1、 November 21,2010 Page 1 SLOW SAND FILTRATION-DEMAND OPERATED AND CLEANED USING BACKWASH November 21,2010 David H.Manz,PhD,P.Eng.,P.Ag VP Marketing and Product Development Oasis Filter International Ltd ABSTRACT A demand operated slow sand filter design that can be demand operated and allows cleanin
2、g using a backwash process is described.The new design named the Manz Slow Sand FilterTM(MSSF),meets or exceeds all of the design criteria specified by the AWWA for traditional slow sand filtration(TSSF)and TSSF performance expectations.The ability to operate the filter as required and ease of clean
3、ing greatly expands slow sand filter applications.The ability to operate the MSSF on a demand basis while retaining the treatment characteristics of TSSF is made possible by recognizing that the biological layer on the surface of the media bed(schmutzdeke and the active or biolayer)is aerobic.The MS
4、SF is designed such that there is always sufficient oxygen available to the biological layer even when there is no flow through the filter thereby keeping it alive.The ability to backwash the MSSF without destroying the biolayer is achieved by recognizing that the biological layer consists of the to
5、p most layer of media particles which have each developed a biofilm and by designing the media bed such that the particles that form the biolayer always remain on the surface of the media bed(after a backwash has been completed).Filter media is never removed or replaced.The design of the MSSF is mor
6、e compact than that of the TSSF,less expensive to construct,simple and inexpensive to operate and able to treat a wider range of water quality than the TSSF.The MSSF technology is presently being used for pathogen removal,turbidity reduction,and iron and manganese removal in both developed and devel
7、oping country environments.Pre-and post treatment greatly enhance the range of applications of the MSSF beyond that associated with simple TSSF technology.Treatment systems using the MSSF technology can be very effective for arsenic removal.Backwash volumes are less than one per cent of production c
8、ompared to greater than five per cent for alternative technologies.The treatment process allows for complete recycling of the backwash water leaving only a very small amount of sludge containing the solids.The MSSF technology can also be used to remove the smallest particulate matter;that is,as a po
9、lishing filter,in circumstances where a biolayer may not be required for treatment.The MSSF technology is modular and can treat water for small to very large communities.Capacities of individual MSSF units range from hundreds to several hundred thousand liters per hour.Treatment plants may incorpora
10、te many MSSF units to achieve capacities of several million liters per hour.November 21,2010 Page 2 MSSF technology or its precursor the BioSand Water FilterTM(BSF)technology,are in use in more than one hundred countries.One treatment plant using the MSSF technology for manganese removal has been su
11、ccessfully operating in Alberta for more than two years.Two other treatment plants in Alberta and Saskatchewan are under construction.Consideration is being given to retrofitting existing TSSF facilities in British Colombia,Ireland and Colombia to use the MSSF technology.INTRODUCTION Traditional or
12、conventional designs for sand filtration remain satisfactory and effective water treatment solutions in many large scale applications.However,the demands for their precise operation to achieve required performance to meet increasingly stringent water treatment regulations often result in excessive c
13、apital and operational financial burdens.Water treatment facilities that are complex to operate,that generate excessive volumes of waste water or that must use chemicals,which may be difficult to manage properly and further complicate waste water disposal are not desirable.Complex water treatment fa
14、cilities require more skilled plant operators,which may not be available or affordable in many circumstances.The development of the Manz Slow Sand Filter(MSSF)grew out of the apparent need to provide an effective,physically simple,operationally simple and robust,low-cost water treatment solution for
15、 use in small to medium scale water treatment plants in circumstances where capital and operational resources are limited.The MSSF combines the water treatment capabilities of the traditional slow sand filtration(TSSF)with the method and apparent convenience of filter cleaning associated with rapid
16、and pressure sand filters.BACKGROUND It is necessary to review the important characteristics of commonly used sand filtration technologies in order to fully appreciate how the significant advantages of the MSSF are realized.Rapid rate granular media filters(rapid sand filter and pressure sand filter)Both rapid sand water filters(exposed to the atmosphere)and pressure sand water filters(in a pressure vessel)are typically used as polishing filters after addition of coagulants,flocculation and clar
