Process and apparatus for the biofiltration of volatile organic compounds

• US 20040152185A1
• Filed: 03/22/2004
• Published: 08/05/2004
• Est. Priority Date: 05/03/2001
• Status: Active Grant

• Current Assignee: BORD NA MONA PLC (Government of Ireland)
• Original Assignee: BORD NA MONA PLC (Government of Ireland)
• Inventors: Egan, Imelda, Phillips, Ian
• Granted Patent: US 7,919,304 B2
• Time in Patent Office: Days
• US Class Current: 435/266
• CPC Class Codes: B01D 53/84 Biological processes
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

A process and system are disclosed for the biofiltration of volatile organic compounds. The process involved recirculating contaminated effluent gas through a biofilter (1), the biofilter (1) having an inlet (20), outlet (15) and micro-organism laden filter media bed (3). The filter media bed additionally having moisture retaining properties. This process has been effective in removing high levels of VOCs from effluent gas streams and also in removing VOCs from an effluent gas stream where the VOC levels and/or volumes of effluent gas vary over time.

Claims

1. A process for the biofiltration of volatile organic compounds (VOCs) of the type comprising delivering contaminated effluent gas through a biofilter (1), the biofilter (1) having an inlet (20), outlet (15) and a micro-organism laden filter media bed (3), the filter media bed (3) additionally having moisture retaining properties and which filter media bed (3) is suitable for the absorption, microbial oxidation and degradation of the VOCs characterised in that the process comprises:

—

delivering contaminated effluent gas to the biofilter inlet (20) at a biofilter throughput rate and removing the filtered gas through the outlet (15) at the same rate; and

recirculating the contaminated effluent gas within the biofilter whereby the rate at which gas passes through the filter media (3) exceeds the biofilter throughput rate at the inlet (20) and outlet (15), and wherein the inlet gas is effectively diluted within the biofilter.

2. A process as claimed in claim 1, in which the VOC concentration at the outlet (15) is monitored.

3. A process as claimed in claim 2 in which the VOC concentration in the output air is monitored and when the VOC concentration exceeds a pre-set limit, recirculation is carried out.

4. A process as claimed in claim 1 or 2, in which the VOC concentration at the inlet (20) is monitored.

5. A process as claimed in any preceding claim, in which the biofilter throughput rate is determined having regard to the volume of effluent gas to be processed.

6. A process as claimed in any preceding claim, in which the number of times recirculation is carried out and hence the media throughput achieved, depends on the backpressure generated by the filter media (3).

7. A process as claimed in any preceding claim, in which recirculation is carried out when the level of VOCs removed by the biofilter (1) is not sufficient to maintain the micro-organisms within the filter media bed (3).

8. A process as claimed in any preceding claim, in which the amount of filter media is chosen having regard to optimum operation below a chosen base inlet VOC concentration and in which the air is recirculated when the concentration exceeds the chosen base concentration.

9. A process as claimed in any preceding claim in which the filter media bed is kept moist by delivering liquid across the filter media bed (3).

10. A process as claimed in claim 9, wherein when the inlet (20) concentration of VOC falls below a preset limit for a predetermined length of time VOCs are added to the filter media bed (3).

11. A process as claimed in claim 10, wherein VOCs are added to the filter media bed (3) by delivering liquid with dissolved VOCs across the filter media bed (3).

12. A process as claimed in claims 9 to 11 in which the liquid delivered across the filter media bed (3) is stimulated electromagnetically.

13. A process as claimed in claims 9 to 12 wherein the liquid is delivered across the filter media bed (3) at a rate of between 20 to 50 l/m³ media/minute.

14. A process as claimed in claim 13 wherein the rate is 30 l/m³ media/minute.

15. A process as claimed in claim 13 wherein the rate increases depending on the levels of VOC passing through the filter media bed (3).

16. A process as claimed in claims 9 to 15 wherein the wetting is achieved by recirculating the liquid over the packing (3) from a storage sump (5).

17. A process for the biofiltration of volatile organic compounds (VOCs) of the type comprising delivering contaminated effluent gas containing odorous compounds through a biofilter having an inlet (20), outlet (15) and a filter media bed (3), the filter media bed (3) having micro-organisms, nourishment and moisture retaining properties which are suitable for the absorption, chemical degradation and microbial oxidation of the VOCs and which process also includes delivering liquid across the filter media bed (3) characterised in that the method comprises:

—

delivering contaminated gas to the biofilter inlet (20) at a filter throughput rate and removing the filtered gas at the same rate;

recirculating the contaminated gas within the biofilter whereby the media throughput of gas through the filter media (3) exceeds the filter throughput rate from inlet (20) to outlet (15); and

electromagnetically stimulating the liquid which is delivered across the filter media bed (3).

18. A process as claimed in claim 17 in which the VOC concentration in the output gas is monitored and when the VOC concentration exceeds a pre-set limit, recirculation is carried out.

19. A process as claimed in claim 17 and 18, wherein when the inlet (20) concentration of VOC falls below a pre-set limit for a predetermined length of time VOCs are added to the filter media bed.

20. A process as claimed in claim 19 wherein VOCs are added to the filter media bed (3) by delivering liquid with dissolved VOCs over the filter media bed (3).

21. A process as claimed in claims 17 to 20 wherein the liquid is delivered across the filter media bed (3) at a rate of between to 20 to 50 l/m³ media/minute.

22. A process as claimed in claim 21 wherein the rate is 30 l/m³ media/minute.

23. A process as claimed in claim 21 wherein the rate increases depending on the levels of VOC passing through the filter media bed (3).

24. A process as claimed in claims 17 to 23, in which the biofilter throughput rate is determined having regard to the volume of effluent gas to be processed.

25. A biofiltration filtration system for the removal of VOCs from contaminated effluent gases of the type comprising a biofilter housing (1), a gas inlet (20) in the housing for reception of the contaminated effluent gas, a gas outlet (15) for delivery of de-contaminated gas from the biofilter, a microbe carrying packing (3) comprising a plurality of randomly arranged elements of calcarous material having a liquid retention portion, many of which are oriented to form an individual and liquid retaining reservoir within the packing characterised in that gas recirculation means are provided for capturing some of the gas adjacent the gas outlet (15) for delivery back into the biofilter housing adjacent the gas inlet (20).

26. A biofiltration system as claimed in claim 25, wherein the filter media (3) has a bulk density of less than 900 g/litre.

27. A biofiltration system as claimed in claim 25 or 26, wherein the filter media (3) has a bulk density of less than 600 g/litre.

28. A biofiltration system as claimed in any of claims 25 to 27, wherein the filter media (3) has a bulk density of approximately 500 g/litre.

29. A biofiltration system as claimed in any of claims 26 to 28, wherein the filter media (3) is spent shell of shellfish.

30. A biofiltration system as claimed in claim 29, wherein the shell material is a half mussel shell (30).

31. A biofiltration system as claimed in claim 30, wherein the mussel shell is of the species Mytilus Edulis.

32. A biofiltration system as claimed in any of claims 25 to 31, wherein at least some of the elements are formed from ground calcarous material mixed with a binding agent.

33. A biofiltration system as claimed in claim 32, wherein the binding agent is acid resistant.

34. A biofiltration system as claimed in claim 33, wherein the binding agent is Keratin.

35. A biofiltration system as claimed in any of claims 25 to 34, wherein the packing includes one or more additional packing materials.

36. A biofiltration system as claimed in claim 35, wherein the additional packing material includes one or more of:

heather, peat nodules, activated carbon, alumina and plastics media.

37. A biofiltration system as claimed in any of claims 25 to 36, including wetting means for wetting the packing.

38. A biofiltration system as claimed in claim 37, wherein the wetting means comprises a spray means (6).

39. A biofiltration system as claimed in claim 37 or 38, wherein the wetting means is operated intermittently.

40. A biofiltration system as claimed in claim 37 or 38 wherein the wetting means is operated substantially continuously.

41. A biofiltration system as claimed in any of claims 37 to 40, wherein the wetting is achieved by recirculating liquid over the packing from a storage sump (5).

42. A biofiltration system as claimed in any of claims 37 to 40;

wherein the wetting is carried out in concurrent flow to the flow of the gas stream through the packing.

43. A biofiltration system as claimed in any of claims 37 to 42, wherein the liquid provided by the wetting means is stimulated electromagnetically.

44. A biofiltration system as claimed in claims 37 to 43 wherein the liquid provided by the wetting means is delivered across the filter media bed (3) at a rate of between 20 to 50 l/m³ media/minute.

45. A biofiltration system as claimed in claim 44 wherein the rate is 30 l/m³ media/minute.

46. A biofiltration system as claimed in claim 44 wherein the rate is dependent on the levels of VOC passing through the filter media bed (3).

47. A biofiltration system for the removal of VOCs from contaminated effluent gas of the type comprising a biofilter housing (2), a gas inlet (20) in the housing for reception of the contaminated effluent gas, a gas outlet (15) for delivery of de-contaminated gas from the biofilter, a microbe carrying packing (3) comprising a plurality of randomly arranged elements of calcarous material having a liquid retention portion, many of which are oriented to form an individual and liquid retaining portion within the packing (3) and a means for wetting the packing (3) characterised in that gas recirculation means are provided for capturing some of the gas adjacent the gas outlet (15) for delivery back into the biofilter housing adjacent the gas inlet (20) and wherein means are also provided for electromagnetic stimulation of the liquid provided by the wetting means.

48. A biofiltration system as claimed in claim 47 wherein the wetting means comprises a spray means.

49. A biofiltration system as claimed in claim 48, wherein the wetting is achieved by recirculating liquid over the packing from a storage sump (5).

50. A biofiltration system as claimed in claims 47 to 49 wherein the liquid provided by the wetting means is delivered across the filter media bed (3) at a rate of between 20 to 50 l/m³ media/minute.

51. A biofiltration system as claimed in claim 50 wherein the rate is 30 l/m³ media/minute.

52. A biofiltration system as claimed in claim 50 wherein the rate is dependent of the levels of VOC passing through the filter media bed (3).

53. A biofiltration system as clamed in claims 47 to 52 wherein the filter media has a bulk density of less than 900 g/litre.

54. A biofiltration system as claimed in claims 47 to 53 wherein the calcareous material is a half mussel shell (30).

55. A biofiltration system as claimed in claim 54 wherein the half mussel shell is of the species Mytilus Edulis