Cyclic aeration system for submerged membrane modules

Abstract

An aeration system for a submerged membrane module has a set of aerators connected to an air blower, valves and a controller adapted to alternately provide a higher rate or air flow and a lower rate of air flow in repeated cycles. In an embodiment, the air blower, valves and controller, simultaneously provide the alternating air flow to two or more sets of aerators such that the total air flow is constant, allowing the blower to be operated at a constant speed. In another embodiment, the repeated cycles are of short duration. Transient flow conditions result in the tank water which helps avoid dead spaces and assists in agitating the membranes.

1 . An apparatus to aerate tank water in one or more tanks containing one or more immersed membrane modules comprising: 
 a) an air delivery network having a plurality of distinct branches;    b) one or more aerators in fluid communication with the distinct branches of the air distribution system and mountable below the membranes;    c) an air supply to provide an initial air flow at an initial flow rate;    d) one or more valves in a valve set in fluid communication with the air supply and having distinct outlets in fluid communication with the distinct branches of the air distribution system; and,    e) a valve set controller to control the valves of the valve set; wherein    f) the valve set controller automatically operates the valves to (i) split the initial air flow such that at least one of the distinct branches of air distribution system receives air at a higher flow rate and at least one other of the distinct branches of the air distribution network receives air at a lower flow rate, the lower flow rate being less than one half of the higher flow rate, and (ii) switch which branch or branches of the air delivery network receive air at the higher flow rate and the lower flow rate in repeated cycles;    g) the membrane modules are collected into filtration zones;    h) the valve set controller is operated to provide aeration at the higher flow rate for a pre-selected length of time to the filtration zones sequentially in a cycle; and,    i) there are between 6 and 12 filtration zones.    
   
   
       2 . In an immersed membrane filtration system having membrane modules collected in filtration zones and permeation and backwashing means, the permeation and backwashing means operable and operated to permeate and backwash the filtration zones in sequence, the improvement comprising; 
 a) a cyclic aeration system as described in  claim 1  operated to provide aeration at the higher flow rate for a preselected length of time to the filtration zones sequentially in a cycle which is no longer than 12 times the preselected length of time; and,    b) operating the backwashing means to backwash the membrane modules in each filtration zone during a period of aeration of that filtration zone.    
   
   
       3 . A process for providing scouring bubbles to membrane modules in an immersed membrane filtration system comprising the steps of, 
 (a) arranging the membrane modules into 6 or more filtration zones;    (b) providing scouring bubbles to each filtration zone sequentially in a repeated cycle, the supply of bubbles to each zone being at a higher flow rate for a first length of time and at a lower rate for a second length of time.    
   
   
       4 . The process of  claim 3  further comprising a step of backwashing the membrane modules in each filtration zone during a period of aeration of that filtration zone.  
   
   
       5 . The process of  claim 3  wherein the second period of time is six times or more than the first period of time.  
   
   
       6 . The process of  claim 3  wherein the total supply of air to the filtration zones remains generally constant.