Water treatment plant with immersed membranes

Abstract

A liquid treatment plant has sets of membrane trains and processing trains with flow between them through channels. Means of withdrawing permeate and sludge from the trains are described. Cyclic aeration is provided to the membrane trains. Methods of foam control, backwashing and chemical cleaning are described. Single membrane trains or process trains may be isolated for various functions. An isolated membrane train may be used to thicken sludge.

1 . A liquid treatment plant having,
 (a) two or more membrane tanks, each membrane tank having an inlet and an outlet;   (b) a train of cassettes of membrane modules located in each membrane tank;   (c) a membrane tank inlet channel in communication with the inlet of each tank; and,   (d) a membrane tank outlet channel in communication with the outlet of each membrane tank.   
     
     
         2 . The plant of  claim 1  wherein a selected membrane tank may be isolated from the membrane tank inlet channel and membrane tank outlet channel. 
     
     
         3 . The plant of  claim 1  further comprising,
 (e) a plurality of processing tanks, each processing tank having an inlet and an outlet; and, 
 (f) a processing tank inlet channel in communication with the inlets of the processing tanks, wherein the outlets of the processing tanks are in communication with the membrane tank inlet channel. 
 
     
     
         4 . The plant of  claim 3  further comprising a processing tank outlet channel in communication with the outlets of the processing tank and the membrane tank inlet channel. 
     
     
         5 . The plant of  claim 4  wherein the liquid surface level in the membrane tank inlet channel is lower than the liquid surface level in the processing tank outlet channel. 
     
     
         6 . The plant of  claim 4  wherein the liquid surface level in the membrane tank inlet channel is higher than the liquid surface level in the processing tank outlet channel. 
     
     
         7 . The plant of  claim 1  wherein the outlets of the membrane tanks comprise weirs or controlled weirs, gates or valves adapted to maintain a generally common liquid level in the membrane tanks. 
     
     
         8 . The plant of  claim 7  wherein the outlets of the membrane tanks comprise weirs. 
     
     
         9 . The plant of  claim 7  wherein aerators in each membrane tank are connected to a common air supply manifold. 
     
     
         10 . The plant of  claim 7  wherein the train in each tank is connected to a common permeate header. 
     
     
         11 . The plant of  claim 1  having a foam sump, the foam sump in communication with the liquid through an opening in the foam sump near the surface level of the liquid. 
     
     
         12 . The plant of  claim 11  wherein the opening has a variable elevation. 
     
     
         13 . The plant of  claim 11  wherein the foam sump is in communication with liquid in a channel. 
     
     
         14 . The plant of  claim 11  further comprising foam passages between a volume of water in direct communication with the foam sump and at least one further upstream volume of water. 
     
     
         15 . The plant of  claim 14  further comprising means to periodically increase the elevation of the liquid surface of the upstream volume to cause a flow of foam over the foam passage. 
     
     
         16 . The plant of  claim 1  wherein each train has a train permeate header and the train headers are attached to a common plant permeate pipe this is in turn connected to a plurality of parallel permeate pumps, wherein each train header has an isolation valve and each permeate pump may be separately turned on or off. 
     
     
         17 . The plant of  claim 1  wherein each train has a train permeate header, the train permeate headers are attached to common plant permeate pipe and the plant permeate pipe is connected to a container adapted to maintain a supply of permeate in the common plant permeate pipe, and a reversible pump in line with each train permeate header, the reversible pump adapted to selectively withdraw permeate from the train or backwash the train. 
     
     
         18 . The plant of  claim 1  wherein aerators associated with each membrane tank are grouped into two or more groups, each group connected to a common air supply manifold, each air supply manifold having an air valve and being connected to a common pipe leading to a supply of air. 
     
     
         19 . The plant of  claim 18  having a valve controller adapted to cyclically open and close each valve. 
     
     
         20 . The plant of  claim 19  wherein each air valve is connected to a separate actuator. 
     
     
         21 . The plant of  claim 1  wherein a second outlet of each membrane tank is in communication with a common tank drain pipe or channel.