1、廢水處置工藝設計及計算第11章6&8節1211-6Surface filtration 外表過濾FiltrationMechanism(機理)Surface filtrationDepth filtrationSurface filtration, a relatively new technology, involves a sieving action similar to a kitchen colander. Surface filtration is used to remove the residual suspended solids from secondary effluen

2、ts and stabilization pond effluents, and as an alternative to depth filtration. Depth filtration was developed originally for the treatment of surface water for potable uses and later adapted for wastewater treatment applications. Depth filtration is used in to achieve supplemental removal of suspen

3、ded solids (including particulate BOD) from wastewater effluents for the following purposes: to allow more effective disinfection; as a pretreatment step for subsequent treatment steps such as carbon adsorption, membrane filtration, or advanced oxidation; to remove chemically precipitated phosphorus

4、.Definition3Surface filtration is gaining in popularity because of the(1)high quality effluent produced, (2)smaller footprint, (3)low backwash rates,(4)reduced maintenance requirements. Surface filtration has been used in several applications including :as a replacement for depth filtration to remov

5、e residual suspended solids from secondary effluents, for the removal of suspended solids and algae from stabilization pond effluents, as a pretreatment operation before microfiltration or UV disinfection.4Available Filtration TechnologiesThe CMF, marketed under the trademark AquaDisk by Aqua-Aerobi

6、c Systems, also consists of several disks mounted vertically in a tank. Each disk is comprised of six equal segments. Operationally, water flows by gravity from the exterior of the disks through the filter medium to an internal collection system. Typically, two types of filter cloth are used: a need

7、le felt cloth made of polyester or synthetic pile fabric cloth. A vacuum system is. Vacuum suction heads, located on either side of the disk, are used to remove the accumulated solids by drawing filtrate water from the filtrate header back through the cloth media while the disk is rotating. 5The DCM

8、F, marketed under the trademark AquaDisk by Aqua-Aerobic Systems, consists of cloth filter elements, which have a diamond shaped cross section. The filter elements are cleaned by a vacuum sweepwhich moves back and forth along the length of the filter, when a predetermined increase in headloss has oc

9、curred. Solids that settle to the bottom of the reactorbelow the filter element are removed6periodically by a vacuum header. Using a diamond shape for the filter, it is possible to increase the cloth filter surface area per unit of aerial surface area. Because higher volumes for filtered water can b

10、e produced per unit area, the DCFM is used in new installations and as a replacement for existing sand filters.Flow capacity: Up to 400 l/s per filter.Filter opening: 10-100 m.Filter media is easy to change thanks to new innovative design.Moving backwash system for better cleaning, minimal water use

11、 and less wear on filter media.The water to be treated flows by gravity into the filter segments from the centre drum. Solids catch on the inside of the filter panels mounted on the two sides of the disc segments.As the solids catch on the inside of the filter media impeding the flow of water throug

12、h the disc, the water level inside the discs begin to rise, triggering a level sensor to start the disc to rotate and a backwash cycle begins.High pressure rinse water backs the solids off the filter media and into the solids collection trough.Typically the backwash requires 1-2% of the total flow a

13、nd filtered water is used.7The Ultrascreen developed by Nova Water technologies that consists of two continu-ously rotating circular screens of woven stainless steel mesh. The liquid to be filtered is introduced between the two screens at right angles to the screens. The filtered effluent that flows

14、 through the screen flows out and is directed to a collection chamber below the screen. Unlike other disk type screens, the discharge from the screen is by gravity as there is no water on the discharge side of the screen. High- pressure water jets are used to clean the accumulated solids from the sc

15、reens.8As the name implies the drum filter is in the shape of a drum. The liquid to be filtered is introduced on the inside of the drum and flows out thought the periphery of the drum, through a filter cloth of polyester or polypropylene or stainless steel, as the drum rotates slowly. When the water

16、 level within the drum rises to specified level, a backwash cycle is initiated to remove the accumulated solids. A high pressure water spray is used to dislodge and remove the accumulated solids as the drum rotates. The solids removed from the drum are collected in a collection trough on the inside

17、of the drum. Drum filter can be installed in concrete, stainlesssteel, or fiberglass tankage. The range of pore openings for the filter cloth range from 10 mm to 1 mm, depending on the application.9Developed by M2 Renewables, the inclined screen is used for the filtration of untreated wastewater. As

18、 the moving screen rotates, solids are accumulated on the screen. When the screen exits the water pool, the accumulated solids are partially dewatered by the force of gravity. The accumulated solids are removed from the screen as it passes over the upper roller. High-pressurewater jets can also be u

19、sed. As noted in Chap. 5, the fact that the screen alters the particle size distribution of the solids to be treated and has a relatively small footprint is significant relative to conventional primaryclarification.1011Description of the Surface Filtration ProcessThe key features of surface filters

20、are the filter configuration, the filter medium, the method used to introduce the liquid to be filtered,the method used to clean the filtering medium, (5) the impact of the accumulation of solids has on process performance.12Filter ConfigurationsSurface filters are available in a variety of configur

21、ations.The most common type of surface filter is comprised of a series of disks attached to a central shaft. The individual disks are made up of two filtering surfaces attached to a metal support frame .The drum filter for effluent filtration is a relatively recent development, although drum filters

22、 are used in a number of filtering applications. Operation of the different surface filters depends on how the liquid to be filtered is applied to the filtering medium and how the filtering material is cleaned of accumulated material.13Filter MaterialsThe filter material used in surface filters can

23、be categorized as two dimensional and three dimensional. Two dimensional mediums are typically made of synthetic fabrics of different weaves and woven metal fabrics (most commonly stainless steel). The most common weave for synthetic materials is known as a plain weave, which is similar to broadclot

24、h. Stainless steel weaves can include plain weave, twilled weave, and Dutch weave wire meshes. Three dimensional filtering mediums include polyester needle felt cloth and synthetic pile fabric cloth.14Flow Path for Liquid to be FilteredThe flow path can also be used to classify surface filters. Basi

25、cally, two methods are used to apply the liquid to be filtered to the filtering medium. In the first, the liquid enters the feed tank and flows from the outside through the filter cloth into a receiving area (out-in). In the second method, the liquid to be filtered is introduced into the annular vol

26、ume between the two filtering surfaces and flows outward through the filtering medium into the collection vessel (in-out).In either case, solids accumulate on the surface in the direction of flow. The direction of flow affects the method to be used for the removal of the accumulated material, the su

27、bmergence (i.e. the active filter area), and the overall depth of the unit.15Cleaning the Filter MediumTwo types of methods are used to remove the accumulated material removed from the fluid: vacuum removal (真空去除)intermittent and/or continuous high-pressure spray washing. 間歇和/或延續高壓噴洗The vacuum remov

28、al system is used for surface filters where the flow is from the outside in whereas the high-pressure water spray nozzles are used where the flow is from the inside to the outside.16Vacuum RemovalWhen the headloss through the CMF reaches a predetermined set point, the disks are cleaned. As the disks

29、 rotate, solids are removed from both sides of the disk by liquid vacuum suction heads, located on either side of each disk, which draws filtered water from the filtrate header back through the cloth media while the disk is rotating. This reversal of flow removes particles that have become entrapped

30、 on the surface and within the cloth medium. The diamond cloth filter is also cleaned by a vacuum sweep which moves back and forth along the length of the filter. Solids that settle to the bottom of the reactor below the filter element are removed periodically by a vacuum header.17High-Pressure Wate

31、r SpraysIn surface filters where the flow is from inside to outside, high-pressure water sprays are used to remove the material that accumulates on the inside of the disk. Most high-pressure water spray wash systems can operate in either an intermittent or continuous backwash mode. In the intermitte

32、nt mode, high-pressure backwash spray jets are activated only when headloss through the filter reaches a preset level or time. Once activated, wash water is sprayed through the filter material from the outside as the disk rotates. The accumulated solids that are dislodged fall into a collection trou

33、gh. When operating in a continuous backwash mode, the production of filtered water and backwashed occur simultaneously. The location and configuration of the high-pressure spray nozzles and solids collection trough are manufacturer specific.18Impact of the Accumulation of Solids on Process Performan

34、ceThe removal of particulate matter with surface filters is illustrated schematically on Fig for partially and completely submerged surface filters. For partially submerged filters see Fig (a), the accumulation of solids on the filter medium occurs between point 1, where the clean filter comes in co

35、ntact with the fluid to be filtered, and point 2, where the filter leaves the fluid. For the completely submerged filter see Fig (b), the accumulation of solids occurs with time until the backwash headloss is reached, at which time the filter is cleaned. 19In both cases, the accumulated material on

36、the surface of the filter begins to act as a filter. The filtering action of the accumulated material is known as auto-filtration. Auto-filtration can be used to explain why material of a smaller size than the pore size of the filter medium can be removed by surface filtration. For both types of sur

37、face filters will depend on the mesh size of the filtering medium, the characteristics of the wastewater, and the filtration rate.20Performance of Surface Filtershydraulic loading rateremoval of turbidity and total suspended solidsvariability of turbidity and TSS removalremoval of different particle

38、 sizesremoval of microorganismbackwash water requirements21Hydraulic Loading RateAs with depth filters, there is a considerable difference in the HLRs over which surface filters operate. Typical HLRs for surface filters are reported in Table. For example, while two surface filters can produce a filt

39、ered effluent with turbidity of 2 NTU or less filtering the same effluent, the HLRs can vary by more that a factor of four or five. As with depth filters, the HLR and the backwash water requirements for surface filters will impact cost and the carbon footprint significantly.22所選外表過濾器操作特征的比較23Removal

40、 of Turbidity and Total Suspended SolidsTo evaluate performance capabilities of surface filtration, a CMF pilot plant was tested using secondary effluent from an extended aeration activated sludge process with a solids retention time greater than 15 d.TSS、濁度值mg/L24The performance of the CMF as compa

41、red to depth filters, all tested with the same activated sludge effluent, is shown on Fig. As shown,the effluent turbidity from the CMF remained constant over a range ofinfluent turbidity values that tested up to 30 NTU. The degree of removal of TSS from settled activated sludge effluent with surfac

42、e filters, as with depth filters, will depend on the SRT污泥停留時間 at which the activated sludge process is operated.Similar results have been reported for other surface filtration technologies.25Variability in Turbidity and Total Suspended Solids Removal26Removal of Different Particle SizesIn comparati

43、ve testing witha granular medium filter, the surface filter consistentlyout performed the granular medium filter in respect toparticle removal (see Fig). The particle size reduction also had a significant impact on the inactivation of total coliform bacteria when used with UV disinfection.27Design C

44、onsiderationsPilot studies are recommended in developing design and operating parameters for new installations. Useful data for design includes the variability of the characteristics of the feed water to be treated the amount of backwash water required for normal operation. The backwash water requir

45、ements are a function of the TSS in the feed water and the solids loading on the filters. If the secondary treatment system is effective in TSS removal, the volume of backwash water can be reduced substantially.282911-8Electrodialysis 電滲析Definition30Electrodialysis (ED) is an electrochemical separat

46、ion process in which mineral salts andother ionic species are transported through ion-selective membranes from one solution toanother under the driving force of a direct current (DC) electric potential. As compared toNF and RO, which transport pure water through the membrane leaving the salts behind

47、,with ED salt is gradually stripped from solution leaving a dilute solution behind containingparticulate matter and neutral species not removed by the ED process. The salt transferredthrough the membrane then forms the concentrate. A typical flow diagram employing(流程圖)electrodialysis for the control

48、 of dissolved solids is shown on Fig.31陽極陰極濃縮鹽水Electrolysis stacks can contain as many as 600 cell pairs. Feed water (filtered wastewater) is pumped through the stack assembly. Typical flux rates are from 35 to 45 L/m2h. Dissolved solids removals vary with the (1) wastewater temperature, (2) amounts

49、 of electric current passed, (3) type and amount of ions, (4) permeability/ selectivity of the membrane, (5) fouling and scaling potential of the feed water, (6) feed water flowrates, and (7) number and configuration of stages.Description of the Electrodialysis ProcessElectrodialysis Reversal反向電滲析In

50、 the early 1970s, the electrodialysis reversal (EDR) process was introduced. An EDR unit operates on the same principle as ED technology, except that both the product and concentrate channels are identical in construction (see Fig). 32陽極陽極陰極陰極電滲析的典型參數33(流量)(水回收率)(除鹽耗費能量)(總溶解固體去除率)(電流效率)(膜電阻)(能量耗費)(電

51、流密度)Power Requirements for Ion TransferThe current required for ED can be estimated using Faradays laws of electrolysis. Because one Faraday of electricity will cause one gram equivalent of a substance to migrate from one electrode to another, the number of gram equivalents removed per unit time is

52、given by:3435In the analysis of the ED process, it has been found that the capacity of the membrane to pass an electrical current is related to the current density (CD) and the normality (N) of the feed solution. Current density is defined as the current in milliamperes that flows through a square centimeter of membrane perpendicular to the current