Improved stability of aerobic granules by selecting slow-growing nitrifying bacteria

This study investigated the feasibility of improving the stability of aerobic granules through selecting slow-growing nitrifying bacteria. For this purpose, four sequencing batch reactors were operated at different substrate N/COD ratios ranging from 5/100 to 30/100. Results showed that aerobic granules formed in all four reactors, and aerobic granulation was a gradual process evolving from the dispersed seed sludge to mature and stable granules, and the whole granulation process could be divided into three phases, i.e. acclimation phase, granulation followed by granule maturation. The observed growth rate and mean size of mature aerobic granules were found to decrease as the substrate N/COD ratio was increased, while nitrifying population was enriched markedly in aerobic granules developed at high substrate N/COD ratios. The enriched nitrifying population in aerobic granules was responsible for the observed low growth rate of aerobic granules. It seems certain that the substrate N/COD ratio is an important factor in selecting nitrifying bacteria in aerobic granules. Aerobic granules with low growth rates showed strong structure and good settleability in terms of specific gravity, SVI and cell hydrophobicity that further lead to high stability as compared to those having high growth rates. This study demonstrated that the selection of slow-growing nitrifying bacteria through controlling substrate N/COD ratio would be a useful strategy for improving the stability of aerobic granules.     

Growth kinetics of aerobic granules developed in sequencing batch reactors

AIMS: This paper attempts to develop a kinetic model to describe the growth of aerobic granules developed under different operation conditions. METHODS AND RESULTS: A series of experiments were conducted by using four-column sequencing batch reactors to study the formation of aerobic granules under different conditions, e.g. organic loading rates, hydrodynamic shear forces and substrate N/COD ratios. A simple kinetic model based on the Linear Phenomenological Equation was successfully derived to describe the growth of aerobic granules. It was found that the growth of aerobic granules in terms of equilibrium size and size-dependent growth rate were inversely related to shear force imposed to microbial community, while a high organic loading favoured the growth of aerobic granules, leading to a large size granule. The effect of substrate N/COD ratio on the growth kinetics of aerobic granules was realized through change in microbial populations, and enriched nitrifying population in aerobic granules developed at high substrate N/COD ratio resulted in a low overall growth rate of aerobic granules. CONCLUSIONS: The proposed model can provide good prediction for the growth of aerobic granules indicated by the correlation coefficient >0.95. SIGNIFICANCE AND IMPACT OF THE STUDY: The kinetic model proposed could offer a useful tool for studying the growth kinetics of cell-to-cell immobilization process. The study confirmed that the growth of aerobic granules and biofilms are subject to a similar kinetic pattern. This work would also be helpful for better understanding the mechanism of aerobic granulation.     

Elemental compositions and characteristics of aerobic granules cultivated at different substrate N/C ratios

The effects of the substrate N/C ratios on the formation, elemental compositions and characteristics of aerobic granules were investigated in four sequencing batch reactors. Results showed that aerobic granules could form at substrate N/C ratios ranging from 5/100 to 30/100 and the substrate N/C ratio had a direct and profound effect on the elemental compositions and characteristics of the aerobic granules. Nitrifying populations in aerobic granules were enriched significantly with the increase in the substrate N/C ratio, while the respective ratio of cell oxygen, nitrogen and calcium to cell carbon were also determined by the substrate N/C ratio. It was found that cell hydrophobicity of aerobic granules was inversely related to the ratio of cell oxygen normalized to cell carbon. Since the cell calcium content in aerobic granules developed at different substrate N/C ratios was even lower than that in the seed sludge, it is reasonable to conclude that the cell calcium would not contribute to aerobic granulation. This study probably for the first time demonstrates that the elemental composition, microbial distribution and characteristics of aerobic granules are related to the substrate N/C ratio applied.     

Microbial community structure in autotrophic nitrifying granules characterized by experimental and simulation analyses

This study evaluates the community structure in nitrifying granules (average diameter of 1600 μm) produced in an aerobic reactor fed with ammonia as the sole energy source by a multivalent approach combining molecular techniques, microelectrode measurements and mathematical modelling. Fluorescence in situ hybridization revealed that ammonia-oxidizing bacteria dominated within the first 200 μm below the granule surface, nitrite-oxidizing bacteria a deeper layer between 200 and 300 μm, while heterotrophic bacteria were present in the core of the nitrifying granule. Presence of these groups also became evident from a 16S rRNA clone library. Microprofiles of NH₄⁺, NO₂^–, NO₃^– and O₂ concentrations measured with microelectrodes showed good agreement with the spatial organization of nitrifying bacteria. One- and two-dimensional numerical biofilm models were constructed to explain the observed granule development as a result of the multiple bacteria–substrate interactions. The interaction between nitrifying and heterotrophic bacteria was evaluated by assuming three types of heterotrophic bacterial growth on soluble microbial products from nitrifying bacteria. The models described well the bacterial distribution obtained by fluorescence in situ hybridization analysis, as well as the measured oxygen, nitrite, nitrate and ammonium concentration profiles. Results of this study are important because they show that a combination of simulation and experimental techniques can better explain the interaction between nitrifying bacteria and heterotrophic bacteria in the granules than individual approaches alone.     

Development and characteristics of phosphorus-accumulating microbial granules in sequencing batch reactors

Phosphorus (P)-accumulating microbial granules were developed at different substrate P/chemical oxygen demand (COD) ratios in the range of 1/100 to 10/100 by weight in sequencing batch reactors. The soluble COD and PO4-P profiles showed that the granules had typical P-accumulating characteristics, with concomitant uptake of soluble organic carbon and the release of phosphate in the anaerobic stage, followed by rapid phosphate uptake in the aerobic stage. The size of P-accumulating granules exhibited a decreasing trend with the increase in substrate P/COD ratio, while the structure of the granules became more compact and denser as the substrate P/COD ratio increased. The P uptake by granules fell within the range of 1.9% to 9.3% by weight, which is comparable with uptake obtained in conventional enhanced biological phosphorus removal (EBPR) processes. It was further found that low aerobic respirometric activity of granules in terms of specific oxygen utilization rate favors P uptake by granules. The results presented would be useful for the further development of a novel granule-based EBPR technology.     

The Role of Cell Hydrophobicity in the Formation of Aerobic Granules

Cell hydrophobicity is an important affinity force in cell self-immobilization and attachment processes. The role of cell hydrophobicity in the formation of aerobic granules has not been clear. Therefore, two series of experiments were conducted to investigate the role of cell hydrophobicity in the formation of aerobic heterotrophic and nitrifying granules in sequencing batch reactors, while the effects of shear strength, hydraulic selection pressure, and organic loading rate on the cell hydrophobicity were also studied. Results showed that the formations of heterotrophic and nitrifying granules were associated very closely with the cell hydrophobicity. The hydrophobicity of granular sludge was nearly twofold higher than that of conventional bioflocs. A high shear force or hydraulic selection pressure imposed on microorganisms resulted in a significant increase in the cell hydrophobicity, while the cell hydrophobicity seemed not to be sensitive to the changes in the organic loading rates in the range studied. In conclusion, the cell hydrophobicity could induce and further strengthen cell–cell interaction, and might be a main triggering force to initiate the granulation of heterotrophic and nitrifying bacteria. Received: 21 May 2002 / Accepted: 21 June 2002     

Fate of 14C-labeled microbial products derived from nitrifying bacteria in autotrophic nitrifying biofilms

The cross-feeding of microbial products derived from 14C-labeled nitrifying bacteria to heterotrophic bacteria coexisting in an autotrophic nitrifying biofilm was quantitatively analyzed by using microautoradiography combined with fluorescence in situ hybridization (MAR-FISH). After only nitrifying bacteria were labeled with [14C]bicarbonate, biofilm samples were incubated with and without NH4+ as a sole energy source for 10 days. The transfer of 14C originally incorporated into nitrifying bacterial cells to heterotrophic bacteria was monitored with time by using MAR-FISH. The MAR-FISH analysis revealed that most phylogenetic groups of heterotrophic bacteria except the beta-Proteobacteria showed significant uptake of 14C-labeled microbial products. In particular, the members of the Chloroflexi were strongly MAR positive in the culture without NH4+ addition, in which nitrifying bacteria tended to decay. This indicated that the members of the Chloroflexi preferentially utilized microbial products derived from mainly biomass decay. On the other hand, the members of the Cytophaga-Flavobacterium cluster gradually utilized 14C-labeled products in the culture with NH4+ addition in which nitrifying bacteria grew. This result suggested that these bacteria preferentially utilized substrate utilization-associated products of nitrifying bacteria and/or secondary metabolites of 14C-labeled structural cell components. Our results clearly demonstrated that the coexisting heterotrophic bacteria efficiently degraded and utilized dead biomass and metabolites of nitrifying bacteria, which consequently prevented accumulation of organic waste products in the biofilm.     

Temporal Variations in Heterotrophic Mesophilic Bacteria from a Marine Shallow Hydrothermal Vent off the Island of Vulcano (Eolian Islands, Italy)

Abstract The fluctuations of the total microbial abundance, the culturable heterotrophic bacterial population, and the composition of heterotrophic bacteria were investigated in relation to environmental parameters in a shallow, marine hydrothermal vent off the Island of Vulcano (Eolian Islands, Italy). Standing stock dynamics were studied by measuring the total population of picoplankton by direct count and the population of viable heterotrophic bacteria in water and sediment samples collected monthly. The environmental factors most strongly linked to the total microbial abundance and heterotrophic bacterial populations were pH and H₂S content in water and C/N ratio in sediment samples. The pattern of variation of microbial populations associated with water was different from those associated with sediment. Assessment of the qualitative composition of aerobic heterotrophic bacterial communities was based on 30 morphological and biochemical characteristics for each strain. Numerical analysis was used for an initial survey of the similarity among the isolates. The data were successively used to determine the structure and the metabolic potential of water and sediment bacteria. Metabolic properties varied between water- and sediment-isolated bacteria. Bacteria from water were structurally more diverse, and active in the use of carbohydrates, than those from sediment. Moreover, most of the sediment bacteria were able to grow at a high temperature (60 and 70°C). The fluctuations of bacterial characteristics in relation to environmental parameters present an evident temporal variation in water, but not in the sediment habitat. Received: 13 January 1997; Accepted: 7 August 1997     

异养硝化-好氧反硝化菌脱氮相关酶系及其编码基因的研究进展

水体氮素污染日益严重,如何经济、高效地去除水体氮素已成为研究热点。近年来,研究人员已从不同环境中分离到许多同时具有异养硝化和好氧反硝化功能的菌株,此类菌生长迅速,可在好氧条件下同时实现硝化和反硝化的过程,并可用于脱除有机污染物,是一类应用潜力巨大的脱氮菌。目前,异养硝化-好氧反硝化菌的脱氮途径和机制主要是通过测定氮循环中间产物或终产物、测定相关酶活性、注释部分氮循环相关基因及参考自养硝化菌和缺氧反硝化菌的氮循环途径等进行研究,其完整的氮素转化途径和氮代谢机制还需要进一步明确。总结了目前异养硝化-好养反硝化菌的脱氮相关酶系及其编码基因的研究进展,以期为异养硝化-好氧反硝化菌的理论研究及其在污水脱氮处理上的应用提供参考。     

Microbial indicators of oil-rich salt marsh sediments

Selected microbial parameters were monitored in sediments from a pristine and an oil-field salt marsh. Although numbers of hydrocarbonoclastic bacteria and fungi were significantly greater in the oil field, the values did not show a strong correlation with levels of hydrocarbons (r = 0.43 and r = 0.49, respectively). However, a high correlation was noted between ratios of hydrocarbonoclastic and total aerobic heterotrophic bacteria and levels of hydrocarbons as well as the relative concentration of hydrocarbons (ratio of hydrocarbons to chloroform extractables) (r = 0.87 and r = 0.77, respectively). Data suggest that this first ratio is a more valid microbial indicator of hydrocarbon abundance than other factors examined. Significant differences in the ratio of pigmented to total colony-forming units, the ratio of different to total colony-forming units, and the diversity index were noted between the natural and oil-field marsh. It is suggested that the presence of hydrocarbons alters the relative abundance of the most predominant aerobic heterotrophic bacteria.     

Fate of 14C-Labeled Microbial Products Derived from Nitrifying Bacteria in Autotrophic Nitrifying Biofilms

The cross-feeding of microbial products derived from ¹⁴C-labeled nitrifying bacteria to heterotrophic bacteria coexisting in an autotrophic nitrifying biofilm was quantitatively analyzed by using microautoradiography combined with fluorescence in situ hybridization (MAR-FISH). After only nitrifying bacteria were labeled with [¹⁴C]bicarbonate, biofilm samples were incubated with and without NH₄⁺ as a sole energy source for 10 days. The transfer of ¹⁴C originally incorporated into nitrifying bacterial cells to heterotrophic bacteria was monitored with time by using MAR-FISH. The MAR-FISH analysis revealed that most phylogenetic groups of heterotrophic bacteria except the β-Proteobacteria showed significant uptake of ¹⁴C-labeled microbial products. In particular, the members of the Chloroflexi were strongly MAR positive in the culture without NH₄⁺ addition, in which nitrifying bacteria tended to decay. This indicated that the members of the Chloroflexi preferentially utilized microbial products derived from mainly biomass decay. On the other hand, the members of the Cytophaga-Flavobacterium cluster gradually utilized ¹⁴C-labeled products in the culture with NH₄⁺ addition in which nitrifying bacteria grew. This result suggested that these bacteria preferentially utilized substrate utilization-associated products of nitrifying bacteria and/or secondary metabolites of ¹⁴C-labeled structural cell components. Our results clearly demonstrated that the coexisting heterotrophic bacteria efficiently degraded and utilized dead biomass and metabolites of nitrifying bacteria, which consequently prevented accumulation of organic waste products in the biofilm.     

Effects of Grazing by Flagellates on Competition for Ammonium between Nitrifying and Heterotrophic Bacteria in Chemostats

The enhanced mineralization of organic nitrogen by bacteriophagous protozoa is thought to favor the nitrification process in soils, in which nitrifying bacteria have to compete with heterotrophic bacteria for the available ammonium. To obtain more insight into this process, the influence of grazing by the bacteriovorous flagellate Adriamonas peritocrescens on the competition for limiting amounts of ammonium between the ammonium-oxidizing species Nitrosomonas europaea and the heterotrophic species Arthrobacter globiformis was studied in the presence of Nitrobacter winogradskyi in continuous cultures at dilution rates of 0.004 and 0.01 h^-1. The ammonium concentration in the reservoir was maintained at 2 mM, whereas the glucose concentration was increased stepwise from 0 to 7 mM. A. globiformis won the competition for limiting amounts of ammonium when the glucose concentration in the reservoirs increased, in agreement with previously described experiments in which the flagellates were not included. The numbers of nitrifying bacteria decreased as the numbers of heterotrophic bacteria rose with increasing glucose concentrations. Critical C/N ratios, i.e., ratios between glucose and ammonium in the reservoirs at which no nitrate was found in the culture vessels, of 12.5 and 10.5 were determined at dilution rates of 0.004 and 0.01 h^-1, respectively. Below these critical values, coexistence of the competing species was found. The numbers of nitrifying bacteria decreased more in the presence of flagellates than in their absence, presumably by selective predation on the nitrifying bacteria, either in the liquid culture or on the glass wall of the culture vessels. Despite this, the rate of nitrate production did not decrease more in the presence of flagellates than in their absence. This demonstrates that no correlation has to be expected between numbers of nitrifying bacteria and their activity and that a constant nitrification rate per cell cannot be assumed for nitrifying bacteria. Above the critical C/N ratios, low numbers of nitrifying bacteria were still found in the culture vessels, probably because of attachment of the nitrifying bacteria to the glass wall of the culture vessels. Like the numbers of heterotrophic bacteria, the numbers of flagellates increased when the glucose concentrations in the reservoirs increased. Numbers of 2 × 10⁵ and 12 × 10⁵ flagellates ml^-1 were found at 7 mM glucose at dilution rates of 0.004 and 0.01 h^-1, respectively. It was concluded that the critical C/N ratios were practically unaffected by the presence of protozoa. Although nitrate production rates were equal in the presence and absence of flagellates, the numbers of nitrifying bacteria decreased more strongly in their presence. This indicates a higher activity per nitrifying cell in the presence of flagellates.     

A Most Probable Number method (MPN) for the estimation of cell numbers of heterotrophic nitrifying bacteria in soil

A Most Probable Number (MPN) method was developed allowing for the first time estimation of populations of bacteria capable of heterotrophic nitrification. The method was applied to an acidic soil of a coniferous forest exhibiting nitrate production. In this soil nitrate production was unlikely to be catalyzed by autotrophic nitrifiers, since autotrophic ammonia oxidizers never could be detected, and autotrophic nitrite oxidizers were usually not found in appreciable cell numbers. The developed MPN method is based on the demonstration of the presence/absence of nitrite/nitrate produced by heterotrophic nitrifying bacteria during growth in a complex medium (peptone-meat-extract softagar medium) containing low concentrations of agar (0.1%). Both the supply of the growing cultures in MPN test tubes with sufficient oxygen and the presence of low agar concentrations in the medium were found to be favourable for sustainable nitrite/nitrate production. The results demonstrate that in the acidic forest soil the microbial population capable of heterotrophic nitrifcation represents a significant part of the total aerobic heterotrophic population. By applying the developed MPN method, several bacterial strains of different genera not previously described to perform heterotrophic nitrification have been isolated from the soil and have been identified by bacterio-diagnostic tests.     

Heterotrophs grown on the soluble microbial products (SMP) released by autotrophs are responsible for the nitrogen loss in nitrifying granular sludge

In this work, nitrogen loss in the nitrite oxidation step of the nitrification process in an aerobic‐granule‐based reactor was characterized with both experimental and modeling approaches. Experimental results showed that soluble microbial products (SMP) were released from the nitrite‐oxidizing granules and were utilized as a carbon source by the heterotrophs for denitrification. This was verified by the fluorescence in situ hybridization (FISH) analysis. Microelectrode tests showed that oxygen diffusion limitation did result in an anoxic micro‐zone in the granules and allowed sequential utilization of nitrate as an electron acceptor for heterotrophic denitrification with SMP as a carbon source. To further elucidate the nitrogen loss mechanisms, a mathematic model was formulated to describe the growth of nitrite oxidizers, the formation and consumption of SMP, the anoxic heterotrophic growth on SMP and nitrate, as well as the oxygen transfer and the substrate diffusion in the granules. The results clearly indicate that the heterotrophs grown on the SMP released by the autotrophs are responsible for the nitrogen loss in the nitrifying granules, and give us a better understanding of the aerobic granules for nitrogen removal. Biotechnol. Bioeng. 2011;108: 2844–2852. © 2011 Wiley Periodicals, Inc.     

土地利用驱动的土壤性状变化影响微生物群落结构和功能

微生物在调节陆地生态系统地球化学循环过程中具有重要作用。土地利用方式改变显著影响土壤微生物群落结构和功能,但对土地利用驱动的土壤性状变化与微生物群落结构和功能关系的研究相对匮乏。依托长期定位监测试验（始于1984年）,通过16S rRNA基因片段和ITS高通量测序,研究了土地利用方式（裸地、农田、草地）驱动的土壤碳氮变化对微生物群落结构和功能的影响。结果表明：对于细菌群落而言,裸地中α-多样性最高、其次是草地、农田中最低,农田和草地中细菌优势菌群变形菌（Proteobacteria）和放线菌门（Actinobacteria）相对丰度较裸地低4.5%、3.9%和5.5%、3.8%;对于真菌群落而言,裸地子囊菌门（Ascomycota）相对丰度最高、农田次之、草地最低;化能异养型、好氧化能异养型细菌相对丰度裸地显著高于农田和草地（P<0.05）,而硝化型和好氧氨氧化型细菌裸地显著低于农田和草地（P<0.05）;腐生型真菌相对丰度大小排序为：裸地>农田>草地。细菌群落变化主要与土壤容重、全氮、矿质氮、C ： N比和微生物量碳有关,而真菌群落与土壤矿质氮有关。细菌和真菌功能菌群主要受土壤容重、土壤有机碳、土壤全氮、C ： N比和微生物量碳影响。因此,土壤容重、土壤全氮、土壤有机碳、C ： N比、微生物量碳、矿质氮差异可能是影响不同土地利用方式中微生物群落和功能变化的主要因素。     

Distinctive microbial ecology and biokinetics of autotrophic ammonia and nitrite oxidation in a partial nitrification bioreactor

Biological nitrogen removal (BNR) based on partial nitrification and denitrification via nitrite is a cost-effective alternate to conventional nitrification and denitrification (via nitrate). The goal of this study was to investigate the microbial ecology, biokinetics, and stability of partial nitrification. Stable long-term partial nitrification resulting in 82.1 +/- 17.2% ammonia oxidation, primarily to nitrite (77.3 +/- 19.5% of the ammonia oxidized) was achieved in a lab-scale bioreactor by operation at a pH, dissolved oxygen and solids retention time of 7.5 +/- 0.1, 1.54 +/- 0.87 mg O(2)/L, and 3.0 days, respectively. Bioreactor ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) populations were most closely related to Nitrosomonas europaea and Nitrobacter spp., respectively. The AOB population fraction varied in the range 61 +/- 45% and was much higher than the NOB fraction, 0.71 +/- 1.1%. Using direct measures of bacterial concentrations in conjunction with independent activity measures and mass balances, the maximum specific growth rate (micro(max)), specific decay (b) and observed biomass yield coefficients (Y(obs)) for AOB were 1.08 +/- 1.03 day(-1), 0.32 +/- 0.34 day(-1), and 0.15 +/- 0.06 mg biomass COD/mg N oxidized, respectively. Corresponding micro(max), b, and Y(obs) values for NOB were 2.6 +/- 2.05 day(-1), 1.7 +/- 1.9 day(-1), and 0.04 +/- 0.02 mg biomass COD/mg N oxidized, respectively. The results of this study demonstrate that the highly selective partial nitrification operating conditions enriched for a narrow diversity of rapidly growing AOB and NOB populations unlike conventional BNR reactors, which host a broader diversity of nitrifying bacteria. Further, direct measures of microbial abundance enabled not only elucidation of mixed community microbial ecology but also estimation of key engineering parameters describing bioreactor systems supporting these communities.     

The effect of hydraulic retention time on the stability of aerobically grown microbial granules

AIMS: The aim of this study is to evaluate the effect of hydraulic retention time (HRT) on the development of aerobically grown microbial granules. METHODS AND RESULTS: Five column-shaped sequential aerobic sludge blanket reactors (SASBRs) were seeded with aerobically grown microbial granules and operated in a cyclic mode at different HRTs. At the shortest HRT of 1 h, the strong hydraulic pressure triggered biomass washout and led to reactor failure. At the longest HRT of 24 h, which represented the weakest hydraulic selection in this study, aerobic granules were gradually substituted by bioflocs because of the lower frequency of volumetric exchange. Within the optimum range of HRTs from 2 to 12 h, however, aerobic granules became stabilized in the presence of adequate hydraulic selection in the reactors, with good mixed liquor volatile suspended solids (MLVSS) retention, high volumetric chemical oxygen demand (COD) removal, low sludge volume index (SVI) values, good effluent quality, low sludge production rate, stronger and more compact structures, high cell hydrophobicity and high ratios of extracellular polysaccharides (PS) to extracellular proteins (PN). CONCLUSIONS: HRTs between 2 and 12 h provided the hydraulic selection pressures favourable for the formation and maintenance of stable aerobic granules with good settleability and activity. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first systematic study on the effect of HRT on heterotrophic aerobic granules. The results of the investigation are useful in understanding how aerobic granules can be applied for wastewater treatment.     

Denitrification capacity of a landfilled refuse in response to the variations of COD/NO3--N in the injected leachate

Effects of different chemical oxygen demand (COD) to nitrate concentration ratios in the injected leachate on the denitrification capacity of landfilled municipal solid waste were evaluated. Results showed that the 6-year-old refuse possessed high denitrification capacity. The nitrate reduction rate increased with the increasing COD concentration in the injected leachate. When the initial COD concentration increased to 6500 mg l(-1), nitrate reduction rate could reach up to 6.85 mg NO3--N l(-1) h(-1). At the initial biodegradable COD/NO3--N ratio lower than the stoichiometric ratio of heterotrophic denitrification, autotrophic bacteria was the dominant microbial communities for denitrification. With the increase of COD/NO3--N ratio, the primary functional denitrifier would shift from autotrophic Thiobacillus denitrificans to heterotrophic Azoarcus tolulyticus. These results suggested that the initial biodegradable COD/NO3--N ratio in the injected leachate should be adjusted to higher than 6.0 for rapid in situ denitrification of 500 mg NO3--Nl(-1).     

Evaluation on factors influencing the heterotrophic growth on the soluble microbial products of autotrophs

In this work, the heterotrophic growth on the microbial products of autotrophs and the effecting factors were evaluated with both experimental and modeling approaches. Fluorescence in situ hybridization (FISH) analysis illustrated that ammonia oxidizers (AOB), nitrite oxidizers (NOB), and heterotrophs accounted for about 65%, 20%, and 15% of the total bacteria, respectively. The mathematical evaluation of experimental data reported in literature indicated that heterotrophic growth in nitrifying biofilm (30–50%) and granules (30%) was significantly higher than that of nitrifying sludge (15%). It was found that low influent ammonium resulted in a lower availability of soluble microbial products (SMP) and a slower heterotrophic growth, but high ammonium (>150 mg N L⁻¹) feeding would lead to purely AOB dominated sludge with high biomass‐associated products contained effluent, although the absolute heterotrophic growth increased. Meanwhile, the total active biomass concentration increased gradually with the increasing solids retention time, whereas the factions of active AOB, NOB, and heterotrophs varied a lot at different solids retention times. This work could be useful for better understanding of the autotrophic wastewater treatment systems. Biotechnol. Bioeng. 2011; 108:804–812. © 2010 Wiley Periodicals, Inc.     

海洋环境异养硝化-好氧反硝化菌的研究进展

异养硝化-好氧反硝化（heterotrophic nitrifying-aerobic denitrification,HN-AD）菌的发现打破了传统的脱氮理论,可以在有氧条件下同时进行硝化和反硝化,成为近年来的研究热点。HN-AD细菌在海洋氮循环中发挥着重要作用。本文对海洋环境中HN-AD菌的多样性和部分已知氮代谢途径及相关酶系进行了介绍,分析了盐度、碳氮比、溶解氧、pH等环境因素对HN-AD菌脱氮效果的影响,对其工艺和技术应用、前景和发展方向进行了综述和展望。