Process control for an immersed membrane system

• US 20070039888A1
• Filed: 07/11/2006
• Published: 02/22/2007
• Est. Priority Date: 07/12/2005
• Status: Active Grant

• Current Assignee: Zenon Technology Partnership
• Original Assignee: Zenon Technology Partnership
• Inventors: Janson, Arnold, Yacoub, Francois, Cote, Pierre, Ginzburg, Boris
• Granted Patent: US 8,357,299 B2
• Time in Patent Office: Days
• US Class Current: 210/650
• CPC Class Codes: B01D 2315/06 Submerged-type; Immersion type
• CPC Class Codes: B01D 2321/00 Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
• CPC Class Codes: B01D 2321/04 Backflushing
• CPC Class Codes: B01D 2321/16 Use of chemical agents
• CPC Class Codes: B01D 2321/185 Aeration
• CPC Class Codes: B01D 61/18 Apparatus therefor
• CPC Class Codes: B01D 61/22 Controlling or regulating
• 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 3/1268 Membrane bioreactor systems
• CPC Class Codes: Y02W 10/10 Biological treatment of water, waste water, or sewage

Abstract

An immersed membrane system or process may use measured or calculated process information to optimize one or more process operating parameters to improve performance or reduce operating costs. An on-line process control system or method may use the resistance in series method in operating an immersed membrane water treatment system. A process control system or process may consider resistance values and adjust operational parameters such as membrane aeration frequency factor, membrane aeration flow, permeate flux, permeation duration, backwash flow and duration, relaxation duration or maintenance or recovery chemical cleaning frequencies in order to reduce the operational costs related to membrane fouling removal.

Claims

1. A process for treating water comprising the steps of,

a) providing a water treatment system having filtering membranes for withdrawing filtered permeate from water being treated and operable according to two or more discrete modes of operation, the modes of operation differing in their effect on the fouling of the membranes;

b) operating the system in one of the modes of operation in each of a plurality of periods of time;

c) determining the value or values of one or more parameters related to a resistance of the membranes from time to time while operating the system;

d) considering one or more of the value or values of the one or more parameters in choosing the mode of operation for one or more of the periods of time.

2. The process of claim 1 wherein the two or more discrete modes of operation differ from each other in relation to one or more of (a) backwashing regimen, (b) permeation regimen, (c) air scouring regimen, (d) membrane chemical cleaning regimen or (e) sludge filterability enhancement regimen.

3. The process of claim 1 wherein the two or more discrete modes of operation differ in the ratio of time in which the membranes are air scoured relative the time in which the membranes are not air scoured.

4. The process of claim 1 wherein the one or more parameters include one or more parameters selected from the group of (a) adsorptive fouling resistance, (b) cake resistance or (c) a change over time in total resistance after backwash.

5. The process of claim 1 wherein the modes of operation differ at least in relation to air scouring regimen and the one or more parameters includes a parameter related to cake resistance.

6. The process of claim 1 wherein step (d) of claim 1 further comprises comparing one or more values of parameters with at least one of a set of two or more reference values associated with each of the values being compared.

7. The process of claim 6 wherein the two or more reference values include a higher value and a lower value and the mode of operation is changed when one or more values of parameters is above its associated higher reference value or below its associated lower reference value.

8. The process of claim 1 wherein changes in mode of operation are made following a hierarchy of available process changes.

9. A process for providing scouring bubbles to a membrane unit comprising the steps of,

a) providing a flow of a gas in the form of bubbles which rise past the membrane unit;

b) alternating the rate of flow of the gas between a value in a first range of flow rates and a value in a second range of flow rates, the second range of flow rates ranging from no flow to a flow rate below the first range of flow rates;

c) altering the length of time that the gas flows at the second flow rate compared to the length of time that the gas flows at the first flow rate considering a parameter related to a resistance of the membrane unit.

10. The process of claim 9 wherein the length of time that gas flows at the second rate does not exceed 60 seconds or is generally continuously for a period of 5 minutes or more or during periods of time other than a period of time near or in which when the membrane unit is backwashed.

11. The process of claim 9 wherein the length of time that gas flows at the higher rate is generally continuous, does not exceed 20 seconds or may exceed 20 seconds but occurs every five minutes or less frequently or at a period of time near or in which the membrane unit is backwashed.

12. A process for operating an immersed membrane filtration system wherein operation of the system is altered considering real-time process information with feedback control to alter the operation of the system.

13. The process of claim 12 wherein the process information includes one or more of:

a. permeate flow

b. reject or concentrate flowrate

c. sludge filterability

d. fluid temperature

e. fluid viscosity

f. fluid suspended solids concentration

g. coagulant or other pretreatment chemical addition rate

h. activated carbon dosage rate or concentration

i. blower inlet air temperature

j. recovery rate (permeate produced/feedwater provided)

k. dissolved oxygen concentration

l. oxygen uptake rate

m. solids retention time

n. mixed liquor recirculation rates.

14. The process of claim 12 wherein the operation of the system is altered according to one or more of the following:

a. select the on and off aeration times during cyclic or intermittent aeration cycle, or

b. select the on and off production times for an individual train, or

c. select the number of trains in operation and design permeate flow for each train as part of a complete system.

15. The process of claim 14 wherein the air is provided either continuously, cyclically or intermittently.

16. The process of claim 12 wherein the control system operates at a fixed aeration rate for a period of time to establish baseline process operating conditions (including permeate flow, transmembrane pressure), then automatically conducts a test in which it adjusts the aeration rate upward or downward by a certain percentage, e.g. 5%, and then determines the affect of the aeration rate change on the key process operating conditions, then the control system assesses if the new aeration rate yields better performance in terms of either actual flow rate or total energy efficiency (flowrate per unit energy input), are based on the results of the test, the control system chooses another aeration rate to be evaluated then this test is repeated until the optimum aeration rate or operating strategy has been determined.

17. The process of claim 12 wherein the control system conducts a test to determine the rate of increase of transmembrane pressure with time without membrane aeration occurring, this “

filterability test”

including an initial “

aeration without permeation”

step (30 seconds to 5 minutes) to reduce the boundary layer to a minimum followed by a “

permeation without aeration”

step (30 seconds-20 minutes) during which transmembrane pressure is monitored, then a second “

aeration without permeation”

step follows during which the majority of the material deposited on the membrane during the earlier step is removed, then the control system correlates the test results (transmembrane pressure increase with time) against a previously input model to determine the optimum aeration rate and operating strategy.

18. The process of claim 12 wherein the control system for the filtration system uses the real-time process measurement results from any of a variety of process instruments and sets the aeration rate or operating conditions based on a previously input model defining the optimum aeration rates or operating conditions as a function of the process parameter results.

19. The process of claim 12 wherein the process information is used to calculate a resistance value.

20. The process of claim 12 wherein the process is altered by altering its A.F.F.