Water filtration using immersed membranes

• US 6,375,848 B1
• Filed: 11/22/1999
• Issued: 04/23/2002
• Est. Priority Date: 11/23/1998
• Status: Expired due to Fees

• Current Assignee: Zenon Technology Partnership
• Original Assignee: Zenon Environmental Incorporated
• Inventors: Janson, Arnold, Singh, Manwinder, Cote, Pierre, Husain, Hidayat, Adams, Nicholas
• Primary Examiner(s): FORTUNA, ANA M
• Application Number:
  US09/444,414
• Time in Patent Office: 883 Days
• Field of Search: 210/636, 210/650, 210/333.01, 210/333.1, 210/500.23, 210/321.78, 210/321.8
• US Class Current: 210/650
• CPC Class Codes: B01D 2311/04 Specific process operations in the feed stream; Feed pretreatment
• CPC Class Codes: B01D 2311/10 Temperature control
• CPC Class Codes: B01D 2311/14 Pressure control
• CPC Class Codes: B01D 2311/2649 Filtration
• CPC Class Codes: B01D 2311/2661 Addition of gas
• CPC Class Codes: B01D 2315/06 Submerged-type; Immersion type
• CPC Class Codes: B01D 2321/04 Backflushing
• CPC Class Codes: B01D 2321/16 Use of chemical agents
• CPC Class Codes: B01D 2321/167 Use of scale inhibitors
• CPC Class Codes: B01D 2321/185 Aeration
• CPC Class Codes: B01D 2321/2066 Pulsated flow
• CPC Class Codes: B01D 2321/2083 By reversing the flow
• CPC Class Codes: B01D 61/145 Ultrafiltration
• CPC Class Codes: B01D 61/146 comprising multiple ultrafiltration steps
• CPC Class Codes: B01D 61/147 Microfiltration
• CPC Class Codes: B01D 61/149 Multistep processes comprising different kinds of membrane processes selected from ultrafiltration or microfiltration
• CPC Class Codes: B01D 61/16 Feed pretreatment
• CPC Class Codes: B01D 61/18 Apparatus therefor
• CPC Class Codes: B01D 61/22 Controlling or regulating
• CPC Class Codes: B01D 63/02 Hollow fibre modules
• CPC Class Codes: B01D 63/031 : Two or more types of hollow fibres within one bundle or within one potting or tube-sheet
• CPC Class Codes: B01D 63/043 : with separate tube sheets
• CPC Class Codes: B01D 65/02 : Membrane cleaning or sterilisation ; Membrane regeneration
• CPC Class Codes: B01D 65/08 : Prevention of membrane fouling or of concentration polarisation
• CPC Class Codes: C02F 1/444 : by ultrafiltration or microfiltration
• CPC Class Codes: C02F 3/1273 : Submerged membrane bioreactors
• CPC Class Codes: Y02W 10/10 : Biological treatment of water, waste water, or sewage

Abstract

A process for operating filtering membranes submerged in a tank involves, in one aspect, periodically deconcentrating the tank by at least partially emptying and refilling the tank with fresh water while permeation continues. In another aspect, long trains of membranes modules are placed in series along a flow path in the tank. In one embodiment, constant aeration is provided to prevent tank water from by-passing the membrane modules while proving controlled mixing such that the average concentration of solids in the tank is lower than the concentration of solids in the tank near an outlet for removing retentate from the tank. In another embodiment, the membrane modules are arranged in a series of filtration zones between a feed water inlet and a retentate outlet of a tank. Permeate is withdrawn from the filtration zones by separate means associated with each filtration zone. Tank water containing rejected solids flows in a tank flow through the filtration zones, increasing in concentration from one zone to the next. A preferred membrane module has membranes transverse to the tank flow and fills a substantial portion of each filtration zone. With either embodiment, aeration, backwashing or packing density of membranes varies between filtration zones and the flow pattern in the tank may be periodically reversed.

Claims

1. A filter for treating water containing solids to produce a permeate lean in solids comprising:

(a) a reactor having a series of successive filtration zones including at least a first and a last filtration zone, each filtration zone being open to the atmosphere and having an inlet and an outlet;

(b) one or more membrane modules in each filtration zone;

(c) permeate collectors in each filtration zone for connecting a permeate side of membranes in the membrane modules in a filtration zone to a source of negative pressure; and

,

(d) a source of negative pressure operable to produce a selected permeate flux from the membrane modules in each filtration zone, the selected permeate flux being similar for each filtration zone,

wherein,

(e) a supply for a feed water containing solids is connected to the inlet of the first filtration zone;

(f) water rich in solids leaves the tank from the outlet of the last filtration zone;

(g) the outlet of each filtration zone other than the last filtration zone is in fluid communication with the inlet of only one of the other filtration zones; and

,

(h) the inlet of each filtration zone other than the first filtration zone is in fluid communication with the outlet of only one of the other filtration zones.

2. The filter of claim 1 wherein the filtering membranes in a first filtration zone have a packing density that is greater than a packing density of filtering membranes in a second filtration zone located closer to the outlet than the first filtration zone.

3. A process for treating water containing solids to produce a permeate lean in solids comprising:

(a) providing a filter according to claim 1;

(b) flowing water containing solids from the first filtration zone to the last filtration zone through the filtration zones successively; and

,

(c) collecting a selected permeate flux from the membrane modules in each filtration zone, the selected permeate flux being similar for each filtration zone.

4. The process of claim 3 further comprising flowing water containing solids downwards during permeation through the one or more membrane modules in each filtration zone.

5. The process of claim 3 including periodically deconcentrating the last filtration zone by draining and refilling it while permeation from the last filtration zone is stopped.

6. The process of claim 3 including reducing the concentration of solids in the water in the tank after periods of at least two hours by rapidly flushing the tank for 25 minutes or less by withdrawing retentate from the outlet and adding feed water to keep the membranes submerged such that average concentration of solids in the tank decreases by at least 60% during the rapid flushing.

7. The process of claim 6 wherein the volume of retentate removed while rapidly flushing the tank is between 20% and 75% of the average volume of water in the tank.

8. The process of claim 7 wherein the filtration zones are aerated and the aeration is biased towards the outlet of the tank.

9. The process of claim 7 further comprising backwashing the membranes from time to time, the amount of backwashing being biased towards the outlet of the tank.

10. A filter for treating water containing solids to produce a permeate lean in solids comprising:

(a) a reactor having a plurality of successive filtration zones;

(b) one or more membrane modules in each filtration zone;

(c) a non-porous casing around the one or more membrane modules in each filtration zone providing a vertical flow channel through the one or more membrane modules;

(d) permeate collectors in each filtration zone for connecting a permeate side of membranes in the membrane modules to a source of negative pressure;

(e) an inlet to supply a feed water containing solids to the top of the vertical flow channel of a first filtration zone;

(f) an outlet for water rich in solids to leave the tank from a last filtration zone; and

,

(g) a plurality of passages between the filtration zones to permit water containing solids to flow from the first filtration zone to the last filtration zone through the filtration zones successively, the passages fluidly connecting the bottom of the vertical flow channel of each filtration zone other than the last filtration zone to the top of the vertical flow channel of only one of the other filtration zones and connecting the top of the vertical flow channel of each filtration zone other than the first filtration zone with the bottom of the vertical flow channel of only one of the other filtration zones.

11. The filter of claim 10 wherein the passages include a weir at the tops of partitions separating the filtration zones and a non-porous casing on the outlet side of the weir positioned to receive the flow from the weir.