Stream productivity analysis with dorm—II: Parameter estimation and sensitivity

The dissolved oxygen routing model DORM, which determines productivity and respiration of a stream biological community, requires in addition to stream geometry and stream flow, parameter values for reaeration coefficients and temperature and dissolved oxygen (DO) limitations on respiration. Illustrated are the methods used to obtain numerical values in a field study at the U.S. EPA Monticello Ecological Research Station. The calculated community productivity and respiration rates are sensitive to certain input parameters and assumptions. Analysis showed that, among the many parameters needed, hydraulic residence time and reaeration coefficients should be determined with utmost care. Other sensitivity tests included temperature effects, half-saturation values and longitudinal dispersion.     

Stream productivity analysis with dorm—III: Productivity of experimental streams

Thirty-two two-station diel dissolved oxygen surveys were made in the experimental streams of the U.S. EPA Monticello Ecological Research Station. The data were analyzed by a numerical Dissolved Oxygen Routing Model (DORM) to determine total community respiratory and photosynthetic rates. The artificial channels consisted of pools and riffles and had pH of 8.0, 6.3 and 5.4. Community photosynthetic production and respiration ranged from highs of 14.8 and 10.7gm⁻² day⁻¹ to lows of 1.5 and 2.6gm⁻² day⁻¹ between June and September 1979. P/R ratios varied from 2.1 in May to 0.6 in August. Seasonal trends were affected by pH and/or age of the channel. The channels also exhibited large diel variations in photosynthetic efficiency, where dependence of photosynthetic production upon light was nonlinear and had a strong hysteresis. This hysteresis cannot be explained by physical processes and is attributed to several biological processes.     

Management of optimum water quality in a stream

An optimal waste discharge policy along a stream is investigated based on a program of minimizing the total cost benefit function on a regional basis. The system consists of a stream along which are located several inputs of waste and intakes of water. The cost benefit function comprises of the sum of the cost of waste treatment and the cost of water treatment minus the benefits derived from maintaining a certain water quality in the stream. The biochemical oxygen demand and the dissolved oxygen are considered to be the primary indicators of water quality. A steady state dispersion model is employed to predict the BOD and DO concentrations along the stream.     

Studies on dissolved oxygen concentration and sludge retention time affecting the full-scale activated sludge process

We have made a series of experiments on dissolved oxygen (DO) concentration and sludge retention time (SRT) to affect the full-scale activated sludge process.

For DO control, a better effluent water quality and a reduced current consumption have been achieved as compared with those in a constant air flow operation. The best control point for the DO control operation is at the outlet side of the aeration tank.

For SRT control, effluent COD seems to fluctuate slightly, and is favorably stable when SRT is between 10 and 20 days. It takes about twice as many days as SRT value set up for the total mass of sludge in the process (M) to be stabilized in case of making set value change as a result of simulation using mathematical models.     

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.     

Multivariate techniques relating macroinvertebrate and environmental data from a river catchment

Macroinvertebrates were collected over 4 years by standard sampling procedures used within the UK Environment Agency (EA). Contemporary environmental data were used to “explain” biological variation using multivariate techniques provided by the program CANOCO. Variations in macroinvertebrate taxa composition, Biological Monitoring Working Party (BMWP) score and average score per taxon (ASPT) primarily reflected changes in habitat across the Mole catchment. When the analysis was restricted to sites overlying the dominant geological stratum (Weald clay) the principal variation in taxa composition, BMWP score and ASPT was most correlated with variation in water quality. Significant correlations between the presence of certain taxa and measurements of dissolved oxygen (DO) provided support for the relative scores attributed to these taxa by the BMWP. The month in which a macroinvertebrate sample was collected was relatively unimportant as an influence on taxa composition.     

Study on two operating conditions of a full-scale oxidation ditch for optimization of energy consumption and effluent quality by using CFD model

The operating condition of an oxidation ditch (OD) has significant impact on energy consumption and effluent quality of wastewater treatment plants (WWTPs). An experimentally validated numerical tool, based on computational fluid dynamics (CFD) model, was proposed to optimize the operating condition by considering two important factors: flow field and dissolved oxygen (DO) concentration profiles. The model is capable of predicting flow pattern and oxygen mass transfer characteristics in ODs equipped with surface aerators and submerged impellers. Performance demonstration and comparison of two operating conditions (existing and improved) were carried out in two full-scale Carrousel ODs at the Ping Dingshan WWTP in Henan, China. A moving wall model and a fan model were designed to simulate surface aerators and submerged impellers, respectively. Oxygen mass transfer in the ditch was predicted by using a unit analysis method. In aeration zones, the mass inlets representing the surface aerators were set as one source of DO. In the whole straight channel, the oxygen consumption was modeled by using modified BOD-DO model. The following results were obtained: (1) the CFD model characterized flow pattern and DO concentration profiles in the full-scale OD. The predicted flow field values were within 1.98 ± 4.28% difference from the actual measured values while the predicted DO concentration values were within −4.71 ± 4.15% of the measured ones, (2) a surface aerator should be relocated to around 15 m from the curve bend entrance to reduce energy loss caused by fierce collisions at the wall of the curve bend, and (3) DO concentration gradients in the OD under the improved operating condition were more favorable for occurrence of simultaneous nitrification and denitrification (SND).     

Causes of low oxygen in a lowland, regulated eutrophic river in Eastern England

In the River Brett, Eastern England, over the period 1955-1998 there was a significant long-term decline in dissolved oxygen (DO), as well as increases in TON (total oxidised nitrogen) and SRP (soluble reactive phosphorus). Flow decreased from 1963 to 1998. Field studies in 1998-2000 showed increased pH and a gradient of DO beneath the filamentous alga Cladophora glomerata. DO decreased through the summer. Macrophytes accounted for 45% of community respiration at the study site, while sediment accounted for 36%. In container studies, muddy sediments had the highest maximum sediment oxygen demand (SOD), but canopies of C. glomerata and Lemna minor together increased the SOD by up to 90% over control samples. During periods of high temperature, abundant growths of C. glomerata and/or L. minor would increase the SOD of organic mud in river areas with shallow, ponded water, eventually leading to anoxic conditions and the release of nutrients from the sediment. If a river had large areas of mud, these processes could dramatically affect the river's oxygen budget, and hence its ecology.     

Measurement and modelling of quality changes in stored untreated grey water

This paper describes an investigation into stored untreated grey water quality processes and the development of a computer simulation for those processes. A laboratory study was carried out to investigate the changes in water quality with increasing residence time, and the results were used to calibrate and verify the model. Model results gave a good fit for dissolved oxygen (DO) concentrations, but only a reasonable fit for chemical oxygen demand (COD). Still, the main trends of model and laboratory COD data were broadly represented. Measurement and model results tend to confirm the initial hypothesis of four major processes in operation: settlement of suspended solids, aerobic microbial growth, anaerobic release of soluble COD from settled organic matter and atmospheric reaeration. Storing grey water for 24 h may significantly improve water quality through rapid settlement of organic particles, however, storage beyond 48 h leads to depleted DO levels and potential aesthetic problems. A more detailed model of COD fractions within grey water (with the relevant measured data) in conjunction with a characterisation of particulate settling velocities should lead to improvements in model predictions.     

Sedimentary microbial oxygen demand for laminar flow over a sediment bed of finite length

Dead organic material accumulated on the bed of a lake, reservoir or wetland often provides the substrate for substantial microbial activity as well as chemical processes that withdraw dissolved oxygen (DO) from the water column. A model to estimate the actual DO profile and the "sedimentary oxygen demand (SOD)" must specify the rate of microbial or chemical activity in the sediment as well as the diffusive supply of DO from the water column through the diffusive boundary layer into the sediment. Most previous experimental and field studies have considered this problem with the assumptions that the diffusive boundary layer is (a) turbulent and (b) fully developed. These assumptions require that (a) the flow velocity above the sediment bed is fast enough to produce turbulent mixing in the boundary layer, and (b) the sediment bed is long. In this paper a model for laminar flow and SOD over a sediment bed of finite length is presented and the results are compared with those for turbulent flow. Laminar flow near a sediment bed is encountered in quiescent water bodies such as lakes, reservoirs, river backwaters, wetlands and ponds under calm wind conditions. The diffusive oxygen transfer through the laminar diffusive boundary layer above the sediment surface can restrict the microbial or chemical oxygen uptake inside the sediment significantly. The developing laminar diffusive boundary layer above the sediment/water interface is modeled based on the analogy with heat transfer, and DO uptake inside the sediment is modeled by Michaelis-Menten microbial growth kinetics. The model predicts that the rate of SOD at the beginning of the reactive sediment bed is solely dependent on microbial density in the sediment regardless of flow velocity and type. The rate of SOD, and the DO penetration depth into the sediment decrease in stream-wise direction over the length of the sediment bed, as the diffusive boundary layer above the sediment/water interface thickens. With increasing length of the sediment bed both SOD rate and DO penetration depth into the sediment tend towards zero if the flow is laminar, but tend towards a finite value if the flow is turbulent. That value can be determined as a function of both flow velocity and microbial density. The effect of the developing laminar boundary layer on SOD is strongest at the very lowest flow velocity and/or highest microbial density inside the sediment. Under quiescent conditions, the effective SOD exerted by a reactive sediment bed of a lake or wetland approaches zero, i.e. no or very little oxygen demand is exerted on the overlying water column, except at the leading edge.     

Diel changes in water chemistry in an arsenic-rich stream and treatment-pond system

Arsenic concentrations are elevated in surface waters of the Warm Springs Ponds Operable Unit (WSPOU), located at the head of the upper Clark Fork River Superfund site, Montana, USA. Arsenic is derived from historical deposition of smelter emissions (Mill and Willow Creeks) and historical mining and milling wastes (Silver Bow Creek). Although long-term monitoring has characterized the general seasonal and flow-related trends in As concentrations in these streams and the pond system used to treat Silver Bow Creek water, little is known about solubility controls and sorption processes that influence diel cycles in As concentrations. Diel (24-h) sampling was conducted in July 2004 and August 2005 at the outlet of the treatment ponds, at two locations along a nearby reconstructed stream channel that diverts tributary water around the ponds, and at Silver Bow Creek 2 km below the ponds. Dissolved As concentration increased up to 51% during the day at most of the stream sites, whereas little or no diel change was displayed at the treatment-pond outlet. The strong cycle in streams is explained by pH- and temperature-dependent sorption of As onto hydrous metal oxides or biofilms on the streambed. Concentrations of dissolved Ca(2+) and HCO(3)(-) at the stream sites showed a diel temporal pattern opposite to that of As, and geochemical modeling supports the hypothesis that the concentrations of Ca(2+) and HCO(3)(-) were controlled by precipitation of calcite during the warm afternoon hours when pH rose above 9.0. Nightly increases in dissolved Mn and Fe(II) concentrations were out of phase with concentrations of other divalent cations and are more likely explained by redox phenomena.     

A dynamic model for DO—BOD relationships in a non-tidal stream

Dynamic models for dissolved oxygen (DO)-biochemical oxygen demand (BOD) interaction in a reach of river are not easily verified owing to the difficulties in obtaining data. In this paper a simple lumped-parameter model is presented and verified by deterministic simulation against field measurements collected over an 80-day period from the River Cam in eastern England. An important feature of the model is a pseudo-empirical term based on sunlight hours which is introduced to predict explicitly the significant effects of algal growth and decay encountered during prolonged sunny, dry weather.     

Predicting oxygen transfer and water flow rate in airlift aerators

Water flow rate, gas-phase holdup, and dissolved oxygen (DO) profiles are measured in a full-scale airlift aerator as a function of applied air flow rate. A model that predicts oxygen transfer based on discrete-bubble principles is applied. The riser DO profiles are used to calculate the initial bubble size. The range of calculated bubble diameters obtained using the model is 2.3-3.1 mm. The Sauter-mean diameter of bubbles measured in the laboratory ranged from 2.7 to 3.9 mm. The riser and downcomer DO profiles and gas holdups predicted by the model are in close agreement with the experimental results. A model that predicts water flow rate based on an energy balance is used to calculate Kt, the frictional loss coefficient for the air-water separator. Excluding the data at the very lowest air flow rate, the range of calculated values for Kt (3-8) is close to a literature value of 5.5 proposed for hydrodynamically similar external airlift bioreactors. The models should prove useful in the design and optimization of airlift aerators.     

Analysis of photosynthetic activity in the most polluted stretch of river Ganga

As a result of the increasing anthropogenic activities in the gangetic plain, Ganga water quantity as well as quality has declined over the years. A major effort to clean Ganga, named Ganga Action Plan (GAP) was instituted by the Government of India in 1984. The emphasis in GAP was on the reduction of organic load on the river through interception, diversion and treatment of wastewater reaching the river, thus maintaining the biochemical oxygen demand (BOD) and dissolved oxygen (DO) levels of river within the acceptable limits. A major criticism of GAP is that the significance of river ecology has not been addressed adequately during its conception and implementation. One of the important aspects from this perspective is the photosynthetic activity in the river Ganga. It has been postulated that photosynthetic activity plays an important role in maintaining high levels of DO in Ganga, and as a result the river can assimilate high organic loads without appreciable depletion in dissolved oxygen levels. Objective of the present study was to assess the photosynthetic activity and oxygen production rates in the river and correlate these values with various water quality parameters. Most polluted stretch of Ganga, which is known as the Kannauj-Kanpur stretch was chosen for this study. Based on the results of the study, it was concluded that despite implementation of phase I of GAP, and consequent diversion and reduction of organic loading to the river, both BOD and DO levels in the river has increased in the entire Kannauj-Kanpur stretch, except at Jajmau, where anaerobically treated effluent is discharged to the river. The nitrogen levels have also increased in the entire Kannauj-Kanpur stretch. Dissolved oxygen (DO) and alkalinity in the river water vary diurnally at all sites. Chlorophyll-a levels and oxygen production rates due to photosynthesis appear to be positively influenced by phosphate levels in the river water. Chlorophyll-a levels appear to be negatively correlated to the Ammonical and total Total Kjeldahl Nitrogen (TKN) content in the river water, suggesting the possibility of release of nutrients due to algal death and decomposition under certain circumstances.     

A model for a nitrifying suspended-growth reactor incorporating intraparticle diffusional limitation

A mathematical model for a nitrifying suspended growth reactor that incorporates intraparticle diffusional limitation is presented. A parameter describing the physical characteristics of floc was introduced to overcome the experimental difficulties in determining floc characteristics. Model validation was carried out by comparing the estimated values of the half-velocity constants for the dissolved oxygen effect on Nitrosomonas and Nitrobacter obtained using the model with and without diffusional limitation terms. A sensitivity analysis revealed the results were affected by uncertainties in assigning values to the kinetic coefficients, but the probability for significant diffusional limitation was high. The significance of the model was demonstrated through computer simulation where the interaction between the floc characteristics parameter (influenced primarily by mixing intensity) and dissolved oxygen were predicted to be significant in influencing nitrogen removal.     

Characteristics of microfiltration membranes in a membrane coupled sequencing batch reactor system

Factors affecting filtration performance were investigated in a sequencing batch reactor (SBR) coupled with a submerged microfiltration module. Special bioreactors for aerobic and anoxic phases were specifically designed in order to differentiate the effect of dissolved oxygen (DO) from that of mixing intensity, on membrane filterability. When the filterability of a submerged microfilter was examined at each SBR phase, DO concentration, as well as mixing intensity proved to have a major influence on the membrane performance regardless of the SBR phase. A higher DO concentration resulted in a slower rise in TMP, corresponding to less membrane fouling, which was investigated in depth through a series of analyses including resistance measurements and compressibility of the cake layer as well as particle sizes as a functions of DO for both aerobic and anoxic phases in SBR.     

Evaluation of cycling patterns of dissolved oxygen in a tropical lake as an indicator of biodegradable organic pollution.

Dissolved oxygen cycling patterns in a tropical lake (Weija Lake) were shown to be useful as a potential indicator of biodegradable organic pollution, by dosing with liquid malt to give an additional organic burden of 2.5 and 5.0 mg l-1 TOC, and monitoring the DO values continuously for 140 h. These loadings were added to water columns (in tubes) suspended from a raft in a lake in south-east Ghana. The addition of organic pollution burden to the lake water produced two main effects: the mean DO value was lowered, and the amplitude of the DO cycle decreased as organic loading increased from 2.5 to 5.0 mg l-1 TOC. There was also an indication of heterotrophic respiration associated with organic inputs for the 5.0 mg l-1 added TOC suggesting a P/R ratio of well below 1.0. Taking the results of a DO cycling computer model together with those from the lake raft experiments, it can be concluded that dissolved oxygen cycles can be a good indicator of biodegradable organic pollution load.     

针阀在城市给水厂和污水厂中的应用

从避免气蚀和调节水、气流量等方面介绍了电动针阀在城市给水厂和污水处理厂中的应用，并结合杭州西区水厂和七格污水处理厂的实例阐述了电动针阀结合流量计在水厂输水管线流量调节中的控制方法，以及溶氧仪和针阀联动控制曝气池DO的应用。     

低溶解氧对生物膜特性的影响研究

通过考察生物膜的生长特性、除污效率、脱氢酶活性以及微生物群落组成,分析了低溶解氧对生物膜特性的影响,验证了在低溶解氧条件下采用生物膜反应器处理低浓度生活污水的可行性.试验发现,在低溶解氧条件下生物膜具有特殊的生长特性与外观结构,对COD、SS的去除率分别达到60%和90%以上;由于液相中的低浓度有机物向生物膜内的扩散通量较小,使其成为生物膜降解活性的主要限制因素;长期在低溶解氧下运行会使生物膜内环境更适合兼性异养菌的生长,而总的细菌含量变化不大,保证了生物膜具有较高的处理效率.这为降低污水处理能耗,拓宽生物膜反应器的应用范围提供了新的思路和理论基础.     

The interaction of treated bleached kraft mill effluent and dissolved oxygen concentration on the survival of the developmental stages of the sheepshead minnow (Cyprinodon variegatus)

The interactions of treated bleached kraft mill effluent (BKME) and dissolved oxygen concentration (DO) on the survival of the embryo, fry, juvenile and adult stages of the sheepshead minnow, Cyprinodon variegatus, were studied under continuous-flow 96 h bioassay conditions. Embryo survival was dependent on effluent concentration only and showed no interaction at nominal DO concentrations of 1.0, 3.0 and 5.0 mg l⁻¹. Survival of the fry was related solely to DO concentration with no interaction with BKME concentrations up to 100%. Juvenile sheepshead minnows showed increased sensitivity to BKME at a nominal DO concentration of 1.0 mg l⁻¹. Adult fish were not affected by BKME at any of the DO concentrations tested. This study shows that the acute toxicity of BKME effluent to sheepshead minnows is a function of the developmental stage of the organism and DO concentration in the receiving stream.