Process for the purification of waste water

• US 4,073,722 A
• Filed: 02/12/1976
• Issued: 02/14/1978
• Est. Priority Date: 09/28/1973
• Status: Expired due to Term

• Current Assignee: Standard Oil Company (BP PLC)
• Original Assignee: Standard Oil Company (BP PLC)
• Inventors: Grutsch, James F., Mallatt, Russell C., Steely, Benjamin F.
• Primary Examiner(s): Wyse, Thomas G.
• Application Number:
  US05/657,497
• Time in Patent Office: 733 Days
• Field of Search: 210/4-7, 210/15, 210/18, 210/195 R, 210/195 S, 210/49, 210/50, 210/59, 210/63 R, 210/16
• US Class Current: 210/624
• CPC Class Codes: C02F 3/121 Multistep treatment
• CPC Class Codes: C02F 3/1215 Combinations of activated sludge treatment with precipitation, flocculation, coagulation and separation of phosphates
• CPC Class Codes: C02F 3/26 using pure oxygen or oxygen-rich gas
• CPC Class Codes: C02F 9/00 Multistage treatment of water, waste water or sewage
• CPC Class Codes: Y02W 10/10 Biological treatment of water, waste water, or sewage

Abstract

Disclosed is a continuous process for purifying contaminated waste water. First the water passes through an equalization zone including at least two separate compartments, in one of which the pH of the water is adjusted to a range of from about 6.5 to 9.5. The water flows through the separate compartments such that the concentration of contaminants in the water exiting the equalization zone will approach about constant concentration which changes only gradually even though influent contaminant concentration changes rapidly. Water in at least one compartment of the equalization zone is aerated so that the dissolved oxygen in the water is at least three parts of dissolved oxygen per million parts of water. Solids are skimmed from the surface of the water in the zone, and coagulant is added to the effluent water from the equalization zone so that colloidal particles in the water flocculate. The water from this equalization zone is then filtered to remove flocculated particles. The effluent from the filter will preferably have less than about ten parts of suspended solids per million parts of water and/or less than about ten parts of oil and grease per million parts of water. This effluent is aerated, preferably by aspiration, and is treated in a four stage biological treating zone. In the first stage, the water contacts an activated sludge which decontaminates the water by biodegrading contaminants. In the second stage, water from the first stage is clarified to separate suspended sludge particles from decontaminated water. The bulk of the separated sludge particles is recycled to the first stage, and the bulk of the clarified, decontaminated water is withdrawn. In the third stage, that portion of the separated sludge particles not recycled is concentrated by removing additional residual water. In the fourth stage, the concentrated sludge particles are digested. In accordance with an important feature of our invention, the water-sludge mix as it flows between the first and second stages is aerated by aspirating air into the water-sludge mix and then subjecting this mix to a high hydrostatic pressure. Preferably the sludge flowing between the second, third and fourth stages is also aerated. The water separated from the second stage is filtered to remove any minute suspended sludge particles which may be present. The preferred filter medium is sand or combinations of sand and coal, and may be followed by treatment with activated carbon. Interstage aeration is conducted at pressures above atmospheric. This ensures substantial transfer of oxygen to the water. Also, activated sludge from the third and fourth stages may be recycled to the activated sludge-water mixture that exited the first stage. The average age of the sludge in the system is greater than ten days. The dissolved oxygen concentration in the water flowing into the second stage clarifier is at least about five parts of dissolved oxygen per million parts of water.

Claims

1. In the activated sludge process wherein a first stage contaminated water containing less than about 20 ppm of hydrocarbons and less than about 20 ppm of solids is contacted with activated sludge for a period of time sufficient to biologically degrade contaminents in the water and in a second stage decontaminated water is separated from the activated sludge, a first portion of said separated sludge being recycled for recontact with the water in the first stage and a second portion of said separated sludge being treated in downstream operations, the improvement comprising:

introducing oxygen into the water and sludge mix entering the second stage so that the sludge in the second zone is maintained in an aerobic state and separated decontaminated water from said second stage contains at least about 3 parts of dissolved oxygen per million parts of water.

2. The improved process of claim 1 wherein the contaminated water entering the first stage contains less than about 10 ppm of hydrocarbons and less than about 10 ppm of solids.

3. The improved process of claim 1 wherein the separated decontaminated water from said stage contains at least about 5 parts of dissolved oxygen per million parts of water.

4. The improved process of claim 1 wherein municipal waste water is subjected to treatment.

5. The improved process of claim 1 wherein waste water from petroleum processing and/or chemical processing is subjected to treatment.

6. The improved process of claim 1 where the oxygen is introduced into the water and sludge mix entering the second stage by aspirating air into a stream of the water and sludge mix flowing between the first and second stages.

7. The improved process of claim 6 where the oxygen in the stream of water and sludge mix flowing between the first and second stage is subjected to a high pressure produced by hydrostatic heads of liquid in the first and second stages.

8. The improved process of claim 1 where the average age of the activated sludge in the first and second stages exceeds ten days.

9. The improved process of claim 1 where a part of the first portion of the separated recycled sludge is mixed with the stream of water and sludge mix flowing between the first and second stages.

10. The improved process of claim 1 where said second portion of the sludge treated in downstream operations is forwarded through a third stage for thickening, and the thickened sludge from the third stage is forwarded to a fourth stage for digestion.

11. The improved process of claim 10 where a portion of the thickened sludge from the third stage is mixed with the water and sludge mix entering the second stage.

12. The improved process of claim 10 where a portion of the digested sludge from the fourth stage is mixed with the water and sludge mix entering the second stage.

13. The improved process of claim 1 where oxygen is introduced into the contaminated water entering the first stage by aspirating air into a stream of said water.

14. The improved process of claim 13 where the oxygen in the stream of water entering the first stage is subjected to high pressure produced by a hydrostatic head of liquor.

15. The improved process of claim 10 where oxygen is introduced into the sludge flowing between the second and third stages, and between the third and fourth stages.

16. A method of pretreating waste water including from about 25 to about 150 parts per million of solids per million parts of water and/or from about 25 to about 300 parts of hydrocarbons per million parts of water upstream of activated sludge treatment comprising, passing the water through an equalization zone including at least two separate water retention compartments in series so that the water is mixed in each compartment and flows from one compartment to the next compartment and a given quantity of water is retained for predetermined period in each of said compartments.

introducing air into the water in at least one of the compartments so that the water in the compartment is vigorously agitated and the effluent in the aerated compartment includes at least three parts of dissolved oxygen per million parts of water,

adjusting the pH of the water in the equalization zone so that the pH of the water in one of the compartments and in the effluent from said zone ranges between about 6.5 and about 9.5,

destabilizing colloidal particles suspended in the water, and

filtering the effluent water from the equalization zone so that said filtered water includes no more than about twenty parts of hydrocarbons per million parts of water and no more than about twenty parts of suspended solids per million parts of water.

17. The method of claim 16 wherein municipal waste water is subjected to treatment.

18. The method of claim 16 wherein waste water from petroleum processing and/or chemical processing is subjected to treatment.

19. The method of claim 16 wherein said filtered water includes no more than about ten parts of hydrocarbons per million parts of water and no more than about ten parts of suspended solids per million parts of water.

20. The process of claim 16 where the difference in temperature between the influent water entering the equalization zone and the effluent water exiting the equalization zone is less than about 20°

F wherein the total retention time in the equalization zone ranges from about 2 to 15 hours.

21. The process of claim 16 where any solid or liquid material floating on the water surface in the equalization zone is removed by skimming.

22. The process of claim 16 where a coagulant or flocculant is added to the water to destabilize the colloidal particles in the water.

23. The process of claim 16 where the water in the first compartment is monitored to detect any rapid change in contaminant concentration.

24. The process of claim 16 where gallic acid or hydroquinone is added to the water in the aerated compartment to accelerate the rate of immediate oxygen demand removal.

25. A continuous process for purifying contaminated water including solids and/or hydrocarbons, comprising:

(a) passing the water through an equalization zone where the pH of the water is adjusted to a range from about 6.5 to 9.5 and the contaminated water is distributed in a larger body of water so that the changes in concentration of contaminants in the effluent water to the equalization zone will produce gradual changes in concentration of contaminants in effluent water from said zone,

(b) aerating the water in the equalization zone so that the dissolved oxygen in the water is at least about three parts of dissolved oxygen per million parts of water,

(c) adding a destabilizing agent to the water so that colloidal particles in the water aggregate,

(d) passing the water from the equalization zone through a filter so that particles and hydrocarbons removed therefrom and the effluent from the filter will have less than about twenty parts of suspended solids per million parts of water and less than about twenty parts of hydrocarbons per million parts of water,

(e) passing effluent from the filter through a multi-stage biological treating zone having a first stage where the water flows into a contact zone and contacts an activated sludge which decontaminates the water by biodegradation of contaminants, a second stage where the water from the first stage is clarified to separate suspended sludge particles from decontaminated water, a portion of said separated sludge particles being recycled to the first stage and the bulk of the clarified decontaminated water being withdrawn from the second stage, a third stage where that portion of the separated sludge particles not recycled are concentrated by removing the bulk of the residual water therefrom, and a fourth stage where said concentrated sludge particles are digested.

(f) aspirating air into the water and sludge mix as it flows between the first and second stages, so that the sludge in the second stage is maintained in an aerobic stage and clarified water from said second stage contains at least about three parts of dissolved oxygen per million parts of water, and

(g) filtering separated water withdrawn from the second stage to remove minute suspended sludge particles not separated from this water in said second stage.

26. The process of claim 25 wherein the effluent water from the equalization zone passing through the filter has less than about ten parts of suspended solids per million parts of water and less than about ten parts of hydrocarbons per million parts of water.

27. The process of claim 25 wherein the clarified water from the second stage contains at least about five parts of dissolved oxygen per million parts of water.

28. The process of claim 25 wherein municipal waste water is subjected to treatment.

29. The process of claim 25 wherein waste water from petroleum processing and/or chemical processing is subjected to treatment.

30. The process of claim 25 including the additional steps of aerating the water entering the first stage and aerating the sludge particle mix as it flows between the second, third and fourth stages.

31. The process of claim 25 where the filtered water from step (g) is contacted with activated carbon.

32. The process of claim 25 where a portion of the sludge from the second stage is mixed with the water and sludge flowing between the first and second stages.

33. The process of claim 25 where a portion of the sludge from the third stage is mixed with the water and sludge flowing between the first and second stages.

34. The process of claim 25 where a portion of the sludge from the fourth stage is mixed with the water and sludge flowing between the first and second stages.

35. The process of claim 25 where the average age of the activated sludge in the biological zone is greater than ten days.

36. The process of claim 25 where the dissolved oxygen concentration in the water flowing to the biological treating zone is at least about three parts of dissolved oxygen per million parts of water.

37. The process of claim 25 where the air, water, and sludge mix entering the second stage of the biological treating zone is confined in a zone of high turbulence.

38. An improved multiple-stage activated sludge process wherein the average age of the activated sludge in the biological zone exceeds ten days comprising

pretreating the contaminated water so that it contains no more than about 20 parts of hydrocarbons per million parts of water and no more than about 20 parts of suspended solids per million parts of water,

contacting said pretreated water with activated sludge in the first stage for a period of time sufficient to biologically degrade contaminants in the water,

introducing oxygen into the water and sludge mix entering the second stage so that the sludge in the second stage is maintained in an aerobic state and separated decontaminated water from said second stage contains at least about 5 ppm dissolved oxygen.

separated decontaminated water from the activated sludge in the second stage and recycling a first portion of said separated sludge for recontact with the water in the first stage, and

treating a second portion of said separated sludge in downstream operations.

39. The process of claim 38 wherein the contaminated water is pretreated so that it contains no more than ten parts of hydrocarbon per million parts of water and/or no more than ten parts of suspended solids per million parts of water.

40. The improved process of claim 38 wherein oxygen is introduced into the water and sludge mix entering the second state so that the sludge in said second stage is maintained in an aerobic stage.

41. In the activated sludge process wherein a first stage contaminated water is contacted with activated sludge for a period of time sufficient to biologically degrade contaminants in the water and in a second stage decontaminated water is separated from the activated sludge, a first portion of said separated sludge being recycled for recontact with the water in the first stage and a second portion of said separated sludge being treated in downstream operations, the improvement comprising:

reducing the level of contaminants in the contaminated water to the first stage to less than about 20 ppm of hydrocarbons and less than about 20 ppm of solids; and

introducing oxygen into the water and sludge mix entering the second stage so that the sludge in the second zone is maintained in an aerobic state and separated decontaminated water from said second stage contains at least about 3 parts of dissolved oxygen per million parts of water.

42. The improved process of claim 41 wherein the contaminated water entering the first stage contains less than about 10 ppm of hydrocarbons and less than about 10 ppm of solids.

43. In a multi-stage activated sludge process wherein a first stage contaminated water is contacted with activated sludge for a period of time to biologically contaminants in the water and in a second stage decontaminated water from the first stage is separated from the activated sludge, the improvement comprising filtering the contaminated water prior to the first stage to reduce the level of oil and grease, and solids so that the waste water to the first stage has less than about 20 ppm of oil and grease and less than about 20 ppm of solids.

44. The process of claim 43 wherein a first portion of said separated sludge is recycled for recontact with the water in the first stage and a second portion of said separated sludge is treated in downstream operations.

45. In a multi-stage activated sludge process wherein a first stage contaminated water is contacted with activated sludge for a period of time to biologically degrade contaminants in the water and in a second stage decontaminated water is separated from the activated sludge, the improvement comprising reducing the oil and grease, and solids content of the waste water to less than about 20 ppm oil and grease and less than about 20 ppm solids, prior to the first stage.

46. The process of claim 45 wherein the oil and grease, and solids content are reduced to less than about 10 ppm each.

47. In an activated sludge process wherein a first stage contaminated water is contacted with activated sludge for a period of time to biologically degrade contaminants in the water and in a second stage decontaminated water from the first stage is separated from the activated sludge, the improvement comprising maintaining the average sludge age in the first and second stages in excess of about ten days and treating the waste water to reduce oil and grease, and solids to less than about 20 ppm oil and grease and less than about 20 ppm solids, prior to the first stage.

48. In the activated sludge process wherein a first stage contaminated water containing less than about 10 ppm of hydrocarbons and less than about 10 ppm of solids is contacted with activated sludge for a period of time sufficient to biologically degrade contaminants in the water and in a second stage decontaminated water is separated from the activated sludge, a first portion of said separated sludge being recycled for recontact with the water in the first stage and a second portion of said separated sludge being treated in downstream operations, the improvement comprising

introducing oxygen into the water and sludge mix entering the second stage so that the sludge in the second zone is maintained in an aerobic state and separated decontaminated water from said second stage contains at least about 5 parts of dissolved oxygen per million parts of water.

49. The improved process of claim 48 where the oxgyen is introduced into the water and sludge mix entering the second stage by aspirating air into a stream of the water and sludge mix flowing between the first and second stages.

50. The improved process of claim 49 where the oxygen in the stream of water and sludge mix flowing between the first and second stage is subjected to a high pressure produced by hydrostatic heads of liquid in the first and second stages.

51. The improved process of claim 48 where the average age of the activated sludge in the first and second stages exceeds ten days.

52. The improved process of claim 48 where a part of the first portion of the separated recycled sludge is mixed with the stream of water and sludge mix flowing between the first and second stages.

53. The improved process of claim 48 where said second portion of the sludge treated in downstream operations is forwarded through a third stage for thickening, and the thickened sludge from the third stage is forwarded to a fourth stage for digestion.

54. The improved process of claim 53 where a portion of the thickened sludge from the third stage is mixed with the water and sludge mix entering the second stage.

55. The improved process of claim 53 where a portion of the digested sludge from the fourth stage is mixed with the water and sludge mix entering the second stage.

56. The improved process of claim 48 where oxygen is introduced into the contaminated water entering the first stage by aspirating air into a stream of said water.

57. The improved process of claim 56 where the oxygen in the stream of water entering the first stage is subjected to high pressure produced by a hydrostatic head of liquid.

58. The improved process of claim 53 where oxygen is introduced into the sludge flowing between the second and third stages, and between the third and fourth stages.

59. A method of pretreating waste water including from about 25 to about 150 parts per million of solids per million parts of water and from about 25 to about 300 parts of hydrocarbons per million parts of water upstream of activated sludge treatment comprising, passing the water through an equalization zone including at least two separate water retention compartments in series so that the water is mixed in each compartment and flows from one compartment to the next compartment and a given quantity of water is retained for predetermined period in each of said compartments,

introducing air into the water in at least one of the compartments so that the water in the compartment is vigorously agitated and the effluent in the aerated compartment includes at least three parts of dissolved oxygen per million parts of water,

adjusting the pH of the water in the equalization zone so that the pH of the water in one of the compartments and in the effluent from said zone ranges between about 6.5 and about 9.5,

destabilizing colloidal particles suspended in the water, and

filtering the effluent water from the equalization zone so that said filtered water includes no more than ten parts of hydrocarbons per million parts of water and no more than ten parts of solids per million parts of water.

60. The process of claim 59 where the difference in temperature between the influent water entering the equalization zone and the effluent water exiting the equalization zone is less than about 20°

F wherein the total retention time in the equalization zone ranges from about 2 to 15 hours.

61. The process of claim 59 where any solid material floating on the water surface in the equalization zone is removed by skimming.

62. The process of claim 59 where a coagulant or flocculant is added to the water to destabilize the colloidal particles in the water.

63. The process of claim 59 where the water in the first compartment is monitored to detect any rapid change in contaminant concentration.

64. The process of claim 59 where gallic acid or hydroquinone is added to the water in the aerated compartment to accelerate the rate of immediate oxygen demand removal.

65. A continuous process for purifying contaminated water including solids and hydrocarbons, comprising

(a) passing the water through an equalization zone where the pH of the water is adjusted to a range from about 6.5 to 9.5 and the contaminated water is distributed in a larger body of water so that the changes in concentration of contaminants in the effluent water to the equalization zone will produce gradual changes in concentration of contaminants is effluent water from said zone,

(b) aerating the water in the equalization zone so that the dissolved oxygen in the water is at least about three parts of dissolved oxygen per million parts of water,

(c) adding a destabilizing agent to the water so that colloidal particles in the water aggregate,

(d) passing the water from the equalization zone through a filter so that particles and hydrocarbons removed therefrom and the effluent from the filter will have less than about ten parts of suspended solids per million parts of water and less than about ten parts of hydrocarbons per million parts of water,

(e) passing effluent from the filter through a multi-stage biological treating zone having a first stage where the water flows into a contact zone and contacts an activated sludge which decontaminates the water by biodegradation of contaminants, a second stage where the water from the first stage is clarified to separate suspended sludge particles from decontaminated water, a porton of said separated sludge particles being recycled to the first stage and the bulk of the clarified decontaminated water being withdrawn from the second stage, a third stage where that portion of the separated sludge particles not recycled are concentrated by removing the bulk of the residual water therefrom, and a fourth stage where said concentrated sludge particles are digested,

(f) aspirating air into the water and sludge mix as it flows between the first and second stages, so that the sludge in the second stage is maintained in an aerobic state and clarified water from said second stage contains at least about five parts of dissolved oxygen per million parts of water, and

(g) filtering separated water withdrawn from the second stage to remove minute suspended sludge particles not separated from this water in said second stage.

66. The process of claim 65 including the additional steps of aerating the water entering the first stage and aerating the sludge particle mix as it flows between the second, third and fourth stages.

67. The process of claim 65 where the filtered water from step (g) is contacted with activated carbon.

68. The process of claim 65 where a portion of the sludge from the second stage is mixed with the water and sludge flowing between the first and second stages.

69. The process of claim 65 where a portion of the sludge from the third stage is mixed with the water and sludge flowing between the first and second stages.

70. The process of claim 65 where a portion of the sludge from the fourth stage is mixed with the water and sludge flowing between the first and second stages.

71. The process of claim 65 where the average age of the activated sludge in the first stage is greater than ten days.

72. The process of claim 65 where the dissolved oxygen concentration in the water flowing to the biological treating zone is at least about three parts of dissolved oxygen per million parts of water.

73. The process of claim 65 where the air, water, and sludge mix entering the second stage of the biological treating zone is confined in a zone of high turbulence.

74. An improved multiple-stage activated sludge process wherein the average age of the activated sludge in the first and second stages exceeds ten days comprising

pretreating the contaminated water so that it contains no more than 10 parts of hydrocarbons per million parts of water and no more than 10 parts of solids per million parts of water,

contacting said pretreated water with activated sludge in the first stage for a period of time sufficient to biologically degrade contaminants in the water,

introducing oxygen into the water and sludge mix entering the second stage so that the sludge in the second stage is maintained in an aerobic stage and separated decontaminated water from said second stage contains at least 5 ppm dissolved oxygen,

separating decontaminated water from the activated sludge in the second stage and recycling a first portion of said separated sludge for recontact with the water in the first stage, and

treating a second portion of said separated sludge in downstream operations.