Method for the treatment of water and wastewater

Abstract

A method and a plant for the treatment of water or wastewater, having impurities therein by filtration through two granular media filter stages ( 1, 2 ) of the moving bed type operated in series, comprising: feeding of said water/wastewater as a first influent to first stage granular media filters; filtration of said first influent in said first stage granular media filters to produce a first effluent; feeding said first effluent as a second influent to second stage granular media filters; and filtration of said second influent in said second stage granular media filters to produce a second effluent; wherein said second stage granular media filters ( 2 ) are operated with intermittent washing of the granular filter media.

1 . A method for the treatment of water or wastewater, having impurities therein, by filtration through two granular media filter stages of the moving bed type operated in series, comprising:
 feeding of said water/wastewater as a first influent to first stage granular media filters;   filtration of said first influent in said first stage granular media filters to produce a first effluent;   feeding said first effluent as a second influent to second stage granular media filters; and   filtration of said second influent in said second stage granular media filters to produce a second effluent;   
       characterized by
 intermittent washing of the granular filter media of said second stage granular media filters. 
 
     
     
         2 . The method according to  claim 1 , characterized in that the second stage granular media filters are operated with continuous filtration. 
     
     
         3 . The method according to  claim 1 , characterized in that the second stage granular media filters are operated with intermittent filtration and that water used for washing of the filter media is replaced with suitably clean water. 
     
     
         4 . The method according to  claim 3 , characterized in that the replacement water consists of water produced as second effluent. 
     
     
         5 . The method according to  claim 1 , characterized in that the first stage granular media filters are operated with continuous filtration and continuous granular media washing. 
     
     
         6 . The method according to  claim 1 , characterized in that the first stage granular media filters are operated with continuous filtration but with intermittent granular media washing. 
     
     
         7 . The method according to  claim 1 , characterized in that the first stage granular media filters are operated with intermittent filtration and intermittent washing and that water used for washing of the filter media is replaced with suitably clean water. 
     
     
         8 . The method according to  claim 7 , characterized in that the replacement water consists of water produced as first and/or second effluent. 
     
     
         9 . The method according to  claim 1 , characterized in that the granular filter media in said granular media filters is washed by removing granular filter media from the bottom part of the filter bed, transporting it to a media washer, washing it and returning it to the top of the granular filter media bed, while a reject consisting of wash water containing pollutants is produced. 
     
     
         10 . The method according to  claim 9 , characterized in that granular filter media is transported from the bottom part of the filter bed with an air lift pump to a media washer, that washed filter media is returned to the top of the granular filter media bed and that reject is discharged through a reject pipe. 
     
     
         11 . The method according to  claim 10 , characterized in that a valve means in the reject pipe is kept open only during the washing of filter media. 
     
     
         12 . The method according to  claim 10 , characterized in that a valve means in the reject pipe is opened a suitable time before starting the air lift pump and is closed at a suitable time after the air lift pump is stopped. 
     
     
         13 . The method according to  claim 11 , characterized in that a continuous fractional flow of water through the reject pipe is maintained between washings. 
     
     
         14 . A plant for the treatment of water or wastewater, having impurities therein, for performing a method according to  claim 1 , comprising at least one first stage free-standing granular media filter module of the moving bed type or at least one filter cell ( 40   a, b, c ) comprising at least one first stage granular media filter module ( 42   a, b, c, d ) of the moving bed type and at least one second stage free-standing granular media filter module of the moving bed type or at least one filter cell ( 46   a, b, c ) comprising at least one second stage granular filter media filter module ( 48   a, b, c, d ) of the moving bed type, operated in series, the effluent from first stage granular media filter module (s) or filter cell (s) being the influent of second stage granular media filter module (s) or filter cell (s), characterized in that the second stage granular media filter module (s) ( 2 ;  48   a, b, c, d ) is (are) arranged to be intermittently washed and is (are) provided with controlled valve means ( 4 ;  33 ;  59 ) for stopping reject flow between washings. 
     
     
         15 . A plant according to  claim 14 , characterized in that the first stage granular media filter modules ( 1 ;  42   a, b, c, d ) are arranged to be intermittently washed and are provided with controlled valve means ( 60 ;  33 ;  58 ) for stopping reject flow between washings. 
     
     
         16 . The plant according to  claim 14 , characterized in that the valve means ( 33 ) comprises a by-pass arrangement ( 34 ,  35 ) which admits a continuous fractional flow of water between washings.