Method, apparatus and biomass support element for biolocical waste water treatment

• US 20040089592A1
• Filed: 12/09/2003
• Published: 05/13/2004
• Est. Priority Date: 05/29/2001
• Status: Abandoned Application

• Current Assignee: Aqwise-Wise Water Technologies Ltd.
• Original Assignee: Aqwise-Wise Water Technologies Ltd.
• Inventors: Shechter, Ronen Itzhak, Levy, Eytan Baruch
• Application Number:
  US10/451,474
• Publication Number:
  US 20040089592A1
• Time in Patent Office: Days
• US Class Current: 210/150
• CPC Class Codes: B01J 19/30 Loose or shaped packing elements, e.g. Raschig rings or Berl saddles, for pouring into the apparatus for mass or heat transfer
• CPC Class Codes: B01J 2219/30223 Cylinder
• CPC Class Codes: B01J 2219/30242 Star
• CPC Class Codes: B01J 2219/30466 Plastics
• CPC Class Codes: B01J 2219/312 Sizes
• CPC Class Codes: C02F 3/02 Aerobic processes
• CPC Class Codes: C02F 3/087 Floating beds with contact bodies having a lower density than water
• CPC Class Codes: C02F 3/10 Packings; Fillings; Grids packing elements in general B01J19/30, B01J19/32
• CPC Class Codes: C02F 3/223 using "air-lift"
• CPC Class Codes: Y02W 10/10 Biological treatment of water, waste water, or sewage

Abstract

A method and apparatus for retrofitting existing waste water treatment facilities having at least one existing basin including installing generally vertical partitions at spaced locations in the existing basin in order to divide the existing basin into a plurality of treatment stage regions, installing at least one air lift in each of the plurality of treatment stage regions, loading each treatment stage regions with a quantity of floatable porous particles, supplying waste water to at least one of the plurality of treatment stage regions and allowing the waste water, but generally not the particles, to flow from the plurality of treatment stage regions to at least another of the plurality of treatment stage regions and operating the air lift in each of the plurality of treatment stage regions to provide aerobic waste water flow therein in operative engagement with the floatable porous particles. A biomass support including a plastic biomass support element having a maximum dimension which does not exceed 50 mm and having a specific gravity of between approximately 0.70-0.91, a method of manufacture of a biomass support and a waste water treatment system employing the biomass support are also disclosed.

Claims

1. A method for retrofitting existing waste water treatment facilities having at least one existing basin comprising:

installing generally vertical partitions at spaced locations in said at least one existing basin in order to divide said at least one existing basin into a plurality of treatment stage regions;

installing at least one air lift in each of said plurality of treatment stage regions;

loading each treatment stage regions with a quantity of floatable porous particles;

supplying waste water to at least one of said plurality of treatment stage regions and allowing said waste water, but generally not said particles, to flow from at least one of said plurality of treatment stage regions to at least another of said plurality of treatment stage regions; and

operating said at least one air lift in each of said plurality of treatment stage regions to provide aerobic waste water flow therein in operative engagement with said floatable porous particles.

2. A method according to claim 1 and wherein at least some of said vertical partitions are spaced from a bottom of said at least one basin in order to allow said waste water to flow thereunder between adjacent ones of said plurality of treatment stage regions.

3. A method according to claim 1 and wherein said at least one air lift comprises at least one air diffuser disposed underlying a peripheral enclosure which defines a column of water which is lifted by air diffusing upwardly from said at least one air diffuser therethrough.

4. A method according to claim 3 and wherein said peripheral enclosure comprises a cylindrical enclosure.

5. A method according to claim 3 and wherein said peripheral enclosure comprises a plurality of spaced generally vertical walls which extend between walls of the basin and are separated from the bottom of the basin.

6. A method according to claim 1 and wherein said floatable particles comprise porous plastic particles having a density lower than that of pure water.

7. A method according to claim 6 and wherein said particles have a specific gravity between 0.65 and 0.95.

8. A method according to claim 6 and wherein said particles have an irregular shape, whose largest dimension is generally between 4-10 mm.

9. A method according to claim 6 and wherein said particles have a total porosity exceeding 50%.

10. A method according to claim 6 and wherein said particles have a mean pore diameter of pores, whose diameter exceeds 10 microns, of about 20 microns.

11. A method according to claim 1 and wherein said generally vertical partitions divide said basin into between 4 and 12 process stages.

12. A method according to claim 1 and wherein said at least one air lift comprises a series of air lifts arranged in said multiple process stages.

13. A method according to claim 12 and wherein said series of air lifts includes at each process stage an initial air lift assembly and at least one intermediate air lift assembly.

14. A method according to claim 13 and wherein said initial air lift assembly includes a upstream partition which extends downwardly from a top location above a water level in said basin to a bottom location spaced from the bottom of said basin.

15. A method according to claim 14 and wherein said upstream partition extends fully from side to side of said basin.

16. A method according to claim 14 and wherein said upstream partition is attached to a deflector which extends in a downstream direction from said upstream partition at said water level.

17. A method according to claim 13 and wherein said initial air lift assembly also includes a downstream partition which extends fully from side to side of said basin but does not extend up to said water level.

18. A method according to claim 13 and wherein said intermediate air lift assembly includes an upstream partition which extends downwardly from a top location below said water level in basin to a bottom location spaced from said bottom of said basin.

19. A method according to claim 1 and wherein said vertical partitions each extend filly from side to side of said basin.

20. A method according to claim 13 and wherein said at least one intermediate air lift assembly comprises an upstream partition separated from a deflector plate which extends in a downstream direction from said upstream partition at said water level.

21. A method according to claim 20 and wherein said at least one intermediate air lift assembly also includes a downstream partition which does not extend up to said water level or as close to said bottom of said basin as does said upstream partition.

22. A method according to claim 1 and wherein said installing also includes installing a final air lift assembly including an upstream partition which extends downwardly from a top location below said water level in said basin to a bottom location spaced from said bottom of said basin and extends fully from side to side of said basin.

23. A method according to claim 22 and wherein said final air lift assembly also includes a downstream partition which also extends fully from side to side of said basin and extends to a top location above said water level and closer to said bottom than does said upstream partition.

24. A method according to claim 23 and wherein said downstream partition is attached to a deflector plate which extends in an upstream direction from downstream partition at a location at said water level.

25. A method according to claim 1 and wherein:

said at least one air lift comprises a plurality of air lift assemblies each including upstream and downstream partitions;

a first plurality of air diffusers are disposed at said bottom of said basin intermediate upstream and downstream partitions of said plurality of air lift assemblies; and

a second plurality of air diffusers, lesser in number than said first plurality of air diffusers, are disposed at said bottom of said basin intermediate said plurality of air lift assemblies.

26. A method according to claim 25 and wherein said first plurality of air diffusers intermediate said upstream and downstream partitions of each air lift assembly causes water to flow upward between said upstream and downstream partitions of each air lift assembly.

27. A method according to claim 26 and wherein said second plurality of air diffusers intermediate said plurality of air lift assemblies allows water to flow downward.

28. A method according to claim 1 and wherein said loading comprises loading 10-40 percent of said volume of said basin with particles in absence of water flow.

29. A method according to claim 1 and wherein said supplying comprises providing a continuous flow of water from said upstream side of said basin from said waste water inlet to said treated water outlet.

30. A method according to claim 29 and wherein said flow is an undulating flow and includes passage under upstream partitions which is of relatively low volume and generally does not carry floating particles into said at least one air lift, thereby constraining said particles to reside outside of and between said at least one air lift.

31. A method according to claim 25 and also comprising controlling the flow velocity of water by controlling operation of said first and second pluralities of air diffusers.

32. A method according to claim 1 and wherein said at least one air lift includes an adjustable angle deflector.

33. A method according to claim 1 and wherein said at least one air lift includes an integral curved downstream partition and deflector.

34. A method according to claim 1 and also comprising installing a denitrification unit in at least one of said plurality of treatment stage regions.

35. A method according to claim 34 and wherein said denitrification unit comprises a plurality of axial pumps which provide lift generally without an air flow, thereby to provide an anoxic de-nitrification process.

36. A method according to claim 1 and wherein said at least one air lift comprises an array of air lifts and wherein said array of air lifts comprises a multiplicity of cylindrical air lifts arranged in said plurality of treatment stage regions and separated by said vertical partitions which extend from a bottom location which is spaced from a bottom of said basin by a first vertical separation.

39. A method according to claim 1 and wherein said operating produces fluidization of said particles.

40. A method according to claim 1 and wherein said operating is operative, when said particles become heavily coated with biomass to cause said particles sometimes to enter said at least one air lift and to be sloughed of some of said biomass as they are propelled upwards by said action of said at least one air lift.

37. A method according to 36 and wherein said cylindrical air lifts each comprise:

a hollow shaft which extends from a bottom location spaced from a bottom of said basin by a second vertical separation which exceeds said first separation;

a deflector which is disposed in spaced relationship over each hollow shaft and is disposed at said water level; and

at least one air diffuser which is disposed underlying each hollow shaft to provide an air lift therethrough, thereby causing water to flow into said hollow shafts and upwardly through said hollow shafts, said deflectors causing said water exiting said tops of said hollow shafts to move sideways and downwardly.

38. A method according to claim 37 and also comprising:

a plurality of air diffusers disposed immediately upstream of each said vertical partition for providing control of particle movement and prevention of particle migration.

41. A method for waste water treatment employing at least one basin comprising:

installing generally vertical partitions at spaced locations in said at least one basin in order to divide said at least one basin into a plurality of treatment stage regions;

installing at least one air lift in each of said plurality of treatment stage regions;

loading each treatment stage regions with a quantity of floatable porous particles;

supplying waste water to at least one of said plurality of treatment stage regions and allowing said waste water, but generally not said particles, to flow from at least one of said plurality of treatment stage regions to at least another of said plurality of treatment stage regions; and

operating said at least one air lift in each of said plurality of treatment stage regions to provide aerobic waste water flow therein in operative engagement with said floatable porous particles.

42. A method according to claim 41 and wherein at least some of said vertical partitions are spaced from a bottom of said at least one basin in order to allow said waste water to flow thereunder between adjacent ones of said plurality of treatment stage regions.

43. A method according to claim 41 and wherein said at least one air lift comprises at least one air diffuser disposed underlying a peripheral enclosure which defines a column of water which is lifted by air diffusing upwardly from said at least one air diffuser therethrough.

44. A method according to claim 43 and wherein said peripheral enclosure comprises a cylindrical enclosure.

45. A method according to claim 43 and wherein said peripheral enclosure comprises a plurality of spaced generally vertical walls which extend between walls of the basin and are separated from the bottom of the basin.

46. A method according to claim 41 and wherein said floatable particles comprise porous plastic particles having a density lower than that of pure water.

47. A method according to claim 46 and wherein said particles have a specific gravity between 0.65 and 0.95.

48. A method according to claim 46 and wherein said particles have an irregular shape, whose largest dimension is generally between 4-10 mm.

49. A method according to claim 46 and wherein said particles have a total porosity exceeding 50%.

50. A method according to claim 46 and wherein said particles have a mean pore diameter of pores, whose diameter exceeds 10 microns, of about 20 microns.

51. A method according to claim 41 and wherein said generally vertical partitions divide said basin into between 4 and 12 process stages.

52. A method according to claim 41 and wherein said at least one air lift comprises a series of air lifts arranged in said multiple process stages.

53. A method according to claim 52 and wherein said series of air lifts includes at each process stage an initial air lift assembly and at least one intermediate air lift assembly.

54. A method according to claim 53 and wherein said initial air lift assembly includes a upstream partition which extends downwardly from a top location above a water level in said basin to a bottom location spaced from the bottom of said basin.

55. A method according to claim 54 and wherein said upstream partition extends fully from side to side of said basin.

56. A method according to claim 54 and wherein said upstream partition is attached to a deflector which extends in a downstream direction from said upstream partition at said water level.

57. A method according to claim 53 and wherein said initial air lift assembly also includes a downstream partition which extends fully from side to side of said basin but does not extend up to said water level.

58. A method according to claim 53 and wherein said intermediate air lift assembly includes an upstream partition which extends downwardly from a top location below said water level in basin to a bottom location spaced from said bottom of said basin.

59. A method according to claim 41 and wherein said vertical partitions each extend fully from side to side of said basin.

60. A method according to claim 53 and wherein said at least one intermediate air lift assembly comprises an upstream partition separated from a deflector plate which extends in a downstream direction from said upstream partition at said water level.

61. A method according to claim 60 and wherein said at least one intermediate air lift assembly also includes a downstream partition which does not extend up to said water level or as close to said bottom of said basin as does said upstream partition.

62. A method according to claim 41 and wherein said installing also includes installing a final air lift assembly including an upstream partition which extends downwardly from a top location below said water level in said basin to a bottom location spaced from said bottom of said basin and extends fully from side to side of said basin.

63. A method according to claim 62 and wherein said final air lift assembly also includes a downstream partition which also extends fully from side to side of said basin and extends to a top location above said water level and closer to said bottom than does said upstream partition.

64. A method according to claim 63 and wherein said downstream partition is attached to a deflector plate which extends in an upstream direction from downstream partition at a location at said water level.

65. A method according to claim 41 and wherein:

said at least one air lift comprises a plurality of air lift assemblies each including upstream and downstream partitions;

a first plurality of air diffusers are disposed at said bottom of said basin intermediate upstream and downstream partitions of said plurality of air lift assemblies; and

a second plurality of air diffusers, lesser in number than said first plurality of air diffusers, are disposed at said bottom of said basin intermediate said plurality of air lift assemblies.

66. A method according to claim 65 and wherein said first plurality of air diffusers intermediate said upstream and downstream partitions of each air lift assembly causes water to flow upward between said upstream and downstream partitions of each air lift assembly.

67. A method according to claim 66 and wherein said second plurality of air diffusers intermediate said plurality of air lift assemblies allows water to flow downward.

68. A method according to claim 41 and wherein said loading comprises loading 10-40 percent of said volume of said basin with particles in absence of water flow.

69. A method according to claim 41 and wherein said supplying comprises providing a continuous flow of water from said upstream side of said basin from said waste water inlet to said treated water outlet.

70. A method according to claim 69 and wherein said flow is an undulating flow and includes passage under upstream partitions which is of relatively low volume and generally does not carry floating particles into said at least one air lift, thereby constraining said particles to reside outside of and between said at least one air lift.

71. A method according to claim 65 and also comprising controlling the flow velocity of water by controlling operation of said first and second pluralities of air diffusers.

72. A method according to claim 41 and wherein said at least one air lift includes an adjustable angle deflector.

73. A method according to claim 41 and wherein said at least one air lift includes an integral curved downstream partition and deflector.

74. A method according to claim 41 and also comprising installing a denitrification unit in at least one of said plurality of treatment stage regions.

75. A method according to claim 74 and wherein said denitrification unit comprises a plurality of axial pumps which provide lift generally without an air flow, thereby to provide an anoxic de-nitrification process.

76. A method according to claim 41 and wherein said at least one air lift comprises an array of air lifts and wherein said array of air lifts comprises a multiplicity of cylindrical air lifts arranged in said plurality of treatment stage regions and separated by said vertical partitions which extend from a bottom location which is spaced from a bottom of said basin by a first vertical separation.

79. A method according to claim 41 and wherein said operating produces fluidization of said particles.

80. A method according to claim 41 and wherein said operating is operative, when said particles become heavily coated with biomass to cause said particles sometimes to enter said at least one air lift and to be sloughed of some of said biomass as they are propelled upwards by said action of said at least one air lift.

77. A method according to 76 and wherein said cylindrical air lifts each comprise:

a hollow shaft which extends from a bottom location spaced from a bottom of said basin by a second vertical separation which exceeds said first separation;

a deflector which is disposed in spaced relationship over each hollow shaft and is disposed at said water level; and

at least one air diffuser which is disposed underlying each hollow shaft to provide an air lift therethrough, thereby causing water to flow into said hollow shafts and upwardly through said hollow shafts, said deflectors causing said water exiting said tops of said hollow shafts to move sideways and downwardly.

78. A method according to claim 77 and also comprising:

a plurality of air diffusers disposed immediately upstream of each said vertical partition for providing control of particle movement and prevention of particle migration.

81. Retrofitted waste water treatment apparatus comprising:

at least one existing basin;

generally vertical partitions located at spaced locations in said at least one existing basin in order to divide said at least one existing basin into a plurality of treatment stage regions;

at least one air lift located in each of said plurality of treatment stage regions; and

a quantity of floatable porous particles loaded into each of said plurality of treatment stage regions, whereby supplying waste water to at least one of said plurality of treatment stage regions and allowing said waste water, but generally not said particles, to flow from at least one of said plurality of treatment stage regions to at least another of said plurality of treatment stage regions and operating said at least one air lift in each of said plurality of treatment stage regions provides aerobic waste water flow therein in operative engagement with said floatable porous particles.

82. Apparatus according to claim 81 and wherein at least some of said vertical partitions are spaced from a bottom of said at least one basin in order to allow said waste water to flow thereunder between adjacent ones of said plurality of treatment stage regions.

83. Apparatus according to claim 81 and wherein said at least one air lift comprises at least one air diffuser disposed underlying a peripheral enclosure which defines a column of water which is lifted by air diffusing upwardly from said at least one air diffuser therethrough.

84. Apparatus according to claim 83 and wherein said peripheral enclosure comprises a cylindrical enclosure.

85. Apparatus according to claim 83 and wherein said peripheral enclosure comprises a plurality of spaced generally vertical walls which extend between walls of the basin and are separated from the bottom of the basin.

86. Apparatus according to claim 81 and wherein said floatable particles comprise porous plastic particles having a density lower than that of pure water.

87. Apparatus according to claim 86 and wherein said particles have a specific gravity between 0.65 and 0.95.

88. Apparatus according to claim 86 and wherein said particles have an irregular shape, whose largest dimension is generally between 4-10 mm.

89. Apparatus according to claim 86 and wherein said particles have a total porosity exceeding 50%.

90. Apparatus according to claim 86 and wherein said particles have a mean pore diameter of pores, whose diameter exceeds 10 microns, of about 20 microns.

91. Apparatus according to claim 81 and wherein said generally vertical partitions divide said basin into between 4 and 12 process stages.

92. Apparatus according to claim 81 and wherein said at least one air lift comprises a series of air lifts arranged in said multiple process stages.

93. Apparatus according to claim 92 and wherein said series of air lifts includes at each process stage an initial air lift assembly and at least one intermediate air lift assembly.

94. Apparatus according to claim 93 and wherein said initial air lift assembly includes a upstream partition which extends downwardly from a top location above a water level in said basin to a bottom location spaced from the bottom of said basin.

95. Apparatus according to claim 94 and wherein said upstream partition extends fully from side to side of said basin.

96. Apparatus according to claim 94 and wherein said upstream partition is attached to a deflector which extends in a downstream direction from said upstream partition at said water level.

97. Apparatus according to claim 93 and wherein said initial air lift assembly also includes a downstream partition which extends fully from side to side of said basin but does not extend up to said water level.

98. Apparatus according to claim 93 and wherein said intermediate air lift assembly includes an upstream partition which extends downwardly from a top location below said water level in basin to a bottom location spaced from said bottom of said basin.

99. Apparatus according to claim 81 and wherein said vertical partitions each extend fully from side to side of said basin.

100. Apparatus according to claim 93 and wherein said at least one intermediate air lift assembly comprises an upstream partition separated from a deflector plate which extends in a downstream direction from said upstream partition at said water level.

101. Apparatus according to claim 100 and wherein said at least one intermediate air lift assembly also includes a downstream partition which does not extend up to said water level or as close to said bottom of said basin as does said upstream partition.

102. Apparatus according to claim 81 and wherein said installing also includes installing a final air lift assembly including an upstream partition which extends downwardly from a top location below said water level in said basin to a bottom location spaced from said bottom of said basin and extends fully from side to side of said basin.

103. Apparatus according to claim 102 and wherein said final air lift assembly also includes a downstream partition which also extends fully from side to side of said basin and extends to a top location above said water level and closer to said bottom than does said upstream partition.

104. Apparatus according to claim 103 and wherein said downstream partition is attached to a deflector plate which extends in an upstream direction from downstream partition at a location at said water level.

105. Apparatus according to claim 81 and wherein:

said at least one air lift comprises a plurality of air lift assemblies each including upstream and downstream partitions;

a first plurality of air diffusers are disposed at said bottom of said basin intermediate upstream and downstream partitions of said plurality of air lift assemblies; and

a second plurality of air diffusers, lesser in number than said first plurality of air diffusers, are disposed at said bottom of said basin intermediate said plurality of air lift assemblies.

106. Apparatus according to claim 105 and wherein said first plurality of air diffusers intermediate said upstream and downstream partitions of each air lift assembly causes water to flow upward between said upstream and downstream partitions of each air lift assembly.

107. Apparatus according to claim 106 and wherein said second plurality of air diffusers intermediate said plurality of air lift assemblies allows water to flow downward.

108. Apparatus according to claim 81 and wherein said loading comprises loading 10-40 percent of said volume of said basin with particles in absence of water flow.

109. Apparatus according to claim 81 and wherein said supplying comprises providing a continuous flow of water from said upstream side of said basin from said waste water inlet to said treated water outlet.

110. Apparatus according to claim 109 and wherein said flow is an undulating flow and includes passage under upstream partitions which is of relatively low volume and generally does not carry floating particles into said at least one air lift, thereby constraining said particles to reside outside of and between said at least one air lift.

111. Apparatus according to claim 105 and also comprising controlling the flow velocity of water by controlling operation of said first and second pluralities of air diffusers.

112. Apparatus according to claim 81 and wherein said at least one air lift includes an adjustable angle deflector.

113. Apparatus according to claim 81 and wherein said at least one air lift includes an integral curved downstream partition and deflector.

114. Apparatus according to claim 81 and also comprising installing a denitrification unit in at least one of said plurality of treatment stage regions.

115. Apparatus according to claim 93 and wherein said denitrification unit comprises a plurality of axial pumps which provide lift generally without an air flow, thereby to provide an anoxic de-nitrification process.

116. Apparatus according to claim 81 and wherein said at least one air lift comprises an array of air lifts and wherein said array of air lifts comprises a multiplicity of cylindrical air lifts arranged in said plurality of treatment stage regions and separated by said vertical partitions which extend from a bottom location which is spaced from a bottom of said basin by a first vertical separation.

119. Apparatus according to claim 81 and wherein said operating produces fluidization of said particles.

120. Apparatus according to claim 81 and wherein said operating is operative, when said particles become heavily coated with biomass to cause said particles sometimes to enter said at least one air lift and to be sloughed of some of said biomass as they are propelled upwards by said action of said at least one air lift.

117. Apparatus according to 116 and wherein said cylindrical air lifts each comprise:

a hollow shaft which extends from a bottom location spaced from a bottom of said basin by a second vertical separation which exceeds said first separation;

a deflector which is disposed in spaced relationship over each hollow shaft and is disposed at said water level; and

at least one air diffuser which is disposed underlying each hollow shaft to provide an air lift therethrough, thereby causing water to flow into said hollow shafts and upwardly through said hollow shafts, said deflectors causing said water exiting said tops of said hollow shafts to move sideways and downwardly.

118. Apparatus according to claim 117 and also comprising:

a plurality of air diffusers disposed immediately upstream of each said vertical partition for providing control of particle movement and prevention of particle migration.

121. Waste water treatment apparatus comprising:

at least one basin;

generally vertical partitions located at spaced locations in said at least one basin in order to divide said at least one basin into a plurality of treatment stage regions;

at least one air lift located in each of said plurality of treatment stage regions; and

a quantity of floatable porous particles loaded into each of said plurality of treatment stage regions, whereby supplying waste water to at least one of said plurality of treatment stage regions and allowing said waste water, but generally not said particles, to flow from at least one of said plurality of treatment stage regions to at least another of said plurality of treatment stage regions and operating said at least one air lift in each of said plurality of treatment stage regions provides aerobic waste water flow therein in operative engagement with said floatable porous particles.

122. Apparatus according to claim 121 and wherein at least some of said vertical partitions are spaced from a bottom of said at least one basin in order to allow said waste water to flow thereunder between adjacent ones of said plurality of treatment stage regions.

123. Apparatus according to claim 121 and wherein said at least one air lift comprises at least one air diffuser disposed underlying a peripheral enclosure which defines a column of water which is lifted by air diffusing upwardly from said at least one air diffuser therethrough.

124. Apparatus according to claim 123 and wherein said peripheral enclosure comprises a cylindrical enclosure.

125. Apparatus according to claim 123 and wherein said peripheral enclosure comprises a plurality of spaced generally vertical walls which extend between walls of the basin and are separated from the bottom of the basin.

126. Apparatus according to claim 121 and wherein said floatable particles comprise porous plastic particles having a density lower than that of pure water.

127. Apparatus according to claim 126 and wherein said particles have a specific gravity between 0.65 and 0.95.

128. Apparatus according to claim 126 and wherein said particles have an irregular shape, whose largest dimension is generally between 4-10 mm.

129. Apparatus according to claim 126 and wherein said particles have a total porosity exceeding 50%.

130. Apparatus according to claim 126 and wherein said particles have a mean pore diameter of pores, whose diameter exceeds 10 microns, of about 20 microns.

131. Apparatus according to claim 121 and wherein said generally vertical partitions divide said basin into between 4 and 12 process stages.

132. Apparatus according to claim 121 and wherein said at least one air lift comprises a series of air lifts arranged in said multiple process stages.

133. Apparatus according to claim 132 and wherein said series of air lifts includes at each process stage an initial air lift assembly and at least one intermediate air lift assembly.

134. Apparatus according to claim 133 and wherein said initial air lift assembly includes a upstream partition which extends downwardly from a top location above a water level in said basin to a bottom location spaced from the bottom of said basin.

135. Apparatus according to claim 134 and wherein said upstream partition extends fully from side to side of said basin.

136. Apparatus according to claim 134 and wherein said upstream partition is attached to a deflector which extends in a downstream direction from said upstream partition at said water level.

137. Apparatus according to claim 133 and wherein said initial air lift assembly also includes a downstream partition which extends fully from side to side of said basin but does not extend up to said water level.

138. Apparatus according to claim 133 and wherein said intermediate air lift assembly includes an upstream partition which extends downwardly from a top location below said water level in basin to a bottom location spaced from said bottom of said basin.

139. Apparatus according to claim 121 and wherein said vertical partitions each extend fully from side to side of said basin.

140. Apparatus according to claim 133 and wherein said at least one intermediate air lift assembly comprises an upstream partition separated from a deflector plate which extends in a downstream direction from said upstream partition at said water level.

141. Apparatus according to claim 140 and wherein said at least one intermediate air lift assembly also includes a downstream partition which does not extend up to said water level or as close to said bottom of said basin as does said upstream partition.

142. Apparatus according to claim 121 and wherein said installing also includes installing a final air lift assembly including an upstream partition which extends downwardly from a top location below said water level in said basin to a bottom location spaced from said bottom of said basin and extends fully from side to side of said basin.

143. Apparatus according to claim 142 and wherein said final air lift assembly also includes a downstream partition which also extends fully from side to side of said basin and extends to a top location above said water level and closer to said bottom than does said upstream partition.

144. Apparatus according to claim 143 and wherein said downstream partition is attached to a deflector plate which extends in an upstream direction from downstream partition at a location at said water level.

145. Apparatus according to claim 121 and wherein:

said at least one air lift comprises a plurality of air lift assemblies each including upstream and downstream partitions;

a first plurality of air diffusers are disposed at said bottom of said basin intermediate upstream and downstream partitions of said plurality of air lift assemblies; and

a second plurality of air diffusers, lesser in number than said first plurality of air diffusers, are disposed at said bottom of said basin intermediate said plurality of air lift assemblies.

146. Apparatus according to claim 145 and wherein said first plurality of air diffusers intermediate said upstream and downstream partitions of each air lift assembly causes water to flow upward between said upstream and downstream partitions of each air lift assembly.

147. Apparatus according to claim 146 and wherein said second plurality of air diffusers intermediate said plurality of air lift assemblies allows water to flow downward.

148. Apparatus according to claim 121 and wherein said loading comprises loading 10-40 percent of said volume of said basin with particles in absence of water flow.

149. Apparatus according to claim 121 and wherein said supplying comprises providing a continuous flow of water from said upstream side of said basin from said waste water inlet to said treated water outlet.

150. Apparatus according to claim 149 and wherein said flow is an undulating flow and includes passage under upstream partitions which is of relatively low volume and generally does not carry floating particles into said at least one air lift, thereby constraining said particles to reside outside of and between said at least one air lift.

151. Apparatus according to claim 145 and also comprising controlling the flow velocity of water by controlling operation of said first and second pluralities of air diffusers.

152. Apparatus according to claim 121 and wherein said at least one air lift includes an adjustable angle deflector.

153. Apparatus according to claim 121 and wherein said at least one air lift includes an integral curved downstream partition and deflector.

154. Apparatus according to claim 121 and also comprising installing a denitrification unit in at least one of said plurality of treatment stage regions.

155. Apparatus according to claim 133 and wherein said denitrification unit comprises a plurality of axial pumps which provide lift generally without an air flow, thereby to provide an anoxic de-nitrification process.

156. Apparatus according to claim 121 and wherein said at least one air lift comprises an array of air lifts and wherein said array of air lifts comprises a multiplicity of cylindrical air lifts arranged in said plurality of treatment stage regions and separated by said vertical partitions which extend from a bottom location which is spaced from a bottom of said basin by a first vertical separation.

159. Apparatus according to claim 121 and wherein said operating produces fluidization of said particles.

160. Apparatus according to claim 121 and wherein said operating is operative, when said particles become heavily coated with biomass to cause said particles sometimes to enter said at least one air lift and to be slouched of some of said biomass as they are propelled upwards by said action of said at least one air lift.

157. Apparatus according to 156 and wherein said cylindrical air lifts each comprise:

a hollow shaft which extends from a bottom location spaced from a bottom of said basin by a second vertical separation which exceeds said first separation;

a deflector which is disposed in spaced relationship over each hollow shaft and is disposed at said water level; and

at least one air diffuser which is disposed underlying each hollow shaft to provide an air lift therethrough, thereby causing water to flow into said hollow shafts and upwardly through said hollow shafts, said deflectors causing said water exiting said tops of said hollow shafts to move sideways and downwardly.

158. Apparatus according to claim 157 and also comprising:

a plurality of air diffusers disposed immediately upstream of each said vertical partition for providing control of particle movement and prevention of particle migration.

161. A biofilm support comprising:

a plastic biofilm support element having a maximum dimension which does not exceed 50 mm and having a specific gravity of between approximately 0.70-0.91.

162. A biofilm support according to claim 161 and wherein said plastic biofilm support element has a generally cylindrical configuration and includes a plurality of radially extending surfaces extending outwardly from a generally solid center.

163. A biofilm support according to claim 161 and wherein said plastic biofilm support element has a plurality of roughened biofilm adherence surfaces integrally formed as one piece therewith.

164. A biofilm support according to claim 162 and wherein said plastic biofilm support element has a plurality of roughened biofilm adherence surfaces integrally formed as one piece therewith.

165. A biofilm support according to claim 162 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

166. A biofilm support according to claim 165 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

167. A biofilm support according to claim 165 and wherein each of said plurality of ribs has a thickness of between 0.5 and 2 mm.

168. A biofilm support according to claim 165 and wherein said plastic biofilm support element includes a strip extending along an outwardly facing edge of each of said radially extending ribs.

169. A biofilm support according to claim 161 and wherein said plastic biofilm support element is formed of a plastic material selected from the following plastic materials:

polyolefin, polystyrene, polyvinyl chloride and polyurethane.

170. A biofilm support according to claim 161 and wherein said plastic biofilm support element is formed of a plastic material mixed with a foaming agent.

171. A biofilm support according to claim 168 and wherein said plurality of ribs and said strips are configured so as to prevent interdigitation between ribs of two separate biofilm support elements.

172. A biofilm support according to claim 161 and being configured so as to prevent mechanically retained joining of two separate biofilm support elements.

173. A biofilm support according to claim 161 and wherein said plastic biofilm support element has a specific gravity of between approximately 0.75-0.89.

174. A biofilm support according to claim 161 and wherein said plastic biofilm support element has a specific gravity of between approximately 0.81-0.87.

175. A biofilm support according to claim 163 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 100-800 microns.

176. A biofilm support according to claim 163 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 200-500 microns.

177. A biofilm support according to claim 164 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

178. A biofilm support according to claim 177 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

179. A biofilm support according to claim 177 and wherein each of said plurality of ribs has a thickness of between 0.5 and 2 mm.

180. A biofilm support according to claim 177 and wherein said plastic biofilm support element includes a strip extending along an outwardly facing edge of each of said radially extending ribs.

181. A biofilm support according to claim 164 and wherein said plastic biofilm support element is formed of a plastic material selected from the following plastic materials:

polyolefin, polystyrene, polyvinyl chloride and polyurethane.

182. A biofilm support according to claim 164 and wherein said plastic biofilm support element is formed of a plastic material mixed with a foaming agent.

183. A biofilm support according to claim 180 and wherein said plurality of ribs and said strips are configured so as to prevent interdigitation between ribs of two separate biofilm support elements.

184. A biofilm support according to claim 164 and being configured so as to prevent mechanically retained joining of two separate biofilm support elements.

185. A biofilm support according to claim 164 and wherein said plastic biofilm support element has a specific gravity of between approximately 0.75-0.89.

186. A biofilm support according to claim 164 and wherein said plastic biofilm support element has a specific gravity of between approximately 0.81-0.87.

187. A biofilm support according to claim 164 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 100-800 microns.

188. A biofilm support according to claim 164 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 200-500 microns.

189. A biofilm support according to claim 184 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

190. A biofilm support according to claim 189 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

191. A biofilm support comprising:

a plastic biofilm support element having a generally cylindrical configuration and including a plurality of radially extending surfaces extending outwardly from a generally solid center.

192. A biofilm support according to claim 191 and wherein said plastic biofilm support element has a plurality of roughened biofilm adherence surfaces integrally formed as one piece therewith.

193. A biofilm support according to claim 191 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

194. A biofilm support according to claim 193 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

195. A biofilm support according to claim 193 and wherein each of said plurality of ribs has a thickness of between 0.5 and 2 mm.

196. A biofilm support according to claim 193 and wherein said plastic biofilm support element includes a strip extending along an outwardly facing edge of each of said radially extending ribs.

197. A biofilm support according to claim 191 and wherein said plastic biofilm support element is formed of a plastic material selected from the following plastic materials:

polyolefin, polystyrene, polyvinyl chloride and polyurethane.

198. A biofilm support according to claim 191 and wherein said plastic biofilm support element is formed of a plastic material mixed with a foaming agent.

199. A biofilm support according to claim 196 and wherein said plurality of ribs and said strips are configured so as to prevent interdigitation between ribs of two separate biofilm support elements.

200. A biofilm support according to claim 191 and being configured so as to prevent mechanically retained joining of two separate biofilm support elements.

201. A biofilm support according to claim 192 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 100-800 microns.

202. A biofilm support according to claim 192 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 200-500 microns.

203. A biofilm support comprising:

a unitary plastic biofilm support element having a maximum dimension which does not exceed 50 mm and includes a plurality of roughened biofilm adherence surfaces integrally formed as one piece therewith.

204. A biofilm support according to claim 203 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

205. A biofilm support according to claim 204 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

206. A biofilm support according to claim 204 and wherein each of said plurality of ribs has a thickness of between 0.5 and 2 mm.

207. A biofilm support according to claim 204 and wherein said plastic biofilm support element includes a strip extending along an outwardly facing edge of each of said radially extending ribs.

208. A biofilm support according to claim 203 and wherein said plastic biofilm support element is formed of a plastic material selected from the following plastic materials:

polyolefin, polystyrene, polyvinyl chloride and polyurethane.

209. A biofilm support according to claim 203 and wherein said plastic biofilm support element is formed of a plastic material mixed with a foaming agent.

210. A biofilm support according to claim 207 and wherein said plurality of ribs and said strips are configured so as to prevent interdigitation between ribs of two separate biofilm support elements.

211. A biofilm support according to claim 203 and being configured so as to prevent mechanically retained joining of two separate biofilm support elements.

212. A biofilm support according to claim 203 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 100-800 microns.

213. A biofilm support according to claim 203 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 200-500 microns.

214. A waste water treatment system comprising:

a basin;

at least one airlift operating in said basin; and

a multiplicity of plastic biofilm support elements disposed in said basin for cooperation with said airlift, said plastic biofilm support elements having a maximum dimension which does not exceed 50 mm and having a specific gravity of between approximately 0.70-0.91.

215. A waste water treatment system according to claim 214 and wherein said plastic biofilm support elements have a generally cylindrical configuration and include a plurality of radially extending surfaces extending outwardly from a generally solid center.

216. A waste water treatment system according to claim 214 and wherein said plastic biofilm support elements have a plurality of roughened biofilm adherence surfaces integrally formed as one piece therewith.

217. A waste water treatment system according to claim 215 and wherein said plastic biofilm support elements have a plurality of roughened biofilm adherence surfaces integrally formed as one piece therewith.

218. A waste water treatment system according to claim 215 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

219. A waste water treatment system according to claim 218 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

220. A waste water treatment system according to claim 218 and wherein each of said plurality of ribs has a thickness of between 0.5 and 2 mm.

221. A waste water treatment system according to claim 218 and wherein said plastic biofilm support elements include a strip extending along an outwardly facing edge of each of said radially extending ribs.

222. A waste water treatment system according to claim 214 and wherein said plastic biofilm support elements are formed of a plastic material selected from the following plastic materials:

polyolefin, polystyrene, polyvinyl chloride and polyurethane.

223. A waste water treatment system according to claim 214 and wherein said plastic biofilm support elements are formed of a plastic material mixed with a foaming agent.

224. A waste water treatment system according to claim 221 and wherein said plurality of ribs and said strips are configured so as to prevent interdigitation between ribs of two separate biofilm support elements.

225. A waste water treatment system according to claim 214 and being configured so as to prevent mechanically retained joining of two separate biofilm support elements.

226. A waste water treatment system according to claim 214 and wherein said plastic biofilm support elements have a specific gravity of between approximately 0.75-0.89.

227. A waste water treatment system according to claim 214 and wherein said plastic biofilm support elements have a specific gravity of between approximately 0.81-0.87.

228. A waste water treatment system according to claim 216 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 100-800 microns.

229. A waste water treatment system according to claim 216 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 200-500 microns.

230. A waste water treatment system according to claim 217 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

231. A waste water treatment system according to claim 230 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

232. A waste water treatment system according to claim 230 and wherein each of said plurality of ribs has a thickness of between 0.5 and 2 mm.

233. A waste water treatment system according to claim 230 and wherein said plastic biofilm support elements include a strip extending along an outwardly facing edge of each of said radially extending ribs.

234. A waste water treatment system according to claim 217 and wherein said plastic biofilm support elements are formed of a plastic material selected from the following plastic materials:

polyolefin, polystyrene, polyvinyl chloride and polyurethane.

235. A waste water treatment system according to claim 217 and wherein said plastic biofilm support elements are formed of a plastic material mixed with a foaming agent.

236. A waste water treatment system according to claim 233 and wherein said plurality of ribs and said strips are configured so as to prevent interdigitation between ribs of two separate biofilm support elements.

237. A waste water treatment system according to claim 217 and being configured so as to prevent mechanically retained joining of two separate biofilm support elements.

238. A waste water treatment system according to claim 217 and wherein said plastic biofilm support elements have a specific gravity of between approximately 0.75-0.89.

239. A waste water treatment system according to claim 217 and wherein said plastic biofilm support elements have a specific gravity of between approximately 0.81-0.87.

240. A waste water treatment system according to claim 217 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 100-800 microns.

241. A waste water treatment system according to claim 217 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 200-500 microns.

242. A waste water treatment system according to claim 237 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

243. A waste water treatment system according to claim 242 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

244. A waste water treatment system comprising:

a basin;

at least one airlift operating in said basin; and

a multiplicity of plastic biofilm support elements disposed in said basin for cooperation with said airlift, said plastic biofilm support elements having a generally cylindrical configuration and including a plurality of radially extending surfaces extending outwardly from a generally solid center.

245. A waste water treatment system according to claim 244 and wherein said plastic biofilm support elements have a plurality of roughened biofilm adherence surfaces integrally formed as one piece therewith.

246. A waste water treatment system according to claim 244 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

247. A waste water treatment system according to claim 246 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

248. A waste water treatment system according to claim 246 and wherein each of said plurality of ribs has a thickness of between 0.5 and 2 mm.

249. A waste water treatment system according to claim 246 and wherein said plastic biofilm support elements include a strip extending along an outwardly facing edge of each of said radially extending ribs.

250. A waste water treatment system according to claim 244 and wherein said plastic biofilm support elements are formed of a plastic material selected from the following plastic materials:

polyolefin, polystyrene, polyvinyl chloride and polyurethane.

251. A waste water treatment system according to claim 244 and wherein said plastic biofilm support elements are formed of a plastic material mixed with a foaming agent.

252. A waste water treatment system according to claim 249 and wherein said plurality of ribs and said strips are configured so as to prevent interdigitation between ribs of two separate biofilm support elements.

253. A waste water treatment system according to claim 244 and being configured so as to prevent mechanically retained joining of two separate biofilm support elements.

254. A waste water treatment system according to claim 245 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 100-800 microns.

255. A waste water treatment system according to claim 245 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 200-500 microns.

256. A waste water treatment system comprising:

a basin;

at least one airlift operating in said basin; and

a multiplicity of plastic biofilm support elements disposed in said basin for cooperation with said airlift, said plastic biofilm support elements having a maximum dimension which does not exceed 50 mm and including a plurality of roughened biofilm adherence surfaces integrally formed as one piece therewith.

257. A waste water treatment system according to claim 256 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

258. A waste water treatment system according to claim 257 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

259. A waste water treatment system according to claim 257 and wherein each of said plurality of ribs has a thickness of between 0.5 and 2 mm.

260. A waste water treatment system according to claim 257 and wherein said plastic biofilm support elements include a strip extending along an outwardly facing edge of each of said radially extending ribs.

261. A waste water treatment system according to claim 256 and wherein said plastic biofilm support elements are formed of a plastic material selected from the following plastic materials:

polyolefin, polystyrene, polyvinyl chloride and polyurethane.

262. A waste water treatment system according to claim 256 and wherein said plastic biofilm support elements are formed of a plastic material mixed with a foaming agent.

263. A waste water treatment system according to claim 260 and wherein said plurality of ribs and said strips are configured so as to prevent interdigitation between ribs of two separate biofilm support elements.

264. A waste water treatment system according to claim 256 and being configured so as to prevent mechanically retained joining of two separate biofilm support elements.

265. A waste water treatment system according to claim 256 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 100-800 microns.

266. A waste water treatment system according to claim 256 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 200-500 microns.

267. A method of manufacturing a plastic biofilm support element comprising:

extruding a plastic material mixed with a foaming agent to produce an elongate extruded plastic material having a specific gravity of between approximately 0.70-0.91;

cooling said elongate extruded plastic material; and

cutting said elongate extruded plastic material to have a maximum dimension which does not exceed 50 mm.

268. A method according to claim 267 and wherein said plastic biofilm support element is extruded to have a generally cylindrical configuration and to include a plurality of radially extending surfaces extending outwardly from a generally solid center.

269. A method according to claim 267 and wherein said plastic biofilm support element is extruded to have a plurality of roughened biofilm adherence surfaces integrally formed as one piece therewith.

270. A method according to claim 268 and wherein said plastic biofilm support element is extruded to have a plurality of roughened biofilm adherence surfaces integrally formed as one piece therewith.

271. A method according to claim 268 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

272. A method according to claim 271 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

273. A method according to claim 271 and wherein each of said plurality of ribs has a thickness of between 0.5 and 2 mm.

274. A method according to claim 271 and wherein said plastic biofilm support element is extruded to have a strip extending along an outwardly facing edge of each of said radially extending ribs.

275. A method according to claim 267 and wherein said plastic biofilm support element is extruded of a plastic material selected from the following plastic materials:

polyolefin, polystyrene, polyvinyl chloride and polyurethane.

276. A method according to claim 267 and wherein said plastic biofilm support element is extruded of a plastic material mixed with a foaming agent.

277. A method according to claim 274 and wherein said plurality of ribs and said strips are configured so as to prevent interdigitation between ribs of two separate biofilm support elements.

278. A method according to claim 267 and wherein said biofilm support element is configured so as to prevent mechanically retained joining of two separate biofilm support elements.

279. A method according to claim 267 and wherein said plastic biofilm support element has a specific gravity of between approximately 0.75-0.89.

280. A method according to claim 267 and wherein said plastic biofilm support element has a specific gravity of between approximately 0.81-0.87.

281. A method according to claim 269 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 100-800 microns.

282. A method according to claim 269 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 200-500 microns.

283. A method according to claim 270 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

284. A method according to claim 283 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

285. A method according to claim 283 and wherein each of said plurality of ribs has a thickness of between 0.5 and 2 mm.

286. A method according to claim 283 and wherein said plastic biofilm support element includes a strip extending along an outwardly facing edge of each of said radially extending ribs.

287. A method according to claim 270 and wherein said plastic biofilm support element is extruded of a plastic material selected from the following plastic materials:

polyolefin, polystyrene, polyvinyl chloride and polyurethane.

288. A method according to claim 270 and wherein said plastic biofilm support element is extruded Of a plastic material mixed with a foaming agent.

289. A method according to claim 286 and wherein said plurality of ribs and said strips are configured so as to prevent interdigitation between ribs of two separate biofilm support elements.

290. A method according to claim 270 and being configured so as to prevent mechanically retained joining of two separate biofilm support elements.

291. A method according to claim 270 and wherein said plastic biofilm support element has a specific gravity of between approximately 0.75-0.89.

292. A method according to claim 270 and wherein said plastic biofilm support element has a specific gravity of between approximately 0.81-0.87.

293. A method according to claim 270 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 100-800 microns.

294. A method according to claim 270 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 200-500 microns.

295. A method according to claim 290 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

296. A method according to claim 295 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

320. A method according to claim 267 and wherein said biofilm support element is configured so as to prevent mechanically retained joining of two separate biofilm support elements.

297. A method of manufacturing a plastic biofilm support element comprising:

extruding a plastic material mixed with a foaming agent to produce an elongate extruded plastic material having a generally cylindrical configuration and including a plurality of radially extending surfaces extending outwardly from a generally solid center;

cooling said elongate extruded plastic material; and

cutting said elongate extruded plastic material to have a maximum dimension which does not exceed 50 mm.

298. A method according to claim 297 and wherein said plastic biofilm support element has a plurality of roughened biofilm adherence surfaces integrally extruded as one piece therewith.

299. A method according to claim 297 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

300. A method according to claim 299 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

301. A method according to claim 299 and wherein each of said plurality of ribs has a thickness of between 0.5 and 2 mm.

302. A method according to claim 299 and wherein said plastic biofilm support element includes a strip extending along an outwardly facing edge of each of said radially extending ribs.

303. A method according to claim 297 and wherein said plastic biofilm support element is extruded of a plastic material selected from the following plastic materials:

polyolefin, polystyrene, polyvinyl chloride and polyurethane.

304. A method according to claim 297 and wherein said plastic biofilm support element is extruded of a plastic material mixed with a foaming agent.

305. A method according to claim 302 and wherein said plurality of ribs and said strips are configured so as to prevent interdigitation between ribs of two separate biofilm support elements.

306. A method according to claim 297 and being configured so as to prevent mechanically retained joining of two separate biofilm support elements.

307. A method according to claim 298 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 100-800 microns.

308. A method according to claim 298 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 200-500 microns.

309. A method of manufacturing a biofilm support element comprising:

extruding a plastic material mixed with a foaming agent to produce an elongate extruded plastic material having a plurality of roughened biofilm adherence surfaces integrally formed as one piece therewith;

cooling said elongate extruded plastic material; and

cutting said elongate extruded plastic material to have a maximum dimension which does not exceed 50 mm.

310. A method according to claim 309 and wherein said plurality of radially extending surfaces are defined by a plurality of radially extending ribs.

311. A method according to claim 310 and wherein said plurality of radially extending ribs comprises between 5 and 9 ribs.

312. A method according to claim 310 and wherein each of said plurality of ribs has a thickness of between 0.5 and 2 mm.

313. A method according to claim 310 and wherein said plastic biofilm support element includes a strip extending along an outwardly facing edge of each of said radially extending ribs.

314. A method according to claim 309 and wherein said plastic biofilm support element is extruded of a plastic material selected from the following plastic materials:

polyolefin, polystyrene, polyvinyl chloride and polyurethane.

315. A method according to claim 309 and wherein said plastic biofilm support element is extruded of a plastic material mixed with a foaming agent.

316. A method according to claim 313 and wherein said plurality of ribs and said strips are configured so as to prevent interdigitation between ribs of two separate biofilm support elements.

317. A method according to claim 309 and being configured so as to prevent mechanically retained joining of two separate biofilm support elements.

318. A method according to claim 309 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 100-800 microns.

319. A method according to claim 309 and wherein said roughened biofilm adherence surfaces have a roughness average (Ra) in the range of 200-500 microns.

321. A method for retrofitting existing waste water treatment facilities having at least one existing basin comprising:

installing generally vertical partitions at spaced locations in said at least one existing basin in order to divide said at least one existing basin into a plurality of treatment stage regions;

installing at least one air lift in each of said plurality of treatment stage regions;

loading each treatment stage regions with a quantity of floatable biomass support elements;

supplying waste water to at least one of said plurality of treatment stage regions and allowing said waste water, but generally not said biomass support elements, to flow from at least one of said plurality of treatment stage regions to at least another of said plurality of treatment stage regions; and

operating said at least one air lift in each of said plurality of treatment stage regions to provide aerobic waste water flow therein in operative engagement with said floatable porous biomass support elements.

322. A method according to claim 321 and wherein at least some of said vertical partitions are spaced from a bottom of said at least one basin in order to allow said waste water to flow thereunder between adjacent ones of said plurality of treatment stage regions.

323. A method according to claim 321 and wherein said at least one air lift comprises at least one air diffuser disposed underlying a peripheral enclosure which defines a column of water which is lifted by air diffusing upwardly from said at least one air diffuser therethrough.

324. A method according to claim 323 and wherein said peripheral enclosure comprises a rectangular cylindrical enclosure.

325. A method according to claim 323 and wherein said peripheral enclosure comprises a plurality of spaced generally vertical walls which extend between walls of the basin and are separated from the bottom of the basin.

326. A method according to claim 321 and wherein said generally vertical partitions divide said basin into between 4 and 12 process stages.

327. A method according to claim 321 and wherein said at least one air lift comprises a series of air lifts arranged in said multiple process stages.

328. A method according to claim 327 and wherein said air lift comprises a plurality of air lift assemblies and wherein at least one of said plurality of air lift assemblies include an upstream partition which extends downwardly from a top location below said water level in basin to a bottom location spaced from said bottom of said basin.

329. A method according to claim 321 and wherein said vertical partitions each extend fully from side to side of said basin.

330. A method according to claim 328 and wherein said at least one air lift assembly also includes a downstream partition which extends downwardly from a top location below said water level in said basin to a bottom location spaced from said bottom of said basin.

331. A method according to claim 321 and wherein:

said at least one air lift comprises a plurality of air lift assemblies each including upstream and downstream partitions;

a first plurality of air diffusers are disposed at said bottom of said basin intermediate said plurality of air lift assemblies; and

a second plurality of air diffusers, lesser in number than said first plurality of air diffusers, are disposed at said bottom of said basin intermediate said upstream and downstream partitions of said plurality of air lift assemblies.

332. A method according to claim 331 and wherein said first plurality of air diffusers intermediate said air lift assemblies causes water to flow upward between said air lift assemblies.

333. A method according to claim 332 and wherein said second plurality of air diffusers intermediate said upstream and downstream partitions of each air lift assembly allows water to flow downward between said upstream and downstream partitions.

334. A method according to claim 321 and wherein said loading comprises loading 10-40 percent of said volume of said basin with biomass support elements.

335. A method according to claim 321 and wherein said supplying comprises providing a continuous flow of water from said upstream side of said basin from said waste water inlet to said treated water outlet.

336. A method according to claim 335 and wherein said flow includes passage under stage separation partitions which does not carry floating biomass support elements across said stage separation partition, thereby constraining said biomass support elements of each stage to reside within that stage and preventing migration of biomass support elements across stage partition assemblies.

337. A method according to claim 331 and also comprising controlling the flow velocity of water by controlling operation of said first and second pluralities of air diffusers.

338. A method according to claim 321 and also comprising installing a de-nitrification unit in at least one of said plurality of treatment stage regions.

339. A method according to claim 338 and wherein said de-nitrification unit comprises at least one axial pump which provides lift generally without an air flow, thereby to provide an anoxic de-nitrification process.

340. A method according to claim 338 and wherein said de-nitrification unit comprises at least one agitator which provides lift generally without an air flow, thereby to provide an anoxic de-nitrification process.

341. A method according to claim 321 and wherein said at least one air lift comprises an array of air lifts and wherein said array of air lifts comprises a multiplicity of rectangular cylindrical air lifts arranged in said plurality of treatment stage regions and separated by said vertical partitions which extend from a bottom location which is spaced from a bottom of said basin by a first vertical separation.

343. A method according to claim 321 and wherein said operating produces fluidization of said biomass support elements.

344. A method according to claim 321 and wherein said vertical partitions comprise:

a first generally vertical partition having respective upstream and downstream surfaces, said first generally vertical partition extending downwardly from a top location above the level of the water in the basin to a bottom location spaced from the bottom of said basin and extending from side to side of said basin;

second and third generally vertical partitions disposed adjacent and in spaced relationship with respect to said upstream and downstream surfaces of said first generally vertical partition, said second and third generally vertical partitions extending from side to side of said basin, and extending upwardly from said bottom of said basin to a top location below the level of water in said basin; and

upwardly inclined flow director panels disposed on respective upstream and downstream surfaces of said first generally vertical partition and being disposed above and spaced from said second and third generally vertical partitions.

342. A method according to 340 and wherein said cylindrical air lifts each comprise:

a hollow shaft which extends from a bottom location spaced from a bottom of said basin by a second vertical separation which exceeds said first separation;

and a plurality of air diffusers which are disposed intermediate said hollow shaft to provide an air lift therethrough, thereby causing water to flow into said hollow shafts and downwardly through said hollow shafts.

345. A method for waste water treatment employing at least one basin comprising:

installing generally vertical partitions at spaced locations in said at least one basin in order to divide said at least one basin into a plurality of treatment stage regions;

installing at least one air lift in each of said plurality of treatment stage regions;

loading each treatment stage regions with a quantity of floatable biomass support elements;

supplying waste water to at least one of said plurality of treatment stage regions and allowing said waste water, but generally not said biomass support elements, to flow from at least one of said plurality of treatment stage regions to at least another of said plurality of treatment stage regions; and

operating said at least one air lift in each of said plurality of treatment stage regions to provide aerobic waste water flow therein in operative engagement with said floatable porous biomass support elements.

346. A method according to claim 345 and wherein at least some of said vertical partitions are spaced from a bottom of said at least one basin in order to allow said waste water to flow thereunder between adjacent ones of said plurality of treatment stage regions.

347. A method according to claim 345 and wherein said at least one air lift comprises at least one air diffuser disposed underlying a peripheral enclosure which defines a column of water which is lifted by air diffusing upwardly from said at least one air diffuser therethrough.

348. A method according to claim 347 and wherein said peripheral enclosure comprises a rectangular cylindrical enclosure.

349. A method according to claim 347 and wherein said peripheral enclosure comprises a plurality of spaced generally vertical walls which extend between walls of the basin and are separated from the bottom of the basin.

350. A method according to claim 345 and wherein said generally vertical partitions divide said basin into between 4 and 12 process stages.

351. A method according to claim 345 and wherein said at least one air lift comprises a series of air lifts arranged in said multiple process stages.

352. A method according to claim 351 and comprises a plurality of air lift assemblies and wherein at least one of said plurality of air lift assemblies include an upstream partition which extends downwardly from a top location below said water level in basin to a bottom location spaced from said bottom of said basin.

353. A method according to claim 345 and wherein said vertical partitions each extend fully from side to side of said basin.

354. A method according to claim 352 and wherein said at least one intermediate air lift assembly also includes a downstream partition which extends downwardly from a top location below said water level in said basin to a bottom location spaced from said bottom of said basin as does said upstream partition.

355. A method according to claim 345 and wherein:

said at least one air lift comprises a plurality of air lift assemblies each including upstream and downstream partitions;

a first plurality of air diffusers are disposed at said bottom of said basin intermediate said plurality of air lift assemblies; and

a second plurality of air diffusers, lesser in number than said first plurality of air diffusers, are disposed at said bottom of said basin intermediate said upstream and downstream partitions of said plurality of air lift assemblies.

356. A method according to claim 355 and wherein said first plurality of air diffusers intermediate adjacent air lift assemblies and intermediate adjacent airlift assembly and stage partition assembly causes water to flow upward between said adjacent air lift assemblies and between adjacent airlift assembly and stage partition assembly.

357. A method according to claim 356 and wherein said second plurality of air diffusers intermediate said upstream and downstream partitions of each air lift assembly allows water to flow downward between said upstream and downstream partitions.

358. A method according to claim 345 and wherein said loading comprises loading 10-40 percent of said volume of said basin with biomass support elements.

359. A method according to claim 345 and wherein said supplying comprises providing a continuous flow of water from said upstream side of said basin from said waste water inlet to said treated water outlet.

360. A method according to claim 359 and wherein said flow includes passage under stage separation partitions which does not carry floating biomass support elements across said stage separation partition, thereby constraining said biomass support elements of each stage to reside within that stage and preventing migration of biomass support elements across stage partition assemblies.

361. A method according to claim 355 and also comprising controlling the flow velocity of water by controlling operation of said first and second pluralities of air diffusers.

362. A method according to claim 345 and also comprising installing a denitrification unit in at least one of said plurality of treatment stage regions.

363. A method according to claim 362 and wherein said de-nitrification unit comprises at least one agitator which provides lift generally without an air flow thereby providing an anoxic de-nitrification process.

364. A method according to claim 362 and wherein said de-nitrification unit comprises at least one axial pump which provides lift generally without an air flow, thereby to provide an anoxic de-nitrification process.

365. A method according to claim 345 and wherein said at least one air lift comprises an array of air lifts and wherein said array of air lifts comprises a multiplicity of rectangular cylindrical air lifts arranged in said plurality of treatment stage regions and separated by said vertical partitions which extend from a bottom location which is spaced from a bottom of said basin by a first vertical separation.

367. A method according to claim 345 and wherein said operating produces fluidization of said biomass support elements.

368. A method according to claim 345 and wherein said vertical partitions comprise:

a first generally vertical partition having -respective upstream and downstream surfaces, said first generally vertical partition extending downwardly from a top location above the level of the water in the basin to a bottom location spaced from the bottom of said basin and extending from side to side of said basin;

second and third generally vertical partitions disposed adjacent and in spaced relationship with respect to said upstream and downstream surfaces of said first generally vertical partition, said second and third generally vertical partitions extending from side to side of said basin, and extending upwardly from the bottom of the basin to a top location below the level of water in said basin; and

upwardly inclined flow director panels disposed on respective upstream and downstream surfaces of said first generally vertical partition and being disposed above and spaced from said second and third generally vertical partitions.

366. A method according to 365 and wherein said cylindrical air lifts each comprise:

a hollow shaft which extends from a bottom location spaced from a bottom of said basin by a second vertical separation which exceeds said first separation;

and a plurality of air diffusers which are disposed intermediate said hollow shaft to provide an air lift therethrough, thereby causing water to flow into said hollow shafts and downwardly through said hollow shafts.

369. Retrofitted waste water treatment apparatus comprising:

at least one existing basin;

generally vertical partitions located at spaced locations in said at least one existing basin in order to divide said at least one existing basin into a plurality of treatment stage regions;

at least one air lift located in each of said plurality of treatment stage regions; and

a quantity of floatable biomass support elements loaded into each of said plurality of treatment stage regions, whereby supplying waste water to at least one of said plurality of treatment stage regions and allowing said waste water, but generally not said biomass support elements, to flow from at least one of said plurality of treatment stage regions to at least another of said plurality of treatment stage regions and operating said at least one air lift in each of said plurality of treatment stage regions provides aerobic waste water flow therein in operative engagement with said floatable biomass support elements.

370. Apparatus according to claim 369 and wherein at least some of said vertical partitions are spaced from a bottom of said at least one basin in order to allow said waste water to flow thereunder between adjacent ones of said plurality of treatment stage regions.

371. Apparatus according to claim 369 and wherein said at least one air lift comprises at least one air diffuser disposed underlying a peripheral enclosure which defines a column of water which is lifted by air diffusing upwardly from said at least one air diffuser therethrough.

372. Apparatus according to claim 371 and wherein said peripheral enclosure comprises a rectangular cylindrical enclosure.

373. Apparatus according to claim 371 and wherein said peripheral enclosure comprises a plurality of spaced generally vertical walls which extend between walls of the basin and are separated from the bottom of the basin.

374. Apparatus according to claim 369 and wherein said generally vertical partitions divide said basin into between 4 and 12 process stages.

375. Apparatus according to claim 369 and wherein said at least one air lift comprises a series of air lifts arranged in said multiple process stages.

376. Apparatus according to claim 375 and comprises a plurality of air lift assemblies and wherein at least one of said plurality of air lift assemblies include an upstream partition which extends downwardly from a top location below said water level in basin to a bottom location spaced from said bottom of said basin.

377. Apparatus according to claim 369 and wherein said vertical partitions each extend fully from side to side of said basin.

378. Apparatus according to claim 376 and wherein said at least one air lift assembly also includes a downstream partition which extends downwardly from a top location below said water level in said basin to a bottom location spaced from said bottom of said basin as does said upstream partition.

379. Apparatus according to claim 369 and wherein:

said at least one air lift comprises a plurality of air lift assemblies each including upstream and downstream partitions;

a first plurality of air diffusers are disposed at said bottom of said basin intermediate said plurality of air lift assemblies; and

a second plurality of air diffusers, lesser in number than said first plurality of air diffusers, are disposed at said bottom of said basin intermediate said upstream and downstream partitions of said plurality of air lift assemblies.

380. Apparatus according to claim 379 and wherein said first plurality of air diffusers intermediate adjacent air lift assemblies and intermediate adjacent airlift assembly and stage partition assembly causes water to flow upward between said adjacent air lift assemblies and between adjacent airlift assembly and stage partition assembly.

381. Apparatus according to claim 380 and wherein said second plurality of air diffusers intermediate said upstream and downstream partitions of each air lift assembly allows water to flow downward between said upstream and downstream partitions.

382. Apparatus according to claim 369 and wherein said loading comprises loading 10-40 percent of said volume of said basin with biomass support elements.

383. Apparatus according to claim 369 and wherein said supplying comprises providing a continuous flow of water from said upstream side of said basin from said waste water inlet to said treated water outlet.

384. Apparatus according to claim 383 and wherein said flow includes passage under stage separation partitions which does not carry floating biomass support elements across said stage separation partition, thereby constraining said biomass support elements of each stage to reside within that stage and preventing migration of biomass support elements across stage partition assemblies.

385. Apparatus according to claim 379 and also comprising controlling the flow velocity of water by controlling operation of said first and second pluralities of air diffusers.

386. Apparatus according to claim 369 and also comprising installing a denitrification unit in at least one of said plurality of treatment stage regions.

387. A method according to claim 386 and wherein said de-nitrification unit comprises at least one agitator which provides lift generally without an air flow thereby providing an anoxic de-nitrification process.

388. Apparatus according to claim 386 and wherein said de-nitrification unit comprises at least one axial pump which provides lift generally without an air flow, thereby to provide an anoxic de-nitrification process.

389. Apparatus according to claim 369 and wherein said at least one air lift comprises an array of air lifts and wherein said array of air lifts comprises a multiplicity of rectangular cylindrical air lifts arranged in said plurality of treatment stage regions and separated by said vertical partitions which extend from a bottom location which is spaced from a bottom of said basin by a first vertical separation.

391. Apparatus according to claim 369 and wherein said operating produces fluidization of said biomass support elements.

392. A method according to claim 369 and wherein said vertical partitions comprise:

a first generally vertical partition having respective upstream and downstream surfaces, said first generally vertical partition extending downwardly from a top location above the level of the water in the basin to a bottom location spaced from said bottom of said basin and extending from side to side of said basin;

second and third generally vertical partitions disposed adjacent and in spaced relationship with respect to said upstream and downstream surfaces of said first generally vertical partition, said second and third generally vertical partitions extending from side to side of said basin, and extending upwardly from the bottom of the basin to a top location below the level of water in said basin; and

upwardly inclined flow director panels disposed on respective upstream and downstream surfaces of said first generally vertical partition and being disposed above and spaced from said second and third generally vertical partitions.

390. Apparatus according to 388 and wherein said cylindrical air lifts each comprise:

a hollow shaft which extends from a bottom location spaced from a bottom of said basin by a second vertical separation which exceeds said first separation;

and a plurality of air diffusers which are disposed intermediate said hollow shaft to provide an air lift therethrough, thereby causing water to flow into said hollow shafts and downwardly through said hollow shafts.

393. Waste water treatment apparatus comprising:

at least one basin;

generally vertical partitions located at spaced locations in said at least one basin in order to divide said at least one basin into a plurality of treatment stage regions;

at least one air lift located in each of said plurality of treatment stage regions; and

a quantity of floatable biomass support elements loaded into each of said plurality of treatment stage regions, whereby supplying waste water to at least one of said plurality of treatment stage regions and allowing said waste water, but generally not said biomass support elements, to flow from at least one of said plurality of treatment stage regions to at least another of said plurality of treatment stage regions and operating said at least one air lift in each of said plurality of treatment stage regions provides aerobic waste water flow therein in operative engagement with said floatable porous biomass support elements.

394. Apparatus according to claim 393 and wherein at least some of said vertical partitions are spaced from a bottom of said at least one basin in order to allow said waste water to flow thereunder between adjacent ones of said plurality of treatment stage regions.

395. Apparatus according to claim 393 and wherein said at least one air lift comprises at least one air diffuser disposed underlying a peripheral enclosure which defines a column of water which is lifted by air diffusing upwardly from said at least one air diffuser therethrough.

396. Apparatus according to claim 395 and wherein said peripheral enclosure comprises a rectangular cylindrical enclosure.

397. Apparatus according to claim 395 and wherein said peripheral enclosure comprises a plurality of spaced Generally vertical walls which extend between walls of the basin and are separated from the bottom of the basin.

398. Apparatus according to claim 393 and wherein said generally vertical partitions divide said basin into between 4 and 12 process stages.

399. Apparatus according to claim 393 and wherein said at least one air lift comprises a series of air lifts arranged in said multiple process stages.

400. Apparatus according to claim 399 comprises a plurality of air lift assemblies and wherein at least one of said plurality of air lift assemblies include an upstream partition which extends downwardly from a top location below said water level in basin to a bottom location spaced from said bottom of said basin.

401. Apparatus according to claim 393 and wherein said vertical partitions each extend fully from side to side of said basin.

402. Apparatus according to claim 400 and wherein said at least one air lift assembly also includes a downstream partition which extends downwardly from a top location below said water level in said basin to a bottom location spaced from said bottom of said basin as does said upstream partition.

403. Apparatus according to claim 393 and wherein:

said at least one air lift comprises a plurality of air lift assemblies each including upstream and downstream partitions;

a first plurality of air diffusers are disposed at said bottom of said basin intermediate said plurality of air lift assemblies; and

a second plurality of air diffusers, lesser in number than said first plurality of air diffusers, are disposed at said bottom of said basin intermediate said upstream and downstream partitions of said plurality of air lift assemblies.

404. Apparatus according to claim 403 and wherein said first plurality of air diffusers intermediate adjacent air lift assemblies and intermediate adjacent airlift assembly and stage partition assembly causes water to flow upward between said adjacent air lift assemblies and between adjacent airlift assembly and stage partition assembly.

405. Apparatus according to claim 404 and wherein said second plurality of air diffusers intermediate said upstream and downstream partitions of each air lift assembly allows water to flow downward between said upstream and downstream partitions.

406. Apparatus according to claim 393 and wherein said loading comprises loading 10-40 percent of said volume of said basin with biomass support elements.

407. Apparatus according to claim 393 and wherein said supplying comprises providing a continuous flow of water from said upstream side of said basin from said waste water inlet to said treated water outlet.

408. Apparatus according to claim 407 and wherein said flow includes passage under stage separation partitions which does not carry floating biomass support elements across said stage separation partition, thereby constraining said biomass support elements of each stage to reside within that stage and preventing migration of biomass support elements across stage partition assemblies.

409. Apparatus according to claim 403 and also comprising controlling the flow velocity of water by controlling operation of said first and second pluralities of air diffusers.

410. Apparatus according to claim 393 and also comprising installing a denitrification unit in at least one of said plurality of treatment stage regions.

411. A method according to claim 410 and wherein said de-nitrification unit comprises at least one agitator which provides lift generally without an air flow thereby providing an anoxic de-nitrification process.

412. Apparatus according to claim 410 and wherein said de-nitrification unit comprises at least one axial pump which provides lift generally without an air flow, thereby to provide an anoxic de-nitrification process.

413. Apparatus according to claim 393 and wherein said at least one air lift comprises an array of air lifts and wherein said array of air lifts comprises a multiplicity of rectangular cylindrical air lifts arranged in said plurality of treatment stage regions and separated by said vertical partitions which extend from a bottom location which is spaced from a bottom of said basin by a first vertical separation.

415. Apparatus according to claim 393 and wherein said operating produces fluidization of said biomass support elements.

416. A method according to claim 393 and wherein said vertical partitions comprise:

a first generally vertical partition having respective upstream and downstream surfaces, said first generally vertical partition extending downwardly from a top location above the level of the water in the basin to a bottom location spaced from said bottom of said basin and extending from side to side of said basin;

second and third generally vertical partitions disposed adjacent and in spaced relationship with respect to said upstream and downstream surfaces of said first generally vertical partition, said second and third generally vertical partitions extending from side to side of said basin, and extending upwardly from the bottom of the basin to a top location below the level of water in said basin; and

upwardly inclined flow director panels disposed on respective upstream and downstream surfaces of said first generally vertical partition and being disposed above and spaced from said second and third generally vertical partitions.

414. Apparatus according to 411 and wherein said cylindrical air lifts each comprise:

a hollow shaft which extends from a bottom location spaced from a bottom of said basin by a second vertical separation which exceeds said first separation;

and a plurality of air diffusers which are disposed intermediate said hollow shaft to provide an air lift therethrough, thereby causing water to flow into said hollow shafts and downwardly through said hollow shafts.