Wedge-wire Screens Research Articles

Hydraulic Analysis of a Passive Wedge Wire Water Intake Screen for Ichthyofauna Protection

A passive wedge screen, thanks to its many functional and environmental advantages, has recently become a popular type of surface water intake for municipal and industrial purposes. The design solutions proposed in this paper for a passive wedge wire screen intake model and two different deflectors have been experimentally tested under conditions that can be considered as no-flow conditions at the hydraulic flume. There was only a slight flow associated with the operation of the screen, while there was almost no flow in the hydraulic channel itself, such that it would be considered a watercourse. A hydraulic analysis was carried out, including velocity distribution around the screen as well as the determination of head losses with or without deflectors installed inside the screen. Lower inlet and inflow velocities to the surface of the water intake reduce the risk of injury or death to small fish and fry as well as attracting pollutants understood as sediments, debris, and plant remains floating in the river. In order to achieve the lowest possible maximum inlet and inflow velocities at the highest possible intake capacity, it was necessary to equalize the approach velocity distributions. It was shown that by using the proposed deflectors, the approach velocity distributions were equalized and the maximum values of inflow and inlet velocities were reduced. A water intake screen with a deflector with an uneven porosity distribution equalized the approach velocities better than a deflector with equal openings, but the differences were small. Installing the wedge screen model reduced the maximum inlet velocity from exceeding 2 m/s to a value of 0.08 m/s, and after installing deflectors with equal and unequal openings to values of 0.06 m/s and 0.05 m/s, respectively. In addition to laboratory tests, the paper describes the numerical simulations performed in ANSYS Fluent software. The results of the simulations made it possible to obtain a broader study, as well as to compare the velocity values obtained at the measuring points during the laboratory tests.

The influence of passive wedge-wire screen aperture and flow velocity on juvenile European eel exclusion, impingement and passage

The European eel (Anguilla anguilla) is a critically endangered catadromous fish. The decline has partly been attributed to water management infrastructure that abstract water from rivers for potable and industrial water supply, irrigation, hydroelectric power generation and flood defence; eels can be impinged on weedscreens and trashracks and entrained in pumps and turbines. The Eel Regulations (England and Wales) 2009 stipulates measures are required to provide safe (upstream and downstream) passage of eels past such hazardous intakes. Preventing impingement and entrainment of upstream migrating (glass eel and elver) and river-resident (yellow) juvenile eels at hazardous intakes may require fine-mesh aperture screens and low approach velocities due to eels' small size and relatively poor swimming capacity but quantitative evidence is lacking. Here, passive wedge-wire screen aperture (1, 2, 3 and 5 mm) and depth-averaged flow velocities (0, 0.1, 0.15 and 0.2 m·s−1) both influenced the fate (i.e., impingement or passage) and behaviour (i.e., migratory separation or behavioural avoidance) of two size classes of juvenile eels (60–80 mm glass eels and 100–160 mm elvers) in an experimental flume. One and 2 mm aperture screens were required to physically exclude 60–80 mm and 100–160 mm, respectively. Up to 90% and 100% of the 60–80 mm and 100–160-mm size class eels were impinged at 0.2 m·s−1 depth-averaged flow velocity, which also positively influence number of screen contacts per eel and time to eel fate (from first contact). A small proportion of 60–80 mm eels (9.2%) did not approach the screen due to migratory separation (i.e., positive rheotaxis) and eels narrower than the screen aperture did not always pass through the screen, and thus other biological or hydraulic processes may also influence screen passage. It is hoped that these findings help improve screening guidance for regulators, key stakeholders and water abstraction managers to further improve protective measures required for critically endangered eels.

Laboratory-based comparison of screening materials for excluding juvenile freshwater fishes from New Zealand water intakes

ABSTRACT Growing demand for water requires resource managers to be innovative to minimise impacts on aquatic ecosystems. There are increasing concerns about fish damage and losses at water intakes, but few studies have examined the effectiveness of different screening material for excluding New Zealand fishes. We experimentally tested six screens (50–100 and 100–200 mm rock bunds, 3 mm woven mesh, 1.5, 2 and 3 mm wedge-wire), on two introduced and five native fish species. Bluegill bully (> 32 mm), common bully (> 30 mm), Canterbury galaxias (> 47 mm) and rainbow trout (> 40 mm) were screened effectively by 3 mm woven mesh and wedge-wire. Chinook salmon (> 43 mm) and īnanga whitebait (> 46 mm) were excluded by 2 mm wedge-wire, but shortfin elvers (< 80 mm) penetrated 3 and 2 mm wedge-wire, and glass eels (< 63 mm) penetrated 1.5 mm wedge-wire. Rock bunds were effective barriers for rainbow trout but were ineffective, and acted as habitat, for bluegill bully, Canterbury galaxias and shortfin eels. We recommend that 1.5 mm wedge-wire screens are used in the tidal zone of New Zealand rivers, 2 mm screens are used beyond this zone with an upstream transition to 3 mm screens dependent on catchment-specific fisheries values.

Surface Tension Effects on Discharge Capacity of Coanda-Effect Screens

AbstractCoanda-effect screens exclude coarse and fine debris from a variety of water intakes. Water overflows an inclined wedge-wire screen with tilted wires that shear high velocity flow from the ...

Dizajn i kompjuterska simulacija automatski kontrolisanog hidromehaničkog sistema za proizvodnju elemenata sita sa klinastim žicom

The article presents a design of mechatronic system used for the production of wire elements used in looped wedge wire screen manufacturing. Details related to the design of the hydromechanical subsystem, the control subsystem, as well as the simulation of the operation process of the entire system are presented

Improving the Energy Balance of Hydrocarbon Production Using an Inclined Solid–Liquid Separator with a Wedge-Wire Screen and Easy Hydrocarbon Recovery from Botryococcus braunii

The green colonial microalga Botryococcus braunii produces large amounts of hydrocarbons and has attracted attention as a potential source of biofuel. When this freshwater microalga is cultured in a brackish medium, the hydrocarbon recovery rate increases; furthermore, the colony size becomes large. In this study, the effects of such changes on the energy balance of harvesting and hydrocarbon recovery were studied via filtrate experiments on an inclined separator and extraction from a concentrated slurry. The inclined separator was effective for harvesting large-colony-forming algae. The water content on the wire screen of slit sizes larger than 150 µm was &lt;80% and a separation rate of &gt;85% could be achieved. The input energy of the harvesting using the brackish medium with this separator was ≈44% of that using the freshwater medium with vacuum filtration, while the input energy of the hydrocarbon recovery using the brackish medium was ≈88% of that using the freshwater medium with pre-heating before n-hexane extraction. Furthermore, the energy profit ratio of the process in the brackish medium was 2.92, which was ≈1.2 times higher than that in the freshwater medium. This study demonstrated that filtration techniques and hydrocarbon recovery from B. braunii with a low energy input through culture in a brackish medium are viable.

Evaluation of wedge wire screen as a new tool for faeces collection in digestibility assessment in fish: The impact of nutrient leaching on apparent digestibility of nitrogen, carbon and sulphur from fishmeal, soybean meal and rapeseed meal-based diets in rainbow trout (Oncorhynchus mykiss)

The study was carried out to evaluate wedge wire screen as a potential tool for collecting fish faeces from the tank outlet water. Apparent digestibility (AD) estimates of carbon (ADC), nitrogen (ADN), sulphur (ADS), organic material (ADORG) and individual amino acids obtained by the wire screen were compared with stripping. Three diets, with fishmeal, soybean meal (SBM) or rapeseed meal (RSM) as main protein source were extruded and fed to triplicate groups of 120-g rainbow trout (Oncorhynchus mykiss). Faeces were obtained by gentle stripping from the distal abdomen, and by collection from a wedge wire screen 15, 30, 60, 120 and 240 min post feeding. ADORG, ADN and ADS obtained by collection on the screen were significantly (P < .05) higher than those obtained by stripping, except for some values for ADC. Differences in AD between stripping and faeces collected with the wire screen were lower than reported for other methods of collection from water media. Most of the increase in AD of nutrients for wedge wire screen occurred during the first 15 min after defecation. The ADORG, ADC, ADN and ADS were lowest in the RSM diet. The AD of amino acids followed the same pattern as ADN. ADS in the rapeseed diet was particularly low (54.7%), compared to the fishmeal (72.4%) and SBM diet (70.1%). In addition to AD of cysteine, low digestibility of glucosinolates, its degradation products and other sulfonated components are likely reasons for the low ADS. Faeces from the RSM based diet had higher dry matter (DM) concentration than the SBM based diet. Faecal DM recovery for SBM was lowest among the diets for both collection methods. The low DM recovery for the SBM faeces did not affect AD estimates of faeces at the different time intervals, possibly due to simultaneous leakage of nutrients and indigestible marker. In conclusion, the use of wedge wire screen for collection of faeces represents an interesting supplement to stripping. The AD estimates had low random variation and nutrient leaching during faeces collection were dependent on dietary composition.

Assessing the use of vibrations and strobe lights at fish screens as enhanced deterrents for two estuarine fishes.

The role of vision and the lateral-line system in fish-screen avoidance behaviours was investigated in shiner surfperch Cymatogaster aggregata and staghorn sculpin Leptocottus armatus. Avoidance experiments were conducted in front of water-diversion-type wedge-wire fish screens in a laboratory flume with a 0.3 m s-1 water velocity. Fish contacted the screens less frequently during the day than night, indicating that fish screen avoidance is visually mediated during the day. Input from the fishes' lateral-line systems was also blocked with streptomycin-sulphate treatments during the night to determine if these fishes use mechanoreceptive cues to guide screen avoidance in darkened conditions. Streptomycin-treated and untreated fish had similar contact rates suggesting that mechanoreceptive guidance was not increasing the fishes' abilities to avoid contact with non-vibrating screens at night. Fishes were stained with 2-(4-(dimethylamino)styryl)-N-ethylpyridinium iodide (DASPEI) to assess the streptomycin treatment's effectiveness. We also tested the fishes' ability to avoid contact with the screens at night, when a strobe light or industrial vibrator was operated on the screens, to respectively increase the screen's visual and mechanoreceptory guidance potential. Cymatogaster aggregata contacted the screens significantly less frequently when they were vibrating, compared with their night-time controls, suggesting useful mechanoreceptive guidance. Leptocottus armatus contacted the screens significantly less frequently under strobe-light illumination, compared with their night-time controls, suggesting useful visual guidance. This research should benefit fishery and water-resource managers, regarding the development of future fish-protection decisions at screened water diversions.

Effectiveness of horizontally and vertically oriented wedge-wire screens to guide downstream moving juvenile chub (Squalius cephalus)

Physical screens are commonly installed to prevent downstream moving fish from entering dangerous areas (e.g. intakes to hydropower turbines, irrigation canals, and fish farms), and divert them to preferred alternative routes (e.g. bypass systems). In northern temperate regions, assessments of the functioning of screens have largely focused on diadromous species (e.g. salmon and eel), while ignoring those with other life history characteristics. Recent developments in physical screens include the usage of horizontally aligned bars as opposed to traditional vertical ones, but a direct comparison in terms of guidance remains untested. To address this and aid in the development of successful screens for the wider fish community, this study compared the efficacy of wedge-wire screens with horizontally and vertically oriented bars to block and divert downstream moving groups of five chub (Squalius cephalus) to a bypass channel installed in a recirculating flume under two discharge regimes. Hydrodynamics differed between horizontal and vertical screens under both flows; the vertical configuration created a higher velocity gradient towards the bypass. Total guidance (the number of bypass entries as a percentage of the number of approaches) was generally low (mean = 17.3% for all treatments), the highest being recorded for the horizontal screen under low discharge (25.3%). Rejections and holding station events, both proxies for fish exhibiting avoidance of the hydrodynamic conditions created by the screen, were lowest under this treatment. Horizontal performed better than vertical screens in guiding fish to the bypass under low but not high discharge. The results confirm that screen functioning is dependent on hydrodynamic conditions as well as the fish’s behavioural response.

Fish, Ice, and Wedge-Wire Screen Water Intakes

AbstractThe U.S. Clean Water Act requires that the Environmental Protection Agency ensures that the location, design, construction, and capacity of water intakes for thermal power plants reflect the best technology available to reduce entrainment mortalities of fish and invertebrates during their early stages of life. Cylindrical wedge-wire screens are an efficient technology for protecting fish and invertebrates at water intakes, as they draw water at low flow velocities through a fine mesh. Although substantially reducing fish and invertebrate mortality, wedge-wire screens run significant risks of blockage by ice. This paper discusses how the characteristics of wedge-wire screens that enhance their ability to reduce mortalities also make them susceptible to blockage by frazil and anchor ice, and presents observations and field data regarding ice formation on a segment of wedge-wire screen placed in a small river. Ice formation on this screen involved initial frazil adhesion with subsequent metamorphism ...

낙농가를 위한 스크루 압착식 축분 고액분리기 연구 I - 젖소용 축분 고액분리기 설계요인시험 구명 -

The study on design criteria of solid-liquid separator for dairy farms was done by testing various screens, presses, and RPMs of screw auger with remodeled screw-press type pig-manure separator. The moisture content of separated solid increase from 68.3% to 74.2% as auger rotating speed increased from 9.8 to 29.2 RPM at 34.8 kPa of pressure and 1.0 mm of slit wedge wire screen condition. The moisture contents of separated solid were 72~77%, work efficiencies were 16~18 kg/min at 1.0 mm of slit wedge wire screen. The efficiency was higher than one at 0.5 mm of slit wedge wire screen, which was used to separate for pig manure. The best work efficiency was 18 kg/min at 42.5 kPa, 1.0 mm slit screen. The separated solid moisture content was 75% at this condition.

Combined Chemical-Biological Treatment for Prevention/Rehabilitation of Clogged Wells by an Iron-Oxidizing Bacterium

Groundwater wells containing large concentrations of ferrous iron face serious clogging problems as a result of biotic iron oxidation. Following a short time after their start off, wells get clogged, and their production efficiency drop significantly up to a total obstruction, making cleanup and rehabilitation an economic burden. The present study was undertaken to test an experimental combined treatment (chemical and biological) for future prevention or rehabilitation of clogged wells. Sphaerotilus natans (an iron-oxidizing bacterium) freshly isolated from a deep well was grown to form biofilms on two systems: coupons and sand buried miniature wedge wire screen baskets. A combined chemical-biological treatment, applied at laboratory scale by use of glycolic acid (2%) and isolated bacteriophages against Sphaerotilus natans (SN1 and ER1-a newly isolated phage) at low multiplicity of infection (MOI), showed inhibition of biofilm formation and inactivation of the contaminant bacteria. In addition to complete inactivation of S. natans planktonic bacteria by the respective phages, earlier biofilm treatment with reduced glycolic acid concentration revealed efficient exopolysaccharide (EPS) digestion allowing phages to be increasingly efficient against biofilm matrix bacteria. Utilization of this combined treatment revealed clean surfaces of a model stainless steel wedge wire screen baskets (commonly used in wells) for up to 60 days.

Electrochemical removal of cadmium from dilute aqueous solutions using a rotating cylinder electrode of wedge wire screens

Rates of mass transfer at rotating cylinder electrodes of wedge wire screens were studied by measuring the limiting current for the cathodic reduction of ferricyanide as test reaction. The experimental data are well correlated by an empirical expression between the Sherwood number and the Reynolds number, both in terms of the internal slot opening as characteristic length, and including two additional dimensionless parameters in order to characterize the geometry of the screens. The performance of an undivided electrochemical batch reactor with a rotating cylinder cathode of wedge wire screens was tested analyzing the cadmium removal from dilute solutions. The effect of cathodic applied potential and size of the screen is studied. Taking into account the residual cadmium concentration the best results were obtained for a cathode potential of −1.1 V vs. SCE at 700 rpm, where the cadmium concentration decreased from 54 to 0.9 mg l−1 after 30 min of electrolysis with a specific energy consumption of 10.7 kWh kg−1 and a normalized space velocity of 3.54 h−1.

Structure of Flow Upstream of Vertical Angled Screens in Open Channels

This paper presents the results of a laboratory study of the structure of flow in a diversion structure with a vertical angled wedge-wire fish screen. This screen had a 103 25 mm mesh and was tested at three angles of 10.4, 17.5, and 26.8°, to the direction of the approaching flow, for two mean velocities of 0.5 and 0.8 m / s, with a depth of flow of about 0.75 m. In this water and fish diversion ~channel or! structure, it was found that the depth of flow at any section is approximately constant with a drop at the screen on the side of the canal and decreased towards the bypass located at the downstream end. The distribution of the velocity component u in the direction of the approaching flow as well as the perpendicular component w and the resultant velocity V was uniform in the vertical direction. The depth averaged mean velocity Vfor different verticals at any section in the diversion structure increased with the longitudinal distance x and was correlated with the relative width, bs / b ~in the diversion structure! for all five experiments. Correlations have been found for the depth averaged transport velocity u8 and the impinging velocity on the screen w8 in terms of the approach velocity U. A general relation has also been developed for the attack angle of the flow on the screen. The downstream part of the screen carried more flow into the canal compared to the upstream part as a result of the uniform mesh size used in this study. The results of this hydraulic study should be useful, particularly for freshwater adult fish, in designing screens in irrigation canals and for micro-hydro sites that use diversion canals.

Swimming Performance and Physiological Stress Responses of Splittail Exposed to a Fish Screen

Fish screens are designed to divert fish away from potentially life-threatening water diversions, yet little is known of the immediate effects of the screens on exposed fish. To determine the effects of screen exposure, splittail Pogonichthys macrolepidotus swimming performance and survival were measured during exposure to a fish screen and bypass channel in a variable-velocity water flume at 12°C for not more than 1.5 h. Four treatment velocities (range, 0–60 cm/s) were used with 20 fish (standard length (±SD) = 5.9 ± 1.3 cm) per experiment, with three replicate experiments per treatment. The sublethal effects of screen exposure were also assessed by measuring physiological stress responses at −2, 0, 0.5, 2, and 24 h following screen exposure. No losses of equilibrium or mortality were associated with any of the velocity treatments. During the control treatment (0 cm/s water velocity through the 0.6-m-wide × 13.7-m-long flume), screen contacts were infrequent (mean total = 2 ± 2), and the mean swimming velocity was 18.8 ± 3.5 cm/s. At increased velocities, screen contacts increased, mean swimming velocities increased (up to 52.3 cm/s), and the fish displayed significant, positive rheotaxis. The number of fish entering the bypass channel and the physiological stress responses (hematocrit, plasma glucose, and lactate concentrations) did not differ significantly among treatments. Since splittail exposed to a wedge-wire fish screen at elevated water velocities similar to those found at large water diversions did not experience significant sublethal effects or increased mortality, it does not appear that the factors contributing to splittail mortality at diversion screening facilities are related to screen exposure.

Hydraulic Performance of Coanda-Effect Screens

A theoretically based computational model is presented for predicting the hydraulic performance of Coanda-effect screens. These screens use a tilted-wire, wedge-wire screen panel to remove thin layers of high-velocity flow from the bottom edge of a supercritical flow. Typical slot openings are 1 mm or less, and the screens are self-cleaning with no moving parts. The discharge characteristics of several screen materials were evaluated in laboratory tests, and a relation was developed for computing the discharge through a tilted- wire screening surface as a function of the Froude number, the specific energy, and the Reynolds and Weber numbers. A model for the performance of complete Coanda-effect screen structures predicts the wetted length of screen required to accept a given flow, or the flow rate through the screen and the bypass flow over a screen that does not accept all of the flow. Predictions from the model compare favorably to results from clean-water laboratory tests of several different prototype-size screen structures. The model will allow designers to accurately size screens and evaluate design alternatives.

Evaluation of the effectiveness of intake wedgewire screens

Abstract The Logan Generating Plant (LGP), owned and operated by US Generating Company, is located on the shore of the Delaware River in New Jersey. It withdraws make-up water from the river to replace evaporative water losses from its closed-cycle cooling tower system. The intake is equipped with two intake conduits that are situated perpendicularly to the current and terminate on the river bottom at depth of approximately 3 m. The intake terminuses are covered by cylinders constructed of 1-mm wedgewire screen. The LGPs intakes are located in an area of the river where striped bass spawn and rear. Previous studies determined that without screening, the plant would withdraw less than 0.03% of the study area’s striped bass. LGP was required to conduct an intake screen performance test to document the plant’s entrainment of striped bass eggs and larvae. Entrainment samples were collected from water filtered through the wedgewire screens. Source water body samples were collected from three transects in the river: one upriver, one down river, and one directly in front of the plant. Sampling at the transect in front of the intake was coordinated to occur at the same time as entrainment sampling. The densities of striped bass larvae in the source water body and in entrainment samples were used to estimate proportional withdrawal. The study found that the wedgewire screens performed better than expected. The average proportional withdrawal of striped bass larvae was 0.003%, an order of magnitude less than the estimate for an unscreened intake.

Fish Collections Taken from a Small Agricultural Water Withdrawal Site on the Groot River, Gamtoos River System, South Africa

Summary Periodic water releases from Beervlei Dam on the Groot River of the Gamtoos River System were planned to flush the riverine pools of brack water and replace the pools with better quality water which was used to flood irrigate lucerne lands. Fish collections were made in a small irrigation canal situated on the banks of the Groot River. Three fish species were collected. Results indicated that up to a total of 131 smallscale redfin minnows, Pseudobarbus asper, are removed from the system every five minutes at this one small water withdrawal site. Larger minnow specimens and carp, Cyprinus carpio, were entrained during high river flows. When the river flow was reduced there were higher catches of young of the year fish. The fish are carried with the pumped water, which is flood irrigated onto lucerne fields, resulting in stranding and eventual mortality. It is recommended that the use of suitable screens, such as wedge-wire screens, could reduce the number of fish removed from the system during thes...

Reductions in Ichthyoplankton Entrainment with Fine-Mesh, Wedge-Wire Screens

The exclusion efficiency of cylindrical wedge-wire screens was investigated at the Chalk Point Steam Electric Station in Aquasco, Maryland, by measuring entrainment of larval bay anchovies Anchoa mitchilli and naked gobies Gobiosoma bosci through screens with slot sizes of 1, 2, and 3 mm and through an unscreened intake. The degree of exclusion by the screens increased with fish size. Fish less than 5 mm long were not excluded by any of the screens. In contrast, more than 80% of larger ichthyoplankton were excluded by all screens. Virtually no ichthyoplankton larger than 10 mm were entrained through the 1-mm screen even when fish of this size were abundant and were entrained through the unscreened intake. The 2-mm and 3-mm-slot screens were not as effective at excluding ichthyoplankton as the 1-mm screen, but the effect of slot size on exclusion efficiency was small relative to the effect of fish size. These results suggest that entrainment through water intake structures can be successfully reduced by wedge-wire screens if the larval fish at risk exceed 5 mm in length.

Effectiveness of Fine Mesh Cylindrical Wedge-Wire Screens in Reducing Entrainment of Lake Michigan Ichthyoplankton

Samples of ichthyoplankton entrained through 2.0-mm and 9.5-mm-slot opening cylindrical wedge-wire screens and through an open pipe (control) were collected in June, July, and August 1979, 1067 m off the southeast shore of Lake Michigan at a depth of 10.7 m. Screens were designed for a flow rate of 1.9 m3 min−1 at 15.2 cm s−1 through slot velocity. Ambient composition and density of ichthyoplankton were determined by net tows. Rainbow smelt (Osmerus mordax), alewife (Alosa pseudoharengus), and yellow perch (Perca flavescens) larvae were common in both entrainment and tow collections. Eggs were found almost exclusively in entrainment collections. Ambient larval fish densities were about 11 times greater than those found in entrainment collections. Total entrainments through either screen and the open pipe were not statistically significant. Larval avoidance and, to a lesser extent, screen exclusion were responsible for the low entrainment. We estimated that about 90% of native fish larvae at the site avoided pumping.Key words: Lake Michigan, fish larvae, fish eggs, ichthyoplankton, entrainment, power plants, avoidance