Specific Nitrate Reduction Rate Research Articles

Effects of salinity on performance and microbial community structure of an anoxic-aerobic sequencing batch reactor

The effects of salinity on the performance and microbial community structure of activated sludge were investigated in an anoxic-aerobic sequencing batch reactor (SBR). The removal efficiencies of chemical oxygen demand (COD) and -N decreased as the influent salinity increased from 0.5% to 6%. The specific oxygen utilization rate of activated sludge increased from 22.47 to 43.16 mg O2 g−1 mixed liquid suspended solids (MLSS) h−1 with the increase in salinity from 0.5% to 4% and subsequently decreased to 18.3 mg O2 g−1 MLSS h−1 at 6% salinity. The specific ammonium oxidation rate (SAOR) and specific nitrite oxidation rate (SNOR) decreased slowly at 0.5–1% salinity and then decreased rapidly with the increase in salinity from 1% to 6%. The SNOR diminished at a faster rate than the SAOR with the increase in salinity from 0.5% to 6%. The specific nitrate reduction rate (SNRR) decreased with the increase in salinity, whereas the SNRR was higher than the sum of SAOR and SNOR at 0.5–6% salinity. The denaturing gradient gel electrophoresis profiles revealed obvious changes in microbial community structure at different salinities. Some microbes were capable of tolerating up to 6% salinity in the SBR, such as Planomonospora sphaerica, Nitrosomonas sp. Is32, and Denitromonas sp. D2–1.

Effects of salinity on performance, extracellular polymeric substances and microbial community of an aerobic granular sequencing batch reactor

The effects of salinity on the performance, extracellular polymeric substances (EPS) and microbial community of granular sludge were evaluated in an aerobic granular sequencing batch reactor (GSBR). The chemical oxygen demand (COD) and NH4+–N removal efficiencies decreased from 92% and 93% to 25% and 21% at 0–8% salinity, respectively. The specific ammonium oxidation rate (SAOR), specific nitrite oxidation rate (SNOR), and specific nitrate reduction rate (SNRR) decreased from 4.6, 5.6 and 43.0mgNg−1MLSSh−1 to 0.5, 0.4 and 9mgNg−1MLSSh−1 at 0–8% salinity, respectively. The specific oxygen utilization rate (SOUR) of granular sludge increased from 30 to 42mgO2g−1MLSSh−1 at 0–3% salinity and subsequently decreased to 11mgO2g−1MLSSh−1 at 8% salinity. The protein (PN) and polysaccharide (PS) contents in loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) increased at 0–8% salinity. The relative hydrophobicity (RH) of granular sludge illustrated good positive linear correlations with the PN/PS ratios in TB-EPS and LB-EPS. The chemical structural changes of LB-EPS and TB-EPS at different salinities were analyzed by three-dimensional excitation–emission matrix (3D-EEM) fluorescence spectroscopy. A good linear correlation was found between sludge volume index (SVI) and LB-EPS (or TB-EPS). The denaturing gradient gel electrophoresis (DGGE) profile revealed that Lactococcus sp. YM05004, Desulfopila sp. PR5_F09 and Demequina oxidasica were present at all the salinities, suggesting these bacteria were capable of tolerating 8% salinity. Some bacteria could utilize nitrate as an electron acceptor and was present at certain salinities, such as Arcobacter defluvii, Halomonas hydrothermalis and Paracoccus denitrificans.

Effects of hexavalent chromium on performance and microbial community of an aerobic granular sequencing batch reactor.

The performance and microbial community of an aerobic granular sequencing batch reactor (GSBR) were investigated at different hexavalent chromium (Cr(VI)) concentrations. The COD and NH4 (+)-N removal efficiencies decreased with the increase in Cr(VI) concentration from 0 to 30mg/L. The specific oxygen utilization rate (SOUR) decreased from 34.86 to 12.18mg/(g mixed liquor suspended sludge (MLSS)·h) with the increase in Cr(VI) concentration from 0 to 30mg/L. The specific ammonium oxidation rate (SAOR), specific nitrite oxidation rate (SNOR), and specific nitrate reduction rate (SNRR) decreased with the increase in Cr(VI) concentration, whereas the SNRR was always higher than the sum of SAOR and SNOR at 0-30mg/L Cr(VI). The scanning electron micrographs (SEM) showed some undefined particles on the surface of filamentous bacteria that might be the chelation of chromium and macromolecular organics at 30mg/L Cr(VI). The denaturing gradient gel electrophoresis (DGGE) profiles revealed that some microorganisms adapting to high Cr(VI) concentration gradually became the predominant bacteria, while others without Cr(VI)-tolerance capacity tended to deplete or weaken. Some bacteria could tolerate the toxicity of high Cr(VI) concentration in the aerobic GSBR, such as Propionibacteriaceae bacterium, Ochrobactrum anthropi, and Micropruina glycogenica.

Kinetics of autotrophic denitrification process and the impact of sulphur/limestone ratio on the process performance

Kinetics of sulphur–limestone autotrophic denitrification process in batch assays and the impact of sulphur/limestone ratio on the process performance in long-term operated packed-bed bioreactors were evaluated. The specific nitrate and nitrite reduction rates increased almost linearly with the increasing initial nitrate and nitrite concentrations, respectively. The process performance was evaluated in three parallel packed-bed bioreactors filled with different sulphur/limestone ratios (1:1, 2:1 and 3:1, v/v). Performances of the bioreactors were studied under varying nitrate loadings and hydraulic retention times (3–12 h). The maximum nitrate reduction rate of 0.66 g L−1 d−1 was observed at the loading rate of in the reactor with sulphur/limestone ratio of 3:1. Throughout the study, nitrite concentrations remained quite low (i.e. below 0.5 mg L−1 . The reactor performance increased in the order of sulphur/limestone ratio of 3:1, 2:1 and 1:1. Denaturing gradient gel electrophoresis analysis of 16S rRNA genes showed quite stable communities in the reactors with the presence of Methylo virgulaligni, Sulfurimonas autotrophica, Sulfurovum lithotrophicum, Thiobacillus aquaesulis and Sulfurimonas autotrophica related species.

Effect of hydraulic retention time on performance of an anoxic–aerobic sequencing batch reactor treating saline wastewater

The effects of hydraulic retention time on the performance and microbial community structure of an anoxic–aerobic sequencing batch reactor treating saline wastewater were investigated. The average removal efficiencies of chemical oxygen demand and ammonia nitrogen decreased from 90 and 85 % to 68 and 71 % with the decrease in hydraulic retention time from 17 to 9 h, respectively. No obvious accumulation of nitrate nitrogen and nitrite nitrogen in the effluent was found. The contents of polysaccharide and protein in extracellular polymeric substances increased with the decrease in hydraulic retention time. The polysaccharide/protein ratio decreased from 1.18 to 1.11 with the decrease in hydraulic retention time from 17 to 9 h. The increase in extracellular polymeric substances with the decrease in hydraulic retention time led to the increase in sludge volume index. The specific ammonium oxidation rate, specific nitrite oxidation rate, specific nitrate reduction rate, and specific oxygen uptake rate increased with the decrease in hydraulic retention time. The diversity indices of microbial community decreased from 2.69 to 2.39 with the decrease in hydraulic retention time from 17 to 9 h. The α-proteobacteria were the dominant groups under hydraulic retention time of 17, 14, 11, and 9 h, which constituted 46, 30, 40, and 40 % of the whole microbial community, respectively.

Removal of nitrates from processing wastewater by cryoconcentration combined with biological denitrification

In this study, the treatment of wastewater with a high nitrate content was investigated using the method of cryoconcentration on a pilot scale. The initial nitrate concentration in the treated wastewater was at 1,500 mg N/l. During 40 h of cryoconcentration of the wastewater, 176.6 kg of ice was produced, corresponding to a total process efficiency of 4.42 kg/h of ice. The crystallization temperature decreased from −0.5 to −9°C during the process. The final concentration of nitrates in the concentrated product was at 37 g N/l, and the conductivity was at 158 mS/cm. The conductivity of the water obtained by melting the ice ranged from 0.98 to 1.4 mS/cm. Concentrates with initial nitrate concentrations of 3, 6, and 9 g N/l were then subjected to microbial denitrification. The values of the specific nitrate reduction rates ranged from 43.1 to 49 mg N/gVSS h.

Reduced isotope fractionation by denitrification under conditions relevant to the ocean

Experiments with two well-studied denitrifiers and one recently isolated marine suboxic zone denitrifier show that the cellular-level denitrification N isotope effect (15ε) is typically lower than the canonical value of ∼25‰ under many conditions prevalent in the ocean. Across all three strains, 15ε is 10–15‰ at cellular nitrate reduction rates that are more representative of the environment than the very high rates under which we and previous investigators measure 15ε to be 20–30‰. A sharp decrease in 15ε is also observed in individual nitrate drawdown assays as the extracellular nitrate concentrations approach 2–35μM and nitrate uptake becomes the rate-limiting step. On an apparently strain-specific basis, lower values of 15ε are observed under diverse conditions common in the natural environment: less reduced carbon sources, small inputs of oxygen, nutrient availability, agitation, and age of starter culture (i.e., initiation of assays with cells that had recently depleted a large previous nitrate amendment or were more recently in the exponential growth (“bloom”) phase). A conserved oxygen-to-nitrogen isotope relationship across the experiments for all three denitrifiers (18ε/15ε=0.93±0.06 (1SD)) supports the interpretation that fractionation is imparted solely by the internal respiratory nitrate reductase, with the amplitude of 15ε varying with the proportional importance of cellular nitrate efflux relative to uptake. Aspects of the 15ε variation are unexpected; nevertheless, the occurrence of lower 15ε is robust. It is uncertain if our lower 15ε estimates apply to oceanic water column denitrification because field studies have generally yielded 15εwc between 20–30‰, more similar to previous culture estimates and our estimates at high cell specific nitrate reduction rates. If denitrification in the ocean’s major suboxic zones does have an 15ε of ∼10–15‰, it would remove an apparent imbalance between global ocean N inputs and outputs previously suggested by fixed N isotope budgeting.

Biological denitrification of brine: the effect of compatible solutes on enzyme activities and fatty acid degradation

The effect of the addition of compatible solutes (ectoine and trehalose) on the denitrification process of saline wastewater was studied. In saline wastewater, it was observed that the initial concentration of nitrates was 500 mg N l−1. A fatty substance isolated from oiled bleaching earth (waste of vegetable oil refining process) was used as a source of carbon. The consortium, which was responsible for the denitrification process originated from the wastewater of the vegetable oil industry. The consortium of microorganisms was identified by the use of restriction fragment length polymorphism of 16S rRNA gene amplicons and sequencing techniques. It was noted that ectoine affects significantly the activity of lipase and nitrate reductase, and resulted in faster denitrification compared to saline wastewater with the addition of trehalose or control saline wastewater (without compatible solutes). It was observed that relative enzyme activities of lipase and nitrate reductase increased by 32 and 35%, respectively, in the presence of 1 mM ectoine. This resulted in an increase in specific nitrate reduction rate in the presence of 1 mM ectoine to 5.7 mg N g−1 VSS h−1, which was higher than in the absence of ectoine (3.2 mg N g−1 VSS h−1). The addition of trehalose did not have an effect on nitrate removals. Moreover, it was found that trehalose was used up completely by bacteria as a source of carbon in the denitrification process. The fatty acids were biodegraded by 74% in the presence of 1 mM ectoine.

Biological Denitrification of High Nitrate Processing Wastewaters from Explosives Production Plant

Wastewater samples originating from an explosives production plant (3,000 mg N l−1 nitrate, 4.8 mg l−1 nitroglycerin, 1.9 mg l−1 nitroglycol and 1,200 mg l−1 chemical oxygen demand) were subjected to biological purification. An attempt to completely remove nitrate and to decrease the chemical oxygen demand was carried out under anaerobic conditions. A soil isolated microbial consortium capable of biodegrading various organic compounds and reduce nitrate to atmospheric nitrogen under anaerobic conditions was used. Complete removal of nitrates with simultaneous elimination of nitroglycerin and ethylene glycol dinitrate (nitroglycol) was achieved as a result of the conducted research. Specific nitrate reduction rate was estimated at 12.3 mg N g−1 VSS h−1. Toxicity of wastewater samples during the denitrification process was studied by measuring the activity of dehydrogenases in the activated sludge. Mutagenicity was determined by employing the Ames test. The maximum mutagenic activity did not exceed 0.5. The obtained results suggest that the studied wastewater samples did not exhibit mutagenic properties.

EFFECTS OF THE COD/NO3 −‐N RATIO AND PH ON THE ACCUMULATION OF DENITRIFICATION INTERMEDIATES WITH AVAILABLE PYRIDINE AS A SOLE ELECTRON DONOR AND CARBON SOURCE

Batch experiments were conducted to investigate the effects of COD/NO3 −‐N ratio and pH on the accumulation of the denitrification intermediates – nitrite and nitrous oxide – with pyridine as the sole electron donor and carbon source. Significant transient accumulation of nitrite was observed at COD/NO3 −‐N ratios in the range of 2–13 and pH in the range of 6.5–9.5. The optimal pH was 7.5 and the minimum COD/NO3 −‐N ratio was 4 for complete denitrification. The pH had a significant effect on denitrification. At a lower pH of 6.5, the reaction was severely inhibited whereas at a higher pH of 8.5 and 9.5, nitrate was completely reduced, but a high concentration of nitrite remained in the reactors while pyridine was almost completely degraded after one hour, even at the COD/NO3 −‐N ratio of 4. While the specific nitrate reduction rate and nitrite reduction rate in the absence of nitrate remained constant at different COD/NO3 −‐N ratios, they increased with the increase in pH. The nitrite reduction was inhibited in the presence of nitrate because of the faster rate of nitrate reduction over nitrite reduction. Nitrous oxide accumulation was also observed with a COD/NO3 −‐N ratio below 3 in the pH range of 7.5–8.5. At a COD/NO3 −‐N ratio of 4 and pH of 6, the production of nitrous oxide was much higher than that at pH 7 and 8.

Application of a membrane bioreactor to denitrification of brine

This study describes a hybrid method of the removal of nitrates from brine, combining biological denitrification with a membrane process. A bioreactor containing the halophilic bacteria H. denitrificans was used to denitrify brine. Brine was enriched with magnesium and potassium ions, microelements, and methanol as a source of carbon. The aim of the study is to determine the efficiency of nitrate removal from brines for various initial inoculum concentration and for different dilution ratios ( D). Fluorescence microscopy was used to detect changes in the counts of live and dead cells within the bioreactor and measure a progressive decrease in filtration efficiency caused by membrane fouling. The highest specific nitrate reduction rate was recorded for the dilution ratio D = 0.6, amounting to 1.30 g NO 3 − – N·g d.s.·day −1.

Biological denitrification of high strength nitrate waste using preadapted denitrifying sludge

Denitrification of synthetic high nitrate waste containing 9032 ppm NO(3)-N (40,000 ppm NO(3)) in a time period of only 6h has been achieved in our previous study using activated sludge. The activated sludge culture was acclimatized by a stepwise increase in the nitrate concentration of synthetic waste. In the present work, studies were carried out on the changing microbial population of the sludge and the physiology of nitrate metabolism during the various stages of adaptation process to high strength synthetic nitrate waste. During the course of adaptation, with an increase in the nitrate concentration, a sharp increase in the number of denitrifiers was found with an equally rapid decrease in the nitrifying community. Two key enzymes involved in the first two steps of the denitrification process were also studied during this period. The results of the study suggest that specific enzyme levels increase as the activated sludge adapts itself to higher nitrate concentrations. Biological denitrification of high nitrate waste is a slow process and to increase the rate of denitrification, parameters such as pH, temperature, C:N and biomass concentration of the process were optimized using orthogonal array method. Optimized conditions increased the specific nitrate reduction rate by 54% and specific nitrite reduction rate by 45%.

Stimulation of bacterial activity by the addition of different PACS

The effect of bacterial adhesion on powdered activated carbon on bacterial activity in non‐toxic wastewater was studied and the difference of powdered activated carbon species on the stimulation of bacterial activity was also evaluated using eight kinds of powdered activated carbon. Pure cultures of Escherichia coli K‐12, which can reduce NO3 ‐ to NO2 ‐ in anoxic conditions, were used. Specific nitrate reduction activity was used as an indicator of bacterial activity. The higher specific nitrate reduction rates were noted in cultures with powdered activated carbon than without powdered activated carbon or with Kaolin. The specific nitrate reduction rate with powdered activated carbon was up to about 1.4 times as high as those without powdered activated carbon. The stimulation of bacterial activity was induced by the adhesion of bacterial cells onto powdered activated carbon. There are powdered activated carbons that can stimulate bacterial activity, whereas not all the powdered activated carbon can stimulate bacterial activity. Surface characteristics like Brunauer‐Emmett‐Teller specific surface areas, total surface acidity, oxygen functional groups, total surface basicity, surface charge, pHpic, iodine number, concentrations of metals, electric resistance, free radical concentration and adsorption capacity of formate did not related with the stimulation of the bacterial activity.

Effect of dissolved oxygen and carbon-nitrogen loads on denitrification by an aerobic consortium.

Four samples of natural ecosystems and one sample from an activated sludge treatment plant were mixed together and progressively adapted to alternating aerobic/anoxic phases in the presence of nitrate in order to enrich the microflora in aerobic denitrifiers. Aerobic denitrifying performances of this mixed ecosystem at various dissolved oxygen concentrations and various carbon-nitrogen loads were evaluated and compared to those obtained with the aerobic denitrifier Microvirgula aerodenitrificans. The consortium and the pure strain exhibited an aerobic denitrifying activity at air saturation conditions (7 mg dissolved oxygen 1(-1)), i.e. there was co-respiration of the two electron acceptors with significant specific nitrate reduction rates. Dissolved oxygen concentrations had no influence on denitrifying performances above a defined threshold: 0.35 mg l(-1) for the consortium and 4.5 mg l(-1) for M. aerodenitrificans respectively. Under these thresholds, decreasing the dissolved oxygen concentrations enhanced the denitrifying activity of each culture. The higher the carbon and nitrogen loads, the higher the performance of the aerobic denitrifying ecosystem. However, for M. aerodenitrificans, the nitrate reduction percentage was affected more by variations in nitrogen load than in carbon load.

Halomonas campisalis sp.nov., a Denitrifying, Moderately Haloalkaliphilic Bacterium

The isolation and characterization of a denitrifying bacterium that is both moderately halophilic and alkaliphilic is described. The organism was isolated for use in the development of a bioprocess that could potentially reduce the costs of ion exchange resin regenerant disposal. The process of ion exchange, after resin regeneration, produces a briny, alkaline waste that is difficult and expensive to dispose. The biological removal of nitrate and subsequent reuse of these brines can potentially provide a cost-saving alternative to disposing of this waste product. To achieve our objective, a moderately halophilic, alkaliphilic bacterium was isolated from sediment samples taken from the salt plain of Alkali Lake in Washington State (USA). The haloalkaliphilic bacterium, designated strain 4A, is motile with rod-shaped cells that are 3 to 5 microm long and 1 microm wide. Electron acceptors used include oxygen, nitrate, and nitrite. In addition, it has similar specific nitrate reduction rates and biomass yields as non-halophilic denitrifying bacteria. It is capable of using a variety of electron donors. This organism can grow at NaCl concentrations ranging from 0.2 to 4.5 M with optimum growth occurring at 1.5 M and pH values ranging from 6 to 12 with 9.5 being the optimum pH. The temperature range for growth of strain 4A is 4-50 degrees C with optimal growth occurring at 30 degrees C. The G + C content is 66 mol%. Phylogenetic analyses based upon 16S rDNA gene sequence placed isolate 4A in the genus Halomonas. In addition, DNA-DNA hybridization experiments clearly indicate that it is a unique species. Phenotypic and phylogenetic studies indicate that isolate 4A represents a new species. We propose the name Halomonas campisalis for this species and strain 4A (ATCC 700597) as the type strain. Due to its denitrification ability, broad carbon utilization range and its high salinity and pH tolerance this organism, and similar ones, hold promise for the treatment of saline, alkaline waste.

Acetate Limitation and Nitrite Accumulation during Denitrification

Nitrite accumulated in denitrifying activated sludge mixed liquor when the carbon and electron source, acetate, was limited. If acetate was added to obtain a carbon-to-nitrogen (C:N) ratio in the range of 2:1 to 3:1, nitrate was completely consumed at the same rate with no nitrite accumulation, indicating that nitrate concentration controlled the respiration rate as long as sufficient substrate was present. However, when acetate was reduced to a C:N ratio of 1:1, while nitrate continued to be consumed, >50% of the initial nitrate-nitrogen accumulated as nitrite and 29% persisted as nitrite throughout an endogenous denitrification period of 8–9 h. While nitrite accumulated during acetate-limited denitrification, the specific nitrate reduction rate increased significantly compared with the rate when excess acetate was provided as follows: 0.034 mg-NO3-N/mg-mixed liquid volatile suspended solids/h versus 0.023 mg-NO3-N/mg-mixed liquid volatile suspended solids/h, respectively. This may be explained by nitrat...

Denitrification of high-nitrate, high-salinity wastewater

Denitrification of a wastewater containing 36,000 mg/L NO 3 − (8,200 mg/L NO 3–N) with ionic strength of 3.0 has been achieved using activated sludge in bench-scale sequencing batch reactors. An activated sludge culture was acclimated to denitrify the wastewater at pH 9, by step-wise increase in wastewater nitrate concentration from 2,700 mg/L NO 3–N to 5,400 mg/L NO 3–N and finally to 8,200 mg/L NO 3–N. Simultaneously, wastewater ionic strength was increased from 0.8 to 2.7 and to 3.0 (5, 16, and 18% total dissolved solids (TDSI). Although complete denitrification occurred, the maximum specific nitrate reduction rate decreased from 50 to 19 mg NO 3–N/g MLSS/h as wastewater nitrate and TDS concentration increased. Also, accumulation of nitrite increased and the maximum nitrite reduction rate decreased. A similar attempt to acclimate activated sludge to denitrify the high-TDS, high-nitrate wastewater at pH 7.5 was unsuccessful.