• Journal of Korean Society on Water Environment
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• v.24 no.6
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• pp.659-669
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• 2008

Two sets of four parallel activated sludge reactors (ASRs) maintaining an MLSS of 3000 mg/L were operated to investigate the effect of DO, HRTs and bio-contact media (BCM) packing ratios on the removal efficiency of organic matters and nitrogen. Packing ratios of BCM to BCM-ASR systems 1, 2, 3, and 4 were 0% (suspended growth only), 10%, 15% and 20%, respectively. All systems were operated at an HRT of 4 hr, 6 hr, and 8 hr, respectively; DO concentration was maintained 0.5~1.0 mg/L and 1.5~2.0 mg/L for each HRT condition. In terms of TSS, TCODcr and SCODcr removal efficiency, all systems had a similar level of the removal efficiency under varied HRTs, and DO. But organic removal efficiency of systems with BCM was approximately 3~5% higher than systems without BCM at the same HRT and the DO. About the nitrification efficiency, with high DO (1.5~2.0 mg/L), as HRT (4 hr, 6 hr, 8 hr) or BCM packing ratio increased, the slight increment of nitrification efficiency was observed. However, under the low DO (0.5~1.0 mg/L), increase of BCM packing ratio and HRT resulted in large increase of the nitrification efficiency. At the same HRT and BCM packing ratio, the nitrification efficiency increased greatly with up to 15% as DO increased. When the HRT increased from 4hr to 8hr, the denitrification efficiency slightly increased by 5~10% only, under all DO conditions. Systems with BCM had higher denitrification efficiency, ranged 62.7~91.1% than systems without BCM showed 32.1~65.6%. And the increase in BCM packing ratio from 10% to 20% resulted in about 14~16% denitrification efficiency increment. BCM packing ratio showed great effect on the denitrification. The increase of the DO (from 0.5~1.0 mg/L to 1.5~2.0 mg/L) at the same HRT and BCM packing ratio resulted in slight decrease of denitrification efficiency with up to 7% for systems with BCM. But for systems without BCM, the denitrification efficiency decreased with up to 28%. In all system, the denitrification efficiency had more influence on the TN removal efficiency than nitrification efficiency. So, BCM packing ratio (0%, 10%, 15%, 20%) has greater effect on the TN removal than HRT and DO. The TN removal efficiency increased as packing ratio of BCM increased with up to 45%. As a result, the highest TN removal efficiency was observed 73.7% at the condition showed the highest denitrification efficiency that DO of 0.5~1.0 mg/L, an HRT of 8 hr, and 20% of BCM packing ratio was maintained.

• Journal of Microbiology and Biotechnology
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• v.25 no.10
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• pp.1670-1679
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• 2015

Two hollow fiber membrane biofilm reactors (HF-MBfRs) were operated for autotrophic nitrification and hydrogenotrophic denitrification for over 300 days. Oxygen and hydrogen were supplied through the hollow fiber membrane for nitrification and denitrification, respectively. During the period, the nitrogen was removed with the efficiency of 82-97% for ammonium and 87-97% for nitrate and with the nitrogen removal load of 0.09-0.26 kg NH₄⁺-N/m³/d and 0.10-0.21 kg NO₃^--N/m³/d, depending on hydraulic retention time variation by the two HF-MBfRs for autotrophic nitrification and hydrogenotrophic denitrification, respectively. Biofilms were collected from diverse topological positions in the reactors, each at different nitrogen loading rates, and the microbial communities were analyzed with partial 16S rRNA gene sequences in denaturing gradient gel electrophoresis (DGGE). Detected DGGE band sequences in the reactors were correlated with nitrification or denitrification. The profile of the DGGE bands depended on the NH₄⁺ or NO₃^- loading rate, but it was hard to find a major strain affecting the nitrogen removal efficiency. Nitrospira-related phylum was detected in all biofilm samples from the nitrification reactors. Paracoccus sp. and Aquaspirillum sp., which are an autohydrogenotrophic bacterium and an oligotrophic denitrifier, respectively, were observed in the denitrification reactors. The distribution of microbial communities was relatively stable at different nitrogen loading rates, and DGGE analysis based on 16S rRNA (341f /534r) could successfully detect nitrate-oxidizing and hydrogen-oxidizing bacteria but not ammonium-oxidizing bacteria in the HF-MBfRs.

• Environmental Engineering Research
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• v.20 no.1
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• pp.79-87
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• 2015

To treat leather industry wastewater (LIW) containing high nitrogen concentration, eight aerobic denitrifiers were isolated from sludge existing in an LIW-treatment aeration tank. Among them, one strain named as KH8 had showed the great ability in denitrification under an aerobic condition, and it was identified as Pseudomonas aeruginosa R12. The aerobic denitrification ability of the strain KH8 was almost comparable to its anaerobic denitrification ability. In lab-scale aerobic denitrifications performed in 1-L five-neck flasks for 48 hr, denitrification efficiency was found to be much improved as the strain KH8 held a great majority in the seeded cells. From the nitrogen balance at the cell-combination ratio of 10:1 (the strain KH8 to the other seven isolates) within the seeded cells, the percentage of nitrogen loss during the aerobic denitrification process was estimated to be 58.4, which was presumed to be converted to $N_2$ gas. When these seeded cells with lactose were applied to plant-scale aeration tank for 56 day to treat high-strength nitrogen in LIW, the removal efficiencies of $COD_{Cr}$ and TN were achieved to be 97.0% and 89.8%, respectively. Under this treatment, the final water quality of the effluent leaving the treatment plant was good enough to meet the water-quality standards. Consequently, the isolated aerobic denitrifiers could be suitable for the additional requirement of nitrogen removal in a limited aeration-tank capacity. To the best of our knowledge, this is the first report of aerobic denitrifiers applied to plant-scale LIW treatment.

• Journal of Environmental Science International
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• v.18 no.2
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• pp.205-213
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• 2009

A laboratory experiment was conducted to investigate nitrogen removal from plating wastewater by a soil reactor. A combination of soil, waste oyster shell and activated sludge were used as a loading media in a soil reactor. The addition of 20% waste oyster shell and activated sludge to the soil accelerated nitrification (88.6% ${NH_4}^{+}-N$ removal efficiency) and denitrification (84.3% ${NO_3}^{-}-N$ removal) in the soil reactor, respectively. In continuous removal, the influent ${NH_4}^{+}-N$ was mostly converted to nitrate nitrogen in the nitrification soil reactor and only a small amount of ${NH_4}^{+}-N$ was found in the effluent. When methanol was added as a carbon source to the denitrification soil reactor, the average removal efficiency of ${NO_3}^{-}-N$ significantly increased. The ${NO_3}^{-}-N$ removal by methanol addition in the denitrification soil reactor was mainly due to denitrification. The phosphorus was removed by the waste oyster shell media in the nitrification soil reactor. Moreover, the phosphorus removal in the denitrification soil reactor was achieved by synthesis of bacteria and the denitrification under anaerobic conditions. The approximate number of nitrifiers and denitrifiers was $3.3{\times}10^5\;MPN/g$ soil at a depth of $1{\sim}10\;cm$ and $3.3{\times}10^6\;MPN/g$ soil at a depth of $10{\sim}20\;cm$, respectively, in the soil reactor mixed with a waste oyster shell media and activated sludge.

• Journal of Microbiology and Biotechnology
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• v.18 no.11
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• pp.1826-1835
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• 2008

An autotrophic denitrification reactor (ADR-l) and a heterotrophic denitrification reactor (HDR-2) were operated to remove nitrate and nitrite in an anoxic environment in raw sewage. The $NO_3$-N removal rate of ADR-l was shown to range from 52.8% to 78.7%, which was higher than the $NO_3$-N removal rate of HDR-2. Specific denitrification rates (SDNR) of ADR-l and HDR-2 were 3.0 to 4.0 and 1.1 to $1.2\;mgNO_3$-N/gVSS/h, respectively. From results of restriction fragment length polymorphism (RFLP) of the 16S rRNA gene, Aquaspirillum metamorphum, Alcaligenes defragrans, and Azoarcus sp. were $\beta$-Proteobacteria that are affiliated with denitritying bacteria in the ADR-l. Specifically, Thiobacillus denitrificans was detected as an autotrophic denitrification bacteria. In HDR-2, the $\beta$-Proteobacteria such as Denitritying-Fe-oxidizing bacteria, Alcaligenes defragrans, Acidovorax sp., Azoarcus denitrificans, and Aquaspirillum metamorphum were the main bacteria related to denitrifying bacteria. The $\beta$-and $\alpha$-Proteobacteria were the important bacterial groups in ADR-l, whereas the $\beta$-Proteobacteria were the main bacterial group in HDR-2 based on results of fluorescent in situ hybridization (FISH). The number of Thiobacillus denitrificans increased in ADR-l during the operation period but not in HRD-2. Overall, the data presented here demonstrate that many heterotrophic denitritying bacteria coexisted with autotrophic denitrifying bacteria such as Thiobacillus denitrificans for nitrate removal in ADR-l. On the other hand, only heterotrophic denitritying bacteria were identified as dominant bacterial groups in HDR-2. Our research may provide a foundation for the complete nitrate removal in raw sewage of low-COD concentration under anoxic condition without any external organic carbon or the requirement of post-treatment.

• Journal of Korean Society on Water Environment
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• v.22 no.3
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• pp.462-467
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• 2006

An improvement of nitrogen and phosphorus removal in SBR using the elutriated acids from the food waste as an external carbon source was investigated in this study. The food waste was elutriated at $35^{\circ}C$ and pH 9 to produce the external carbon source. The elutriate of food waste were continuously collected. The elutriated liquid contained VFAs of 39,180 mg/L representing soluble COD of 44,700 mg/L. The SBR showed poor denitrification and EBPR (enhanced biological phosphorus removal) without elutriated VFAs addition. An average denitrification rate was 0.4 mg NOx-N/g MLVSS/day. In turn, EBPR was also inhibited by this poor denitrification because the remaining nitrate in anaerobic phase resulting a poor denitrification. On the other hand, the denitrification in anoxic phase significantly improved with an elutriated VFAs addition. Nitrate removal was 82% while the denitrification rate was 2.9 mg NOx-N/g MLVSS/day with 18.4 mL/cycle of elutriated VFAs. With the enhanced denitrification, nitrate concentration in anaerobic phase could effectively be controlled to a very low level. The elimination of nitrate inhibition in anaerobic phase resulted enhancement of EBPR. The specific phosphate release rate was $1.9mg\;PO_4^{3-}-P/g\; MLVSS/day$ with less than 0.5 mg/L of $PO_4^{3-}-P$ concentration.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.16 no.2
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• pp.81-96
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• 2011

Sediment oxygen demand(SOD) and denitrification rates were measured in four major estuaries(Suncheon Bay, Seomjin river estuary, Goseong stream estuary and Masan Bay) in south coast of Korean peninsula from March of 2009 to May 2010 to estimate organic matter cleaning capacity. SOD was estimated from the temporal dissolved oxygen concentration change and isotopic pairing technique was employed to measure denitrification. Sediment oxygen demand(SOD) was ranged from -5.1 to 24.6 mmole $O_2m^{-2}d^{-1}$ and denitrification rate was ranged from 0.0 to 3.9 mmole $N_2m^{-2}d^{-1}$in the study area. SOD was the highest in Masan Bay(-2.2 to 19.2, average = 10.2 mmole $O_2m^{-2}d^{-1}$) and Suncheon, Goseong, Tae-an and Seomjin followed. Denitrification was also the highest in Masn Bay(0.0 to 3.9, average = 1.0 mmole $N_2m^{-2}d^{-1}$) and Goseong, Seomjin, Suncheon and Taean followed. The effect of benthic photosynthesis by microphytobenthos on denitrification was evident in some season of Tae-an, Seomjin, and Masn Bay. The increased oxygen level produced by photosynthesis stimulated nitrification without severe adverse effect on denitrification and, as a result, coupled nitrification and denitrification was enhanced in these areas. A difference of seasonal patterns of denitrification at each site depended on relative importance of denitrification on different nitrate source($D_w$: nitrate from water column and $D_n$: nitrated produced during nitrification). Denitrification was maximum during spring in Goseong, Suncheon and Masan Bay. On the contrary, denitrification was the highest during summer in Tae-an and Seomjin estuary.

• Korean Journal of Microbiology
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• v.50 no.2
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• pp.137-151
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• 2014

Various studies have been conducted to investigate effects of dams on river ecosystems, but less information is available regarding damming impacts on downstream denitrification. We measured denitrification enzyme activity (potential denitrification rate) and denitrifier abundances (using nirS, nirK, and nosZ as markers) in dammed headstreams of the Nakdong River in South Korea. Sediments in Phragmites-dominated riparian areas and in-stream areas across streams (dammed vs. reference) with different streambed materials (gravel and sand) were sampled occasionally. We hypothesized that (i) the higher available N and C contents in sediments downstream of dams foster larger denitrifier communities than in the reference system and (ii) differences in potential denitrification rates across the systems correspond with denitrifier abundances. Despite 30 years of different hydrological management with dams and greater inorganic N and DOC contents in sediments downstream of dams, compared to the references, abundances of denitrifier communities and potential denitrification rates within the whole sediment were not significantly different across the systems. However, nirS and nosZ denitrifier abundances and potential denitrification rates were considerably increased in specific sediments downstream of dams (gravelly riparian and sandy in-stream) with regard to flooding events and seasonal temperature variation. nirK was not amplified in all sediments. Canonical correspondence analyses (CCA) revealed that the relationship between abundances of denitrifier communities and nutrient availabilities and potential denitrification rates was a weak one.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.2
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• pp.199-206
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• 2008

Simultaneous nitrification and denitrification means that nitrification and denitrification occur concurrently in the same reaction vessel under low DO concentration. Some mathematical models developed to simulate simultaneous nitrification and denitrification reaction, but they have the complex model structures or have limitations of model application. To solve these problems, if possible that predict the behavior of simultaneous nitrification and denitrification reaction by activated sludge model, structures of the model is less complex than previous models and applies the various operation conditions. But original activated sludge models have difficulties in representing the denitrification reaction under aerobic condition. So the aim of this study is to interpret simultaneous nitrification and denitrification reaction by modifying activated sludge model. Original activated sludge model No.1(ASM1) was selected and modified. The simulation result in modified ASM1 predicted appropriately for the measured data. This indicates the structures of ASM1 are properly improved for interpretation of simultaneous nitrification and denitrification reaction.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.17 no.2
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• pp.120-129
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• 2012

We investigated seasonal variation of sediment-water oxygen and inorganic nitrogen fluxes, and denitrification at tidal flat sediments located in the Nakdong River Estuary from July 2005 to September 2006. Net oxygen fluxes, measured with sediment incubations at in situ temperature, varied from -37.0 to $0.5mmol\;O_2\;m^{-2}\;d^{-1}$. Oxygen fluxes into the sediments from the overlying water increased due to the increased water temperature. Denitrification rate ($4{\sim}2732{\mu}mol\;N\;m^{-2}\;d^{-1}$) in this study was higher compared to the other Korean coast measured with the same method. Denitrification showed the same seasonal variation as oxygen fluxes. Denitrification rate based on $^{15}N$-nitrate showed a strong correlation with nitrate flux into the sediments from the overlying water. Denitrification via "water column supplied nitrate ($D_w$)", calculated from Isotope pairing technique, also correlated well with nitrate flux into the sediments. Nitrate from water column seems to account for seasonal variation of denitrification in Nakdong River Estuary. To understand general patterns and trends of biogeochemical processes of sediments in the Nakdong River Estuary, we categorized biogeochemical fluxes measured in this study according to direction and sizes of fluxes. Type 1(high oxygen and inorganic nitrogen fluxes into the sediments and high denitrification) occurred in summer, whereas Type 2(low oxygen and inorganic nitrogen fluxes into the sediments and low denitrification) occurred in rest of the season. Intertidal flat sediments seem to react sensitively to influence of freshwater from the Nakdong River.