Method for inhibiting growth of bacteria or sterilizing around separating membrane

• US 6,468,430 B1
• Filed: 03/20/2000
• Issued: 10/22/2002
• Est. Priority Date: 07/21/1998
• Status: Expired due to Term

• Current Assignee: Toray Industries Incorporated
• Original Assignee: Toray Industries Incorporated
• Inventors: Miyoshi, Toshihiro, Nakaoki, Yuichiro, Kimura, Takuhei, Ito, Yohito, Fusaoka, Yoshinari
• Primary Examiner(s): Drodge, Joseph W.
• Application Number:
  US09/508,886
• Time in Patent Office: 946 Days
• Field of Search: 210/199, 210/259, 210/321.69, 210/636, 210/639, 210/650-652, 210/752, 210/139, 210/198.1, 210/764, 210/641, 210/702, 210/724, 210/749, 210/754, 210/743, 422/28
• US Class Current: 210/636
• CPC Class Codes: A61L 2/18 Liquid substances or solutions comprising solids or dissolved gases
• CPC Class Codes: B01D 2311/04 Specific process operations in the feed stream; Feed pretreatment
• CPC Class Codes: B01D 2311/12 Addition of chemical agents
• CPC Class Codes: B01D 2311/18 pH control
• CPC Class Codes: B01D 2321/162 Use of acids
• CPC Class Codes: B01D 61/025 Reverse osmosis; Hyperfiltration
• CPC Class Codes: B01D 61/04 Feed pretreatment
• CPC Class Codes: B01D 65/022 Membrane sterilisation

Abstract

In the invention, the pipe lines around permselective membranes and the surfaces of permselective membranes are intermittently disinfected by adding an inexpensive acid such as sulfuric acid or the like to pre-treated crude water so as to make the water have a pH of 4 or lower. Accordingly, the invention provides a method of surely disinfecting the permselective membranes in membrane separation systems.

Claims

1. A method of bacteriostatsis or disinfection of permselective membranes in a membrane separation apparatus for water purification, comprising intermittently subjecting crude water to acid treatment at a pH of 4 or lower during the operation of the membrane separation apparatus, wherein the acid treatment is carried out for a duration of from about 0.5 to about 2.5 hours at intervals of at least once per week to maintain bacteriostatis or disinfection;

and then applying the crude water to the membranes.

2. The method of bacteriostasis or disinfection for permselective membranes as claimed in claim 1, wherein the crude water is subjected to acid treatement at a pH of 3.4 or lower.

3. The method of bacteriostasis or disinfection for permselective membranes as claimed in claim 2, wherein the crude water is subjected to acid treatment at a pH of 2.6 or lower.

4. The method of bacteriostatis or disinfection for permselective membranes as claimed in claim 3, wherein the frequency of the acid treatment is once at intervals of from 2 to 7 days.

5. The method of bacteriostasis or disinfection for permselective membranes as claimed in claim 1, wherein the permselective membranes are reverse osmosis membranes.

6. The method of bacteriostasis or disinfection for permselective membranes as claimed in claim 1, wherein the crude water to be treated is seawater.

7. The method of bacteriostasis or disinfection for permselective membranes as claimed in claim 1, wherein the acid treatment is effected with at least 120 ppm of sulfuric acid added to the crude water.

8. A method for separating or purifying water in a membrane separation apparatus, comprising the method of bacteriostasis or disinfection for permselective membranes as claimed in claim 1.

9. The method for separating and purifying water as claimed in claim 8, wherein the crude water to be treated is seawater.

10. The method for separating and purifying water as claimed in claim 9, wherein the crude water to be treated is previously subjected to intermittent disinfection with chlorine.

11. The method for separating and purifying water as claimed in claim 8, wherein the crude water to be treated is previously subjected to intermittent disinfection with chlorine.

12. A pre-treatment method comprising:

providing a reverse osmosis membrane treatment apparatus comprising a first duct for feeding crude water to a sand filter and means for intermittently subjecting the crude water to acid treatment at a pH of 4 or lower during the operation of the pre-treatment apparatus at time periods and durations effective to maintain bacteriostatis or disinfection.

13. The pre-treatment method of claim 12, wherein said apparatus further comprises a second duct for feeding the crude water from the sand filter to a safety filter, a third duct for feeding the crude water from the safety filter to a reverse osmosis membrane treatment apparatus and a flocculant feeder for feeding a flocculant to the first duct.