design of sludge thickener


); Integration of measurement and control instruments to optimise the process and reduce operating costs; Extensive and customisable first-class components. Via Gessi 16 A blanket of sludge is maintained by controlled removal which may be continuous at a low rate. The primary variables for flotation thickening are: (1)Pressure, (2) recycle ratio, (3) feed solids concentration, (4) detention period, (5) air-to-solids ratio, (6) type and quality of sludge, (7) solids and hydraulic loading rates, and (8) use of chemical aids. 48022 Lugo, RA - Italy Gravity Thickening: This process involves the concentration of thin sludges to more dense sludge in special circular tanks designed for this purpose. thickener area can be determined by using Equation 7.46(3) as follows: A good selection for this application is to provide two 27-to 30-ft diameter units equipped with vertical pickets. x\o6a,>zk^?dL'"d[Cd&)4)I"Ym~oK9~Gf,9>$$y$%/*9z"K.o_8YQ//_|A:-m'"M>.I,OE-NJE8~~]~]oGCQ&P|_~5WV\F]F]OH;+YRUJ5cgkV{ o^$. <> The spiral screw mixes sludge slowly inside the drum so that water can come out from sludge very effectively. Thickening of sludge increases its solids content and reduces the volume of free water thereby minimizing the unit load on downstream processes such as digestion and dewatering. All Rights Reserved 2022 . Similar to gravity sedimentation, the type and quality of sludge to be floated affects the unit performance. <>>> FIG. 1. Best DIY Hacks for Saving Money on Electricity, For the purposes of this example, the solids to be thickened are excess activated sludge with an initial solids concentration of 7 gm/l (0.434 lb/ft3). The spiral screw transports the sludge along the drum and finally out from the drum. When released into the separation area of the thickening tank, the buoyed solids rise under hindered conditions analogous to those in gravity settling and can be called hindered separation or flotation. This sludge continuously enters the thickener, and the thickened sludge is continuously withdrawn at a concentration of 21 gm/l (1.302 lb/ft3). endobj They have the disadvantages of high capitals, maintenance and power costs and often a poor, solids-capture efficiency if chemicals are not used for bio sludges. Conduct settling tests at various initial solids concentrations (a through d in panel A), covering the range of expected thickener influent solids concentrations; 2. The upward moving particles form a sludge blanket on the surface of the flotation thickener. <>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 595.32 841.92] /Contents 4 0 R/Group<>/Tabs/S/StructParents 0>> Centrifugation: Centrifugation has been demonstrated to be capable of thickening a variety of wastewater sludges. The result is optimised flocculant consumption, high supernatant clarity and a constant density of thickened sludge. AES Arabia Ltd.Powered by AES Arabia Ltd. % A gravity thickener is similar to a conventional sedimentation tank in design, but has a more steep floor slope. The G L is determined from data plots (see Figure 7.46.2) 0.52 lb/ft2/hr. Wastewater treatment plants commonly use thickening devices to increase the solids concentration at the end of a particular process step within the activated sludge process. Diemme Filtration high-rate sludge thickeners are the result of many years of experience in solid-liquid separation in a wide range of industries such as mining, chemical, metallurgical, water treatment and many others. stream Flotation thickening is most applicable to activated sludges but higher float concentrations can be achieved by combining primary with activated sludge. Our commitment to Research & Development has allowed us to propose innovative solutions to optimise performance and reduce plant and operating costs. It may also be used to concentrate sludge to primary tanks or a mixture of primary and excess activated sludge prior to high rate digestion. A cross sectional view of the typical Gravity thickener is given below. 2. Compute values of the flux rate G for a variety of solids concentrations (G = solids concentration, lb/ft3 X settling velocity, ft/hr), and plot as in panel C; and 5. %PDF-1.5 ); Design of mechanical parts under the most severe conditions to ensure performance and reliability over time; Optimisation of the tanks structural design (static and dynamic analysis, seismic, FEM modelling, weight optimisation, etc. Induced Air / Gas Flotation Separator(IGF). 3 0 obj

Primary sludge is normally not fed to centrifuge as it may contain abrasive material. Dissolved Air Floatation: The objective of flotation-thickening is to attach a minute air bubble to suspended solids and cause the solids to separate from the water in an upward direction. Dissolved air flotation depends on the formation of small diameter bubbles resulting from air released from solution after being pressurized to 40 to 60 psi. +39 0545 20611 The required. Equal or greater concentrations may be achieved by combining sludges in gravity thickening units. The drum thickener is closed and compact construction, which makes the equipment easy to locate and avoid annoyance from odour and splashing. The rotary drum thickener consists of the following components: stainless steel structural frame, sludge distribution system, filtering drum, filtering drum washing system, drum drive system, full set of covers, electric control panel (optional). Depending on project specifications, they can be made entirely of carbon steel, stainless steel (with or without a rubber lining) or with a concrete tank. Centrifuges are commonly used for thickening WAS (Waste Activated Sludge). Diemme Filtration high-rate sludge thickeners achieve very high productivity and are designed to complement Diemme Filtration filter presses. The most commonly used thickening processes include gravity thickening, dissolved air flotation, and rotary drum thickening. In addition of being effective in thickening, they have additional advantage of less space requirement, less odour potential & housekeeping requirement. endobj Water flows out through surface of the drum and sludge is transported by the spiral screw along the drum and finally out from the end of the drum. The degree of adhesion depends on surface properties of the solids. 2 0 obj Sludge solids are floated by the air bubbles that attach themselves to and are enmeshed in the floc particles. Centrifuges are a compact, simple, flexible, self-contained unit. 4 0 obj The sludge thickeners can be produced in sizes up to and exceeding 40 m in diameter and Bridge or Column versions are available . Drum thickener selection is done according to following: Type of sludge, inlet DS concentration, required outlet concentration, organic matters content, the material of construction which consists of the central shaft, spiral screw and the surface of the drum prevents the direct sludge flow through the drum from the begin to the end. The cleaning of the drum surface is carried out by pressure water-jet. This is due to the fact that the solid particles have a specific gravity lower than water when the bubble is attached. There is nozzle pipe inside the basin of drum thickener for surface washing. Washing operates according to the adjustable timer program. It is a complex design that requires the application of CFD modelling, which is included in the skillset of Diemme Filtration technical staff. 7.46.2 Gravity thickener design data plots. Centrifugal thickening is acceleration of sedimentation through the use of centrifugal force. Since the solubility of air increases with pressure, substantial quantities of air can be dissolved. The steeper slope reduces the raking problems by providing more gravity. With one unit in service, the unit overflow rate (rate of effluent discharge) is as follows: Continue reading here: Disc Centrifuge with Nozzle Discharge, 5 different sources of water pollution and how to stop them, Summary and Conclusions - Wastewater Treatment, Biological Oxidation - Wastewater Treatment, Aerated Grit Chamber - Wastewater Treatment, Removing Iron Salts - Wastewater Treatment. From a process point of view, the performance of the sludge thickener is dependent on the ability of the system to bind the solid particles to the flocculant. Data plot procedure: 1. Sludge is usually pumped continuously from the settling tank to the thickener which has a low overflow rate so that the excess water overflows and the sludge solids concentrate in the bottom. <> Plot Vs values versus solids concentration, and construct a line of best fit; 4. Centrifuge thickening is also becoming more common. Air in excess of the decreased solubility, resulting from the release of the pressurized flow into a chamber at near atmospheric pressures, comes out of solution to form the minute air bubbles. The volume of sludge to be concentrated is 5200 gph (693.3 ft3/hr). info@diemmefiltration.com. Determine the value of the limiting flux rate GL as the intercept on the flux rate axis of a line tangent to the flux curve drawn from the desired underflow solids concentration. In current flotation practice, two general approaches to pressurization are used: (1) Air charging and pressurization of recycled clarified effluent or some other flow used for dilution, with subsequent addition to the feed sludge; and (2) Air charging and pressurization of the combined dilution liquid and feed sludge. Inside the feedwell, the incoming current provides the necessary mixing energy for the solids to agglomerate to form flocs which then settle to the bottom of the tank. Its use is largely restricted to the watery excess sludge from the activated sludge process. The outlet side is higher. 1 0 obj This occurs in the heart of the sludge thickener, represented by its feedwell. A sludge with a solids content of 8 -10 percent or more can be produced by this method. 3. The speed of the drum rotation can be adjusted by frequency converter. This means that with an original sludge of two percent, about four-fifths of the water has been removed, and one of the objectives in sludge treatment has been attained. The horizontal position of the thickener can be lifted up to 10 degree. The thickening tank is equipped with slowly moving vertical paddles built like a picket fence. Comprehensive laboratory tests on customer samples (selection and dosage of coagulants and flocculants, static and dynamic tests, rheology, mineralogy, etc. Tanks range from 6 20 m dia & side water depth (SWD) may vary from 3 4 m. Floor slope is varies from 1:4 to 1:6 depending upon the type of sludge, time required for thickening & storage volume to absorb peak solids load. Determine the settling velocity Vs for each concentration as the slope of a line tangent to the initial lineal settling rate portion of each curve; 3. AES can offer gravity thickening, dissolved air flotation (DAF) thickening, centrifugal thickening, and rotary drum thickening depending upon the process application & space availability. Sludge is led inside and through the drum over the flow edge. endobj The type of thickening selected is usually determined by the size of a wastewater plant, its physical constraints and the downstream process.

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