Simultaneous nitrification and denitrification in activated sludge system under low oxygen concentration

Simultaneous nitrification and denitrification (SND), which is more economical compared with the traditional method for nitrogen removal, is studied in this paper. In order to find the suitable conditions of this process, a mixed flow activated sludge system under low oxygen concentration is investigated, and some key control parameters are examined for nitrogen removal from synthetic wastewater. The results show that SND is accessible when oxygen concentration is 0.3–0.8 mg/L. The nitrogen removal rate can be obtained up to 66.7% with solids retention time (SRT) of 45 d, C/N value of 10, and F/M ratio of 0.1 g COD/(g MLSS·d). Theoretical analysis indicates that SND is a physical phenomenon and governed by oxygen diffusion in flocs.     

Linking abundance and diversity of sponge-associated microbial communities to metabolic differences in host sponges

Many sponge species contain large and diverse communities of microorganisms. Some of these microbes are suggested to be in a mutualistic interaction with their host sponges, but there is little evidence to support these hypotheses. Stable nitrogen isotope ratios of sponges in the Key Largo, Florida (USA) area grouped sponges into species with relatively low δ¹⁵N ratios and species with relatively high δ¹⁵N ratios. Using samples collected in June 2002 from Three Sisters Reef and Conch Reef in the Key Largo, Florida area, transmission electron microscopy (TEM) and denaturing gradient gel electrophoresis were performed on tissues of the sponges Ircinia felix and Aplysina cauliformis, which are in the low δ¹⁵N group, and on tissue of the sponge Niphates erecta, which is in the high δ¹⁵N group. Results showed that I. felix and A. cauliformis have large and diverse microbial communities, while N. erecta has a low biomass of one bacterial strain. As the low δ¹⁵N ratios indicated a microbial input of nitrogen, these results suggested that I. felix and A. cauliformis were receiving nitrogen from their associated microbial community, while N. erecta was obtaining nitrogen solely from external sources. Sequence analysis of the microbial communities showed a diversity of metabolic capabilities among the microbes of the low δ¹⁵N group, which are lacking in the high δ¹⁵N group, further supporting metabolic differences between the two groups. This research provides support for hypotheses of mutualisms between sponges and their associated microbial communities.     

土－水系统中脱氮化作用与硝化作用的耦合关系

对氮肥的两种主要化学形态（即硝态氮和铵态氮）在土－水系统中的形态转化过程及控制因素进行了探讨。结果表明：供试系统中硝化作用与脱氮化作用都较强烈，硝化作用先于脱氮化作用，其速度明显比脱氮化作用快。硝化作用与脱氮化作用的耦合是氮化合物转化的核心机制。决定亚硝酸盐积累的主要因素是温度。     

Factors affecting simultaneous nitrification and denitrification in an SBBR treating domestic wastewater

An aerobic sequencing batch biofilm reactor (SBBR) packed with Bauer rings was used to treat real domestic wastewater for simultaneous nitrification and denitrification. The SBBR is advantageous for creating an anoxic condition, and the biofilm can absorb and store carbon for good nitrification and denitrification. An average concentration of oxygen ranging from 0.8 to 4.0 mg/L was proved very efficient for nitrification and denitrification. Volumetric loads of TN dropped dramatically and effluent TN concentration increased quickly when the concentration of average dissolved oxygen was more than 4.0 mg/L. The efficiency of simultaneous nitrification and denitrification (SND) increased with increasing thickness of the biofilm. The influent concentration hardly affected the TN removal efficiency, but the effluent TN increased with increasing influent concentration. It is suggested that a subsequence for denitrification be added or influent amount be decreased to meet effluent quality requirements. At optimum operating parameters, the TN removal efficiency of 74%–82% could be achieved.     

膜生物反应器（MBR）处理垃圾渗滤液的脱氮研究

采用一体式MBR处理垃圾渗滤液,系统考察MBR对COD、NH4＋-N和TN的去除效果。结果表明：可将垃圾渗滤液的COD降至650-1 500 mg·L-1范围;在HRT为1.5 d、DO为0.75-1.20 mg·L-1、不排泥条件下运行时,对TN质量浓度低于2 300 mg·L-1、容积负荷低于0.25 kg.m-3.d-1（以N计）的渗滤液进行处理,MBR对NH4＋-N与TN的去除率可分别达到87%和72%以上。在MBR处理垃圾渗滤液的运行中发现,膜的污染速度较快,并且呈现＂两段性＂的规律,采用碱＋氧化剂的清洗方式可有效去除膜污染,降低过膜压力。     

Microbial associations in sponges. I. Ecology,physiology and microbial populations of coral reef sponges

Illumination, current strength and physical turbulence influence the distribution of 4 tropical sponges. Three sponges with cyanobacteria in exposed tissues grow only in poen shallow habitats: Pericharax heteroraphis in moderate-current, lowturbulence regions on the reef slope; Jaspis stellifera in low-current, moderate-turbulence regions of the outer reef flat; and Neofibularia irata in moderate-current, high-turbulence areas below the reef crest. Ircinia wistarii contains no cyanobacteria and occurs in deeper, strong-current, high-turbulence regions. N. irata agressively overgrows neighbouring corals and its growth form is influenced by the current strength. The sponges efficiently filter bacteria from the water. The efficiency is related to the aquiferous structure, particularly the size of choanocyte chambers, and is unrelated to the existing bacterial populations in sponge tissue. The numbers of bacteria associated with the sponges are proportional to the sponge mesohyl density, with the dense sponges J. stellifera and I. wistarii containing many bacteria whereas P. heteroraphis is not dense and has few bacteria.     

Preparation and characterization of a novel microorganism embedding material for simultaneous nitrification and denitrification

A novel microorganism embedding material was prepared to enhance the biological nitrogen removal through simultaneous nitrification and denitrification. Polyvinyl alcohol (PVA), sodium alginate (SA) and cyclodextrin (CD) were used to compose gel bead with embedded activated sludge. The effects of temperature, CD addition and concentrations of PVA and SA on nitrogen removal were evaluated. Results show that the gel bead with CD addition at 30°C contributed to the highest nitrogen removal efficiency and nitrogen removal rate of 85.4% and 2.08 mgL·(L·h)^–1, respectively. Meanwhile, negligible NO₃ ^– and NO₂ ^– were observed, proving the occurrence of simultaneous nitrification and denitrification. The High-Throughput Sequencing confirms that the microbial community mainly contained Comamonadaceae in the proportion of 61.3%. Overall, CD increased gel bead’s porosity and resulted in the high specific endogenous respiration rate and high nitrogen removal efficiency, which is a favorable additional agent to the traditional embedding material.

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基于BaPS技术的高山草甸土硝化和反硝化季节变化

应用气压分离(BaPS)技术测定了川西北高山草甸土硝化和反硝化季节动态变化.结果表明:植物生长季节内,土壤总硝化、反硝化和N2O释放率的变化趋势一致,即从6月份(硝化率:N 8.40 mg kg-1 d-1;反硝化率:N 0.48 mg kg-1 d-1;N2O释放率:N 84.48 靏 kg-1 d-1)开始增加,7月份(N 19.36 mg kg-1 d-1;N 0.60 mg kg-1 d-1;N 100.13 靏 kg-1 d-1)达到最大值,然后开始下降,到9月份(N 1.81 mg kg-1 d-1;N 0.24 mg kg-1 d-1;N 40.09 靏 kg-1 d-1)降为最小值.氮素物质基础(NO3--N和NH4 -N)不是影响该高山草甸土硝化和反硝化的主要因素,土壤温度和湿度是该高山草甸土硝化、反硝化作用的主要影响因子.     

Nitrous oxide nitrification and denitrification 15N enrichment factors from Amazon forest soils.

The isotopic signatures of 15N and 18O in N2O emitted from tropical soils vary both spatially and temporally, leading to large uncertainty in the overall tropical source signature and thereby limiting the utility of isotopes in constraining the global N2O budget. Determining the reasons for spatial and temporal variations in isotope signatures requires that we know the isotope enrichment factors for nitrification and denitrification, the two processes that produce N2O in soils. We have devised a method for measuring these enrichment factors using soil incubation experiments and report results from this method for three rain forest soils collected in the Brazilian Amazon: soil with differing sand and clay content from the Tapajos National Forest (TNF) near Santarém, Pará, and Nova Vida Farm, Rond?nia. The 15N enrichment factors for nitrification and denitrification differ with soil texture and site: -111 per thousand +/- 12 per thousand and -31 per thousand +/- 11 per thousand for a clay-rich Oxisol (TNF), -102 per thousand +/- 5 per thousand and -45 per thousand +/- 5 per thousand for a sandier Ultisol (TNF), and -10.4 per thousand +/- 3.5 per thousand (enrichment factor for denitrification) for another Ultisol (Nova Vida) soil, respectively. We also show that the isotopomer site preference (delta15Nalpha - delta15Nbeta, where alpha indicates the central nitrogen atom and beta the terminal nitrogen atom in N2O) may allow differentiation between processes of production and consumption of N2O and can potentially be used to determine the contributions of nitrification and denitrification. The site preferences for nitrification and denitrification from the TNF-Ultisol incubated soils are: 4.2 per thousand +/- 8.4 per thousand and 31.6 per thousand +/- 8.1 per thousand, respectively. Thus, nitrifying and denitrifying bacteria populations under the conditions of our study exhibit significantly different 15N site preference fingerprints. Our data set strongly suggests that N2O isotopomers can be used in concert with traditional N2O stable isotope measurements as constraints to differentiate microbial N2O processes in soil and will contribute to interpretations of the isotopic site preference N2O values found in the free troposphere.     

Nitrogen cycling in microbial mats: rates and patterns of denitrification and nitrogen fixation

Spatial and temporal variations in nitrogen fixation and denitrification rates were examined between July 1991 and September 1992 in the intertidal regions of Tomales Bay (California, USA). Microbial mat communities inhabited exposed mudflat and vegetated marsh surface sediments. Mudflat and marsh sediments exhibited comparable rates of nitrogen fixation. Denitrification rates were higher in marsh sediments. Nitrogen fixation rates were lowest during January at both sites, whereas highest rates occurred during summer and fall. Denitrification rates were highest during fall and winter months in marsh sediments, while rates in mudflat sediments were highest during summer and fall. In mudflat sediments, nitrogen fixation and denitrification rates, integrated over 24 h, ranged from 6 to 79 mg N m^-1 d^-1 and 1 to 10 mg N m^-2 d^-1, respectively. Rates of denitrification represented between 6 and 20% of nitrogen fixation rates during the day, but exceeded or were equivalent to nitrogen fixation rates at night. The highest integrated rates of both nitrogen fixation and denitrification occurred during July, whereas, the highest percent loss occurred during spring when denitrification rates amounted to 20% of nitrogen fixation rates during the day. Over an annual cycle, inputs of fixed N to mudflat communities occurred exclusively during daylight. These results underscore the importance of determining integrated diel rates of both nitrogen fixation and denitrification when constructing N budgets. Using this approach, it was shown that microbial denitrification can represent a significant loss of combined nitrogen from mats on daily as well as monthly time scales.     

Nitrification and denitrification in biological activated carbon filter for treating high ammonia source water

Since the ammonia in the effluent of the traditional water purification process could not meet the supply demand, the advanced treatment of a high concentration of NH₄ ⁺-N micro-polluted source water by biological activated carbon filter (BACF) was tested. The filter was operated in the downflow manner and the results showed that the removing rate of NH₄ ⁺-N was related to the influent concentration of NH₄ ⁺-N. Its removing rate could be higher than 95% when influent concentration was under 1.0 mg/L. It could also decrease with the increasing influent concentration when the NH₄ ⁺-N concentration was in the range from 1.5 to 4.9 mg/L and the dissolved oxygen (DO) in the influent was under 10 mg/L, and the minimum removing rate could be 30%. The key factor of restricting nitrification in BACF was the influent DO. When the influent NH₄ ⁺-N concentration was high, the DO in water was almost depleted entirely by the nitrifying and hetetrophic bacteria in the depth of 0.4 m filter and the filter layer was divided into aerobic and anoxic zones. The nitrification and degradation of organic matters existed in the aerobic zone, while the denitrification occurred in the anoxic zone. Due to the limited carbon source, the denitrification could not be carried out properly, which led to the accumulation of the denitrification intermediates such as NO₂ ^?. In addition to the denitrification bacteria, the nitrification and the heterotrophic bacteria existed in the anoxic zone.     

Dynamics of a chemostat with three competitive hydrogen oxidizing denitrifying microbial populations and their efficiency for denitrification

In this work, competition for two nitrogen resources (nitrate-, nitrite-nitrogen) between three hydrogen oxidizing denitrifying populations (Acidovorax sp. strain Ic3 (X₁), Paracoccus sp. strain Ic1 (X₂), and Acinetobacter sp. strain Ic2 (X₃)) was examined. The dynamics of three systems of microbial populations (system I: X₁ − X₃, system II: X₂ − X₃, and system III: X₁ − X₂ − X₃), grown in a chemostat, was studied using bifurcation analysis. The chemostat is the most common type of biological reactor used for the study of microbial growth under controlled conditions. The effect of the operating parameters (i.e., dilution rate and feed nitrate nitrogen concentration) on the long-term behavior of the systems showed that X₃ was the predominant population for a wide range of combinations of dilution rate and feed nitrate nitrogen concentration. Also, coexistence of two populations (X₂X₃, X₁X₃) was observed. The results of the bifurcation analysis were also used to determine the denitrification rate and the nitrite nitrogen accumulation for each of the three systems as a function of the dilution rate (up to 0.17 h⁻¹) and the feed nitrate nitrogen concentration (up to 300 mg/L). The highest denitrification rate was achieved by system I (28 mg/Lh). A comparison between the three systems showed that the nitrite nitrogen concentration in system I was less than the one in system III, while the two systems gave similar denitrification rates. The second system had the greatest accumulation of nitrites with the lowest denitrification rate.     

1株贫营养好氧反硝化菌的分离鉴定及其脱氮特性

从水库底泥样品中,以硝酸盐为唯一氮源进行驯化、分离筛选出1株能在贫营养及好氧条件下进行高效反硝化的菌株PY8,经过电镜形态学观察、生理生化和16S rDNA序列分析,并基于16SrDNA序列结果,构建了该菌株的系统发育树,最终确定菌株PY8为根瘤菌Rhizobiumsp.。考察了初始pH值、温度、C/N、初始硝酸钠质量浓度、投菌量对菌株PY8硝酸盐还原活性的影响,以及该菌株的异养硝化性能。结果表明,在pH6.0～10.0,温度25～30℃,C/N1.0～9.0,初始硝酸钠质量浓度0.01～0.50g·L-1,投菌量1%～15%时,菌株PY8培养72h后的硝氮去除率可达到95%以上。另外,该菌株具有同时硝化-反硝化作用,在培养过程中氨氮去除率可达到58%左右。实验结果表明,菌株PY8在微污染水体生物脱氮领域中具有很大的应用潜力。     

Ecology of toxicity in marine sponges

An investigation of the ecology of toxicity in marine sponges from different latitudes on the North American continent was made. Results indicated that toxicity in sponges increased with decreasing latitude. Three of the 34 species (9%) of sponges from San Juan Island, Washington, USA (48°N), were toxic to fishes. Nine of the 44 species (20%) of sponges from Santa Catalina Island, California, USA (33°N), were toxic. Seven of the 11 species (64%) of sponges from Zihuatanejo Bay, Guerrero, México (17°N), were toxic. Twenty-seven of the 36 species (75%) of sponges from La Blanquilla, Veracruz, México (19°N), were toxic. Most of these toxic sponges are openly exposed to fishes. The most common exposed sponges proved to be highly toxic to fishes. Force-feeding experiments conducted with wrasses demonstrated the effectiveness of the toxin of sponges. A hypothesis is proposed which explains the relationship between species diversity of fishes and sponge toxicity with latitude.     

Microbial associations in sponges. III. Ultrastructure of the in situ associations in coral reef sponges

Symbiotic cyanobacteria are associated with marine sponges in three ways: the majority are free-living in the mesohyl; large aggregates occur in cyanocytes (specialized, vacuolated archeocytes); and few are present in digestive vacuoles. The cyanobacteria in Jaspis stellifera and Neofibularia irata are morphologically similar to those described in Mediterranean sponges, whereas those in Pericharax heteroraphis are different. The freeliving bacterial populations are morphologically similar, although the number of bacteria varies between the species. The fourth sponge Ircinia wistarii contains a mixed bacterial population unlike those in the other sponges. Sponge digestion of microbial associates is rare and not considered to contribute significant nutrients.     

Differences in chloroplast ultrastructure of Phaeocystis antarctica in low and high light

Phaeocystis antarctica Karsten exhibits optical changes in pigment packaging during acclimation to drastically different light levels. Here, the three-dimensional morphological rearrangements are shown for two light conditions mimicking limiting and saturating conditions for photosynthesis. Cultures of P. antarctica were grown semi-continuously under light-limiting conditions for growth (14 μmol quanta m⁻² s⁻¹) and a light-saturating condition (259 μmol quanta m⁻² s⁻¹) for growth. Increased numbers of thylakoids were observed under the low light treatment. In contrast, there were less amounts of thylakoid stacking in each chloroplast under the high light treatment. Electron microscopic tomographic reconstructions illustrate the complexity of the chloroplast organelle where the thylakoids ‘interact’ with the pyrenoid and the chloroplast membrane. Highly complex characteristics, such as bi- and tri-furcations in the thylakoid stacks, were continuous throughout the chloroplast. Other organelles, such as the Golgi apparatus and dense vesicles that may potentially affect cellular scattering and absorption were also observed in both high and low light. These three dimensional thylakoid arrangements have profound implications for cellular photophysiology. They represent a new view of algal chloroplast structure, and provide a starting point for more accurate optical modeling studies.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Carbon conversion and metabolic rate in two marine sponges

The carbon metabolism of two marine sponges, Haliclona oculata and Dysidea avara, has been studied using a ¹³C isotope pulse-chase approach. The sponges were fed ¹³C-labeled diatoms (Skeletonema costatum) for 8 h and they took up between 75 and 85%. At different times, sponges were sampled for total ¹³C enrichment, and fatty acid (FA) composition and ¹³C enrichment. Algal biomarkers present in the sponges were highly labeled after feeding but their labeling levels decreased until none was left 10 days after enrichment. The sponge-specific FAs incorporated ¹³C label already during the first day and the amount of ¹³C label inside these FAs kept increasing until 3 weeks after labeling. The algal-derived carbon captured by the sponges during the 8-h feeding period was thus partly respired and partly metabolized during the weeks following. Apparently, sponges are able to capture enough food during short periods to sustain longer-term metabolism. The change of carbon metabolic rate of fatty acid synthesis due to mechanical damage of sponge tissue was studied by feeding sponges with ¹³C isotope–labeled diatom (Pheaodactylum tricornutum) either after or before damaging and tracing back the ¹³C content in the damaged and healthy tissue. The filtration and respiration in both sponges responded quickly to damage. The rate of respiration in H. oculata reduced immediately after damage, but returned to its initial level after 6 h. The ¹³C data revealed that H. oculata has a higher metabolic rate in the tips where growth occurs compared to the rest of the tissue and that the metabolic rate is increased after damage of the tissue. For D. avara, no differences were found between damaged and non-damaged tissue. However, the filtration rate decreased directly after damage.     

Isolation of cellulolytic microbes from the intestinal tract of the pinfish,Lagodon rhomboides: size-related changes in diet and microbial abundance

Pinfish, Lagodon rhomboides (Linneaus), undergo a gradual ontogenetic dietary shift during their first year of life, marked by an increase in the consumption of plant material. To determine if this shift in diet was associated with a change in the microbial flora of the intestinal tract that may assist in degradation of plant material, stomach contents were analyzed and microbes in the intestinal tract were isolated from fish ranging from 20 to 139 mm standard length. These fish were collected from Core Sound, North Carolina, USA between March and September 1991. Plant material increased from 16% of dry weight of stomach contents in pinfish under 40 mm standard length (SL) to 65% in pinfish above 120 mm SL, confirming previous observations of a diet-related ontogenetic change in L. rhomboides. Comparison of the total cultivatable facultative and anaerobic microbial flora isolated from the intestinal tract contents of pinfish ranging in size from 26 to 139 mm SL showed a 10-fold increase between fish <40 and fish >40 mm SL, with maximum population densities of approximately 2x10⁷ colony forming units (CFU) g^-1 of intestine including contents. The percentage of microbial isolates examined capable of hydrolyzing carboxymethylcellulose (CMC) increased from 12% in fish <40 mm SL to 13 to 50% in fish >40 mm SL, although there was no strict increase with increasing fish size classes. Although the percentage of CMC-hydrolytic microbial isolates varied with respect to fish SL, the percentage of skim-milk hydrolytic (proteolytic) isolates remained relatively constant (4% of total isolates) irrespective of fish SL and dietary composition. Results presented in this study document the first isolation of carboxymethylcellulase producing microbes from the intestinal tract of any fish and demonstrate that the ontogenetic dietary shift in L. rhomboides is paralleled by qualitative and quantitative changes in the intestinal microbial community. The use of strict anaerobic sampling methods in the preparation of intestinal contents from wild-captured fresh specimens was essential in obtaining these isolates.     

Evidence of high organotrophic potentiality of bacteria in the deep ocean

The organotrophic potentiality of heterotrophic microorganisms 50 cm above the ocean floor (5,207 m depth) was measured in situ, at a station in the subarctic Pacific Ocean (44° N; 154° E). In certain enriched deep-sea samples incubated in situ, the microorganisms exhibited nearly the same organotrophic activity as those in the surface water layers. Rod-shaped barophilic bacteria (0.4 to 0.6 μ x 1.0 to 2.0 μ), which multiplied at a generation time of about 10 h, were responsible for this activity.     

Coral mortality following extreme low tides and high solar radiation

Extreme tidal events are one of the most predictable natural disturbances in marine benthic habitats and are important determinants of zonation patterns in intertidal benthic communities. On coral reefs, spring low tides are recurrent disturbances, but are rarely reported to cause mass mortality. However, in years when extremely low tides coincide with high noon irradiances, they have the potential to cause widespread damage. Here, we report on such an event on a fringing coral reef in the central Great Barrier Reef (Australia) in September 2005. Visual surveys of colony mortality and bleaching status of more than 13,000 corals at 14 reef sites indicated that most coral taxa at wave-protected sites were severely affected by the event. Between 40 and 75% of colonies in the major coral taxa (Acropora, Porites, Faviidae, Mussidae and Pocilloporidae) were either bleached or suffered partial mortality. In contrast, corals at wave-exposed sites were largely unaffected (<1% of the corals were bleached), as periodic washing by waves prevented desiccation. Surveys along a 1–9 m depth gradient indicated that high coral mortality was confined to the tidal zone. However, 20–30% of faviid colonies were bleached throughout the depth range, suggesting that the increase in benthic irradiances during extreme low tides caused light stress in deeper water. Analyses of an 8-year dataset of tidal records for the area indicated that the combination of extended periods of aerial exposure and high irradiances occurs during May–September in most years, but that the event in September 2005 was the most severe. We argue that extreme low-tide, high-irradiance events are important structuring forces of intertidal coral reef communities, and can be as damaging as thermal stress events. Importantly, they occur at a time of year when risks from thermal stress, cyclones and monsoon-associated river run-off are minimal.