 kg m−2 month−1 at non-colonized stretches of the Sallingbach. At all study stretches, redox potentials in the interstitial zone varied around 300 mV which constitutes the boundary value between oxic and anoxic conditions. Results of chemical water analyses indicated high nitrogen loads. Nitrate nitrogen concentrations averaged between 4.1 and 6.5 mg NO3–N/l at all study stretches, significantly exceeding the currently proposed threshold value of 2.0 mg/l for functional U. crassus streams. The results in this study suggest that U. crassus is more tolerant to eutrophic habitat conditions than previously expected. Our findings show that currently considered physicochemical parameters and high fine sediment deposition cannot mechanistically explain the occurrence of U. crassus in the stream.

Application and kinetic evaluation of upflow anaerobic biofilm reactor for nitrogen removal from wastewater by Anammox process

The lab-scale upflow anaerobic biofilm reactor was successfully operated for the treatment of synthetic wastewater with high nitrogen load by Anammox (anaerobic ammonium oxidation) process. During the entire period of operation, the reactor temperature was kept at 35±1°C. The operational strategy consisted of both increasing the ammonium and nitrite concentrations from 60 to 700mgN/L and from 80 to 920 mgN/L, respectively and decreasing the hydraulic retention time from 24 to 6 h, at each step. The highest achieved removal efficiency of ammonium and nitrite were 91 and 93%, respectively. Consequently, due to their acceptable performance for nitrogen removal in previous researches, modified Stover-Kincannon and Grau second-order models were used in this study. According to the experiment results, the model validity testing showed that the Stover-Kincannon model was a little more appropriate for the description of nitrogen removal in the reactor, even though both models gave high correlation coefficients (R2=0.999).

Turbulence and nutrient interactions that control benthic algal production in an engineered cultivation raceway

Flow turbulence can be a controlling factor to the growth of benthic algae, but few studies have quantified this relationship in engineered cultivation systems. Experiments were performed to understand the limiting role of turbulence to algal productivity in an algal turf scrubber (ATS) for benthic algal cultivation. Volumetric flow rate and wave surge frequency were independently manipulated in an ATS operating over a range of nitrogen loading rates, and the effects on algal biomass productivity were measured through periodic sacrificial harvest. Productivity followed a saturation relationship versus nitrogen loading rate for the range of turbulence conditions. When flow rate was held constant, a maximum productivity of 26.8gdWm−2d−1 was observed at a wave surge frequency of 17min−1 at high nitrogen loading rates, with lower productivities at higher and lower frequencies. The productivity was similar (26.4gdWm−2d−1) when the volumetric flow rate was increased with surge frequency held constant. Productivity was influenced by wave surge power, itself strongly determined by wave amplitude as set by volumetric flow rate. These results contribute to the understanding of the limiting factor effects of flow turbulence on algal production that can inform the optimization of the benthic algal cultivation.

Partial nitrification and anammox process: A method for high strength optoelectronic industrial wastewater treatment

Completely autotrophic nitrogen removal over nitrite (CANON) process was employed in an 18 L sequencing batch reactor (SBR) for treatment of optoelectronic industrial wastewater containing high strength ammonium nitrogen (3712 ± 120 mg NH4+-N L−1). About 89% of total nitrogen and 98% of NH4+-N removal efficiencies were observed at the loading rate of 909 g N m−3 d−1 and the HRT of 4 d. A profound variation in the performance of CANON process was experienced at high DO exposure (above 1 mg L−1) and high nitrite concentration (above 100 mg L−1). Inhibition due to high DO exposure was found to be reversible phenomenon whereas the synergistic inhibition of nitrite, free ammonia and free nitrous acid was irreversible. The fluctuation of reactor temperature between 17 and 37 °C did not affect the performance of CANON system. The CANON process was stably controlled at high nitrogen loading rate for more than one month. The co-existence of aerobic and anaerobic ammonium oxidizing bacteria in the reactor was detected by The PCR analysis. About 5 fold increase in amount of anammox bacteria over a period of 258 days was confirmed from the results of qPCR on day 487.

N2O emissions from a one stage partial nitrification/anammox process in moving bed biofilm reactors

Nitrous oxide (N2O) emissions from wastewater treatment are getting increased attention because their global warming potential is around 300 times that of carbon dioxide. The aim of the study was to measure nitrous oxide emissions from one stage partial nitrification/anammox (Anaerobic Ammonium Oxidation) reactors, where nitrogen is removed in a biological way. The first part of the experimental study was focused on the measurements of nitrous oxide emissions from two pilot scale reactors in the long term; one reactor with intermittent aeration at 25 °C and the other reactor with continuous aeration at 22-23 °C. The second part of the experiment was done to evaluate the influence of different nitrogen loads and aeration strategies, described by the ratio between the non-aerated and aerated phase and the dissolved oxygen concentrations, on nitrous oxide emissions from the process. The study showed that 0.4-2% of the nitrogen load was converted into nitrous oxide from two reactors. With higher nitrogen load, the amount of nitrous oxide emission was also higher. A larger fraction of nitrous oxide was emitted to the gas phase while less was emitted with the liquid effluent. It was also found that nitrous oxide emissions were similar under intermittent and continuous aeration.

Effects of trout farms on stream macroinvertebrates: linking farm-scale disturbance to ecological impact

Trout farms are a significant component of the Australian aquaculture industry, but there have been no studies on the ecological impacts of Australian trout farms. I analysed biolog- ical monitoring data from 5 trout farms in the Goulburn Valley, Victoria, Australia. Using multi- variate ordination and a Bayesian hierarchical model, I compared macroinvertebrate assemblages from upstream of the farms to those downstream, and related upstreamdownstream differences in invertebrate assemblage condition to 5 farm-scale indices of disturbance. I found clear, but small, ecological impacts of individual farms (i.e. upstream to downstream differences in inverte- brates), with between-farm variation in impacts largely explained by the indices of disturbance. The greatest impacts were seen for farms with high production intensity that utilise a high propor- tion of stream discharge, export a high relative load of nitrogen to the stream and are in areas of good biological condition. Recent research has explored operational and engineering solutions that reduce the downstream ecological impacts of trout farms. Adoption of such practices may help such farms to minimise impacts on streams.