Uncertainty in dissolved oxygen prediction due to variability in algal photosynthesis

The contribution of variance in river community metabolism to overall uncertainty in predictions from dissolved oxygen models is evaluated using Monte Carlo simulation. Results using a modification of the Streeter-Phelps model to include a term for mean daily net production show that uncertainty in parameters used to describe community metabolism must be considered when probability distributions of dissolved oxygen in rivers are estimated. This conclusion is shown to be valid for a range of conditions and is therefore applicable to all but heavily polluted or highly turbid streams. Use of a refined version of the oxygen balance equation that accounts for diel variation in algal productivity demonstrates that variance in dissolved oxygen in rivers is likely to be much larger than that predicted by models that use mean daily values of net production.     

Dynamics of dissolved oxygen during algal bloom in Lake Kasumigaura, Japan

Dynamics of dissolved oxygen during an algal bloom were studied in Lake Kasumigaura. Great amounts of oxygen arose from photosynthesis, and the concentration of dissolved oxygen reached 190% of saturation at 12 h. The majority of the dissolved oxygen produced was liberated into the atmosphere or consumed by microorganisms. Only minor fractions were transported into the dysphotic zone due to the low eddy diffusion coefficient in deeper waters of the euphotic zone.     

溶解氧对CASS工艺影响的研究

就曝气时间段DO的变化对处理效果的影响进行了实验,研究结果发现DO在3．0mg／L时COD去除率达90．7％;CASS工艺对NH3-N的去除效果随DO浓度降低而变坏;对TN的去除最佳点也是在130浓度为3．0mg／L时,去除率为73．3％;对TP的去除率在DO浓度为1．0～3．0时均能达到94％;CASS出水均能达标排放。     

An interlaboratory study of dissolved oxygen in water

Dissolved oxygen concentrations in water samples free from chemical reductants may be stabilised by the addition of mercuric chloride (40 g m⁻³) and storage in gas-tight bottles. This preservation technique has been used in an interlaboratory study of dissolved oxygen analysis in New Zealand laboratories. At reference concentrations of 1.20 and 5.86 g m⁻³, there was a significant positive bias in results reported for both the Winkler method (0.24 and 0.22 g m⁻³ respectively) and the membrane electrode method (0.59 and 0.62 g m⁻³ respectively). Inadequate precautions to avoid sample aeration during handling and analysis probably caused the bias.     

The effect of dissolved oxygen concentration on nitrification

The effect of dissolved oxygen concentration on the rate of nitrification has been investigated by a number of researchers using both pure and mixed cultures, and cultures found in wastewater treatment systems. The maximum growth rate of both nitrification reactions are reported to be affected by dissolved oxygen concentration over the range of 0.3 mg l⁻¹ to as much as 4.0 mg l⁻¹. In some instances, it has been reported that a dissolved oxygen concentration in excess of 4.0 mg l⁻¹ is required to achieve maximum nitrification rates, while other investigators have found that only 0.5 to 1.0 mg l⁻¹ is required.It has been proposed that several factors are responsible for the wide range of reported nitrification rates with varying dissolved oxygen concentrations. Among these factors are the effects of oxygen diffusion in flocs, variation between measured results due to steady-state and dynamic measuring techniques, and double-substrate limited kinetics. This paper reviews the nitrification literature with respect to the effects of dissolved oxygen concentration, and shows that double-substrate limiting kinetics could account for the variation in the reported results.     

Effect of temperature and dissolved oxygen on biodegradation of nitrilotriacetate

The effect of temperature and dissolved oxygen on the rate of biodegradation of nitrilotriacetate (NTA) was examined in water samples collected from the Rur River. Biodegradation of NTA was first order with respect to NTA concentration over a concentration range of 50–1000 μg l⁻¹. First order rate constants showed a typical temperature dependency (temperature coefficient, Q₁₀ = 2) and biodegradation of NTA was observed over a temperature range of 2–24°C. The effect of temperature on the rate of NTA biodegradation was described by the Arrhenius equation, with calculated activation energies in the range reported for ordinary enzyme reactions. Biodegradation of NTA was also observed at low dissolved oxygen concentrations (0.3 mg l⁻¹), although at reduced rates compared to high oxygen concentrations (13 mg l⁻¹). Biodegradation of NTA was oxygen-dependent, suggesting an obligate oxygen requirement for the initial steps in NTA metabolism by natural microbial communities in surface waters. In general, our results indicate that NTA biodegradation will occur in natural waters under conditions of low temperature and low dissolved oxygen and also at low NTA concentrations.     

Continuous analysis of dissolved gaseous mercury in freshwater lakes

The concentration of dissolved gaseous mercury (DGM) in freshwaters changes more quickly than the 40-min processing time of current analytical methods. A new method for continuous field analysis of DGM was developed using a Tekran 2537A to achieve a DGM analysis time of 5 min. Samples were concurrently analyzed for temperature, oxygen, conductivity, pH, and oxidation-reduction potential using a Hydrolab. The detection limit for DGM ranged between 5 and 20 fmolL(-1) with 99% removal efficiency. Control experiments showed that there was no interference due to methyl mercury, which is present in similar concentrations to DGM. Controlled experiments comparing continuous DGM analysis with discrete DGM analysis showed that the results are not significantly affected by typical variations in water temperature (4-30 degrees C), oxidation-reduction potential (135-355 mV), dissolved organic carbon (4.5-10.5 mgL(-1)), or pH (3.5-7.8). The continuous analysis was within 4.5% of the discrete analysis when compared across 12 samples analyzed in triplicate. The field performance of this method was tested over two 48-h periods in two lakes in Kejimkujik Park, Nova Scotia where over 1000 data points were collected.     

溶解氧在线分析仪技术及其应用

介绍了sc100^TMLDO^TM型溶解氧监测仪的工作原理和技术规格，阐述了溶解氧在线监测仪在污水处理、纯水生产、水体环境和发酵工业中的应用，指出溶解氧传感器采用荧光受激敏感技术，克服了以往扩散型传感器的维护量大和易受干扰的缺点，值得推广该仪器的应用。     

Temporal variability of dissolved P speciation in a eutrophic reservoir--implications for predicating algal growth

Weak-anion exchange chromatography was used to explore the temporal variability in the speciation of dissolved P in the surface layer of a eutrophic reservoir. Authentic free ortho-P ion was the most common form of P on three of the five sampling occasions-including during a bloom of the green algae Botryococcus braunii indicating that the bloom was not P limited. Conversely, the absence of authentic ortho-P during a bloom of the dinoflagellate Ceratium hirundinella suggested the bloom was either P limited or co-limited. These observations were confirmed by algal-growth bioassay experiments.     

On the electrochemical measurement of dissolved oxygen in water

Some practical aspects of the application of an electrochemical Clark-type sensor are discussed. Attention is paid to improvement of its function.     

Modeling anaerobic bioreactor landfills in methanogenic phase: long term and short term behaviors

We have developed a mathematical model to simulate the behavior of real bioreactor landfills in the anaerobic methanogenic phase. This coupled model is composed of a two-phase flow and a biological model based on Darcy's law and Monod's model, respectively. This model considers bacterial activity and biological behavior as a function of temperature and makes it possible to study the thermo-biological behavior of bioreactor landfills with temperature changes. In this model we consider different effects of saturation on solid waste degradation. These effects consist of increasing hydrolysis with saturation and also decreasing the concentration of volatile fatty acids (VFAs) and activating the methanogenic biomass. This paper presents first the mathematical coupled model and the numerical methods used to solve the conservation equations. The numerical model is then used to simulate two bioreactor landfills. This paper presents the results of long and short (with leachate recirculation) term numerical simulations comparing them with site results. Finally results as well as advantages and drawbacks of the model are discussed. The results show that the mathematical model is able to reproduce the hydro-thermo-biological behavior of a bioreactor landfill in different conditions, with and without leachate recirculation, and leads to a better understanding of important thermal and biological parameters.     

The extended Kalman filter for forecast of algal bloom dynamics

A deterministic ecosystem model is combined with an extended Kalman filter (EKF) to produce short term forecasts of algal bloom and dissolved oxygen dynamics in a marine fish culture zone (FCZ). The weakly flushed FCZ is modelled as a well-mixed system; the tidal exchange with the outer bay is lumped into a flushing rate that is numerically determined from a three-dimensional hydrodynamic model. The ecosystem model incorporates phytoplankton growth kinetics, nutrient uptake, photosynthetic production, nutrient sources from organic fish farm loads, and nutrient exchange with a sediment bed layer. High frequency field observations of chlorophyll, dissolved oxygen (DO) and hydro-meteorological parameters (sampling interval Δt = 1 day, 2 h, 1 h, respectively) and bi-weekly nutrient data are assimilated into the model to produce the combined state estimate accounting for the uncertainties. In addition to the water quality state variables, the EKF incorporates dynamic estimation of algal growth rate and settling velocity. The effectiveness of the EKF data assimilation is studied for a wide range of sampling intervals and prediction lead-times. The chlorophyll and dissolved oxygen estimated by the EKF are compared with field data of seven algal bloom events observed at Lamma Island, Hong Kong. The results show that the EKF estimate well captures the nonlinear error evolution in time; the chlorophyll level can be satisfactorily predicted by the filtered model estimate with a mean absolute error of around 1-2 μg/L. Predictions with 1-2 day lead-time are highly correlated with the observations (r = 0.7-0.9); the correlation stays at a high level for a lead-time of 3 days (r = 0.6-0.7). Estimated algal growth and settling rates are in accord with field observations; the more frequent DO data can compensate for less frequent algal biomass measurements. The present study is the first time the EKF is successfully applied to forecast an entire algal bloom cycle, suggesting the possibility of using EKF for real time forecast of algal bloom dynamics.     

Measurement of sediment oxygen demand for modelling dissolved oxygen distribution in tidal Keelung River

The Keelung River is one of the major branches of the Danshuei River estuarine system, which runs the metropolitan capital city of Taipei, Taiwan, and receives a large of amount of wastewater. The dissolved oxygen (DO) concentration is generally low in the tidal portion of the Keelung River. Hypoxia/anoxia occurs often, particularly during a low-flow period. The sediment oxygen demand (SOD) amounts to a significant value, hence increasing the total oxygen demand load of the river. The present work reports on laboratory SOD made on grab sediment core samples in situ that are undisturbed. The results reveal that SOD values fluctuate with variations in seasons and are higher in summer due to a high-temperature effect. It was found in the laboratory tests that the average SOD (at 20 °C) value is 0.76 g/m²/day and the maximum SOD (at 20 °C) value reaches 1.58 g/m²/day. The mean values of measured SOD at each station were adopted in the vertical two-dimensional water quality model to simulate the DO distribution along the tidal Keelung River. The simulated results are in reasonable agreement with the measured DO distribution in the river. Model sensitivity analyses were also conducted with increasing and decreasing SOD. It reveals that SOD is an important parameter that affects the DO distribution in the tidal estuary.     

Effects of dissolved oxygen on kraft pulp mill effluent toxicity

Effects of reduced dissolved oxygen on the toxicity of kraft mill effluent to juvenile coho salmon, Oncorhynchus kisutch, were determined in short-term, constant-flow bioassays conducted in freshwater. Effects of dissolved oxygen on toxicity demonstrated for a wide range of oxygen concentrations, viz., from 3.4 to approximately 9 mg 1⁻¹, at water temperatures of 12 ± 1°C. With each successive lower oxygen level tested, the median survival time of the test fish and the 24-h tl_m values were lower. Possible factors influencing observed results are discussed, as is application of results for protection of fish in waters receiving kraft mill wastes.     

Long-term storage of natural water samples for dissolved oxygen determination

A method for preserving natural water samples for dissolved oxygen analysis is recommended. The conventional method of using greased glass stoppers have been found to cause an increase in oxygen concentration by 12% over 1-month period as a result of evaporation of water sample through micro-gaps and concurrent intrusion of air into the water sample bottles. Sealing the sample bottles with water has been found to be the optimal storage method. It permits a 100.2 +/- 0.3% recovery of dissolved oxygen concentration from storage seawater samples over 4 months.     

The dynamics of suspended algal populations in the lower Wye catchment

The algae of the R. Wye and its tributary the R. Lugg were described principally from samples collected from 7 sites in the lower Wye catchment during 1980 and 1981. The density of algae in the Wye was found to be correlated with river flow and solar radiation, highest numbers (12.5 × 10⁵ cells ml⁻¹), principally of Scenedesmus and Cyclotella, occurring at low stable flows and relatively high solar radiation. Algal populations in the Lugg were much smaller ( 1.3 × 10³cells ml⁻¹) than those of the Wye and were principally composed of species derived from the periphyton. Downstream increases in load (cell density × flow) of both Scenedesmus and Cyclotella in the Wye were generally equivalent to about 0.3 division d⁻¹; these rates were lower than those obtained in laboratory culture and this was probably largely related to underestimates arising from algal removal by filter feeders (principally simuliid larvae). Potential problems arising from the treatment of Wye water supporting substantial algal growths are considered: these include haloform production, deoxygenation in a transfer pipeline, algal penetration into potable supply and taste and odour.     

连续梁桥施工中的挠度监测和控制

结合温福铁路莲花岗大桥连续梁桥的现场施工实例,对连续梁桥施工的挠度监测方法进行了系统的阐述,并具体分析了莲花岗大桥各个施工阶段的变形,为施工过程的挠度控制提供了科学依据。     

Study of dissolved silicon and nitrate dynamics in a freshwater stream.

Dissolved reactive silicon and nitrate were measured at weekly intervals over a 3 year period (1991-94) on a 1.2km reach of a gauged Dorset Mill Stream. In addition, dissolved nitrite was measured over a 8 month period from the spring to late autumn in 1992. Two intensive studies with sampling at 2h intervals were also completed in low and high riverflow conditions. The results were analysed using a mass-balance approach with the loss and gains in nutrients dissolved in the water expressed in terms of areal rates. Losses of both nutrients occurred during periods of low streamflow in spring and summer. Losses of silicon are attributed to growth of epilithic diatoms whereas nitrate losses are consistent with a number of processes including the growth of aquatic plants, the development of epilithic biofilms and nitrogen transformations, such as denitrification, in bed-sediments. Stream water gained dissolved nitrite during its passage through the section. Silicon losses from the stream amounted to between 52 and 63 mmol m(-2) d(-1) (expressed per area of bed-sediment) for the spring periods in 1992-94. Nitrate losses were more variable with overall rates between 24 and 89 mmol m(-2) d(-1) for the summer periods in 1991-93.