Sensitivity analysis of a biofilm model describing a one-stage completely autotrophic nitrogen removal (CANON) process.

A mathematical model for nitrification and anaerobic ammonium oxidation (ANAMMOX) processes in a single biofilm reactor (CANON) was developed. This model describes completely autotrophic conversion of ammonium to dinitrogen gas. Aerobic ammonium and nitrite oxidation were modeled together with ANAMMOX. The sensitivity of kinetic constants and biofilm and process parameters to the process performance was evaluated, and the total effluent concentrations were, in general, found to be insensitive to affinity constants. Increasing the amount of biomass by either increasing biofilm thickness and density or decreasing porosity had no significant influence on the total effluent concentrations, provided that a minimum total biomass was present in the reactor. The ANAMMOX process always occurred in the depth of the biofilm provided that the oxygen concentration was limiting. The optimal dissolved oxygen concentration level at which the maximum nitrogen removal occurred is related to a certain ammonium surface load on the biofilm. An ammonium surface load of 2 g N/m2. d, associated with a dissolved oxygen concentration level of 1.3 g O2/m3 in the bulk liquid and with a minimum biofilm depth of 1 mm seems a proper design condition for the one-stage ammonium removal process. Under this condition, the ammonium removal efficiency is 94% (82% for the total nitrogen removal efficiency) (30 degrees C). Better ammonium removal could be achieved with an increase in the dissolved oxygen concentration level, but this would strongly limit the ANAMMOX process and decrease total nitrogen removal. It can be concluded that a one-stage process is probably not optimal if a good nitrogen effluent is required. A two-stage process like the combined SHARON and ANAMMOX process would be advised for complete nitrogen removal.     

The Potential for Nitrogen Fixation in a Lake Receiving Sewage Effluent (Grasmere, English Lake District)

The potential for nitrogen fixation in the water column and sediment of Grasmere (English Lake District) was investigated using the acetylene reduction technique, with reference to seasonal changes and concentrations of dissolved oxygen and inorganic nitrogen in the epilimnion and hypolimnion. Potential rates of nitrogen fixation and MPN counts of nitrogen-fixing bacteria correlated with each other and with decreases in dissolved oxygen concentration. The results suggested that selective changes in the nitrogen-fixing microflora took place during the period of thermal stratification. Neither light-dependent fixation, nor cyanobacteria could be detected in water column samples, and acetylene reduction was detected, for most of the season, only in samples of water and sediment to which a source of carbon and phosphorus had been added. The possible role of the sewage effluent in suppressing nitrogen fixation is discussed.     

Solubility and diffusion of nitrogen in maltodextrin/protein tablets

The gas transport properties of compacted tablets consisting of an amorphous mixture of maltodextrin and sodium caseinate were studied by dissolving nitrogen gas in the tablets and then determining the gas release over time as a function of temperature and water activity. Gas was dissolved in the tablet matrix by heating the tablets under pressure, generally to temperatures above the glass transition temperature of the matrix, holding them at these conditions for a specified time and then rapidly cooling them while maintaining the external pressure. The solubility of nitrogen was found to be largely determined by the free volume of the matrix, which in turn can be influenced to some degree by thermal and pressure treatments during gas loading. At the levels of free volume studied, the dissolved nitrogen is densely packed in the free volume, the packing density being virtually independent of the externally applied pressure. Release of gas from the tablets at temperatures below the glass transition temperature is generally well described by Fickian diffusion. The effective diffusion coefficient of gas release is strongly dependent on the microstructure and porosity of the tablet matrix, and an approximate model describing the relationship between tablet structure and rate of gas release is formulated. The model is in semiquantitative agreement with the rates of gas diffusion obtained for tablets and dense granules. Owing to the structural heterogeneity and variability of the tablets and the history-dependent properties of the tablet matrix, the effective diffusion coefficients of gas release from the tablets showed a relatively large spread. The temperature dependence of diffusional release follows an Arrhenius relation below the glass transition temperature. This allows the prediction of the nitrogen retention in the tablets as function of time, temperature and pressure.     

疫霉属菌种的液氮超低温保藏

对疫霉属的15个种68株菌和霜疫霉2株菌进行了液氮超低温的保藏试验并得到成功。比较了冷冻速度、保护剂和解冻速度对菌存活的影响。严格控制每分钟降温摄氏1度直到-40℃后再放入液氮罐中,对疫霉和霜疫霉来说都是非常必要的。这种降温程序可通过简单设备人工操作达到。而直接由室温降到-150℃以下会损伤菌种以致死亡。在所用的保护剂中,不论10％甘油还是5-15％二甲基亚砜都能起到保护作用。尚看不出对那种保护剂有特别的要求,似可任意选用。至于解冻条件,由液氮中取出放置在38℃水浴中快速融化与在20℃水浴中中等速度融化效果相等,对菌的成活都没有太大影响。我们的试验肯定了在有保护剂存在下,用慢速冷冻可以在液氮中保存疫霉和霜疫霉。     

Limitation of primary production by heterotrophic assimilation and transformation of inorganic nutrients

The planktonic environment is usually characterized by non-steady state conditions with events of phytoplankton blooms and sedimentation. Inorganic nutrients are stripped from the water column by sedimentation and end up in the sediments where they may be permanently deposited, or nitrogen may be liberated as nitrogen gas by denitrification. A major part of the denitrification activity is a coupled process of nitrification and denitrification which is dependent on a good supply of oxygen to the sediment. Urea may constitute a major part of the total outflux of dissolved N compounds from the sediment.     

Dissolved oxygen content in microbiological nutrient media

The modification of a highly sensitive method for the determination of the concentration of dissolved oxygen in liquid culture media and in water is described. This modification permits the easy conversion of the relative readings of electrode membrane transducers for measuring the partial pressure of oxygen into the readings characterizing the absolute concentration of oxygen in the medium (mg/cu. dm). The content of dissolved oxygen in microbiological media and in water depends on the amount of dissolved mineral salts, amino acids and peptides (the products in incomplete proteolysis), as well as on temperature. The maximum level of oxygen saturation in liquid culture media at 37 degrees C is different for various types of media and constitutes their peculiar characteristic, determined in the process of aeration under experimental conditions.     

Sensitivity of infrared water vapor analyzers to oxygen concentration and errors in stomatal conductance

Use of infrared analyzers to measure water vapor concentrations in photosynthesis systems is becoming common. It is known that sensitivity of infrared carbon dioxide and water vapor analyzers is affected by the oxygen concentration in the background gas, particularly for absolute analyzers, but the potential for large errors in estimates of stomatal conductance due to effects of oxygen concentration on the sensitivity of infrared water vapor analyzers is not widely recognized. This work tested three types of infrared water vapor analyzers for changes in sensitivity of infrared water vapor analyzers depending on the oxygen content of the background gas. It was found that changing from either 0 or 2% to 21% oxygen in nitrogen decreased the sensitivity to water vapor for all three types of infrared water vapor analyzers by about 4%. The change in sensitivity was linear with oxygen mole fraction. The resulting error in calculated stomatal conductance would depend strongly on the leaf to air vapor pressure difference and leaf temperature, and also on whether leaf temperature was directly measured or calculated from energy balance. Examples of measurements of gas exchange on soybean leaves under glasshouse conditions indicated that changing from 21% to 2% oxygen produced an artifactual apparent increase in stomatal conductance which averaged about 30%. Similar errors occurred for `conductances' of wet filter paper. Such errors could affect inferences about the carbon dioxide dependence of the sensitivity of photosynthesis to oxygen. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of fermentation conditions on N2 fixation by Methylococcus capsulatus

Nitrogen fixation has been investigated during chemostat fermentations with a culture of Methylococcus capsulatus with natural gas. It is demonstrated that nitrogen fixation occurs under conditions when either nitrate or ammonia as nitrogen source is insufficient for the growth on fixed supply of methane and oxygen. The fixation occurs contrary to expectations within a wide range of dilution rates and with variation of concentration of liquid source of nitrogen. An O₂ optimum is determined for the nitrogenase system of the culture in an assay. During fermentation a complete abolishment of nitrogenase reaction is attained at 15% air saturation (dissolved oxygen). Conditions for N₂ fixation is unaltered with change of pH from 6.8 to 5.7.     

A method for the control of the dissolved oxygen tension in microbial cultures

A method for the control of dissolved oxygen tension in growing microbial cultures is described. The apparatus consists of a motor-driven air sparge pipe which may be lowered or raised to give a variable point of entry of the air stream into the culture liquid and hence a variable gas dispersion and gas–liquid contact time. Control of the sparge pipe position is by means of a feedback control loop consisting of a dissolved oxygen probe, an on/off controller, and a reversing electric motor which drives the sparge pipe. The difficulty presented by the relatively slow response of the oxygen probe has been overcome by incorporating an adjustable rate of control action.     

A method for simultaneous determination of solubility and transfer coefficient of oxygen in aqueous media using off-gas mass spectrometry

A static method was developed that simultaneously determined the solubility of oxygen and the oxygen-transfer coefficient in a stirred bioreactor. It was based on the static method developed by van Sonsbeek et al. to determine the ka in a liquid-impelled loop reactor. Only physical properties of the liquid were used to determine both parameters using a mass spectrometer. Data about the solubility of oxygen in water are available from the literature. Therefore, the solubility of oxygen in water was used to compare our data with published data. Furthermore, the solubility of oxygen in trypticase soy broth was compared to literature data. No significant deviations between our data and literature data could be observed. Our static method and the commonly applied dynamic method to determine the oxygen-transfer coefficient yielded similar results. The effect of temperature on the oxygen-transfer coefficient could be expressed as the activation energy needed for the transition of oxygen from the gas to the water phase. This was verified using the Arrhenius equation. (c) 1994 John Wiley & Sons, Inc.     

过水性湖泊自净能力的动态变化

通过对过水性湖泊骆马湖1991—2003年出、入湖口附近主要水质指标监测资料的分析,研究了湖泊湿地自净能力的变化情况。结果表明:1991—2003年,各采样点水质指标无显著变化,但出、入湖口水质差异显著,表明骆马湖目前尚有较强的自净能力;各采样点间主要水质指标的变异系数逐渐减小,表明湖泊对水体总氮、溶解氧、挥发酚、非离子氨、砷等主要富营养化物质和污染物的净化能力不断减小,湿地生态系统的自净能力显著下降。总氮、溶解氧及部分外源污染物指标在不同采样点间的变异系数可作为湿地生态系统自净能力与健康状况的重要参考指标。     

Aerobic degradation of toluene in a closed chemostat with and without a head space outlet

The present paper describes the continuous aerobic cultivation of a Pseudomonas strain with toluene as the substrate in a closed chemostat with oxygen or air as the gas phase. Due to the constant supply of a nitrogen-saturated aqueous medium, nitrogen passes from the liquid phase of the chemostat into the gas phase (head space). This results in an increasing nitrogen content (asymptotic approach to 100%). The concomitant decrease in the partial pressure of the oxygen in the gas phase finally leads to an oxygen limitation for the bacteria in the medium and an incomplete toluene degradation. The critical nitrogen content of the gas phase at which oxygen limitation begins depends on the toluene concentration in the incoming medium. However, when the gas is continuously removed from the head space, the nitrogen content reaches a steady-state value of less than 100%, depending on the flow rate of the outgoing gas. The oxygen limitation and the associated incomplete toluene degradation can be prevented in this way. The method of gas removal from the head space to avoid oxygen limitation is also applicable when the reactor is supplied with air instead of oxygen. Waste waters contaminated with highly volatile pollutants can thus be biologically decontaminated under aerobic conditions, without shifting the pollution problem from the liquid to the gas phase.     

玄武湖菹草种群的发生原因及人工收割对水环境的影响

利用以沉水植物为主的水生植物进行水体生态修复是目前研究的热点问题, 为研究南京玄武湖2005-2006年的菹草(Potamogeton crispus)种群发生的原因及人工收割对水体的影响, 对玄武湖不同湖区定期监测其透明度、溶解氧、pH、TN、TP等水质指标, 并进行分析, 结果表明: 对湖泊蓝藻水华的应急处理, 使水体透明度提高179.5%, DO含量增高24.1%, TN、TP分别降低54.1%、74.5%, pH由9.1降至8.7, 水质改善是菹草种群萌发并能大规模生长的主要原因。而菹草生长阶段短期内对菹草进行大规模收割使水体DO含量降低42.1%, 透明度下降51.5%(P0.05), 收割虽从水体中携带走部分氮、磷营养盐, 但差异不显著(P0.05), 且收割后TP出现升高现象。故在对草藻型湖泊生态修复过程中, 可先期通过物理或化学手段改善水体透明度、调节pH、降低营养盐, 使其满足水生植物萌发及幼苗生长的需求, 为水生植物后期存活并生长打下基础, 在后期生态管理过程中, 应逐步收割植株, 缓慢从水体携带营养盐, 以达到改善水质, 恢复及重建水生生态系统的目的。       

Centroid search optimization of cultural conditions affecting the production of extracellular proteinase by Pseudomonas fragi ATCC 4973

The production of extracellular proteinase by Pseudomonas fragi ATCC 4973 grown in a defined citrate medium, containing glutamine as the sole nitrogen source, was determined under varying cultural conditions. Simultaneous evaluation of cultural conditions using a 'centroid search' optimization technique showed that the optimum cultural conditions for proteinase production by Ps. fragi were: incubation temperature, 12.5 degrees C; incubation time, 38 h; initial pH, 6.8; organic nitrogen concentration, 314 mmol nitrogen/l (glutamine); a gas mixture containing 16.4% oxygen flowing over the medium (7.42 ppm dissolved oxygen). Oxygen was the major factor influencing proteinase production by Ps. fragi. The results may have applications in the storage of fluid milk. Centroid search optimization was shown to be suitable for microbiological experiments.     

Mathematical model for a three-phase fluidized bed biofilm reactor in wastewater treatment

A mathematical model for a three phase fluidized bed bioreactor (TFBBR) was proposed to describe oxygen utilization rate, biomass concentration and the removal efficiency of Chemical Oxygen Demand (COD) in wastewater treatment. The model consisted of the biofilm model to describe the oxygen uptake rate and the hydraulic model to describe flow characteristics to cause the oxygen distribution in the reactor. The biofilm model represented the oxygen uptake rate by individual bioparticle and the hydrodynamics of fluids presented an axial dispersion flow with back mixing in the liquid phase and a plug flow in the gas phase. The difference of settling velocity along the column height due to the distributions of size and number of bioparticle was considered. The proposed model was able to predict the biomass concentration and the dissolved oxygen concentration along the column height. The removal efficiency of COD was calculated based on the oxygen consumption amounts that were obtained from the dissolved oxygen concentration. The predicted oxygen concentration by the proposed model agreed reasonably well with experimental measurement in a TFBBR. The effects of various operating parameters on the oxygen concentration were simulated based on the proposed model. The media size and media density affected the performance of a TFBBR. The dissolved oxygen concentration was significantly affected by the superficial liquid velocity but the removal efficiency of COD was significantly affected by the superficial gas velocity. An erratum to this article can be found online at .     

Temperature and Dissolved Oxygen Determine Submersion Time in Aquatic Beetle <Emphasis Type="Italic">Peltodytes callosus</Emphasis> (Coleoptera: Haliplidae)

Global climate change affects aquatic habitats in a number of ways that pose challenges for aquatic insect populations. Increasing water temperature and corresponding decreases in dissolved oxygen can impact respiratory behaviors, even in air-breathing aquatic taxa. Crawling water beetles (Coleoptera: Haliplidae) exhibit a combined respiratory strategy that employs an air store that is periodically replenished at the water surface. The frequency at which beetles surface to replenish the bubble is determined both by oxygen demand and by the capacity of the air store to uptake oxygen from the surrounding water via diffusion. However, little is known of how changes in water temperature and dissolved oxygen will affect submersion time. We investigated this question in Peltodytes callosus, a species of crawling water beetle that is widely distributed across the American West. We manipulated temperature and dissolved oxygen to mimic changes associated with global climate change and recorded the time between surfacing events. We found that beetles stayed submerged for shorter durations in response to both increasing water temperature and decreasing dissolved oxygen. Our results suggest that beetles may be able to modify their surfacing behavior to respond to climate-induced changes in water quality.     

稻田水氮氧环境因子对水稻生长发育、光合作用和氮利用的调控研究进展

水分和氮素是影响水稻生长发育的两个重要环境因子。适宜的水氮耦合模式可通过“以水调氮、以水控氧”调控稻田根际氮形态和溶氧量等环境因子,促进良好根系形态构建,提高叶片光合速率和光合产物“源-库”分配平衡,提高水稻群体质量和产量形成。同时,稻田水氮氧环境因子驱动的微生物调控机制在水稻-土壤系统氮高效利用方面也发挥重要作用。本文重点阐述了水氮耦合下水分、氮形态和溶氧量对水稻生长发育、光合作用、碳氮代谢、稻田氮转化过程及其微生物调控机制等方面的研究进展,展望并提出了未来亟待加强的研究方向:1)开展水氮耦合下水稻根际溶氧量时空动态分布特征及氧环境调控关键因子研究;2)明确不同基因型水稻根源信号增氧响应特征及其对水稻生长发育的影响调控机制;3)阐明根际氧环境驱动的关键微生物过程对稻田氮转化和氮素利用的影响。     

层次分析法对南水北调中线水源区的水质评价

层次分析法(AHP)是一种多指标多因素综合评价法,其理论内容深刻而表现形式简单,包括递阶层次结构模型、判断矩阵的建立及其求值、一致性检验和综合指数计算等运算过程.在南水北调中线水源区3个采样点进行了2a的水体浮游植物和9项理化指标的检测,并应用层次分析法通过季节4因素和6项理化指标对水质进行综合评价.结果表明:层次分析综合指数PI在3采样点有差异并且变化灵敏,渠首 (陶岔S1 ) PI=0.5697,水质属于污染;库心 (小太平洋S2 ) PI=0.3619,水质属于尚清洁;丹江入库上游 (大石桥S3 ), PI=0.7755,水质属于中污染;AHP分析结果与实际基本相符.根据结果分析认为:层次分析法做为综合评价法对水质评价有重要性,值得推广应用;丹江口水库是重要的水资源,但目前水质状况并不理想,因此做好水源区的长期生态监测,加强理论和技术研究,改善水质,极为重要.     

Apparent zero-order kinetics of phenol biodegradation by substrate-inhibited microbes at low substrate concentrations

The reaction kinetics for phenol biodegradation at low substrate concentrations can be estimated based on the analysis of changes in the dissolved oxygen concentration in the bulk liquid during biodegradation. The measured oxygen concentration changes with an interesting behavior as biodegradation proceeds. The oxygen concentration in the bulk liquid decreases rapidly in the early stages of degradation and subsequently decreases linearly and then rapidly recovers to the initial saturated level. Taking into account the oxygen transfer rate between gas and liquid phases and oxygen consumption rate by microbes, the change in the dissolved oxygen concentration can be simulated with an unsteady state mass balance equation and three kinetic models for the rate of phenol metabolism: a substrate-inhibited model; a zero-order model; and a combined model. In the combined model, it is assumed that, at phenol concentrations above 10 mg/L, the degradation rate is expressed by a substrate-inhibited model; whereas at concentrations below 10 mg/L the zero-order model is applied. It was found that the characteristics of the change in the dissolved oxygen concentration, especially the rapid increase at the end of degradation, can only be described by the combined kinetic model. This result suggests that conventional Haldane-type kinetics would be unsuitable for estimating the phenol consumption rate at low phenol concentrations, in particular, at concentrations less than 10 mg/L. (c) 1996 John Wiley & Sons, Inc.