Specific Denitrification Rate Research Articles

The role of benthic foraminifera in the benthic nitrogen cycle of the Peruvian oxygen minimum zone

Abstract. The discovery that foraminifera are able to use nitrate instead of oxygen as an electron acceptor for respiration has challenged our understanding of nitrogen cycling in the ocean. It was thought before that only prokaryotes and some fungi are able to denitrify. Rate estimates of foraminiferal denitrification have been very sparse and limited to specific regions in the oceans, not comparing stations along a transect of a certain region. Here, we present estimates of benthic foraminiferal denitrification rates from six stations at intermediate water depths in and below the Peruvian oxygen minimum zone (OMZ). Foraminiferal denitrification rates were calculated from abundance and assemblage composition of the total living fauna in both surface and subsurface sediments, as well as from individual species specific denitrification rates. A comparison with total benthic denitrification rates as inferred by biogeochemical models revealed that benthic foraminifera probably account for the total denitrification in shelf sediments between 80 and 250 m water depth. The estimations also imply that foraminifera are still important denitrifiers in the centre of the OMZ around 320 m (29–50% of the benthic denitrification), but play only a minor role at the lower OMZ boundary and below the OMZ between 465 and 700 m (2–6% of total benthic denitrification). Furthermore, foraminiferal denitrification has been compared to the total benthic nitrate loss measured during benthic chamber experiments. The estimated foraminiferal denitrification rates contribute 2 to 46% to the total nitrate loss across a depth transect from 80 to 700 m, respectively. Flux rate estimates range from 0.01 to 1.3 mmol m−2 d−1. Furthermore we show that the amount of nitrate stored in living benthic foraminifera (3 to 3955 μmol L−1) can be higher by three orders of magnitude as compared to the ambient pore waters in near-surface sediments sustaining an important nitrate reservoir in Peruvian OMZ sediments. The substantial contribution of foraminiferal nitrate respiration to total benthic nitrate loss at the Peruvian margin, which is one of the main nitrate sink regions in the world ocean, underpins the importance of the previously underestimated role of benthic foraminifera in global biogeochemical cycles.

Determination of kinetic parameters in a pilot scale BNR system treating municipal wastewater

Kinetics for the biological processes of nitrification, denitrification and carbon oxidation were studied in the aerobic and anoxic phases of a pilot scale Biological Nutrient Removal (BNR) plant treating municipal wastewater. The configuration of the treating system is based on the combination of the UCT (University of Cape Town) design and the step feeding process in a cascade denitrification. In order to study the process kinetics and to obtain reliable values for the investigated kinetic parameters batch experiments were performed. For this purpose, continuous feeding of the treating system was interrupted for a given period of time and the pilot plant was turned into a batch mode of operation. Thereafter, addition of NO3 --N and NH4 +-N into the anoxic and aerobic compartments of the treating plant, respectively, followed, whereas adequate initial concentration of a carbon source (municipal wastewater or synthetic substrate) was ensured in the mixed liquor. Experimental data indicated that the examined biological processes followed saturation kinetics. The maximum specific denitrification rate, qDN,max , was found to obtain values, depending on the type of the carbon source, between 0,045 and 0,390 gNO3 --N/(gXHET·d), whereas the extremely low value of the half saturation constant for the denitrification process (Km,NO3-N << 1mgN/l) indicated its description by zero order kinetics. The maximum specific nitrification rate, qN,max, was determined to vary in a narrow frame, between 1,28 and 1,60 gNH4 +- N/(gXAO·d). The half saturation constant for the nitrification process, Km,NH4-N, was estimated graphically at 3,1 – 6,1 gNH4 +-N l-1, corresponding to 62 – 122 μgNH3-N l-1. These values are considered to be in good agreement with the literature. The determination of kinetic parameters can be considered as a useful tool for the process design, operation and improvement of wastewater treatment plants. Furthermore, the study of the biological process kinetics contributes to the better understanding and outline of the complicated biological processes that contemporarily take place within the various phases of BNR wastewater treatment plants.

Applicability of industrial wastewater as carbon source for denitrification of a sludge dewatering liquor

The applicability of four industrial waste streams from potato processing, canola processing and oil refining, biodiesel production (glycerol), and glycol as substitutes to methanol and ethanol in denitrification of anaerobically digested sludge dewatering liquor (centrate) was evaluated in bench-scale sequencing batch reactors. It was found that glycerol was the best substitute with the specific denitrification rate (SDNR) of 13 mg NO 3-N/(g VSS·h) followed by potato processing wastewater at 12 mg NO 3-N/(g VSS·h ). Both substrates produced faster SDNR than methanol's 10 mg NO 3-N/(g VSS·h ); however, they were inferior to ethanol's 17 mg NO 3-N/(g VSS·h ). Glycol had SDNR of 8 mg NO 3-N/(g VSS·h ) and demonstrated a very fast acclimation rate, i.e. the response in increased denitrification rate was visible in three days following glycol addition. Canola processing and oil refining wastewater was considered an inappropriate carbon source due to a low SDNR of 5 mg NO 3-N/(g VSS·h ) and apparent inhibitory effect on nitrification.

Effect of supplying a carbon extracting solution on denitrification in horizontal subsurface flow constructed wetlands

Denitrification strongly depends on the availability of carbon source in constructed wetlands (CWs). In this study, several relevant carbon source extracting solutions made from hydrolyzate of selected wetland litters were added to CWs for nitrogen removal enhancement. The feasibility of supplying a carbon extracting solution to improve potential denitrification rate in horizontal subsurface flow constructed wetland was deeply investigated. Combinations of different hydraulic retention time (HRT, especially for 2-day and 4-day) with different influent COD/N ratios were designed to prove the enhancement on denitrification by carbon source supplement. In addition, specific denitrification rate (SDNR) was calculated for the comparison of the nitrogen removal at different COD/N ratios. The sequential operation results on total nitrogen (TN) and nitrate (NO3−-N) removal efficiencies were obtained in CW system with an influent COD/N ratio of 4.0. The accumulation of nitrite (NO2−-N) was found to be closely related to the removal of NO3−-N. Meanwhile, no obvious accumulation of NO2−-N was found when the removal of NO3−-N was relatively high.

Enhanced denitrification with external carbon sources in a biological anoxic filter

Three parallel biological anoxic filters (BaFs) were operated to investigate the denitrification kinetics of methanol, brewery wastewater and bakery wastewater. The experiment was conducted within the temperature range of 15-20 °C, with an influent nitrate and carbon dosage of 30 mg/L and 150 mg COD/L (COD: chemical oxygen demand). The denitrification efficiencies of brewery wastewater, bakery wastewater and methanol were 84, 66 and 74%, specific denitrification rates were 1.44, 1.11 and 1.24 kg NO(3)-N/m(3) d, and total nitrogen (TN) removal rates were 74, 62 and 66%, respectively. The volatile attached solid (VAS) tests reveal that methanol has the minimum net biomass yield, so it needs the least carbon to nitrogen (expressed in COD to nitrate, C/N) ratio for complete denitrification. While the brewery wastewater and bakery wastewater need higher C/N ratio to remove all nitrate nitrogen, and they both may need pretreatment to remove phosphate when used as external carbon sources.

COD fractionation and denitrification potential of sonicated waste activated sludge liquids

This study characterized sonicated waste activated sludge (WAS) liquids as a possible carbon source for nitrogen removal. In this context, the effect of sonication density on chemical oxygen demand (COD) and nitrogen release was determined by particle size distribution (PSD) analysis and anoxic batch experiments. The increase in ultrasonic density from 0.8 W/mL to 1.6 W/mL had a slight impact on the soluble COD/total COD ratio. The high ultrasonic energy input increased the solubilization of nitrogenous organic substances and resulted in a low COD/TKN (total Kjeldahl nitrogen) ratio, which is not appropriate for nutrient removal systems. The change in ultrasonic power had a significant effect on COD fractionation of sonicated WAS liquid. The COD fraction at the size ranges higher than 1600 nm decreased from 44% to 3% as the energy input increased. The increase in specific energy raised the COD fraction, at the size ranges of<2 nm, from 11% to 23%.The PSD-based COD fractionation showed that increasing the sonication density markedly changed the size distribution. The anoxic batch tests indicated that the specific denitrification rate of sonicated WAS liquid was in the range of that reported for the slowly biodegradable fraction of the domestic wastewater and higher than those reported for agro-food wastewater.

Using porous ceramic media in the upflow packed-bed reactor (UPBR) system for nitrogen removal via autotrophic nitrification and denitrification

In this study, the feasibility of an innovative upflow packed-bed reactor (UPBR) system using porous sulfur and lime ceramic media (CERAMED-L and CERAMED-SL) to remove nitrogen for wastewater treatment was evaluated. The specific lime dissolution rates for CERAMEDs in the UPBRs show an inverse proportion to pH and resulted in 2.32 g as CaCO3 kg−1 CERAMED-L d−1 and 1.64 g as CaCO3 kg−1 CERAMED-SL d−1 at a pH 6.7. The calculated specific nitrification rate resulted 1.73–2.29 kg NH4 +-N m−3 CERAMED-L d−1, with a F/M ratio in the range 0.08–0.31 g NH4 +-N g−1 VS d−1. The alkalinity shortage in the feed solution seemed to be overcome by supplying specific alkalinity of 3.88 kg as CaCO3 m−3 CERAMED-L d−1 through the dissolution of lime from CERAMED-L. Autotrophic denitrification efficiencies were in the range of 83–96% during the test period, and the average specific denitrification rates of 0.97–1.92 kg NO3 −N m−3 CERAMED-SL d−1 and 0.19–0.36 g NO3 −-N g−1 VS d−1 were obtained.

Denitrification with corncob as carbon source and biofilm carriers

In this research the agricultural by-product corncob was investigated as a carbon source as well as a biofilm carrier to remove organic matter, expressed as chemical oxygen demand (COD) and nitrate nitrogen (nitrate-N), from wastewater in a batch laboratory reactor. The performance of a reactor with corncob as the carbon source and the biofilm carrier was compared with a control batch reactor with suspended plastic carriers and glucose as the sole carbon source. With 60 vol% of corncob carriers inside the reactor, a soluble COD/N ratio of 4.2 g COD g N(-1) was enough for total denitrification, nearly half of the control reactor (9.5 g COD g N(-1)), at 23 h reaction time. The specific denitrification rate decreased with increasing soluble COD consumption for both reactors. Nitrate and COD removal efficiencies decreased with shorter retention times, with accentuated effects in the reactor. This study suggested corncob as a feasible carbon source and that reaction time was a limiting factor with corncob used as the carbon source for denitrification.

Comparison of A&lt;sup&gt;2&lt;/sup&gt;/O and Membrane Bioreactor Processes for Municipal Wastewater Treatment: Nutrient Removal Performance and Sludge Characteristics

The performance of nitrogen and phosphorus removal was investigated in pilot-scale A2/O, A2/O-MBR and mA2/O-MBR processes for treating municipal wastewater. The results show that these processes had a similar COD and ammonia removal efficiency, but A2/O process had better denitrification efficiency than MBR processes. In order to explain the difference of nitrogen and phosphorus removal performance in the investigated processes, specific oxygen uptake rate (SOUR), specific denitrification rate (SDNR), anaerobic release rate and anoxic and aerobic uptake rate of the activated sludge taken from A2/O and mA2/O-MBR processes were compared. The results show that the activated sludge of mA2/O-MBR process had a higher nitrifying activity in aerobic tank than A2/O process, the denitrifying activity in anoxic tanks were roughly equal and A2/O process had a higher denitrifying phosphorus removal activity in anoxic tank than mA2/O-MBR process.

Advancing post-anoxic denitrification for biological nutrient removal

The objective of this research was to advance a fundamental understanding of a unique post-anoxic denitrification process for achieving biological nutrient removal (BNR), with an emphasis on elucidating the impacts of surface oxygen transfer (SOT), variable process loadings, and bioreactor operational conditions on nitrogen and phosphorus removal. Two sequencing batch reactors (SBRs) were operated in an anaerobic/aerobic/anoxic mode for over 250 days and fed real municipal wastewater. One SBR was operated with a headspace open to the atmosphere, while the other had a covered liquid surface to prevent surface oxygen transfer. Process performance was assessed for mixed volatile fatty acid (VFA) and acetate-dominated substrate, as well as daily/seasonal variance in influent phosphorus and ammonia loadings. Results demonstrated that post-anoxic BNR can achieve near-complete (>99%) inorganic nitrogen and phosphorus removal, with soluble effluent concentrations less than 1.0 mgN L −1 and 0.14 mgP L −1. Observed specific denitrification rates were in excess of typical endogenous values and exhibited a linear dependence on the glycogen concentration in the biomass. Preventing SOT improved nitrogen removal but had little impact on phosphorus removal under normal loading conditions. However, during periods of low influent ammonia, the covered reactor maintained phosphorus removal performance and showed a greater relative abundance of polyphosphate accumulating organisms (PAOs) as evidenced by quantitative real-time PCR (qPCR). While GAOs were detected in both reactors under all operational conditions, BNR performance was not adversely impacted. Finally, secondary phosphorus release during the post-anoxic period was minimal and only occurred if nitrate/nitrite were depleted post-anoxically.

하수 고도처리를 위한 유로변경형 MBR공정의 개발

This study was performed to investigate the characteristics of nutrient removal of municipal wastewater in membrane bioreactor system. Membrane bioreactor consists of four reactors such as two intermittently anaerobic tanks, the oxic tank and the sludge solubilizaion tank with an internal recycle. The hydraulic retention time (HRT) and flux were 6.5 hours and (LMH), respectively. The removal efficiency of , SS, TN and TP were 94.0%, 99.3%, 99.9%, 69.9%, and 66.9%, respectively. The estimated true biomass yield, specific denitrification rate (SDNR), specific nitrification rate (SNR), specific phosphorus release rate (SPRR) and specific phosphorus uptake rate (SPUR) were 0.34 kgVSS/kgBOD d, , , 16.0 mgP/gVSS d and 2.1 mgP/gVSS d, respectively. The contents of nitrogen and phosphorus of biomass were 8.9% and 3.5% on an average.

Innovative anaerobic upflow sludge blanket filtration combined bioreactor for nitrogen removal from municipal wastewater

In this research, a novel laboratory scale anaerobic/upflow sludge blanket filtration combined bioreactor was designed and operated to improve the efficiency of the upflow sludge blanket filtration process for the simultaneous removal of phosphorus and nitrogen from wastewater. The anaerobic/upflow sludge blanket filtration technique was developed by adding an anaerobic reactor to its influent and operated by varying the main process parameters in order to gain the optimum conditions. The results showed that biological removal efficiency of nitrogen and preservation of sludge blanket strongly depend on wastewater characteristics, hydraulic retention time, sludge age and process controlling parameters. The combined bioreactor performed a total nitrogen removal efficiency of 96.6 % with the sludge age of 25 days, total hydraulic retention time of 24 h and optimum chemical oxygen demand/nitrogen/phosphorus ratio of 100/ 5/1. This ratio also improved the compaction quality of sludge blanket in the upflow sludge blanket filtration clarifier. The average specific nitrification and denitrification rates occurred during the process can be expressed as 4.43 mg NOx- N produced/g VSS.d and 5.50 mg NOx-N removed/g VSS.d at the optimum ratio, respectively. To avoid sludge rising due to denitrification process, the optimum total hydraulic retention time of 16 to 24 h was achieved based on the effluent quality. This study suggested that the anaerobic/upflow sludge blanket filtration bioreactor at the optimum operational conditions can be an effective process for removal of nutrients from municipal wastewater.

Comparison of denitrification at low temperature using encapsulated Paracoccus denitrificans, Pseudomonas fluorescens and mixed culture

The aim of this work was to compare denitrification activity of three types of encapsulated biomass containing pure culture of Paracoccus denitrificans or Pseudomonas fluorescens or mixed culture of psychrophilic denitrifiers cultivated at 5°C from activated sludge. The experiments were held with synthetic wastewater containing 50mgL−1NNO3- under the temperature 15, 10, 8 and 5°C. Specific denitrification rates related to the weight of pellets and to the protein content were calculated and the temperature coefficients describing the dependence of denitrification rate on the temperature were determined. Although the mixed culture showed the highest denitrification rate at the temperatures below 10°C, using of pellets containing pure culture is recommended as the mixed culture has slow growth rate and its activity at temperatures above 10°C is very low.

Calcium augmentation for enhanced denitrifying granulation in sequencing batch reactors

This study investigated calcium augmentation for enhanced denitrifying granulation in sequencing batch reactors (SBRs) supplemented with different calcium concentrations of 0, 50 and 100 mg Ca 2+ l −1, respectively. Results showed that high calcium concentration would favor the formation of big and fast-settling denitrifying granules. Extracellular proteins (PN) were found to increase, whereas extracellular polysaccharides (PS) almost remained unchanged with granulation in all three SBRs. Moreover, the PN contents in mature denitrifying granules were positively related to feed calcium concentration. These suggested that PN would play a more important role than PS in denitrifying granulation process. It was also revealed that about 2.5–2.9% of calcium in denitrifying granules was bound with extracellular polymeric substances (EPS), and further helped to strengthen the structure of denitrifying granules. Mature denitrifying granules cultured with 50 mg Ca 2+ l −1 exhibited the highest specific denitrification rate (DNR) of 1040 mg N g −1 VSS d −1.

2,4-D removal via denitrification using volatile fatty acids

Many countries have waters contaminated with both herbicides and nitrates; however, information is limited with respect to removal rates for combined nitrate and herbicide elimination. This research investigates the removal of 2,4-D via denitrification, with a particular emphasis on the effect of adding naturally generated volatile fatty acids (VFAs). The acids were produced from an acid-phase anaerobic digester with a mean VFA concentration of 3153±801 mg/L (as acetic acid). Initially, 2,4-D degrading bacteria were developed in an SBR fed with both sewage and 2,4-D (30-100 mg/L). Subsequent denitrification batch tests demonstrated that the specific denitrification rate increased from 0.0119±0.0039 using 2,4-D alone to 0.0192±0.0079 g NO₃-N/g VSS per day, when 2,4-D was combined with natural VFAs from the digester. Similarly, the specific 2,4-D consumption rate increased from 0.0016±0.0009 using 2,4-D alone to 0.0055±0.0021 g 2,4-D/g VSS per day, when using 2,4-D plus natural VFAs. Finally, a parallel increase in the percent 2,4-D removal was observed, rising from 28.33±11.88 using 2,4-D alone to 54.17±21.89 using 2,4-D plus natural VFAs.

Nitrogen removal in submerged MBR with intermittent aeration

For this paper, synthetic wastewater was treated in two membrane bioreactors, with an accent on the removal of total nitrogen through nitrification and denitrification processes conducted as a batch process and as a process with continuous feed inflow. In the first bioreactor, with the flat sheet membrane, the specific denitrification rate during the batch process was 1.83 mg NO3 −-N/g MLSS h, with the glucose added all at once at the start of the process. When the glucose was being added continuously, specific denitrification rate was 1.2 mg NO3 −-N/g MLSS h. Without added glucose, specific denitrification rate was 0.4 mg NO3 −-N/g MLSS h. Nitrogen removal was conducted with continuous feed inflow and with intermittent aeration with a different duration of aeration and non-aeration phases. The best results in the experiment were achieved when the aeration regime was set to 60 minutes aeration and 120 minutes without aeration, resulting in the reduction of total nitrogen from 45 mg/L to about 12 mg/L. In ...

Diagnosis and Quantification of Glycerol Assimilating Denitrifying Bacteria in an Integrated Fixed-Film Activated Sludge Reactor via13C DNA Stable-Isotope Probing

Glycerol, a byproduct of biodiesel and oleo-chemical manufacturing operations, represents an attractive alternate to methanol as a carbon and electron donor for enhanced denitrification. However, unlike methanol, little is known about the diversity and activity of glycerol assimilating bacteria in activated sludge. In this study, the microbial ecology of glycerol assimilating denitrifying bacteria in a sequencing batch integrated fixed film activated sludge (SB-IFAS) reactor was investigated using (13)C-DNA stable isotope probing (SIP). During steady state SB-IFAS reactor operation, near complete nitrate removal (92.7 ± 5.8%) was achieved. Based on (13)C DNA clone libraries obtained after 360 days of SB-IFAS reactor operation, bacteria related to Comamonas spp. and Diaphorobacter spp. dominated in the suspended phase communities. (13)C assimilating members in the biofilm community were phylogenetically more diverse and were related to Comamonas spp., Bradyrhizobium spp., and Tessaracoccus spp. Possibly owing to greater substrate availability in the suspended phase, the glycerol-assimilating denitrifying populations (quantified by real-time PCR) were more abundant therein than in the biofilm phase. The biomass in the suspended phase also had a higher specific denitrification rate than the biofilm phase (p = 4.33e-4), and contributed to 69.7 ± 4.5% of the overall N-removal on a mass basis. The kinetics of glycerol based denitrification by suspended phase biomass were approximately 3 times higher than with methanol. Previously identified methanol assimilating denitrifying bacteria were not associated with glycerol assimilation, thereby suggesting limited cross-utilization of these two substrates for denitrification in the system tested.

Comparison of biological removal via nitrite with real-time control using aerobic granular sludge and flocculent activated sludge

The process of nitrification-denitrification via nitrite for nitrogen removal under real-time control mode was tested in two laboratory-scale sequencing batch reactors (SBRs) with flocculent activated sludge (R1) and aerobic granular sludge (R2) to compare operational performance and real-time control strategies. The results showed that the average ammonia nitrogen, total inorganic nitrogen (TIN), and chemical oxygen demand (COD) removal during aeration phase were 97.6%, 57.0%, and 90.1% in R2 compared with 98.6%, 48.7%, and 88.1% in R1. The TIN removed in both SBRs was partially due to the presence of simultaneous nitrification-denitrification via nitrite, especially in R2. The specific nitrification and denitrification rates in R2 were 0.0416 mg NH₄+ -N/gSS-min and 0.1889 mg NO X)⁻-N/gSS-min, which were 1.48 times and 1.35 times that of R1. The higher rates for COD removal, nitrification, and denitrification were achieved in R2 than R1 with similar influent quality. Dissolved oxygen (DO), pH, and oxidization reduction potential, corresponding to nutrient variations, were used as diagnostic parameters to control the organic carbon degradation and nitrification-denitrification via nitrite processes in both SBRs. The online control strategy of granular SBR was similar to that of the SBR with flocculent activated sludge. However, a unique U-type pattern on the DO curve in granular SBR was different from SBR with flocculent activated sludge in aerobic phase.

Denitrification in sediments as a major nitrogen sink in the Baltic Sea: an extrapolation using sediment characteristics

Abstract. Rates of denitrification in sediments were measured with the isotope pairing technique at different sites in the southern and central Baltic Sea. The rates varied between 0.5 μmol N m−2 h−1 in sands and 28.7 μmol N m−2 h−1 in muddy sediments and showed a good correlation to the organic carbon contents of the surface sediments. N-removal rates via sedimentary denitrification were estimated for the entire Baltic Sea calculating sediment specific denitrification rates and interpolating them to the whole Baltic Sea area. Another approach was carried out by using the relationship between the organic carbon content and the rate of denitrification. The N-removal by denitrification in sediments varied between 426–652 kt N a−1, which is around 48–73% of the external N inputs delivered via rivers, coastal point sources, and atmospheric deposition. Moreover, an expansion of the anoxic bottom areas was considered under the assumption of a rising oxycline from 100 to 80 m water depth. This leads to an increase of the area with anoxic conditions and an overall decrease in sedimentary denitrification by 14%. Overall, we show here that this type of data extrapolation is a powerful tool to estimate the nitrogen losses for a whole coastal sea and may be applicable to other coastal regions and enclosed seas.

Post-anoxic denitrification driven by PHA and glycogen within enhanced biological phosphorus removal

The objective of this research was to interrogate and develop a better understanding for a process to achieve post-anoxic denitrification without exogenous carbon augmentation within enhanced biological phosphorus removal (EBPR). Sequencing batch reactors fed real wastewater and seeded with mixed microbial consortia were operated under variable anaerobic-aerobic-anoxic and organic carbon loading conditions. The process consistently achieved phosphorus and nitrogen removal, while the observed specific denitrification rates were markedly higher than expected for post-anoxic systems operated without exogenous organic carbon addition. Investigations revealed that post-anoxic denitrification was predominantly driven by glycogen, an intracellular carbon storage polymer associated with EBPR; moreover, glycogen reserves can be significantly depleted post-anoxically without compromising EBPR. Success of the proposed process is predicated on providing sufficient organic acids in the influent wastewater, such that residual nitrate carried over from the post-anoxic period is reduced and polyhydroxyalkanoate (PHA) synthesis occurs.