Application of Cross-Flow Microfiltration for the Treatment of Combined Sewer Overflow Wastewater

Application of cross-flow microfiltration with and without backpulsing is evaluated for the treatment of dilute primary sewage effluent simulating combined sewer overflow wastewater. Four alpha alumina ceramic membranes of various pores sizes (0.2–5.0?μm) were tested to understand the impact of cross-flow velocity and transmembrane pressure on the permeate water quality and flux rate. The 0.2 and 0.8?μm membranes produced a permeate water quality that is likely to be suitable for surface water discharge. The combination of permeate chemical and biological water quality and long-term flux rates suggest that a 0.2?μm membrane would be the most appropriate membrane for the treatment of combined sewer overflow wastewater within sewersheds.     

Parsimonious Model for Combined Sewer Overflow Pollution

The reservoir concept for flow modeling has been generalized for the purpose of the parsimonious modeling of combined sewer overflow pollution. Conceptual models have been used for the buildup and washoff of pollutants on the paved surfaces, and the transport of these pollutants in the sewer system (advection, dispersion, sedimentation, and resuspension). For the parsimonious modeling of the water quality of the sewage in the effluent of the combined sewer system, the conceptual submodels of these different processes were lumped into one single model equation. When ancillary structures such as a storage sedimentation tank are present at the combined sewer overflow, the additional effect of advection, dispersion, storage, and sedimentation is considered in a similar parsimonious conceptual way. Such a parsimonious model aims to reduce the model complexity, and therefore the number of calibration parameters. In most practical cases of urban drainage modeling, water quality data are extremely limited and consequently only a small number of parameter values can be identified from the data. The proposed model is tested on the basis of 10-min and hourly concentration measurements for total suspended solids, settleable solids, biochemical oxygen demand, and ammonia at the outlet of the combined sewer system of the village of Dessel (Belgium), which were available in this case only for six overflow events.     

CFD Modeling of Solid Separation in Three Combined Sewer Overflow Chambers

The knowledge of solid behavior in combined sewer overflow (CSO) chambers is a great challenge for the protection of receiving watercourses. Moreover, great attention must be given to the occurrence of deposits on the bed of the chamber because they may lead to operation problems. In this paper, we investigate the capability of a particle tracking approach to determine the solid separation in CSO chambers. This is done by comparing simulations and experimental data collected in three small-scale models, as reported by Kehrwiller 1995. The trap, reflect, and bed shear stress (BSS) boundary conditions are compared. We propose to use the Shields relationship for evaluating the critical BSS. Finally, we propose a methodology for predicting the solid separation in CSO chambers using computational fluid dynamics.     

Pilot Scale Demonstration of Cross-Flow Ceramic Membrane Microfiltration for Treatment of Combined and Sanitary Sewer Overflows

A pilot scale investigation was undertaken at the Allegheny County Sanitary Authority (ALCOSAN) for approximately 12 months to evaluate the feasibility of using cross-flow microfiltration for the treatment of primary sewage effluent simulating combined and sanitary sewer overflows. Ceramic membranes of various pores sizes (0.05–1.4?μm) were tested to understand the impact of cross-flow velocity, transmembrane pressure, and feed suspended solids on permeate water quality and permeate flux rate. A 0.2?μm membrane operated with a 1.8?m/s cross-flow velocity, a transmembrane pressure below 2.1 bar and a backpulse frequency of 60 s showed the best performance among the conditions evaluated in this study. The 0.2?μm membrane consistently met water quality objectives for fecal coliforms, E Coli, enterococci, BOD5, and suspended solids independent of the feed concentration, suggesting that direct discharge to surface water may be feasible. Feed suspended solids concentration and temperature influenced membrane permeate flux. Membrane cleaning with alkaline sodium hypochlorite solution is recommended as the first step followed by nitric acid cleaning if needed.     

Hydraulics of Broad-Crested Weirs with Varying Side Slopes

The flow of water over a trapezoidal, broad-crested, or embankment weir with varying upstream and downstream slopes has been investigated. Data are presented comparing the effect of slopes of 2H:1V, 1H:1V and vertical in various combinations on the upstream and downstream faces of the weir. Pressure and surface profiles were self-similar for all cases tested. Increasing the upstream slope to the vertical decreased the height of the surface profile and, hence, the static pressure of the crest. It also reduced the discharge coefficient. The variation in downstream static pressures was negligible though. Varying the downstream slope had a negligible effect on the surface and pressure profiles over the weir. Changes in flow were constrained to the region downstream of the crest. Cavitation could occur at the downstream corner of the weir if the upstream head was sufficiently high and a sloped face was used. This paper presents data that will be of use in the design of hydraulic structures for flow control and measurement.     

Bottom Slot Discharge Outlet for Combined Sewer Diversion Structure

The concept of a bottom slot outlet was developed to serve as a combined sewer overflow diversion structure to convey flow to deep tunnel storage under free discharge conditions and pass the remaining volume once storage capacity is exceeded with minimum backwater effects. In order to test the concept, a 1:19.5 scale model was constructed and tested over a range of discharges in order to determine the required slot length to pass a certain discharge. Different bottom slopes and slot widths were tested. For subcritical approach flow, the flow in the structure passed through critical depth at the upstream end of the slot, eliminating the possibility of backwater effects. The results were found to be nearly independent of the bottom slope for typical small slopes in sewer systems, and a simple dimensionless relation was developed to relate the slot length to other parameters. A mathematical model combining continuity and energy relations for the remaining flow in the structure with an orifice relation for flow through the slot was capable of reproducing the observed experimental results.     

Hydraulic Design of a Tilting Weir Allowing for Periodic Fish Migration

The hydraulic design of a tilting weir is presented, which allows for periodic exchange of potadromous fish between freshwater ecosystems. The application domain includes inland waters that need to be isolated hydraulically, preserving the existing ecological connection with the surrounding areas as much as possible. In the absence of a hydraulic gradient, the weir is opened in its neutral position and fish can bypass through passages sideways of the weir. When a hydraulic gradient develops in either of two directions, the weir rotates until a new balance of moments of force is reached, while fish can still bypass. Above a threshold value of the hydraulic gradient, the weir falls shut. When the hydraulic gradient returns to zero, the weir reopens, restoring the ecological connection. Four variants of the weir were investigated in the Hydraulics Laboratory at Wageningen University. The versatility of the design is demonstrated by showing that the hydraulic gradients required for closure and reopening can be manipulated largely independently. Patterns of flow velocity and turbulence kinetic energy were analyzed, which suggest that relevant fish species can bypass the weir unimpeded. The effectiveness of the weir will mainly depend on hydrostatic aspects, which determine when the weir is opened and closed, and on the absence of large hydraulic gradients in the migration season.     

Global Predictive Real-Time Control of Sewers Allowing Surcharged Flows

A global predictive real-time control strategy minimizing overflow volumes from combined sewers during rainfalls is presented. For an optimal use of controlled sewer transport and storage capacities, the proposed strategy allows surcharged flows. Flows and piezometric heads in the sewer are computed according to flow inputs by a hydraulic simulation model. The optimal operation of the regulators controlling these flow inputs is determined on a finite control horizon using the generalized reduced gradient optimization algorithm. The control strategy was applied to the 23 rain events that occurred during the summer of 1989 on the urban area drained by the Marigot interceptor in Laval, Canada. In this application, the admitted intensity of surcharges was varied to assess this parameter impact on total overflow volumes. A comparison between performances of the proposed strategy and a local reactive control was also carried out. Results obtained indicate that the global predictive control can reduce overflow volumes during rainstorms and that this reduction may be improved by allowing surcharged flows.     

Single- and Multievent Optimization in Combined Sewer Flow and Water Quality Model Calibration

Over the last three decades, storm-water quality modeling has been used increasingly commonly to describe the general system behavior and assess the pollution loads transferred in and spilled out of combined sewer systems. The calibration of quality models is, in most cases, based on conventionally obtained calibration data, e.g., by automated sampling. Long-term high-resolution online measurement data are available for the Graz West catchment (Graz, Austria), allowing an assessment of the full dynamics of discharge and pollution concentrations. This paper focuses on the application and comparison of single-event and two different multievent optimization schemes for sewer-water quality model calibration. While both single- and multievent optimization lead to satisfying results for the calibration events in discharge calibration, it is shown that validation events are better reproduced by using multievent calibration. Single- and multievent autocalibration of pollution concentration is based on the best dataset obtained from the discharge calibration. As for discharge, the pollutographs are reproduced satisfactorily, and multievent calibration is more stable. In all cases, the two multievent approaches performed equally well.     

Combined Flow over Weir and under Gate

Problems related to sedimentation and deposition can be minimized by using a system where weirs and gates are combined. Given its applications, the hydraulics of simultaneous flow over weir and under gate, in particular, the determination of the stage–discharge relationship, is of interest. Although previous approaches have been based on regression or dimensional analysis, the current work describes a physically based approach. Models of sharp-edged weirs and gates with no lateral contraction are combined. To calibrate and validate the proposed model, experiments have been carried out in a laboratory flume applying different submergence conditions. It was found that the model is able to predict the stage–discharge relationship with reasonable accuracy.     

Dissipation of Turbulent Kinetic Energy near a Bubble Plume

Profiles of the rate of dissipation of turbulent kinetic energy were inferred from temperature microstructure measurements near a bubble plume at the center of a tank with diameter of 13.7 m and maximum depth of 8.3 m. Six sets of between 18 and 51 profiles were collected at airflow rates of 0.1–0.6 L/s, measured at atmospheric pressure, and ensemble-averaged dissipation profiles were calculated. The dissipation in all cases was between 10?8 and 10?6?m2/s3 in most of the profile, but it increased sharply near the water surface. Energy considerations are used to discuss the experimental results in terms of previous numerical models of bubble plume turbulence. Two previous numerical studies show that the turbulence dissipates between 15 and 30% of the available power. In the experiments, the fraction is less than 1% because some of the energy of the plume is used to generate waves on the water surface and the profiles used to compute the volume-averaged dissipation were relatively far from the bubble plume.     

Hydraulics of Stacked Drop Manholes

This paper presents the results of an experimental investigation on flows inside stacked drop manholes (SDM). An SDM consists of two identical rectangular or square manhole chambers stacked together at an elevation difference. SDMs for different conditions were assessed on their ability to dissipate the energy of the approaching flow and their suitability to perform adequately under different flow conditions. Flow regimes were classified based on the inflow conditions and geometry of the structure in the first chamber and downstream outflows in the second chamber. An analysis based on the integral momentum equation was developed to estimate pool depths and energy losses under critical flow conditions. A fully surcharged stage with inflow and outflow pipes running full was also tested and velocity profiles were measured at a horizontal center plane to the opening connecting both shafts. Additionally, air flow rates were measured to assess the air demand into a large-height SDM.     

Performance of Wet Weather Treatment Facility for Control of Combined Sewer Overflows: Case Study in Cincinnati, Ohio

Efforts aimed at reducing pollutant loads from combined sewer overflows (CSOs) on the Muddy Creek receiving waters in Cincinnati, Ohio have been underway in recent years. This includes an investigation of the treatment performance of a flow-through wet weather treatment facility (WWTF) using off-line sedimentation tanks, fine screening and chemical disinfection (disinfection was inactive during this study). Calculations using hydrographs and water quality samples collected at the WWTF during rain events established the mass of biochemical oxygen demand (BOD)5, chemical oxygen demand, and total suspended solids (TSS) removed. Ten storm events sampled from January to September 2002 helped characterize pollutant removal efficiencies for flow-through treatment. Pollutant removal was classified into four components: flow to the wastewater treatment plant (WWTP), sedimentation, storage, and screening. Most pollutant removal was achieved through settling and storage in the treatment tanks, with removal efficiencies of 20–50% for BOD5 and 25–70% for TSS commonly observed. Owing to the high pollutant load in the early portion of the CSO hydrograph, first-flush containment, or capturing and conveying the early portion of the runoff event to the WWTP, was the most efficient treatment method for every storm investigated.     

Modeling a Retention Treatment Basin for CSO

Combined sewer overflows (CSOs) result in hazardous and unsightly contamination of receiving waters, particularly swimming areas. The removal of suspended solids and associated biological oxygen demand (BOD) can accelerate the recovery following a CSO event. This paper presents a numerical model to simulate the solids removal efficiency of a retention treatment basin (RTB) that utilizes polymers to improve the flocculation and settling rates for the suspended solids. The model includes settleable, nonsettleable, and floatable solids. The sludge is treated as a non-Newtonian fluid. Discrete, zone, and compression settling/floatation regimes are included. In-tank flocculation and a storage zone for sludge flushing are also included in the model. The model was calibrated and validated with data from a RTB pilot plant, and was applied to evaluate preliminary designs for a prototype RTB for the City of Windsor. The calibrated model showed that the optimum location of the target baffle was approximately 30% of the distance to the scum baffle. For design flows of 20?m/h and run durations of up to 2?h, it was found that the removal was insensitive to slopes from ?1 to ?3% and depths greater than 2.5?m (L/H = 10). The simulations indicate that 70 to 78% of solids removal can be achieved at surface overflow rates up to 25?m/h.     

Real-Time Detection of Sanitary Sewer Overflows Using Neural Networks and Time Series Analysis

Sanitary sewer overflows (SSOs) are becoming of increasing concern as a health risk. Utilities and regulators have taken preventive measures but many overflows still occur and are not identifiable, especially in access-challenged locations. Several mathematical approaches are presented for detecting if a disruption in the system is impending or occurring based on measurements at one or more locations in the system. Time series analysis and neural networks are used as prediction tools for expected depths and flows for single measurement locations and a neural network is developed for a multiple monitor system. Control limit theory is applied in all cases for identifying significant deviations of measured values from the expected values that suggest a SSO is occurring. Data from Pima County Wastewater Management’s monitoring system are used in two case studies.     

Design of Circular Urban Storm Sewer Systems Using Multilinear Muskingum Flow Routing Method

In this study, a multilinear Muskingum method is presented for hydrologic routing through circular conduits. In order to increase accuracy, the reference discharge is assumed to be a nonlinear function of conduit diameter, Manning coefficient, bed slope, and peak discharge of the inflow hydrograph. The reference discharge function has been determined using a nonlinear regression technique. Flow depths are computed at every time step by solving the continuity equation using an implicit finite difference scheme. Many storm hydrographs were routed through circular conduits of various sizes by the proposed model. The calculated routed hydrographs and water surface profiles indicate close agreement with those obtained by solving Saint Venant equations. Using this method, a branched urban sewer system was designed. This indicates that the method can be easily implemented for design purposes because of its simplicity, accuracy, and computational efficiency.     

Settling Velocity Grading of Particle Bound PAHs: Case of Wet Weather Flows within Combined Sewer Systems

The elaboration, management, and design of the sedimentation devices require an improved knowledge not only on the suspended solids (SS) settling velocity but also on the distributions of these particulate pollutants by category of SS settling velocity. Nevertheless, there is currently a lack of available data regarding the settling velocity grading of particle bound pollutants. As a consequence, this study investigating the settling velocity grading of particle bound polycyclic aromatic hydrocarbons (PAHs) in wet weather flows within combined sewers was launched. The pursed objectives were to compare the SS and PAH settling velocity grading curves and hence to assess whether or not PAHs were associated with a specific settling velocity category. Investigations were carried out for three storms at two sampling sites within the Parisian combined sewer. Results indicate that most of PAHs seem to be preferentially associated with particles with a settling velocity >0.3?mm?s?1.     

组合式飞剪剪臂优化设计

组合飞剪的特点是剪切机构即可以在曲柄模式下工作、也可以在回转模式下工作,在棒材生产线中应用比较广泛。但曲柄模式向回转模式转换时由于曲柄轴与剪头固定销轴之间接触面积小、冲击大而容易损坏。曲柄轴损坏后需要飞剪开箱更换,用时较长。针对此问题对组合式飞剪剪臂进行了优化设计改造,从而避免了因曲柄轴损坏造成的长时间设备停机。     

Case Study: Refinement of Hydraulic Operation of a Complex CSO Storage/Treatment Facility by Numerical and Physical Modeling

The performance of a combined sewer overflow (CSO) storage/treatment facility in North Toronto, Ont., Canada, was investigated by conjunctive numerical and physical (hydraulic) modeling. The main objectives of the study were to (1) assess the feasibility of increasing the hydraulic loading of the CSO facility without bypassing; and (2) establish a verified numerical model of the facility for future work. The numerical model [a commercial computational fluid dynamics (CFD), PHOENICS] was validated and verified using results from a hydraulic scale model (1:11.6). The results obtained show that the CFD model can simulate hydraulic conditions in the facility well, as demonstrated by accurate reproduction of the filling rate, water levels at various locations, flow velocities in feed pipes, and overflows from the inflow channel. Numerical simulations identified excessive local head losses and helped select structural changes to reduce such losses. The analysis of the facility showed that with respect to hydraulic operation, the facility is a complex, highly nonlinear hydraulic system. Within the existing constraints, a few structural changes examined by numerical simulation could increase the maximum treatment flow rate in the CSO storage/treatment facility by up to 31%.