11 Aerators for Water, Waste Water or Sewage; Filter Systems to Remove Suspended Materials, Oil or Other Contaminants from Water and Parts Thereof, Comprising Filter Vessels, Strainer Nozzles, Underdrains, Wash Troughs, Surface Wash Sweeps and Filter Media; Solids Contact Reactors for the Clarification, Color Removal and/or Softening of Water by the Use of Combinations of Lime, Soda Ash, Barium, Coagulants, Polymers; Ion Exchangers and Their Regeneration Systems, Comprising Exchange Vessels and Their Underdrains, Distributors, Collectors, Storage Tanks, Dilution Tanks, Chemical Transfer Pumps, Ejectors to Produce Vacuum, Piping and Valves; Reverse Osmosis Systems, Comprising Reverse Osmosis Membrane Modules, Pumps, Control Cabinets, Storage Tanks and Pumps for Module Cleaning Solutions, Storage Tanks with Pumps and Controls for Adjusting pH; Solids Contact Reactors for the Clarification, Softening, Phosphate Reduction, Metallic Ion Reduction, or Combinations Thereof of Water, Waste Water or Sewage; Screens; Clarifier Systems to Remove Suspended Materials by Sedimentation or Flotation or Combination of the Two, and Parts Thereof, Comprising Clarifiers, Skimmers and Air Saturation Tanks; Digester Systems for Wastewater or Sewage Sludges, Comprising Fixed or Floating Tank Covers, Gas Holding Tank Covers, Mixers and Heaters; Activated Sludge Treatment Systems, Comprising Vessels, Porous Diffuser or Turbine Dispenser Aeration Devices, Air Lifts, Sludge Removal by Circular Rake or Longitudinal Flight Type Clarifiers, Air Blowers or Parts Thereof; Grit Removers Employing Controlled Settling to Separate Grit from the Organics Carried by Wastewater or Sewage; Belt Type Sludge Dewatering Presses