Shipboard wastewater treatment system

• US 6,361,695 B1
• Filed: 09/30/2000
• Issued: 03/26/2002
• Est. Priority Date: 10/02/1999
• Status: Expired due to Fees

• Current Assignee: Zenon Environmental Incorporated (Veolia Environnement SA)
• Original Assignee: Zenon Environmental Incorporated (Veolia Environnement SA)
• Inventors: Tonelli, Fernando A., Liu, Ming Gang, Behmann, Henry, Husain, Hidayat
• Primary Examiner(s): Simmons, David A.
• Assistant Examiner(s): PRINCE JR, FREDDIE GARY
• Application Number:
  US09/677,703
• Time in Patent Office: 542 Days
• Field of Search: 210/614, 210/620, 210/621, 210/622, 210/629, 210/631, 210/195.1, 210/201, 210/202, 210/206, 210/220, 210/259, 210/359, 210/195.2
• US Class Current: 210/614
• CPC Class Codes: B01D 2311/04 Specific process operations in the feed stream; Feed pretreatment
• CPC Class Codes: B01D 2311/14 Pressure control
• CPC Class Codes: B01D 2311/246 Concentration control
• CPC Class Codes: B01D 2311/2661 Addition of gas
• CPC Class Codes: B01D 2313/70 Control means using a programmable logic controller [PLC] or a computer
• CPC Class Codes: B01D 2315/06 Submerged-type; Immersion type
• CPC Class Codes: B01D 2321/04 Backflushing
• CPC Class Codes: B01D 2321/185 Aeration
• CPC Class Codes: B01D 2321/2058 by vibration of the membrane, e.g. with an actuator
• CPC Class Codes: B01D 2321/28 by soaking or impregnating
• CPC Class Codes: B01D 61/145 Ultrafiltration
• CPC Class Codes: B01D 61/147 Microfiltration
• CPC Class Codes: B01D 61/16 Feed pretreatment
• CPC Class Codes: B01D 61/18 Apparatus therefor
• CPC Class Codes: B01D 63/02 Hollow fibre modules
• CPC Class Codes: B01D 63/043 with separate tube sheets
• CPC Class Codes: B01D 65/08 Prevention of membrane fouling or of concentration polarisation
• CPC Class Codes: C02F 1/32 with ultraviolet light
• CPC Class Codes: C02F 1/444 by ultrafiltration or microfiltration
• CPC Class Codes: C02F 2103/002 Grey water, e.g. from clothes washers, showers or dishwashers
• CPC Class Codes: C02F 2103/005 : Black water originating from toilets
• CPC Class Codes: C02F 3/1268 : Membrane bioreactor systems
• CPC Class Codes: Y02W 10/10 : Biological treatment of water, waste water, or sewage

Abstract

A method and system for treating wastewater in an onboard ship sewage treatment system having controlled suspended solids, the method comprising the steps of collecting wastewater in a collection tank and transferring the wastewater to a bioreactor to oxidize organic material contained in the wastewater by adding oxygen-containing gas thereto. The bioreactor is operated to provide a mixed liquor having a solids concentration of at least 5 g/l and the solids concentration is continuously increased in the mixed liquor in the bioreactor to not greater than 30 g/l. When the solids concentration in the mixed liquor reaches at least 15 g/l, a portion of the mixed liquor is removed from the bioreactor. Thereafter, wastewater is added to the bioreactor to decrease the solids concentration of remaining or residual mixed liquor to not less than 5 g/l. The bioreactor is further operated to increase the solids content again. A hollow fiber membrane is used to remove water from the mixed liquor to provide treated effluent.

Claims

1. A method for treating wastewater in an onboard ship treatment system having controlled suspended solids, the method comprising the steps of:

(a) providing wastewater in a bioreactor to oxidize organic material contained in said wastewater by adding oxygen-containing gas thereto;

(b) operating said bioreactor to provide a mixed liquor having a solids concentration of at least 5 g/l;

(c) continuously increasing said solids concentration in said mixed liquor in said bioreactor to not greater than 30 g/l;

(d) when the solids concentration in said mixed liquor reaches at least 15 g/l, removing a portion of the mixed liquor from said bioreactor;

(e) thereafter adding wastewater to said bioreactor to decrease said solids concentration of remaining mixed liquor to not less than 5 g/l;

(f) then further operating said bioreactor to increase said solids content again;

(g) providing a module having an array of hollow fiber membranes in a membrane container in liquid communication with said bioreactor;

(h) sweeping said hollow fiber membranes with gas;

(j) directing a flow of mixed liquor from said bioreactor to said container to cover said membranes to avoid substantial exposure of said hollow fibers membrane during motion of said ship;

(k) returning concentrate and mixed liquor from said hollow fiber membrane container to said bioreactor; and

(l) removing purified water from said mixed liquor through said hollow fiber membranes as permeate to provide treated effluent.

2. The method in accordance with claim 1 wherein said oxygen-containing gas is oxygen or is oxygen-enriched air.

3. The method in accordance with claim 1 including sweeping said hollow fiber membranes with air bubbles.

4. The method in accordance with claim 1 including the step of screening said wastewater using a vibrating screen to remove fibrous material to avoid entanglement of said fibrous material with said hollow fiber membranes.

5. The method in accordance with claim 1 including continuously increasing said solids content in said bioreactor to a concentration level of not greater than 25 g/l.

6. The method in accordance with claim 1 including operating said bioreactor until said solids concentration reaches a level of at least 20 g/l prior to removing a portion of the mixed liquor from the bioreactor.

7. The method in accordance with claim 1 including collecting said wastewater in a collection tank and then transferring said wastewater to said bioreactor.

8. The method in accordance with claim 1 wherein said hollow fiber membranes employ a trans-membrane pressure differential in the range of 0.5 to 25 psi to draw permeate through said membrane.

9. The method in accordance with claim 1 including the step of increasing said solids concentration to not greater than 25 g/l in a period of about 10 to 20 days.

10. The method in accordance with claim 1 wherein said removing a portion includes the step of removing from about ½

to about ¾

of the volume of said liquor from said bioreactor and leaving about ¼

to ½

residual mixed liquor having a solid concentration of at least 15 g/l.

11. The method in accordance with claim 1 including the step of applying air on a continuous basis to said membrane at a rate of about 0.005 to 0.5 ft³/min/ft² of membrane surface.

12. The method in accordance with claim 1 including adding air from a gas-dispersing means, the air having a bubble size in the range of 0.5 to 5 mm.

13. The method in accordance with claim 1 including disposing said hollow fiber membranes substantially horizontally in said membrane container and dispersing said gas from underneath said hollow fiber membranes.

14. A method for treating wastewater in an onboard ship sewage treatment system having controlled suspended solids, the method comprising the steps of:

(a) collecting wastewater in a collection tank;

(b) transferring said wastewater to a bioreactor to oxidize organic material contained in said wastewater by adding oxygen or oxygen-enriched air thereto;

(c) operating said bioreactor to provide a mixed liquor having a solids concentration of at least 5 g/l;

(d) continuously increasing said solids concentration in said mixed liquor in said bioreactor to not greater than 25 g/l;

(e) when the solids concentration in said mixed liquor reaches at least 15 g/l, removing about ½

to about ¾

of the volume of said mixed liquor from said bioreactor to provide a residual mixed liquor;

(f) thereafter adding wastewater to said bioreactor to decrease said solids concentration of residual mixed liquor to not less than 5 g/l;

(g) then further operating said bioreactor to increase said solids content again;

(h) providing a hollow fiber membrane module container in liquid communication with said bioreactor;

(i) disposing a hollow fiber membrane module substantially horizontally in said membrane container;

(j) locating a gas dispersing means in said container beneath said hollow fiber membrane for gas sweeping said hollow fibers with air;

(k) directing a flow of mixed liquor from said bioreactor to said container to cover said membranes to avoid substantial exposure of said hollow fibers membrane during motion of said ship;

(l) returning concentrate from said hollow fiber membrane container to said bioreactor; and

(m) removing purified water from said mixed liquor through said hollow fiber membranes as permeate to provide treated effluent.

15. The method in accordance with claim 14 including the step of screening said wastewater using a vibrating screen to remove fibrous material to avoid entanglement of said fibrous material with said hollow fiber membranes.

16. The method in accordance with claim 14 including operating said bioreactor until said solids concentration reaches a level of at least 20 g/l prior to removing a portion of the mixed liquor from the bioreactor.

17. The method in accordance with claim 14 wherein said treated effluent has a BOD of less than 10 mg/l.

18. The method in accordance with claim 14 wherein said hollow fiber membranes employ a trans-membrane pressure differential in the range of 0.5 to 25 psi to draw permeate through said membrane.

19. The method in accordance with claim 14 including the step of applying air on a continuous basis to said membrane at a rate of about 0.005 to 0.5 ft³/min/ft² of membrane surface.

20. The method in accordance with claim 14 including adding air from said gas-dispensing means, the air having a bubble size in the range of 0.5 to 5 mm.

22. The system in accordance with claim 20 including a vibrating screen for screening said wastewater prior to entering said membrane container to remove fibrous material to avoid entanglement of said fibrous material with said hollow fiber membranes.

21. An onboard ship sewage treatment system for treating wastewater, the system having controlled suspended solids, the system comprised of:

(a) a collection tank for collecting wastewater;

(b) a bioreactor in liquid communication with said collection tank for receiving wastewater, said bioreactor designed to oxidize organic material contained in said wastewater by adding oxygen-containing gas thereto, said bioreactor designed;

(i) to be operated at a mixed liquor having a solids concentration of at least 5 g/l;

(ii) to continuously increase said solids concentration in said mixed liquor in said bioreactor to not greater than 30 g/l;

(iii) for removing a portion of the mixed liquor from said bioreactor when the solids concentration in said mixed liquor reaches at least 15 g/l;

(iv) to decrease said solids concentration of remaining mixed liquor to not less than 5 g/l by adding wastewater thereto; and

(v) for further operating said bioreactor to increase said solids content again;

(c) a hollow fiber membrane module container in liquid communication with said bioreactor;

(d) a fiber membrane module disposed substantially horizontally in said membrane container;

(e) a gas dispersing means located in said container beneath said hollow fiber membrane module designed for sweeping said hollow fibers with gas, said container designed to receive mixed liquor from said bioreactor to a level which covers said membranes to avoid substantial exposure of said hollow fibers membrane during motion of said ship;

(f) a concentrate return line for returning concentrate from said hollow fiber membrane container to said bioreactor; and

(g) means for producing a reduced pressure on the inside of said hollow fiber membranes for removing purified water from said mixed liquor through said hollow fiber membranes as permeate to provide treated effluent.

23. A method for treating wastewater in an onboard ship treatment system having controlled suspended solids, the method comprising the steps of:

(a) providing said wastewater in a bioreactor to oxidize organic material contained in said wastewater by adding oxygen-containing gas thereto;

(b) operating said bioreactor to provide a mixed liquor having a solids concentration of at least 5 g/l, the bioreactor capable of being operated by increasing said solids concentration in said mixed liquor in said bioreactor to not greater than 30 g/l;

(c) when the solids concentration in said mixed liquor reaches at least 15 g/l, removing a portion of the mixed liquor from said bioreactor;

(d) thereafter adding wastewater to said bioreactor to decrease said solids concentration of remaining mixed liquor to not less than 5 g/l;

(e) then further operating said bioreactor;

(f) monitoring the dissolved oxygen (DO) content of said mixed liquor to provide a DO measurement;

(g) relaying said DO measurement to a logic controller;

(h) in said logic controller, comparing said DO measurement to previous DO measurements to provide a comparison;

(i) in response to said comparison, maintaining or changing feed rate of said oxygen-containing gas to said mixed liquor to accommodate changes in organic flow rate to said bioreactor;

(j) providing a hollow fiber membrane module container in liquid communication with said bioreactor;

(k) disposing a hollow fiber membrane module in said membrane container;

(l) locating a gas dispersing means in said container for sweeping said hollow fibers with gas;

(m) directing a flow of mixed liquor from said bioreactor to said container to cover said membranes to avoid substantial exposure of said hollow fibers membrane during motion of said ship;

(n) returning concentrate from said hollow fiber membrane container to said bioreactor; and

(o) removing purified water from said mixed liquor through said hollow fiber membranes as permeate to provide treated effluent.

24. The method in accordance with claim 23 wherein said oxygen-containing gas is air.

25. The method in accordance with claim 23 including sweeping said hollow fiber membranes with air.

26. The method in accordance with claim 23 including the step of screening said wastewater prior to said membrane module container using a vibrating screen to remove fibrous material to avoid entanglement of said fibrous material with said hollow fiber membranes.

27. The method in accordance with claim 23 including operating said bioreactor to increase said solids content to a concentration level of not greater than 25 g/l.

28. The method in accordance with claim 23 including operating said bioreactor until said solids concentration reaches a level of at least 20 g/l prior to removing a portion of the mixed liquor from the bioreactor.

29. The method in accordance with claim 23 wherein said treated effluent has a BOD of less than 10 mg/l.

30. The method in accordance with claim 23 wherein said hollow fiber membranes employ a trans-membrane pressure differential in the range of 0.5 to 25 psi to draw permeate through said membrane.

31. The method in accordance with claim 23 including the step of increasing said solids concentration to not greater than 25 g/l in a period of about 10 or 20 days.

32. The method in accordance with claim 23 wherein said removing a portion includes the step of removing from about ½

to about ¾

of the volume of said liquor from said bioreactor and leaving about ¼

to ½

residual mixed liquor having a solid concentration of at least 15 g/l.

33. The method in accordance with claim 23 including the step of applying air on a continuous basis to said membrane at a rate of about 0.005 to 0.5 ft³/min/ft² of membrane surface.

34. The method in accordance with claim 23 including adding air from said gas-dispersing means, the air having a bubble size in the range of 0.5 to 5 mm.

35. A method for treating wastewater in an onboard ship treatment system having controlled suspended solids, the method comprising the steps of:

(a) providing wastewater in a bioreactor to oxidize organic material contained in said wastewater by adding oxygen-containing gas thereto;

(b) operating said bioreactor to provide a mixed liquor having a solids concentration of at least 5 g/l;

(c) permitting said solids concentration in said mixed liquor in said bioreactor to increase during said operating to not greater than 25 g/l;

(d) when the solids concentration in said mixed liquor reaches at least 15 g/l, removing about ½

to about ¾

of the volume of said mixed liquor from said bioreactor to provide a residual mixed liquor;

(e) thereafter adding wastewater to said bioreactor to decrease said solids concentration of residual mixed liquor to not less than 5 g/l;

(f) then further operating said bioreactor to increase said solids content again;

(g) monitoring the dissolved oxygen (DO) content of said mixed liquor to provide a DO measurement;

(h) relaying said DO measurement to a logic controller;

(i) in said logic controller, comparing said DO measurement to previous DO measurements to provide a comparison;

(j) in response to said comparison, maintaining or changing feed rate of said oxygen-containing gas to said mixed liquor to accommodate changes in organic flow rate to said bioreactor;

(k) providing a hollow fiber membrane module container in liquid communication with said bioreactor;

(l) disposing a hollow fiber membrane module substantially horizontally in said membrane container;

(m) locating a gas dispersing means in said container beneath said hollow fiber membrane for sweeping said hollow fibers with gas;

(n) directing a flow of mixed liquor from said bioreactor to said container to cover said membranes to avoid substantial exposure of said hollow fibers membrane during motion of said ship;

(o) returning concentrate from said hollow fiber membrane container to said bioreactor; and

(p) removing purified water from said mixed liquor through said hollow fiber membranes as permeate to provide treated effluent.

36. A method for treating wastewater in an onboard ship treatment system wherein mixed liquor having high solids content generated in the system is discharged periodically, the method comprising the steps of:

(a) introducing wastewater to a bioreactor to oxidize organic material contained in said wastewater by adding oxygen-containing gas thereto;

(b) operating said bioreactor to provide a mixed liquor having a solids concentration of at least 5 g/l and to increase said solids concentration in said mixed liquor to not greater than 25 g/l;

(c) when the solids concentration in said mixed liquor reaches at least 15 g/l, removing a portion of the mixed liquor from said bioreactor and adding wastewater to said bioreactor to obtain a solids concentration of not less than 5 g/l;

(d) monitoring the dissolved oxygen (DO) content of said mixed liquor to provide a DO measurement;

(e) relaying said DO measurement to a logic controller;

(f) in said logic controller, comparing said DO measurement to previous DO measurements to provide a comparison;

(g) in response to said comparison, maintaining or changing feed rate of said oxygen-containing gas to said mixed liquor to accommodate changes in organic flow rate to said bioreactor;

(h) providing a hollow fiber membrane module container in liquid communication with said bioreactor, said container having;

(i) a hollow fiber membrane module disposed therein; and

(ii) gas dispersing means in said container for sweeping said hollow fibers with gas;

(i) directing a flow of mixed liquor from said bioreactor to said container to maintain said container sufficiently full to avoid substantial exposure of said hollow fiber membranes during ocean motion of said ship;

(j) returning concentrate from said hollow fiber membrane container to said bioreactor; and

(kl) removing purified water from said mixed liquor through said hollow fiber membranes as permeate to provide treated effluent.

37. A method for treating wastewater in an onboard ship treatment system wherein mixed liquor having high solids content generated in the system is discharged periodically, the method comprising the steps of:

(a) providing wastewater to a bioreactor to oxidize organic material contained in said wastewater by adding oxygen-containing gas thereto;

(b) operating said bioreactor to provide a mixed liquor having a solids concentration of at least 5 g/l and not greater than 25 g/l;

(c) monitoring the dissolved oxygen (DO) content of said mixed liquor to provide a DO measurement;

(d) relaying said DO measurement to a logic controller;

(e) in said logic controller, comparing said DO measurement to previous DO measurements to provide a comparison;

(f) in response to said comparison, maintaining or changing feed rate of said oxygen-containing gas to said mixed liquor to accommodate changes in organic flow rate to said bioreactor;

(g) providing a hollow fiber membrane module container in liquid communication with said bioreactor, said container having;

(i) a hollow fiber membrane module disposed therein; and

(ii) gas dispersing means in said container disposed for sweeping said hollow fibers with gas;

(h) directing a flow of mixed liquor from said bioreactor to said container to maintain said container sufficiently full to avoid substantial exposure of said hollow fibers membrane during ocean motion of said ship;

(i) returning concentrate and mixed liquor from said hollow fiber membrane container to said bioreactor; and

(j) removing purified water from said mixed liquor through said hollow fiber membranes as permeate to provide treated effluent.